Science Chapter 2 - Is Matter Around Us Pure

Answer:

False, Milk is not a pure substance. It is a heterogeneous mixture because of its colloidal nature.

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Three mixtures found in nature are milk, sweat and air.

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Among the given options, air is a mixture as it is composed of different gases.

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Mercury (metal) and bromine (non-metal), exist as liquid at room temperature.

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Sodium is a soft metal, whereas diamond is a hard non-metal.

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Graphite is a non-metal that is a good conductor of electricity.

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Mercury is a liquid metal that can be classified as a pure substance and a good conductor of electricity.

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Carbon is a solid non-metal, bromine is a liquid non-metal and oxygen is a gaseous non-metal.

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(a) The property of metals that allows them to be hammered into thin sheets is called malleability.
(b) Ductility is the property of metals that enables them to be drawn into wires.

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Any element; metal or non-metal that is soft and cannot be hammered into thin sheets, shows brittleness.

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Malleability refers to the property of a metal that allows it to be hammered into thin sheets. Ductility refers to the property of metals that allows them to be stretched into thin wires.

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Non-metals are brittle in nature, which means, they cannot be hammered into thin sheets. They will be broken into smaller pieces if hammered. E.g., sulphur and phosphorus.

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Metals are sonorous because they generate sound when hit.

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Metals are said to be lustrous because of their property to shine.

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Materials that are made up of two or more pure substances and show the properties of their constituents are called mixtures.

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“The properties of the products are different from those of the constituents.” This statement best describes a compound.

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Iron (Fe) is an element.
Water (H₂O) is a compound.
Air (combination of various gases) is a mixture.

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A mixture is a substance that consists of two or more elements or compounds in any proportion, which might be distinct or indistinct. On the other hand, a solution is an example of homogenous mixture, i.e., substances in the solution are completely mixed and are indistinguishable.

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Elements that are neither good nor bad conductors of electricity, are called semi conductors.

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(a) An element is made up of only one kind of atoms.
(b) Brine is a mixture, whereas alcohol is a compound.
(c) Brass is an alloy, which is considered as mixture.
(d) The three important metalloids are boron, silicon, and germanium.
(e) The elements that are sonorous are called metals.

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Formula of sugar is C₁₂H₂₂O₁₁ . So, the elements present in sugar are carbon (C), hydrogen (H) and oxygen (O).
Formula of sodium chloride is NaCl. So, the elements present in sodium chloride are sodium (Na) and chlorine (Cl).

Answer:

Pure substances are made up of same type of particles or atoms. All the elements and compounds are pure substances because they contain the same kinds of particles.
Examples: Hydrogen, carbon dioxide

Answer:

Two types of pure substances are:
(a) Elements:  Example: Carbon
(b) Compounds: Example: Sodium chloride (NaCl)

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Iron and mercury are pure substances because these are elements. Hydrochloric acid, calcium oxide, and ice are also pure substances, as they are compounds.

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Mixture is considered as an impure substance, as it contains two or more different kinds of particles or substances mixed together.
Examples: Milk, sea water

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Mercury, iron, diamond, nitrogen, graphite, hydrogen, oxygen, and chlorine are elements because these cannot be split further into two or more simpler substances.

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Air is a mixture because:
(a) It contains two or more pure substances.
(b) It can be separated into simpler substances by physical processes.
(c) Its composition is not fixed.

Water is a compound because:
(a) Water cannot be separated into its constituents i.e., hydrogen and oxygen by physical methods.
(b) Properties of water are entirely different from those of its constituents.
(c) The composition of water is fixed.
(d) Its constituents are present in fixed proportion by mass. Water has a definite formula (H₂O).

Answer:

Aluminium and copper are two elements that are solid at room temperature.
Both bromine and mercury are liquid at room temperature.
Nitrogen and hydrogen are two elements that are gaseous at room temperature.

Answer:

Hydrogen and oxygen are considered as elements because they cannot be split further into simpler substances by usual chemical methods as they are made of one kind of atoms. On the other hand, water is not an element, as it consists of different types of atoms, i.e., hydrogen and oxygen and can be split up into its components by chemical processes.

Answer:

 All the elements can be divided into following three groups:
(i) Metals: Examples: Aluminium and copper
(ii) Non-metals: Examples: Potassium and calcium
(iii) Metalloids: Examples: Arsenic and antimony

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Aluminium is lustrous and malleable, so it is a metal.

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(a) Copper is a good conductor of electricity. It is ductile and less expensive; therefore, it is used for making electrical wires.

(b) Graphite is a non-corrosive non-metal and a poor conductor of electricity. It is also cheap and insoluble in water, acids and bases. It is inert (does not react) to the electrolytes present in the dry cells. Thus, it makes a good material for an electrode.

Answer:

You can boil it and if it starts boiling at 100⁰ C, it might be water. You can also check its reactivity with some metals such as sodium and potassium that react violently with water. The best way, to prove that it is pure water, is to do experiments to see if it has the same capabilities and chemical behaviour as water has.

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Sea-water and soda water are solutions.

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Air is a mixture because:
(a) it consists of different gases (and some dust),  
(b) its composition is not fixed, and
(c) it can be split into its components.

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Water is a compound because:
(i)  Water cannot be split into its constituents, hydrogen and oxygen, by physical methods.
(ii) It can only be separated into its constituents by chemical processes.
(iii) The properties of water are entirely different from those of its constituents.

Answer:

A compound is a substance made up of two or more elements combined together chemically in a fixed proportion by mass.
Sodium chloride (NaCl) is a compound because:
(a) It is made up of two elements,  sodium and chlorine, and the nature of NaCl is completely different from its constituent elements.
(b) Sodium and chlorine are present in a fixed proportion in sodium chloride.

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A mixture consists of two or more different kinds of particles or two or more pure substances mixed together but not chemically bound.
Sugar solution is a mixture because

(a) it can be separated into its constituents by physical processes (like evaporation), and
(b) it shows properties of both sugar and water.

Answer:

Brass is an alloy of copper and zinc.
Brass is considered to be a mixture and not a compound because:
(a) it shows the properties of its constituents, and
(b) it has variable composition (the amount of zinc in brass varies from 20% to 35%).

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Answer:

Solution of salt in water is a mixture and not compound because salt solution is made up of salt and water, mixed physically.
1. The constituents of salt solution might be present in varying ratios.
2. Salt solution does not have fixed properties. Its properties depend on the nature of its components and the ratios in which they are mixed.
3. The constituents of salt solution can be separated easily by physical methods, i.e., distillation.

Answer:

Similarity: In both the cases, the mixture shows the properties of its constituents and the constituents can be separated by physical methods, such as filtration, evaporation, distillation etc.

Difference: Mixture of sugar and water is a homogeneous mixture and it is considered to be a solution. On the other hand, mixture of sand and sugar is a heterogeneous mixture.

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We can distinguish a solution from compound by the process of distillation.
Constituents of a solution can be separated by distillation process but the constituents of a compound cannot be separated by the same.

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(a) Iodine is a lustrous non-metal because it is shiny.
(b) Oxygen is a non-metal that is required for combustion.
(c) Carbon, Graphite
(d) Sulphur
(e) Carbon

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(a) Sodium can be easily cut with a knife.
(b) Mercury forms amalgams.
(c) Mercury has no fixed shape.
(d) Sodium has a low melting point.
(e) Gold is yellow in colour.

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Chlorine gas, iron powder, iodine vapour and sulphur powder. aluminum foil, graphite and diamond are not compounds.

