What is the number of moles of electrons passed when current of 5 ampere is passed through a solution of $\text{FeCl}_3$ for 20 minutes?
Show Hint
Do not let the chemical formula $\text{FeCl}_3$ trick you into overcomplicating things with valency factors or equivalence ratios!
When a question asks for the "moles of electrons passed," it is purely tracking the total electric charge flowing through the wire: $\text{Moles of } e^{-} = \frac{I \times t}{96500}$.
Step 1: Understand what is asked.
A current of 5 A flows for 20 minutes. We must find how many moles of electrons passed through. The salt $\text{FeCl}_3$ is just extra detail here, since we only want the total electrons.
Step 2: Recall the charge formula.
Total charge $Q$ (in coulombs) is current times time:
\[ Q = I \times t \]
Time must be in seconds.
Step 3: Change minutes into seconds.
\[ t = 20 \times 60 = 1200\ \text{s} \]
Step 4: Find the total charge.
\[ Q = 5 \times 1200 = 6000\ \text{C} \]
Step 5: Use the Faraday idea.
One mole of electrons carries a charge of about $96500\ \text{C}$ (one faraday). So the moles of electrons are the total charge divided by this:
\[ \text{moles} = \frac{6000}{96500} \approx 0.0622 \]
Step 6: Write in scientific form and match.
\[ \text{moles} \approx 6.22 \times 10^{-2} \]
This rounds to the closest option, $6.25 \times 10^{-2}$.
\[ \boxed{6.25 \times 10^{-2}\ \text{mol}} \]