Question

How many faraday of electricity is required to produce 10 g of calcium metal (molar mass = 40 $\text{g}\ \text{mol}^{-1}$) from calcium ions?

• A. 1.5 F
• B. 2.0 F
• C. 0.50 F
• D. 1.0 F

Hint:

Always write down the half-reaction first to see how many electrons are transferred per ion. For Group 2 elements like Ca, Mg, and Ba, it is always 2 Faradays per mole.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to calculate the amount of charge in Faradays required to deposit a specific mass of calcium metal from its ionic state.

Step 2: Key Formula or Approach:
The reduction reaction for calcium ions is:
$$\text{Ca}^{2+} + 2\text{e}^- \rightarrow \text{Ca}$$ This indicates that 1 mole of calcium metal requires 2 moles of electrons, which is equivalent to 2 Faradays (F) of electricity.

Step 3: Detailed Explanation:
First, find the number of moles of calcium in 10 g:
$$\text{Moles of Ca} = \frac{\text{Given Mass}}{\text{Molar Mass}} = \frac{10}{40} = 0.25\ \text{mol}$$ Since 1 mole of Ca requires 2 F of electricity:
$$\text{Electricity required} = 0.25\ \text{mol} \times 2\ \text{F/mol} = 0.50\ \text{F}$$

Step 4: Final Answer:
The required electricity is 0.50 F, matching option (C).