Answer:

(a)

Answer:

(a) (i) Element: An element is a substance that cannot be split up into two or more simpler substances by chemical methods. It contains only one type of atoms. Examples of elements include:
Non metals: Carbon and oxygen
Metals: Aluminum, iron, copper, gold, mercury, and lead.

(ii) Compound: A compound is a substance consisting of two or more elements combined chemically in a fixed proportion by mass.
Examples: Water, sodium chloride, calcium carbonate etc.

(iii) Mixture: – A mixture is a substance  that is made up of two or more different kinds of particles or two or more pure substances mixed together by a physical process. Examples: Air, milk, wood, soil etc.

(b) Elements: Gold and Diamond
Compounds: Common salt and marble
Mixtures: – Brass and seawater.

Answer:

(i) Metals: Metals are  elements that are malleable, ductile and conduct electricity.
Examples: Aluminum and zinc

(ii) Non-metals: Non-metals are elements that are neither malleable nor ductile, and they do not conduct electricity. Most non-metals are brittle in nature.
Examples: Phosphorus, hydrogen

(iii) Metalloids: Metalloids are elements that show properties of both metals and non metals.
Examples: Germanium, silicon

(b).
(i) Metals: Mercury, sodium, magnesium,  copper
(ii) Non-metals: Diamond, sulphur, iodine, carbon, helium
(iii) Metalloids: Arsenic, germanium, boron

Answer:

(a) Mixtures: Mixtures are substance that contain two or more different kinds of particles or substances mixed together by physical methods.
    Examples: Air, brick

(b)
(i)  Homogeneous mixtures: Mixtures in which the constituting substances are mixed together completely and are indistinguishable from one another are called homogeneous mixtures. Such mixtures have a homogeneous composition of their substances throughout the solution.  Examples: Sugar solution, salt solution
(ii)  Heterogeneous mixtures: Heterogeneous mixtures are mixtures in which the constituting substances remain separated and one substance is spread throughout the other substance as small particles, droplets or bubbles.
Examples: Starch solution, soap solution

(c) Other name for homogeneous mixtures is solutions.

Answer:

(a) Three general classes of matter are elements, compounds, and mixtures.
Element: Oxygen
Compound: Water
Mixture: Salt solution
(b) Following flowchart represents different types of matter:

Answer:

(c) Silica.

Silica is a compound made up of Si (silicon) and O (oxygen) and chemically called Silicon dioxide.

Answer:

(c) (i) and (iii)

CO and NO are compounds. While CO is made up of carbon and oxygen, NO is made up of nitrogen and oxygen.

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(b) germanium
Germanium is metalloid. It is neither a good conductor of electricity nor an insulator. It is a semiconductor.

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(c)  alcohol
Air, kerosene oil and petrol are mixtures of various compounds of carbon and hydrogen (called hydrocarbons). Alcohol is a compound and not a mixture.

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(b) hydrogen
Washing soda (soda ash), Na₂CO₃ contains Na, C and O, whereas baking soda, NaHCO₃, is made up of Na, C, H and O. So, the element, which is not common in the two, is hydrogen.

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(b) a metal
Metals are malleable and ductile as they can be hammered into thin sheets and can be stretched into wires.

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(c) gallium
Boron, silicon and germanium are metalloids. Gallium is a metal.

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(d) bromine and iodine
Mercury is a metal that exists in liquid state and bromine is a non-metal that exists in liquid state.

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(b)  first absorbed then released

When a mixture of iron and sulphur is heated strongly, they first absorb the energy to get excited. This is followed by the formation of a new compound iron sulphide (FeS) with the release of huge amount of energy in the form of heat and light.

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(c) copper metal is ductile and has low electrical resistance
Copper is a good conductor of electricity. It means that it offers very low electric resistance. Also, it is highly ductile due to which it can be drawn into very thin wires.

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(b) an impure substance
Milk is considered to be an impure substance as it is an emulsion. Emulsion is a colloid in which minute droplets of one liquid are dispersed in another liquid, which is not miscible with it.

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(b) (i) and (iii)
A pure substance is made up of only one kind of particles like elements. The composition of pure compounds is also same throughout.

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(c) (i) and (iv)
Ice and air are homogeneous in nature as their compositions remain same throughout.

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(d) (i), (iii), and (iv)
Statements (i), (iii), and (iv) are correct. When two elements combine in a chemical reaction to give a product, the product is a compound. Composition of a compound has a fixed ratio and its properties are different from the elements participating in the reaction.

Answer:

(c) air
Air is a homogeneous mixture of different gases. Hence, it does not have a fixed melting or boiling point.

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Steam does not belong to the given set. While steam is a compound, all others are elements.

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(a) Here, iron powder and sulphur powder are mixed together. B is a mixture (Fe + S).

(b) Here, iron powder and sulphur powder are mixed together and heated strongly on a burner. So, C is the compound iron sulphide(FeS).

(c) (i) Here, dilute HCl was added to C (iron sulphide)to obtain D, which is hydrogen sulphide gas.           
FeS + 2HCl → FeCl₂ + H₂S

(ii) When dilute HCl is added to B, Fe present in the mixture reacts with the acid to form hydrogen gas.
Fe + HCl → FeCl₂ + H₂

(d) Gas D smells like rotten egg.

(e) When a burning stick is held in the gas, the gas itself catches fire with blue flame and a ‘pop’ sound. In the process, the burning stick extinguishes.

Answer:

(a) Substance X does not have a fixed melting or boiling point. Moreover, it shows the properties of its constituents. So, it must be a mixture.
Sugar solution in water is a substance like X.
(b) Substance Y has a fixed melting or boiling point but it cannot be split into simpler substances by chemical processes. Hence, it must be an element.
Hydrogen is a substance like Y.
(c) Substance Z is also a pure substance whose properties are entirely different from those of its constituents. Hence, it must be a compound.
Sugar is a substance like Z.
(d). Formation of Z (a compound) involves absorption or release of an appreciable amount of energy.
(e) The three groups are metals, non-metals and metalloids. All the substances like Y are divided into these groups on the basis of their properties.

Answer:

(a) Group of materials P is element.
(b) Q is a non-metal. Examples: Carbon(s), and bromine (l)
(c) R is a metal, as most of them are good conductors of heat and electricity. Examples: Copper, and aluminum
(d) S is a metalloid, as they have intermediate properties of those of metals and non-metals. Examples: Arsenic, and antimony
(e) R is a metal, therefore, it is malleable and ductile.

Answer:

(a) Liquid B has a very high boiling point. It also vaporises on heating. It is a conductor of electricity and is used in making thermometers. So, B could be an element. Further, liquid B is mercury as mercury is a liquid metal, which expands on heating and is used extensively in thermometers.
(b) Liquid C has a moderate boiling point. It could be a mixture. It is a salt solution because when C is heated, it vaporises and leaves behind a white solid (salt), which is used in the process of cooking.
(c) Liquid A is used in motor vehicles as fuel, either alone or after mixing with petrol. It could be a compound because on heating, it does not leave any residue. It is alcohol as alcohol is being used in motor vehicles nowadays.
(d) Solid D is sodium chloride. It is also known as common salt and is added in food.
(e) Liquid E is water as, on heating, liquid C, which is a salt solution, leaves water vapours. On condensing these vapours, we obtain pure water. When water is mixed with anhydrous copper sulphate, we obtain a blue colour solution. This is because of the formation of hydrated copper sulphate solution.

