Here are 50 Assertion and Reason questions for CBSE Class 12 Chemistry, Chapter 6: "General Principles and Processes of Isolation of Elements." These questions are based on the NCERT Class 12 Chemistry textbook .
Reason (R): In this method, the ore particles are preferentially wetted by water and float over the surface, while impurities settle down.
Answer: (3)
Explanation: Froth flotation method is used for sulphide ores,
where the ore is wetted with oil to float, and impurities are left behind. The
assertion is correct, but the reason is incorrect.
Reason (R): Leaching is based on the principle of selective solubility of the ore in a solvent.
Answer: (1)
Explanation: Leaching involves dissolving the ore in a solvent
(e.g., using NaCN for gold ores), and the ore is selectively soluble in the
solvent. Both the assertion and reason are correct, and the reason explains the
assertion.
Reason (R): In this process, gold is dissolved in a dilute solution of sodium cyanide to form a soluble complex, [Au(CN)₂]⁻.
Answer: (1)
Explanation: The cyanide process involves the dissolution of
gold as a soluble complex with cyanide, making both the assertion and reason
correct, and the reason explains the assertion.
Reason (R): Electrolysis is used to reduce metal ions to their elemental form, as seen in the extraction of metals like aluminium.
Answer: (1)
Explanation: Electrolysis is the process of using electrical
energy to reduce metal ions into their elemental forms, which explains both the
assertion and reason.
Reason (R): In calcination, the ore is heated in the absence of air to remove volatile impurities like water and carbon dioxide.
Answer: (1)
Explanation: Calcination is the heating of ores in the absence
of air to remove volatile impurities, which makes both the assertion and reason
correct, and the reason explains the assertion.
Reason (R): In roasting, ores are heated in the presence of excess air to remove sulphur and other impurities.
Answer: (1)
Explanation: Roasting involves heating ores in the presence of
air, which helps convert them into their oxides and removes impurities such as
sulphur. The reason correctly explains the assertion.
Reason (R): The Hall-Héroult process involves the electrolysis of molten bauxite, which is a complex compound.
Answer: (3)
Explanation: The Hall-Héroult process involves the electrolysis
of alumina (Al₂O₃) dissolved in molten cryolite, not directly molten bauxite.
The assertion is correct, but the reason is incorrect.
Reason (R): In this process, carbon acts as a reducing agent and removes oxygen from the iron ore to produce iron.
Answer: (1)
Explanation: Iron is extracted by reducing haematite (Fe₂O₃)
with carbon (in the form of coke) in a blast furnace, which is explained
correctly by the reason.
Reason (R): Froth flotation separates copper ores from unwanted impurities by forming a froth of air bubbles.
Answer: (1)
Explanation: Froth flotation is used to concentrate ores,
including copper ores, by separating them from the impurities. Both the
assertion and reason are correct and related.
Reason (R): Roasting of zinc blende in the presence of oxygen leads to the conversion of ZnS to ZnO and the release of sulphur dioxide.
Answer: (1)
Explanation: Zinc blende (ZnS) is roasted in the presence of
oxygen, which oxidizes it to form zinc oxide (ZnO) and releases sulphur dioxide
(SO₂). The reason correctly explains the assertion.
Reason (R): Cyanide reacts with silver to form a soluble complex, [Ag(CN)₂]⁻, which can then be separated.
Answer: (1)
Explanation: The cyanide process is used for the extraction of
silver by forming a soluble complex with cyanide, as described in the reason.
Reason (R): Electrolytic reduction involves using electric current to separate the metal from its ionic form in the ore.
Answer: (1)
Explanation: Electrolytic reduction involves the use of
electric current to reduce metal ions to their elemental form, which is used in
the extraction of metals like aluminium.
Reason (R): Roasting helps in converting the ores into their oxides by heating them in air.
Answer: (1)
Explanation: Roasting is the heating of ores in the presence of
air, which leads to oxidation reactions that convert ores into oxides. The
reason explains the assertion.
Reason (R): Aluminium is extracted from its ore, bauxite, by electrolytic reduction of alumina (Al₂O₃).
Answer: (1)
Explanation: Aluminium is extracted through the Hall-Héroult
process, which is an electrolytic process, as described in the reason.
Reason (R): Electrolytic reduction requires molten electrolytes, which are maintained at high temperatures to reduce the resistance of the electrolytes.
Answer: (1)
Explanation: High temperatures are required in the electrolysis
of alumina to maintain the molten state of the electrolyte, enabling efficient
reduction of alumina. The reason explains the assertion.
Reason (R): Concentration removes impurities from the ore, increasing the metal content, making the extraction process more efficient.
