This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemical Principles of Metallurgy”.
1. Which of the following metals are reduced from molten salt solutions by electrolysis?
Explanation: Highly electropositive metals are reduced to metals from molten salt solutions by electrolysis. Aluminium being a highly electro positive metal is separated from bauxite by the process known as Hall-Heroult process.
2. What is the process used to extract sodium from halide ores such as sodium chloride (NaCl)?
a) Pyro metallurgy
b) Hydro metallurgy
c) Electro metallurgy
d) Magnetic separation
Explanation: Sodium is a highly electro positive metal and can be easily extracted from sodium chloride through a process known as electro metallurgy or electrolysis. Pyro metallurgy and hydro metallurgy are used to extract metals such as copper, iron, silver etc.
3. What is the term given to the extraction of aluminium from bauxite by using electrochemical process?
a) Baeyer’s process
b) Hall-Heroult process
c) Mc-Arthur process
d) Blasts process
Explanation: Hall-Heroult process is a smelting process to reduce bauxite to a nearly pure aluminium. Bauxite is dissolved in a molten electrolyte composed of sodium, fluorine and aluminium and is maintained at a high temperature. In this process aluminium is accumulated at the cathode and oxygen gas at the anode.
4. What is the anode and cathode used in Hall-Heroult process?
a) Zinc and copper
b) Iron and copper
c) Carbon and zinc
d) Graphite and carbon
Explanation: In the extraction of aluminium from bauxite the anode and cathode must be inert electrodes like graphite and carbon so that they do not take part in the reaction. At the end of the process the metal is accumulated at cathode and it is easier to collect the aluminium from carbon electrode as it does not react with aluminium.
5. In the metallurgy of aluminium, purified bauxite is mixed with Na2AlF6.
Explanation: In the metallurgy of aluminium, purified bauxite (Al2O3) is mixed with Na3AlF6 and CaF2 to lower the melting point and to increase conductivity. This mixture is fused and used as an electrolyte in Hall-Heroult process.
6. What is the net reaction in Hall-Heroult process?
a) 2Al2O3 + 3C → 4Al + 3CO2
b) 4Al2O3 + 3C → 4Al + 6CO2
c) F2 + Al2O3 → Al + F2O3
d) Na3AlF6 → AlF3 + 3NaF
Explanation: The reaction involved in Hall-Heroult process are:-
Na3AlF6 → AlF3 + 3NaF
AlF3 → Al+3 + 3F–
Cathode: Al+3 + 3e– → Al
Anode: 6F– → 3F2 + 6e–
F2 + Al2O3 → AlF3 + O2
C + O2- → CO or CO2 + 2e–
The overall reaction may be written as 2Al2O3 + 3C → 4Al + 3CO2.
7. What is the temperature maintained in Hall-Heroult process?
a) 800°-840° C
b) 840°-880° C
c) 900°-940° C
d) 940°-980° C
Explanation: A high temperature of about 1100°C need to be maintained to keep the electrolyte in molten state but mixing the electrolyte with feldspar and cryolite brings down the temperature to about 940° – 980° C and also increases conductivity.
8. Electrochemical processes in metallurgy are spontaneous.
Explanation: The Electrochemical reaction can be made spontaneous by keeping the potential difference between the electrodes positive (E°c > E°a). Gibbs free energy G° = -nFE°, if E° is positive then Gibbs energy G° is negative making the overall reaction spontaneous.
9. Which of the following is an example of electrochemical principles of metallurgy?
a) Baeyer’s process
b) Solvay process
c) Bergius process
d) Hall-Heroult process
Explanation: Hall-Heroult process is an electrochemical process to reduce bauxite to a nearly pure aluminium. Bauxite is dissolved in a molten electrolyte composed of sodium, fluorine and aluminium and is maintained at a high temperature. In this process aluminium is accumulated at the cathode and oxygen gas at the anode.
10. Which of the following is the most suitable ore to undergo electrochemical process?
Explanation: Bauxite is an ore of aluminium and most suitable ore to undergo electrochemical process. Aluminium is a high electro positive metal and can be extracted from concentrated bauxite by electrolysis and the process is knows as Hall-Heroult process.
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