In Faradays law of electrolysis, a graph of the mass deposited against the quantity of electricity is plotted. The slope of the graph gives?

Analyze the question: A graph of mass deposited (m) against quantity of electricity (Q) is plotted. We need to know what the slope represents.

Concept: Faraday's first law of electrolysis says the mass of a substance deposited during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte:

m ∝ Q m = zQ

where z is the electrochemical equivalent (ECE) of the substance, in kg/C or g/C. Since Q = It, this is also written as m = zIt.

Solution:

1. Compare m = zQ with the straight-line equation y = mx + c (c = 0 here).
2. Mass m is on the vertical axis (y), and charge Q is on the horizontal axis (x).
3. Slope = Δm / ΔQ = z.

So the slope is the electrochemical equivalent of the substance, which is the mass deposited per unit charge.

Checking the other options:

• A. Energy released: not related to the m-Q relationship.
• C. Current flowing: current would be Q/t, which needs time on an axis.
• D. Charge released: charge is the x-axis quantity, not the slope.

Answer: B, the electrochemical equivalent.

Exam tip: For any graph question, write down the formula, then match it to y = mx + c. Here, m = zQ means the slope is z. Also remember: m-Q graph slope = ECE, and m-t graph slope = zI.