Answer: (1)
Explanation: Ore concentration is crucial as it increases the
purity of the metal, making the subsequent extraction steps more efficient. The
reason explains the assertion.
Reason (R): Carbon monoxide reacts with metal oxides to reduce them to their elemental form by displacing oxygen.
Answer: (1)
Explanation: Carbon monoxide is a powerful reducing agent and
is used to reduce metal oxides to metals, as seen in the extraction of iron from
haematite.
Reason (R): In a blast furnace, iron ore is reduced by carbon, and impurities are removed as slag.
Answer: (1)
Explanation: The extraction of iron from haematite involves
reduction by carbon in a blast furnace and removal of impurities as slag, which
is explained in the reason.
Reason (R): Smelting involves heating the concentrated ore with a reducing agent to extract the metal.
Answer: (1)
Explanation: Smelting is used to extract metals by heating ores
with a reducing agent, which is a key step in the extraction of copper. The
reason explains the assertion.
Reason (R): Leaching uses solvents to dissolve metal ores, making it useful for extracting metals from ores with low concentrations of metal.
Answer: (1)
Explanation: Leaching is effective for extracting metals from
low-grade ores by dissolving the desired metal into a solvent. The reason
explains the assertion.
Reason (R): Zinc oxide is reduced to zinc metal by the action of coke at high temperatures.
Answer: (3)
Explanation: Zinc is not extracted using coke in a blast
furnace like iron. The reduction process for zinc usually involves other methods
such as using carbon or through the electrolytic reduction of zinc ores. Hence,
the assertion is correct, but the reason is incorrect.
Reason (R): Cyanide forms a soluble complex with gold ions, facilitating its extraction.
Answer: (1)
Explanation: Gold is extracted using the cyanide process, where
cyanide forms a soluble complex with gold ions, allowing its extraction. Both
the assertion and reason are correct and related.
Reason (R): Flux is a substance that reacts with impurities to form a molten slag, which is easily removed.
Answer: (1)
Explanation: Flux helps in removing impurities from ores during
the extraction process by forming slag with impurities. The reason correctly
explains the assertion.
Reason (R): In the leaching process, a solvent is used to dissolve the desired metal from its ore, leaving the impurities behind.
Answer: (1)
Explanation: Leaching is indeed a chemical method where
solvents are used to selectively dissolve metals from their ores, making it an
effective extraction method. Both the assertion and reason are correct.
Reason (R): In the Bayer process, bauxite is treated with sodium hydroxide to produce alumina (Al₂O₃).
Answer: (1)
Explanation: The Bayer process is used to extract alumina
(Al₂O₃) from bauxite, which is the first step in aluminium extraction. Both the
assertion and reason are correct, and the reason explains the assertion.
Reason (R): In this process, aluminium oxide is reduced electrolytically in molten cryolite.
Answer: (1)
Explanation: The Hall-Héroult process involves the electrolytic
reduction of alumina (Al₂O₃) in molten cryolite to produce aluminium. The reason
correctly explains the assertion.
Reason (R): Froth flotation relies on the difference in hydrophobicity between the ore and impurities, and oxide ores do not have enough difference.
Answer: (1)
Explanation: Froth flotation is more effective for sulphide
ores, not oxide ores, because oxide ores do not have the required hydrophobic
properties to separate effectively. The reason correctly explains the assertion.
Reason (R): Coke reduces iron oxides to iron and provides the necessary heat for the reaction in the blast furnace.
Answer: (1)
Explanation: Coke is used as both a reducing agent and a fuel
in the extraction of iron, where it reduces iron oxides and provides heat. The
reason explains the assertion.
Reason (R): Roasting involves heating the ore in excess air to convert sulphides into oxides, releasing sulphur dioxide.
Answer: (1)
Explanation: Roasting is used to convert copper sulphide (Cu₂S)
to copper oxide (CuO), and in the process, sulphur dioxide (SO₂) is released.
The reason explains the assertion.
Reason (R): The ore particles become hydrophobic in oil and hydrophilic in water, allowing selective separation.
Answer: (3)
Explanation: The froth flotation method involves oil for making
the ore particles hydrophobic, and air bubbles are used to separate the ore from
impurities. The reason is incorrect because water doesn't make the ore
hydrophilic in this method; rather, water is used to separate the impurities.
Reason (R): Cyanide reacts with the gold to form [Au(CN)₂]⁻, which can then be separated from the ore.
Answer: (1)
Explanation: Cyanide forms a soluble complex with gold,
allowing it to be extracted from the ore. Both the assertion and reason are
correct and related.
Reason (R): Roasting is used for the oxidation of ores, while calcination removes volatile impurities by heating the ore in the absence of air.
