Question:
What is the quantity of electricity required to produce \(8\) g of Mg (molar mass = \(24 \text{g mol}^{-1}\)) from \(\text{MgCl}_2\) solution ?
What is the quantity of electricity required to produce \(8\) g of Mg (molar mass = \(24 \text{g mol}^{-1}\)) from \(\text{MgCl}_2\) solution ?
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Mg2+ needs 2 faradays per mole; find moles of Mg first.
Updated On: Oct 1, 2026
- \(0.222\) F
- \(0.444\) F
- \(0.666\) F
- \(0.888\) F
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Faraday's first law says the mass deposited is proportional to the charge passed. One mole of electrons carries 1 faraday (96500 C).
Step 2: Key Reaction:
\[ \text{Mg}^{2+} + 2e^- \rightarrow \text{Mg} \]
So 2 mol of electrons, that is 2 F, are needed to deposit 1 mol of Mg.
Step 3: Detailed Explanation:
Moles of Mg \(= 8/24 = 0.333\) mol.
Charge needed \(= 0.333 \times 2 \text{ F} = 0.666 \text{ F}\).
Step 4: Why the other options are wrong.
0.222 F is one third of the answer, from using the 1:1 ratio with a wrong molar mass. 0.444 F and 0.888 F do not match 8 g with a charge of 2 F per mole.
Final Answer:
The quantity of electricity needed is \(0.666\) F, option (C). \[ \boxed{0.666 \text{ F}} \]
Faraday's first law says the mass deposited is proportional to the charge passed. One mole of electrons carries 1 faraday (96500 C).
Step 2: Key Reaction:
\[ \text{Mg}^{2+} + 2e^- \rightarrow \text{Mg} \]
So 2 mol of electrons, that is 2 F, are needed to deposit 1 mol of Mg.
Step 3: Detailed Explanation:
Moles of Mg \(= 8/24 = 0.333\) mol.
Charge needed \(= 0.333 \times 2 \text{ F} = 0.666 \text{ F}\).
Step 4: Why the other options are wrong.
0.222 F is one third of the answer, from using the 1:1 ratio with a wrong molar mass. 0.444 F and 0.888 F do not match 8 g with a charge of 2 F per mole.
Final Answer:
The quantity of electricity needed is \(0.666\) F, option (C). \[ \boxed{0.666 \text{ F}} \]
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