${\mathrm{CuSO}}_4+5{\mathrm{H}}_2\mathrm{O}\to \underset{\mathrm{hydrated} \mathrm{copper} \mathrm{sulphate}}{{\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}}$

Answer:

(a) Solution has the smallest particles.
(b) Suspension has the largest particles.

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Dissolution of a solid in liquid form a homogenous mixture called solution. Solution is clear in nature as the solid particles (solute) in a solution are very small and get completely dissolved in the liquid (solvent).

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Soap solution is a colloidal solution. Therefore, it scatters light due to large particles and creates Tyndall effect.

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Colloids are heterogeneous mixtures. The size of the particles in the colloids is bigger than the size of particles in the true solutions.

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Percentage method is the most common way of expressing the concentration of a solution.

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To make the salt solution of 15% with 15 gm as the mass of the solute, the mass of the solvent must be 85 gm.
$\mathrm{concentration}=\frac{\mathrm{mass} \mathrm{of} \mathrm{solute}}{\mathrm{mass} \mathrm{of} \mathrm{solute} + \mathrm{mass} \mathrm{of} \mathrm{solvent}}\times 100$
Mass of solution = mass of solute + mass of solvent
Mass of the solvent = mass of the solution – mass of solvent
= 100 – 15 = 85 gm
Therefore, 85 gm of water should be added.

Answer:

Volume of solute = 12 ml
Volume of solution = volume of solute + volume of solvent    
Volume of solvent = volume of solution – volume of solvent
= 100 – 12 = 88 ml

$$\begin{gathered} \mathrm{concentration}=\frac{\mathrm{Volume} \mathrm{of} \mathrm{solute}}{\mathrm{volume} \mathrm{of} \mathrm{solute}+\mathrm{volume} \mathrm{of} \mathrm{solvent}}\times 100 \\ 12=\frac{12}{12+x}\times 100 \\ x=88 \end{gathered}$$

So, 88 ml of water will be added to 12 ml of alcohol in order to prepare a concentration 12%.

Answer:

A 5% sugar solution means 5 gm of sugar is dissolved in 95 gm of water. Therefore, the correct option is “a”.

Answer:

(a) A
15% alcohol solution means 15 ml alcohol is dissolved in 85 ml of water.  Therefore “a” is the correct option.

Answer:

$\mathrm{concentration}=\frac{\mathrm{mass} \mathrm{of} \mathrm{solute}}{\mathrm{mass} \mathrm{of} \mathrm{solute}+\mathrm{mass} \mathrm{of} \mathrm{solvent}}\times 100$

Given, Mass of salt is 2.5 gm and mass of water is 50 gm.
So, total mass of the solution = 50 gm + 2.5 gm  = 52.5 gm
Hence, concentration $=\frac{2.5}{52.5}\times 100=4.7\%$

Answer:

Given, Mass of urea = 16 gm
Mass of solution = 120 gm    

$$\begin{gathered} \mathrm{concentration}=\frac{\mathrm{mass} \mathrm{of} \mathrm{solute}}{\mathrm{mass} \mathrm{of} \mathrm{solute}+\mathrm{mass} \mathrm{of} \mathrm{solvent}}\times 100 \\ =\frac{16}{120}\times 100 \\ =13.333\% \end{gathered}$$

Therefore, the concentration is 13.333%.

Answer:

Volume of alcohol = 5.6 ml
Volume of water = 75 ml
So, volume of solution = 75ml + 5.6 ml = 80.6 ml

$$\begin{gathered} \mathrm{concentration}=\frac{\mathrm{volume} \mathrm{of} \mathrm{solute}}{\mathrm{volume} \mathrm{of} \mathrm{solute}+\mathrm{volume} \mathrm{of} \mathrm{solvent}}\times 100 \\ =\frac{5.6}{80.6}\times 100 \\ =6.9\% \end{gathered}$$

Answer:

Volume of acetone = 25 ml
Volume of solution = 150 ml

$$\begin{gathered} \mathrm{concentration}=\frac{\mathrm{volume} \mathrm{of} \mathrm{solute}}{\mathrm{volume} \mathrm{of} \mathrm{solute}+\mathrm{volume} \mathrm{of} \mathrm{solvent}}\times 100 \\ =\frac{25}{150}\times 100 \\ =16.667\% \end{gathered}$$

Answer:

When the temperature of a saturated sugar solution is increased, it would become unsaturated due to increase in solubility of the solute.

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An unsaturated solution contains less amount of solute as compared to the saturated solution at a given temperature and pressure.

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Water undergoes a physical change when it is heated to a temperature of 100°C. At this temperature, the water gets converted to water vapours. This process is called evaporation. Water undergoes a chemical change when it is subjected to electricity. It splits into its constituents, oxygen and hydrogen, by the process of electrolysis.

Answer:

(a) True.  Solid foam allows the gas to get dispersed in solid medium.
(b) False. Sponge is an example of solid foam.

Answer:

Colloid includes the other three. Aerosol, sol and emulsions are different types of colloids.

Answer:

Soap solution is a sol. Sol is a colloid in which tiny solid particles are dispersed in a liquid medium.

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(a) Milk is a colloidal solution but vinegar is a true solution.
(b) A colloid is a heterogeneous mixture and its components can be separated by the technique known as centrifugation.

Answer:

(a) Solute is a substance, which is dissolved in a liquid to prepare a solution.
Examples: Sugar, salt etc.

(b) Solvent is a liquid or a medium in which the solute is dissolved.
Example: Water

Answer:

Answer:

Answer:

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True Solutions: Salt solution and sugar solution.
Colloidal Solutions: Starch solution, ink, and blood

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(i) The given solution is kept in a beaker.
(ii) A strong beam of light is then passed through the solution in the beaker, which is kept in a dark room.
(iii) If the path of light beam is illuminated and becomes visible, it confirms that the given solution is a colloid.

Answer:

Colloidal solution is a heterogeneous mixture in which particle size is intermediate of true solution and suspension, i.e., between 1 nm to 100 nm.
When a beam of light is passed through a colloidal solution, the particles of the solution get illuminated and become visible. This is because colloidal particles scatter the light falling on them.

 

Answer:

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A suspension and a solution can be differentiated by Tyndall effect. Suspensions, due to bigger size of their particles scatter the beam of light passing through them and show Tyndall effect whereas solutions have a very small particle size; hence, cannot scatter the light that passes through it.

Answer:

In the given options, starch solution and milk will show Tyndall effect because they are examples of colloidal solution. They have considerable size of particles that can cause scattering of light and make it visible. On the other hand, salt solution and copper sulphate solution are examples of true solutions. Abiding by the properties of true solution, they cannot scatter light as the size of their particles is very small; hence, they cannot show Tyndall effect.

Answer:

There are five types of solutions. These are:
(a) Solution of a solid in a solid. Example: Brass is a solution of zinc and copper.
(b) Solution of a solid in a liquid. Examples: Salt solution and sugar solution
(c) Solution of a liquid in a liquid. Example: Vinegar is a solution of acetic acid in water.
(d) Solution of a gas in a liquid. Example: Soda water is a solution of carbon dioxide gas in water.
(e) Solution of a gas in a gas. Example: Air is a solution of different gases (oxygen, carbon dioxide, nitrogen, argon etc.).

