The electrochemical equivalent of silver is 0.0012g/C. If 36.0g of silver is to be deposited by electrolysis…

Analyze the question

We need the current that deposits 36.0 g of silver in 5 minutes, given the electrochemical equivalent (e.c.e.) z = 0.0012 g/C.

Concept

Faraday's first law of electrolysis: m = zIt

• m = mass deposited (g)
• z = electrochemical equivalent (g/C)
• I = current (A)
• t = time (seconds)

Rearranging: I = m / (z t)

Solution

1. Convert time to seconds: t = 5 min × 60 = 300 s
2. Substitute:

I = 36.0 / (0.0012 × 300)

3. Denominator: 0.0012 × 300 = 0.36

4. I = 36.0 / 0.36 = 100 A

Answer

The current must be 100 A, which is option B.

Tip

Always convert minutes to seconds before using m = zIt. If you forget, you get 36 / (0.0012 × 5) = 6000 A, which is exactly the trap option A. Also, check the units of z (g/C), because they tell you the time must be in seconds so that charge Q = It is in coulombs.