Answer: (1)
Explanation: Roasting is used for the oxidation of ores (e.g.,
sulphides), while calcination removes volatile impurities such as water or
carbon dioxide. The reason explains the assertion.
Reason (R): Copper is first smelted to obtain impure copper, which is then purified by electrolysis.
Answer: (1)
Explanation: Copper is extracted by smelting and then purified
by electrolysis to obtain pure copper. Both the assertion and reason are correct
and related.
Reason (R): Sodium chloride reacts with impurities in the ore to form a slag, which is easily separated from the metal.
Answer: (1)
Explanation: Sodium chloride is used as a flux to combine with
impurities and form slag during the extraction of metals, which can be easily
removed. The reason explains the assertion.
Reason (R): Carbon reacts with oxygen in metal oxides to produce carbon dioxide, thus reducing the metal to its elemental form.
Answer: (1)
Explanation: Carbon is commonly used as a reducing agent to
remove oxygen from metal oxides during extraction, forming carbon dioxide in the
process. The reason explains the assertion.
Reason (R): Iron oxide (Fe₂O₃) is reduced by carbon in the blast furnace, and impurities form a slag with calcium silicate.
Answer: (1)
Explanation: Iron extraction involves reducing iron oxide by
carbon and forming slag to remove impurities, as described in the reason.
Reason (R): Cryolite lowers the melting point of alumina and increases its conductivity for the electrolytic reduction process.
Answer: (1)
Explanation: Alumina (Al₂O₃) is dissolved in molten cryolite to
make the electrolysis process more efficient by lowering the melting point and
increasing conductivity.
Reason (R): Different methods are applied depending on the type of ore, such as roasting, calcination, or electrolysis.
Answer: (1)
Explanation: Metallurgical processes involve both chemical and
physical methods, and the choice of method depends on the type of ore. The
reason explains the assertion.
Reason (R): In roasting, ores are heated in the presence of air to convert them into oxides.
Answer: (1)
Explanation: Roasting involves heating ores in the presence of
air to convert them into oxides and remove impurities like sulphur and arsenic.
Reason (R): Coke serves as both a fuel and a reducing agent in the extraction process.
Answer: (1)
Explanation: Coke is used as both a fuel and a reducing agent
to extract metals like iron, as described in the reason.
Reason (R): Cyanide reacts with silver to form a soluble complex, allowing it to be separated from the ore.
Answer: (1)
Explanation: The cyanide process is used for the extraction of
silver, where cyanide forms a soluble complex with silver, making extraction
possible.
Reason (R): Leaching uses a solvent to selectively dissolve the metal from the ore, leaving behind the impurities.
Answer: (1)
Explanation: Leaching selectively dissolves metal from ores
using a solvent, which is then separated from the impurities, as explained in
the reason.
Reason (R): Carbon monoxide acts as a reducing agent to reduce iron oxides to iron.
Answer: (1)
Explanation: Carbon monoxide is used as a reducing agent to
reduce iron oxides to iron in the blast furnace. The reason explains the
assertion.
Reason (R): Calcium carbonate reacts with impurities to form calcium silicate, which is removed as slag.
Answer: (1)
Explanation: Calcium carbonate is added to the blast furnace to
react with impurities and form slag, which is then removed. The reason explains
the assertion.
Reason (R): Froth flotation separates the copper ore from the gangue based on their differential properties.
Answer: (1)
Explanation: Froth flotation is used to concentrate copper ore
by separating it from the gangue based on their differences in surface
properties.
Reason (R): Roasting involves heating the ore in air, causing sulphur to be oxidized to form sulphur dioxide.
Answer: (1)
Explanation: Roasting is a process where ores are heated in
air, and sulphur is oxidized to form sulphur dioxide, which is then removed.
Reason (R): The method is effective as it uses a solvent to selectively dissolve the metal, leaving impurities behind.
Answer: (1)
Explanation: Leaching is particularly useful for extracting
metals from low-grade ores by dissolving metals with solvents, as explained in
the reason.
Reason (R): In this process, alumina is reduced by electrolysis to produce aluminium metal.
Answer: (1)
Explanation: The Hall-Héroult process involves the electrolytic
reduction of alumina to produce aluminium metal, as described in the reason.
Reason (R): Physical methods like magnetic separation and chemical methods like roasting are employed to extract metals from ores.
Answer: (1)
Explanation: Both physical and chemical methods are used in the
extraction of metals, with physical methods like magnetic separation and
chemical methods like roasting.
Reason (R): Leaching uses a solvent to dissolve the desired metal from the ore, leaving the impurities behind.
Answer: (1)
Explanation: Leaching is a chemical process that selectively
dissolves metals from ores, making it an effective method for extraction. The
reason explains the assertion.