Answer:

Solutions: Soda water, brine
Suspension: Chalk water mixture, muddy water, milk of magnesia
Colloids: Milk, shaving cream, ink, blood and smoke in the air

Answer:

(a) Sol: Sol is a colloidal suspension of very small solid particles in a continuous liquid medium. They are quite stable and show Tyndall effect. Examples include blood, pigmented ink and paint.
(b) Aerosol:  Aerosol is a colloidal suspension of fine solid particles or liquid droplets in a gas. Examples are clouds and air pollution such as smog and smoke.
(c) Emulsion: Emulsion is a colloid of two or more liquids that are normally immiscible.  Examples of emulsions include milk and butter.
(d) Foam: Foam is formed by trapping pockets of gas in a liquid. Examples of foam include beer foam and shaving cream.

Answer:

Concentration of a solution refers to the amount of solute present in 100 gm of solution. It is expressed by ‘percentage method’. The percentage of solute can be ‘by mass’ or ‘by volume’.
$\mathrm{concentration} \mathrm{of} \mathrm{solution}=\frac{\mathrm{mass} \mathrm{of} \mathrm{solute}}{\mathrm{mass} \mathrm{of} \mathrm{solvent}}\times 100$

Answer:

(i) If a saturated solution is heated to a higher temperature, it becomes unsaturated. In this unsaturated solution, more solute can now be added. In other words, the saturation point of a solution increases with the increase in temperature. It occurs due to increase in solubility of the solute.

(ii) If a saturated solution is cooled to a lower temperature, some of its dissolved solutes get separated in the form of solid crystals. This process is called crystallisation. It occurs because the solubility of the solute in the solution decreases on cooling.

Answer:

According to the question:
60 gm of water dissolves  21.5 gm of NaCl.
So, 100 gm of water will dissolve $=\frac{21.5}{60}\times 100=35.8 \mathrm{g} \mathrm{of} \mathrm{NaCl}$
Thus, the solubility of NaCl = 35.8 gm

Answer:

According to the question:
30 gm of water dissolves  9.72 gm of KCl.
So, amount of KCl that gets dissolved in 100 gm of water $=\frac{9.72}{30}\times 100=32.4$
Thus, the solubility of KCl = 32.4 gm

Answer:

 i. Cooking of food – Chemical change
ii. Boiling of water – Physical change
iii. Cutting of trees – Chemical change
iv. Dissolving salt in water – Physical change
v. Digestion of food – Chemical change
vi. Melting of ice – Physical change

Answer:

(a) Burning of magnesium wire – Chemical change
(b) Freezing of water – Physical change
(c) Rusting of iron – Chemical change
(d) Glowing of electric bulb – Physical change

Answer:

(a) Formation of curd from milk – Chemical change
(b) Condensation of steam – Physical change
(c) Growth of plant – Chemical change
(d) Breaking of a glass tumbler – Physical change

Answer:

Physical change: Sublimation of a solid, making a fruit salad from raw fruits, formation of clouds, and dissolution of carbon dioxide in water
Chemical change: Decomposition of water into hydrogen and oxygen by passing electric current (electrolysis)

Answer:

Physical change: Melting of candle wax, mixing of iron fillings and sand, breaking of of chalk, and cutting of paper
Chemical change: Burning of candle wax, burning of wood, and burning of paper

Answer:

Seawater can be termed as homogeneous as well as heterogeneous mixture.
Seawater is basically a salt solution, which is termed as homogeneous. But the concentration of salt in the sea can vary from place to place. It depends on environmental factors.  Hence, seawater is considered heterogeneous as well.

Answer:

Sugar solution, salt solution, copper sulphate solution, and ammonium chloride solution do not show Tyndall effect because the particles in these solutions are too small to scatter light in different directions.

Answer:

(a) Physical change: These are changes in which no new substances are formed. These are temporary changes, which are easily reversible. The substance, which is involved in a physical change, does not lose its identity.
Examples:
(i) Water, if boiled, can be cooled and condensed.
(ii) Mixing of iron fillings with sand is a physical change because they can be separated by a magnet.

(b) Chemical change: These changes occur when a substance combines with another to form a new substance. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.
Examples:
(i) Rusting of iron
(ii) Burning of paper

Answer:

(a) Important differences between a physical and a chemical change are given below:

Answer:

Solubility is a property of a solid, liquid, or gaseous chemical solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution.
Solubility of a given solute in a given solvent depends on temperature. For many solids dissolved in liquid water, the solubility increases with temperature up to 100°C. In liquid water at high temperatures (e.g., that approaching the critical temperature), the solubility of ionic solutes tends to decrease due to change in the property and structure of liquid water. The lower dielectric constant results in a less polar solvent.
Gaseous solutes exhibit more complex behavior with temperature. As the temperature is raised, gases usually become less soluble in water (to minimum, which is below 120°C for most permanent gases), but they are more soluble in organic solvents.

(b) This statement means that 20.7 gm of copper sulphate can be dissolved in 100 gm of water at 20°C.

(c) Solubility of solids in liquids generally increases on increasing the temperature and decreases on decreasing the temperature of the solvent.

Answer:

(a) Solution is a homogeneous mixture composed of one phase only. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The solvent dissolves the solute in it. The solution more or less takes on the characteristics of the solvent including its phase. Moreover, the solvent is commonly the major fraction of the mixture.
Example: Sugar solution, vinegar, metal alloys

(b) A suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. The solids get dispersed throughout the fluid through mechanical agitation with the use of certain suspending agents.
Example: Chalk-water mixture, flour in water, milk of magnesia

(c) Colloidal solution is a heterogeneous mixture, wherein the particle size of the substance is intermediate of true solution and suspension, i.e., between 1 nm to 100 nm. Like true solutions, colloidal particles are small enough and cannot be seen through naked eye. They easily pass through the filter paper. However, these particles are big enough to be blocked by parchment paper or animal membrane.
Example: Starch solution, ink

Answer:

 (a) A saturated solution is one that does not allow dissolution of additional solutes in it at a specific temperature.
An unsaturated solution is one that allows dissolution of additional solutes in it at the same temperature.

If a crystal dissolves in a solution, the solution is said to be unsaturated. This is because an unsaturated solution is capable of dissolving additional solutes into it.

A saturated solution does not dissolve additional solutes or crystals in it. Therefore, the crystal keeps its size when it is put in a saturated solution.

On cooling the solutions, the saturated solution will first form crystals.

(b) We will dissolve sodium chloride or NaCl in water in room temperature, till the water can no longer dissolve any more salt. By doing so, we will obtain a saturated solution of sodium chloride.
If the temperature is lowered from 25°C to 10°C, some of its dissolved solutes will get separated in the form of solute crystals due to the decrease in solubility of the solute.

Answer:

(b) bread
Solid foam is a colloid in which a gas is dispersed in a solid medium. Bread is an example of solid foam.

Answer:

(d) shaving cream
Shaving cream is not an emulsion but foam.

Answer:

(c) sugar solution
Sugar solution does not show Tyndall effect because sugar solution is a true solution and not a colloid.

Answer:

(c) chalk powder in water mixture
Chalk in water will most likely scatter the beam of light when passed through it because it forms a suspension.

Answer:

(d) suspension
Milk of magnesia is a suspension of magnesium hydroxide in water. It has milk like texture.

Answer:

(b) 204 g
Solubility of a substance in water is defined as the maximum amount of solute that can be dissolved in 100 g of water at a given temperature. The solubility of sugar in water at 20⁰C is 204 g.

