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Electrochemistry question

2024 · 29 Jan · Shift 2 · Q25
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Electrochemistry question

2024 · 29 Jan · Shift 2 · Q25

JEE MainChemistryElectrochemistryNumerical+4 / −1
A constant current was passed through a solution of AuCl4−\mathrm{AuCl}_4^{-}AuCl4−​ ion between gold electrodes. After a period of 10.0 minutes, the increase in mass of cathode was 1.314 g1.314 \mathrm{~g}1.314 g. The total charge passed through the solution is ‾×10−2 F\underline{\hspace{2cm}}\times 10^{-2} \mathrm{~F}​×10−2 F. (Given atomic mass of Au=197\mathrm{Au}=197Au=197)
Numerical answer
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Correct answer: 2

  1. Identify the cathode reaction

At the cathode, gold is deposited from AuCl4−\mathrm{AuCl_4^-}AuCl4−​:

AuCl4−+3e−→Au+4Cl−\mathrm{AuCl_4^- + 3e^- \rightarrow Au + 4Cl^-}AuCl4−​+3e−→Au+4Cl−

So, 1 mole of Au requires 3 moles of electrons.

  1. Calculate moles of gold deposited

Given mass of Au deposited = 1.314 g1.314\,\mathrm{g}1.314g

Molar mass of Au = 197 g mol−1197\,\mathrm{g\,mol^{-1}}197gmol−1

n(Au)=1.314197n(\mathrm{Au}) = \frac{1.314}{197}n(Au)=1971.314​

n(Au)=0.00667 moln(\mathrm{Au}) = 0.00667\,\mathrm{mol}n(Au)=0.00667mol

  1. Calculate moles of electrons passed

Since 1 mol Au needs 3 mol e−e^-e−,

n(e−)=3×0.00667=0.0200 moln(e^-) = 3 \times 0.00667 = 0.0200\,\mathrm{mol}n(e−)=3×0.00667=0.0200mol

  1. Convert to faradays

1 faraday = 1 mole of electrons.

Therefore, total charge passed = 0.0200 F0.0200\,\mathrm{F}0.0200F

0.0200 F=2.00×10−2 F0.0200\,\mathrm{F} = 2.00 \times 10^{-2}\,\mathrm{F}0.0200F=2.00×10−2F

  1. Fill in the blank

The question asks for

‾×10−2 F\underline{\hspace{2cm}} \times 10^{-2}\,\mathrm{F}​×10−2F

So the required integer is:

2\boxed{2}2​

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