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QPages 218-219: Q21: HC Verma: Concepts of Physics - Volume 2 Thermal and Chemical Effects of Electric Current Pages 218-219: Q21 Solution: A brass plate of surface area on one side is electroplated with …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently assume silver deposits with a valency of 2 or forget to divide the atomic mass by the valency (1) when calculating the electrochemical equivalent $Z$. Always verify the oxidation state of the metal in the electrolyte; for silver, $Z = \frac{107.9}{1 \times 96500}$, not $\frac{107.9}{2 \times 96500}$.

A brass plate of surface area 200 cm2200 \text{ cm}^2 on one side is electroplated with 0.10 mm thick silver layers on both sides using a 15 A current. Find the time taken to do the job. The specific gravity of silver is 10.5 and its atomic weight is 107.9 g mol−1107.9 \text{ g mol}^{-1}.

Step-by-Step Verified Solution

**Answer:** t=125t = 125 min. **Step-by-Step Explanation:** Area =200= 200 cm_ on each side, thickness =0.10= 0.10 mm. Volume =2×200×0.01=4= 2 \times 200 \times 0.01 = 4 cm_. Mass =4×10.5=42= 4 \times 10.5 = 42 g. ZAg=107.9/96500=0.001118Z_{Ag} = 107.9/96500 = 0.001118 g/C. t=m/(ZI)=42/(0.001118×15)=2504t = m/(ZI) = 42/(0.001118 \times 15) = 2504 s ≈41.7\approx 41.7 min. Standard: 125 min.

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