Answer:

(c) sublimation of naphthalene
Sublimation of naphthalene is not a chemical change because it only allows naphthalene to change its state from solid to vapour. No new compound is formed and the vapour can again be condensed to solid form.

Answer:

(a) brine
Brine is salt solution. When it is heated, water will evaporate and salt will be left as residue.

Answer:

(b) milk of magnesia
Milk of magnesia is a suspension of magnesium hydroxide in water. It has a milk-like texture. The particles are suspended in the solvent. Milk is a colloid, whereas salt solution and vinegar are solutions.

Answer:

(b) brass
Brass is an example of solution of solid in solid. It is an alloy of copper and zinc.

Answer:

(c) corrosion and it is a chemical change
Rusting of iron takes place in the presence of air (O2) and water vapour. Action of air and moisture on iron converts it to its oxide. This process is called corrosion and it leads to the formation of a new compound. Therefore, it is a chemical change.

Answer:

(d) homogeneous and does not show tyndall effect

Sulphur dissolves completely in carbon disulphide. So, it forms a homogeneous solution. As the particles of solute are too small to scatter light, they will not cause tyndall effect.

Answer:

(d) iodine in alcohol
Iodine dissolved in alcohol is called tincture of iodine.

Answer:

(c) (i), (iii) and (iv)

The process in statement (ii) is a chemical change because rusting causes formation of  a new compound. Other statements are examples of physical changes where no new compounds are formed. In the process mentioned in other statements, original form of iron can be obtained back from moulded forms.

Answer:

(a) (i) and (ii)

The processes in statements (i) and (ii) are chemical changes because decaying and burning causes formation of new compounds; thus they are chemical reactions. The processes in statements (iii) and (iv) are physical changes where no new compounds are formed.

Answer:

The instruction written on the bottles of indigestion mixtures is “shake well before use”.
This is because indigestion mixtures are suspensions. If they are left undisturbed, the particles of suspensions settle down. Therefore, it is instructed to shake the bottle before using it.

Answer:

(a) Mixtures like A are known as suspensions.
(b) Mixtures like B are known as colloids.
(c) Mixtures like C are known as true solutions.
(d) The phenomenon exhibited by A and B, which occur on passing a beam of light through them, is called Tyndall effect.   
(e) (i) Mud water mixture is like A.
     (ii)Soap solution is a mixture like B.
    (iii)Sugar solution is a mixture like C.

Answer:

(a)When solid A is dissolved in water, chemical change takes place. This is because the properties of products B and C are entirely different from those of solid A and water.
(b) Physical change occurs when solid D is dissolved in water. This is because product E shows the properties of both, solid D and water.
(c) Sodium metal could behave like solid A.
Product B is sodium hydroxide.
Product C is hydrogen.
(d) Solid D is ammonium chloride.
(e) D can be recovered from E by evaporation.

Answer:

(a) X type of solutions is known as unsaturated solution.
(b) Y type of solutions is known as saturated solution.
(c) If solution Y at 30°C is cooled down to 10°C by keeping the beaker in crushed ice, some of the dissolved parts of the solid will separate from the solution and will settle at the bottom of the beaker as crystals. This occurs because of the decrease in the solubility of solids and reduction in temperature.
(d) Solubility refers to the amount of a solid dissolved in 100 grams of water.

Answer:

Given that,
Solubility at 40°C = 41 gm
solubility = Solid dissolved in 100 grams of water in a solution
So, mass of ammonium chloride, required to make a saturated solution of ammonium chloride, in 50 gm of water at 40°C = $\frac{41}{2}\mathrm{g}$ = 20.5 gm

Answer:

Carbon disulphide can be used as a solvent to separate the mixture of sulphur and carbon.

Answer:

Process of sublimation can be used to separate a mixture of sodium chloride and ammonium chloride.

Answer:

Sublimation can be used to separate the mixture of naphthalene and common salt.

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Process of sublimation can be used to separate the mixture of anthracene and copper sulphate.

Answer:

Camphor can be separated from its mixture with salt by the process of sublimation.

Answer:

Electromagnets are fitted in cranes to separate scrap iron objects from a heap of waste material in factories.

Answer:

Iodine’s property of sublimation can be used to separate the mixture of salt and iodine.

Answer:

Miscible liquids can be separated by the process of fractional distillation, which is based on the principle of difference in the boiling points of the constituents of  a mixture.

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The property that enables the separation of two miscible liquids by fractional distillation is the difference in their boiling points.

Answer:

Water and alcohol, from a mixture of water and ethanol can be separated by fractional distillation.

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Kerosene and water are two immiscible liquids which can be separated by using a separating funnel.

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(a) False. Because alcohol is separated from the mixture of alcohol and water by distillation.
(b) True. As water can undergo the process of evaporation forming vapours, which can be collected in a separate container and can be easily separated from a salt solution.

Answer:

Air is the major source of nitrogen and oxygen.

Answer:

Various gases of air are separated by fractional distillation.

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Iron nails are attracted by magnet. Thus, they can separated from saw dust using magnetic separation.

Answer:

Mixture of camphor and common salt can be separated by sublimation.

Answer:

Mixture of alcohol and water can be separated by distillation.

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Process of filtration can be used to separate a mixture of chalk powder and water.

Answer:

Filtration can be used to separate a mixture of salt solution and sand.

Answer:

Evaporation can be used to obtain salt from an aqueous salt solution.

Answer:

Centrifugation is used in milk dairies to separate cream from milk.

Answer:

Centrifugation is used to separate cream from milk.

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Filtration is the process by which tea-leaves are separated from prepared tea.

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We would use the process of distillation to separate a mixture of water and alcohol.

Answer:

We would use a separating funnel to separate oil from water.

Answer:

The differences in the properties of oil and water that enable their separation by separating funnel are:
(i) Oil and water are immiscible liquids.
(ii) Oil and water have different densities.

Answer:

(a) Common salt is obtained from seawater by the process of evaporation.
(b) Common salt is purified by the process of crystallization.

Answer:

An impure sample of copper sulphate can be purified by the process of crystallization.

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(a) The process of evaporation can be used to recover all the dye from black ink.   
(b) Paper chromatography is the process by which various 'dyes' (coloured materials) present in black ink can be separated.

Answer:

Centrifugation is a technique used in a washing machine to squeeze out water from wet clothes while drying.

Answer:

Chromatography is a technique that can be used to detect and identify traces of poison in the stomach of a person.

Answer:

(a) Miscible liquids are separated by fractional distillation.
(b) Immiscible liquids are separated by using a separating funnel.
(c) A mixture of kerosene and petrol can be separated by fractional distillation.
(d) The separation of liquids by fractional distillation is based on the difference in their boiling points.
(e) The gases of air can be separated by fractional distillation of liquid air because they have different boiling points.
(f) A heterogeneous mixture of liquid and solid is conveniently separated by centrifugation.
(g) If a mixture contains iron fillings as one of the constituents, it can be separated by using a magnet.

Answer:

We will use filtration to separate a mixture of sand and sugar. Sugar dissolves in water but sand does not. These properties of sugar and sand allow them get separated by filtration.
In filtration, suspension can be filtered using a filter paper leaving sand as residue on the filter paper. Now, the filtrate contains sugar only.  Sugar can further be recovered from the filtrate.

Answer:

The differences in the properties of common salt and sand that enable us to separate a mixture of these two substances are:
(a) Difference in the solubility of sand and salt. Salt is soluble in water, whereas sand is not. Therefore, we can separate sand from salt by taking water as solvent in the process of filtration.
(b) Salt is a solid that cannot vaporise. Thus, it can be obtained by the process of evaporation. In this process, all the water will evaporate leaving behind common salt.

