This set of Class 12 Chemistry Chapter 6 Multiple Choice Questions & Answers (MCQs) focuses on “Extraction of Crude Metal from Concentrated Ore”.
1. What is the type of metallurgy in which the ore is leached and the metal is collected by using electrolysis?
a) Zone refining
d) Thermite process
Explanation: Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials.
2. A metal found in a free state is called nugget.
Explanation: The statement is true. For example, we will take gold in this case, it’s a transition element and it is one of the least reactive chemical elements and is solid under standard conditions. So it exists in free elemental form as nuggets.
3. When is the ore subjected to leach?
a) When the ore is in immiscible liquid
b) When the impurity is in immiscible liquid
c) When both ore and impurity are insoluble in water
d) When only impurity is soluble in water
Explanation: The ore is subjected to leaching when both the ore and impurity are insoluble in water. Leaching process is commonly referred to as extraction. This is a process in which water soluble substances are washed out from soil or wastes.
4. Which of the following statements is wrong?
a) During smelting, flux is used to remove gangue as slag
b) The slag formed during smelting has low melting point and is heavier than metal
c) Calcination of ore is carried out without the presence the oxygen
d) Roasting is carried out in the presence of oxygen
Explanation: Smelting is the process of extraction of a metal from its oxide by reduction with carbon (coke). Alkali metals, alkaline earth metals, etc. cannot be prepared by reduction of their respective oxides with carbon. The slag formed during smelting has high melting point and is lighter than the metal.
5. Roasting results in the formation of oxides. But why are oxide ores are subjected to roasting?
a) To avoid gangue particles
b) To get crude metal with using oxidizing agent
c) To remove volatile impurities in the form of their oxides
d) To make the ore porous
Explanation: Oxide ores are subjected to roasting to remove the volatile impurities in the form of their oxides. It is easier to obtain metals from their oxides (by reduction) than from carbonates or sulphides. So before reduction can be done, the ore is converted into metal oxide.
6. Which of the following ores are concentrated by froth flotation?
c) Copper pyrites
Explanation: The froth flotation method is widely used for the concentration of sulphide ores such as zinc blende (ZnS), copper pyrites (CuFeS2), galena (PbS), etc. This method is based upon the fact that the surface of the sulphide ores is preferentially wetted by oils while that of gangue is preferentially wetted by water.
7. Copper is extracted from low grade copper ores.
Explanation: The statement is true. Copper is extracted by hydrometallurgy from low grade copper ores. It is leached out using acid or bacteria.The conversion of copper consists of a series of physical and electrochemical processes. The solution containing Cu2+ is treated with scrap iron, zinc or hydrogen.
8. What is the main reaction occurring in the blast furnace during extraction of iron from haematite?
a) Fe2O3 + 3CO → 2Fe + 3CO2
b) FeO + SiO2 → FeSiO2
c) Fe2O3 + 3C → 2Fe + 3CO
d) Fe2O3 + CO2 → FeCO3 + O2
Explanation: The main reaction occurring in the blast furnace during extraction of iron from haematite is:
Fe2O3 + 3CO → 2Fe + 3CO2
This reaction involves the reduction of iron (III) oxide to iron and oxidation of carbon monoxide to carbon dioxide.
9. How is ore-dressing of iron done?
a) Froth Flotation
b) Magnetic separation
c) Hand picking
d) By wetting
Explanation: In magnetic separators, the effect of magnetism is used to separate ferromagnetic materials from non-magnetic materials. In principle, this process is also suitable for the iron ores siderite and hematite, which become weakly magnetic when heated.
10. Which of the following metals is not extracted by electrolysis?
Explanation: Actually the extraction of a metal from its ore depends upon the selection of a proper reducing agent. Iron is a moderately active metal and its oxides can be reduced using carbon and not by using electrolysis. Reactive metals, such as aluminium, are extracted by electrolysis, while a less reactive metal, such as iron, may be extracted by reduction with carbon.
Sanfoundry Global Education & Learning Series – Chemistry – Class 12.
To practice all chapters and topics of class 12 Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.