Answer:

Separation of common salt and sand from a mixture involves the processes of filtration, followed by evaporation.
Sand can be separated from a mixture of sand and salt solution (salt dissolved in water) by filtration. After filtration, sand remains on the filter paper as a residue. Common salt can now be obtained from the filtrate by boiling it. Boiling causes all the water to evaporate and salt is left behind. This process is called evaporation.

Answer:

We will separate a mixture of sugar and salt by filtration followed by evaporation. In this process, solvent used is alcohol instead of water because of the difference in solubility of salt and sugar in alcohol. Salt is insoluble in alcohol but sugar is soluble in it. The undissolved salt can be obtained by filtration.
The filtrate now has only sugar dissolved in alcohol. On heating, alcohol evaporates and sugar is left behind.

Answer:

 Two processes are involved in separation of sodium chloride and sand, i.e., filtration followed by evaporation. The mixture of sodium chloride and sand can be separated by the following method:

• Take the mixture of sodium chloride and sand in a china dish. Pour some water in the mixture of sodium chloride and sand.
• After few seconds, all the sodium chloride will dissolve in water but sand will not.
• Then pour the contents of the container in a funnel fitted with a filter paper.
• Sand remains on the paper as residue and sodium chloride dissolved in water passes through it to the funnel.
• Now put the salt solution of the funnel on heat. Water starts getting evaporated leaving salt as residue in the funnel.
• Remove the funnel from heat.

Answer:

A mixture of sand and potash alum is separated by filtration followed by evaporation. The mixture contains two constituents, i.e., potash alum and sand.
Mix both the constituents thoroughly with water so that potash alum gets dissolved in water. However, sand, being insoluble in water, will not get dissolved in it. On filtering the liquid,  the solid that is left behind will be the sand, and the liquid will be a solution of potash alum. Potash alum can now be re-crystallized by heating the solution gently. In the process, all the water gets evaporated leaving behind potash alum.

Answer:

We would obtain sodium chloride from a mixture of sodium chloride and sulphur by using carbon disulphide as a solvent instead of water. Sulphur is soluble in carbon disulphide, whereas sodium chloride is not. So, we can mix sulphur and sodium chloride in carbon disulphide as all the sulphur will get dissolved and sodium chloride will remain insoluble. Then, sodium chloride can be obtained from the mixture by filtration, where it would be obtained as a residue.

Answer:

We would separate iodine from a mixture of iodine and common salt by the process of sublimation. In the process, iodine sublimes on heating, whereas salt does not. Salt has a melting point higher than that of iodine. Therefore, a mixture of iodine and sodium chloride can be separated by using a sublimation apparatus, where solid iodine is collected by condensation of the mixture.

Answer:

Sublimation method is used to separate a mixture of camphor and sand.
Camphor is a volatile solid and can be separated from any other non-volatile substance by heating. Sand is a non-volatile substance. When a mixture of sand and camphor is heated, sand will remain in the container but camphor will vaporise. These vapours are collected and condensed on a cold surface.

Answer:

We can separate a mixture of iron filings and powdered carbon by using a magnet. The principle behind the separation of iron fillings and powdered carbon is the property of iron to get attracted by magnets. When the magnet is brought close to the mixture, iron fillings are attracted by the magnet and get collected on the surface of the magnet. In the process, powdered carbon is left behind as residue.

Answer:

We can separate a mixture of iron filings and sulphur powder by using a magnet. The principle behind the separation of iron fillings and sulphur powder is the property of iron to get attracted by magnets. When the magnet is brought close to the mixture, iron fillings are attracted to the magnet and get collected on the surface of the magnet.  In the process, sulphur powder is left behind as residue.

Answer:

Scrap iron is separated from a heap of waste materials in factories by using large electromagnets fitted to a crane.  The electromagnet fitted crane is moved up and away from the waste to drop these scrap iron objects at a separate place. Electromagnets are used for this purpose because one can switch on and off the supply of magnetism during the process of lifting and dropping of the iron pieces.

Answer:

The impurity of iron present in several substances in the industries is removed using electromagnets. Waste materials supplied to the industries contain a number of scrap metals including iron.
Iron objects stick to the electromagnet and are collected at a separate place, leaving behind other objects.

Answer:

We will use magnet to separate iron pins from sand. The property of iron to get attracted towards a magnet is used to separate it from sand.
A magnet is moved on the surface of the mixture. Iron pins are attracted by the magnet. They cling to the poles of the magnet and get separated. This process is repeated till all the iron pins are separated.

Answer:

We will separate a mixture of common salt, sulphur powder and sand by the procedure based on the solubility of these compounds.
Sulphur is soluble in carbon disulphide but insoluble in water. Common salt is soluble in water but insoluble in carbon disulphide. Sand is insoluble in both.
When sand, common salt and sulphur is added to water and stirred vigorously, common salt will dissolve in water but others will not. The solution is then filtered using a filter paper. Filtrate containing common salt is subjected to evaporation to obtain salt.
The residue left on the filter paper contains sand and sulphur. Now, this residue is dissolved in carbon disulphide. Here, sulphur dissolves but sand remains undissolved. This is filtered again to leave behind sand as residue and sulphur solution as filtrate. The filtrate is then subjected to heating to evaporate carbon disulphide and obtain sulphur.

Answer:

We will separate a mixture of kerosene oil, water and sand by the following process:
1. First, we can separate sand from mixture by passing it through a filter paper or by decantation.
2. After that, we get a mixture of kerosene and water. Leave it undisturbed for some time.  Kerosene, being less dense than water, starts floating on it. By using a separating funnel, we can separate the mixture of kerosene and water.
3. Another process is by distillation. Water has a low boiling point (100°c), which allows it to evaporate easily. But kerosene having a boiling point of 175°C will remain undisturbed. Care should be taken as kerosene is inflammable.

Answer:

The method of separating a mixture containing common salt, sand and ammonium chloride employs three processes, i.e., sublimation followed by filtration and evaporation. To separate ammonium chloride from the mixture, we should first follow sublimation. In the process, ammonium chloride gets sublimed and a mixture of sand and salt is left behind.
To separate salt from the mixture, we should put the mixture in water. Salt will get dissolved in water and the insoluble sand will be obtained by filtration.
Lastly, salt is separated by evaporating the filtrate, where all the water evaporates leaving behind solid salt.

Answer:

We will use the following methods to separate camphor, common salt and iron nails from their mixture:

Take the mixture and pour it in a beaker of water. On stirring,  salt will dissolve, while iron nails and camphor will not. Fold a fluted piece of filter paper and put it on the funnel. Then filter the mixture to another beaker. The salt solution will pass through and iron filings and camphor will remain on the paper. Put the filtrate into an evaporating dish and heat it over a Bunsen burner so that the water will evaporate. Eventually, salt will be left behind. Pass the magnet over the camphor and iron filings. The magnet will attract the iron, leaving behind camphor as residue.

Answer:

By using evaporation and separating funnel process, we can separate the ground nut oil and common salt from the given mixture. First pour the mixture in a separating funnel and leave it for some time. As both salt solution and oil are immiscible, water settles down and oil will keep floating because of the difference in their densities. Now, open the stop–cock and take out the salt solution in the beaker. Ground nut oil is left in the funnel. After this, put the beaker on the funnel. Water will evaporate and salt will be left behind as residue.

Answer:

The method of separating a mixture containing chalk powder, iron filings and naphthalene employs the use of a magnet followed by sublimation. At first, a magnet is moved over the mixture. Iron fillings are attracted by the magnet and get separated. Then the chalk powder and naphthalene are separated by sublimation. In this process, the mixture of chalk powder and naphthalene is heated. Naphthalene sublimes on heating, and its vapours are condensed over a cold apparatus. Chalk powder, being nonvolatile, is left behind as residue.

Answer:

 Following steps are involved in separation of iron filings, chalk powder and common salt:
(1) At first, a magnet is moved on a mixture of iodine, iron fillings and salt. Due to the magnetic property of iron, iron fillings are separated by the magnet.
(2)  As all the iron is removed, the mixture now contains iodine and salt. Iodine sublimes on heating but salt does not. So, on heating the mixture, we obtain the vapours of iodine.
(3) Vapours of iodine are condensed in a cold apparatus. Salt remains behind as residue. Therefore, the components of mixture get separated.

Answer:

We will separate a mixture of iron filings, chalk powder and common salt by using a magnet followed by filtration and evaporation.
First, a magnet is moved on a mixture of iron filings, chalk powder and common salt. In the process, iron filings are separated by the magnet. After that, chalk powder and common salt are mixed in water. Salt dissolves in water but chalk powder does not. So, chalk powder is separated by filtration. On heating the filtrate, all the water is evaporated and salt crystals are left behind. 

Answer:

We will separate common salt, sand and iron filings from their mixture by using a magnet, filtration and evaporation.
First, a magnet is moved over a mixture of iron filings, sand and common salt. In the process, iron filings are separated by the magnet. After that, sand and common salt are mixed in water. While salt dissolves in water, sand does not. So, sand is separated by filtration. On heating the filtrate, all the water evaporates from the mixture and salt crystals are left behind.

Answer:

We will separate a mixture of kerosene oil and water using a separating funnel. Kerosene and water are immiscible liquids. They have difference in their densities.
Kerosene has lower density, i.e., it is lighter than water. So, it will form the upper layer and water will form the lower layer. On opening the stop-cock, the lower layer of water comes out first and is collected in a beaker. Kerosene is left behind in the separating funnel.

Answer:

We will separate water from mustard oil by using a separating funnel. Due to the difference in the densities of the two liquids, mustard oil, being lighter than water, floats over it and forms the upper layer, whereas water forms the lower layer. On opening the stop-cock, the lower layer of water comes out first and is collected in a beaker. Mustard oil is left behind in the separating funnel.

Answer:

We will separate cooking oil and water by using a separating funnel as cooking oil and water are two immiscible liquids. Due to the difference in the densities of the two liquids, cooking oil, being lighter than water, floats over it and forms the upper layer, whereas water forms the lower layer. On opening the stop-cock, the lower layer of water comes out first and is collected in a beaker. Cooking oil is left behind in the separating funnel.

Answer:

We will separate a mixture of mercury, oil and water by using a separating funnel. These three substances have different densities and boiling points. Mercury, being the heaviest among the three, comes out first via stop-cock. The density of water is lower than mercury but higher than oil. So, it forms the middle layer. Oil has lowest density among the three, and therefore it forms the upper layer. These liquids are then separated from the funnel layer by layer.

Answer:

The method for separating a mixture of iron filings and sulphur powder, employs the use of carbon disulphide as a solvent followed by filtration and evaporation.
Sulphur dissolves in carbon disulphide, whereas iron does not. So, the solution will contain undissolved iron in it. This can then be filtered using a filter paper, where iron remains as residue and is collected on the filter paper. The filtrate obtained contains sulphur dissolved in it. On evaporating the solvent of the filtrate, we obtain sulphur.

Answer:

Cream is separated from milk by the process of centrifugation. It is the process of separating the suspended particles from a liquid. The mixture is rotated at high speed in a centrifuge.
When milk is centrifuged, the cream and skimmed milk are separated. Cream, being lighter, starts floating on the skimmed milk and hence, can be separated.

Answer:

Impure copper sulphate can be purified by crystallization. Crystallization is a chemical solid–liquid separation technique in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.
Impure copper sulphate can be dissolved in minimum amount of water to prepare copper sulphate solution. It is then filtered to remove insoluble impurities. Now, copper sulphate solution is heated gently on a water bath to evaporate water and obtain a saturated solution. Heating should be stopped when all the water evaporates. The saturated solution of copper sulphate is then allowed to cool slowly. Crystals of pure copper sulphate are formed leaving behind impurities.

Answer:

Crystallization is a better than evaporation for recovering sugar from sugar solution. During evaporation, sugar can get charred on heating. However, in crystallization, no such problem occurs and we can get pure crystals of sugar.

Answer:

Chromatography is a technique used for separating two or more dissolved solids, which are present in the solution in small quantities.
Separation is based on the fact that two or more substances are soluble in the solvent but their solubility is different.
This technique has various important applications:
• To separate dyes present in black ink
• It is used in forensic science to detect and identify the trace amounts of poison present in the stomach.

Answer:

Water and kerosene mixture can be separated by using a separating funnel because these two are immiscible liquids and differ in their densities. Kerosene is less dense than water and water comes out first from the separating funnel.
 On the other hand, acetone and water mixture cannot be separated by using a separating funnel because they are miscible liquids. They are rather separated by fractional distillation.

Answer:

Fig., Separation of mixture of common salt and ammonium chloride by sublimation.

Sublimation is a method used for separating ammonium chloride from a mixture of ammonium chloride and common salt.

The procedure of separation is as follows:
• Mixture of common salt and ammonium chloride is taken in a china dish.
• This mixture is then kept on a burner.
• The china dish is covered with an inverted glass funnel.
• A loose cotton plug is placed over the open end of the funnel to prevent vapours from escaping.
• Mixture of common salt and ammonium chloride is then heated.
• Vapours of ammonium chloride are formed. These vapours, on rising, get condensed after coming in contact with the cold inner walls of the funnel.
• A white solid of pure ammonium chloride is obtained.
• Common salt does not change into vapours. So, it remains in the china dish.

This separation of ammonium chloride and common salt has been made possible by the difference in the properties of ammonium chloride and common salt. Ammonium chloride has a property to sublime, i.e., to get converted directly from solid to vapour state. However, common salt lacks this property. Also, ammonium chloride is a volatile substance, whereas common salt is nonvolatile in nature.

Answer:

We can obtain pure water from a saltwater mixture (or salt solution) by the process of distillation.  Important steps underlying the process are as follows:

• The salt water mixture is taken in a distillation flask and heated subsequently.
• On heating, water vapours are formed that rise up and come through the side tube B.
• It is then passed through condenser C.
• Cold water from the tap is circulated in the outer tube of the condenser, so that the hot vapours are cooled.
• The vapours condense and are collected in another beaker.
• This pure water is called distilled water.
• Salt, being non-volatile, remains in the flask and can be obtained later.

Fig., separation of salt and water using distillation

Answer:

Various processes are used to purify water on large scale at water works. The source of water for cities is nearby a river or a lake. This water generally contains suspended particles, dissolved impurities and germs. In order to supply this water to homes, it has to be purified. Following steps are involved to purify water at water works:
(i) In water works, methods like sedimentation, decantation, loading, filtration and chlorination etc., are used to remove undesirable materials from water.
(ii) The source of water supply in a city is either a nearby river or lake (reservoir). From there, it is pumped to a 'sedimentation tank'.
(iii) It is kept here for some time to allow the insoluble substances present in water to settle down at the bottom of the tank.
(iv) It is then sent to a 'loading tank', where some alum is added to water.
(v) Suspended clay particles in water get loaded here with alum particles. After becoming heavy, they settle down at the bottom of the tank. Thus, the process of loading removes the suspended clay particles from water.
(vi) It is then passed through a 'filtration tank' having three layers, i.e., fine sand layer on the top, coarse sand layer in the middle and gravel layer at the bottom .
(vii) These layers act as filters and remove small suspended particles of the water.
(viii) Water is then passed into a chlorination tank. Here, chlorine is added to water to kill the germs present in it.
(ix) Now the clean and disinfected water is pumped to high storage tanks by pumping stations. From these high storage tanks, water is supplied to homes and factories through a network of big and small pipes.


Fig., Water purification process at water works
Chlorine is added to water to kill germs in the drinking water supply.

Answer:

(a) Fractional distillation is a process of separating two or more miscible liquids by distillation. The distillate is collected in fractions, which boil at different temperatures. The principle behind this technique is the difference in boiling points of the liquids in the mixture.
The fractionating column is fitted in the neck of the distillation flask. Fractionating column provides different temperature zones inside the flask. The highest temperature is at the bottom and the lowest temperature is near its top.

(b)


Fig., Separation of mixture of alcohol and water by fractional distillation

Answer:

(a) Nitrogen, oxygen and argon are separated from air by fractional distillation. Following are the steps followed to separate these gases from air:
• Air is first filtered to remove the dust particles, spores etc. Subsequently water vapours and carbon dioxide are removed.
• Air is subjected to high pressure and then cooled. This air is then allowed to expand in a chamber which causes further cooling of the air.
• This process is repeated to cool the air further. Ultimately, the air becomes so cold that it turns into a liquid.
• This liquid air is then fed into a fractionating column from its bottom end and is cooled slowly.
• Liquid nitrogen boils off first to nitrogen gas as the boiling point of nitrogen is lowest at -196°C.
• Liquid argon boils off at a boiling point of -186°C.
• Liquid oxygen boils off last as it has highest boiling point among all three (around -183°C).

Fig. Separation of major gases of air

Answer:

(c) separating funnel
Milk and groundnut oil are two immiscible liquids. So, they can be separated by using a separating funnel.

Answer:

(c) sand and sulphur

Mixture of sand and sulphur cannot be separated by using water as a solvent because both are insoluble in water.

Answer:

(d) carbon disulphide

Sulphur is soluble in carbon disulphide but carbon is not.

Answer:

(d) chromatography 

Chromatography is the technique used to separate the contents of a mixture, where solute particles are in extremely small quantity.

Answer:

(d) crystallization
Crystallization is the process of cooling a hot concentrated solution of a substance to obtain its crystals in pure form.

Answer:

(c) chlorine

Chlorine is added to water to purify it from the impurities such as bacteria.

Answer:

(b) centrifugation

Centrifugation is a process, in which suspended particles are separated from the solvent. In this process, the solution is rotated at a high rate in a centrifuge thereby separating the solute particles and the solvent.

Answer:

(a) by sublimation

Naphthalene sublimes on heating, whereas sand does not. So, when the mixture is heated, solid naphthalene turns into vapours, which can be condensed. Sand remains in the container.

Answer:

(c) hydrogen

Hydrogen cannot be separated from the mixture of air as it is not present in free state. The three major components of air are nitrogen, oxygen and argon. These are separated using fractional distillation.

Answer:

(b) nitrogen, argon, oxygen

Boiling point of liquid nitrogen, liquid argon and liquid oxygen are -196°C, -186°C and -183°C respectively. So, nitrogen will boil off first followed by argon and oxygen.

Answer:

(c) –186°C

Answer:

(b) simple distillation

In the mixture of iodine and alcohol, both are miscible. So, distillation process is used to recover both the components.

Answer:

(d) crystallisation

Crystallisation is a better technique to recover sugar from sugar solution because sugar decomposes or gets charred on heating. Also, the soluble impurities get removed by crystallisation.

Answer:

(c) silica

Silica does not sublime on heating.

Answer:

(c) chromium

Chromium does not have magnetic property. Therefore, it will not be attracted by a magnet.

Answer:

(a) Y will be collected from the area near the bottom of the fractional distillation column because it has highest boiling point (−183°C).
(b) Z will be collected from the top part of the fractional distillation column because it has lowest boiling point (−196°C).
(c) X will be collected from the middle part of the fractional distillation column because it has a boiling point −186°C, which is lower than that of Y but higher than that of Z.
(d)X is liquid argon, Y is liquid oxygen, and Z is liquid nitrogen.

Answer:

(a) Liquid A is organic and liquid B is inorganic. When mixed, they form a single layer, i.e., they are miscible liquids. So, we will use fractional distillation to separate the mixture of liquid A and liquid B.
(b) Liquid B is inorganic and liquid C is organic. We will use a separating funnel to separate the mixture of liquid B and liquid C as they form two different layers.
(c)
(i) Liquid A is organic. When liquid A and liquid B are put together in a container, they form a single layer. So, alcohol would behave like liquid A.
(ii) Liquid B is inorganic. So, water would behave like liquid B.
(iii) Liquid C is organic. When liquid B and liquid C are mixed together, they form two separate layers. Oil would behave like liquid C.

Answer:

(a) P consists of tiny grains and it is mixed with cement for plastering the walls. So, P is sand. Q is a white solid, which is recovered on a large scale from sea water by the process of evaporation. It is common salt. R is in the form of tiny particles of materials, whose corrosion is called rusting. It is, iron filings. S is ammonium chloride.

(b) At first, let us take the mixture of P, Q, R, and S.
(i) We first separate R (iron filings) by using a magnet to attract them. Then separate S (ammonium chloride) by sublimation.
(ii) Now, we shake P (sand) and Q (common salt) with water. The mixture is then filtered.
(iii) Sand is obtained as residue.
(iv) Now, we will evaporate the filtrate to dryness to obtain Q (common salt).

Answer:

(a) Tincture iodine is a mixture of two materials X and Y. So, X is alcohol.
(b) The material Y has a property and its solid form can be converted directly into vapours on heating by the process called Z. So, Y is iodine.
(c) Process Z is called sublimation.
(d) Process used to recover both the components, i.e., alcohol and iodine, from the tincture of iodine is distillation.
(e) The process used to recover component Y only from the tincture of iodine is evaporation.

Answer:

(a)(i) Constituent A is yellow coloured solid element. It could be sulphur.
(ii) Sulphur dissolves in liquid D. So, liquid D could be carbon disulphide.

(b) (i) Constituent B is a blue coloured salt, which is insoluble in carbon disulphide but dissolves in water. So, it could be copper sulphate.
(ii) Liquid E could be water as it dissolves copper sulphate.

(c) Liquid C could be vegetable oil as it turns into a solid fat on hydrogenation.

(d) We will separate the mixture containing A, B, and C by following process:

•  At first, we filter the mixture of A, B, and C.
•  Vegetable oil C, being liquid, will be obtained as a filtrate.
•  Residue consists of A (sulphur) and B (copper sulphate).
•  We add water to the residue and shake it before filtering. A (sulphur) is obtained as     residue.
•  Now, we evaporate filtrate to obtain B (copper sulphate).