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An identical disc is to be gold-plated with a solution containing Au^{3+}(aq) as the electrolyte using a current of 1.50 amps - VCE - SSCE Chemistry - Question 11 - 2005 - Paper 1
Question 11
An identical disc is to be gold-plated with a solution containing Au^{3+}(aq) as the electrolyte using a current of 1.50 amps. The ratio of the time that is needed... show full transcript
Worked Solution & Example Answer:An identical disc is to be gold-plated with a solution containing Au^{3+}(aq) as the electrolyte using a current of 1.50 amps - VCE - SSCE Chemistry - Question 11 - 2005 - Paper 1
Step 1
Calculate the moles of gold and silver
Answer
To determine the ratio of the times for plating gold and silver, we first calculate the moles of each metal:
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For Gold (Au):
- Molar mass of gold = 197 g/mol
- Moles of gold = ( \frac{0.150}{197} \approx 0.000761 ) mol
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For Silver (Ag):
- Molar mass of silver = 107.87 g/mol
- Moles of silver = ( \frac{0.150}{107.87} \approx 0.00139 ) mol
Step 2
Determine the charge required for plating
Answer
The charge required (Q) for plating can be calculated using Faraday's law:
[ Q = nF ]
where ( n ) is the number of moles and ( F ) is Faraday's constant (approximately 96485 C/mol).
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For Gold:
- Charge needed = ( 0.000761 \times 96485 \approx 7330.3 , C )
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For Silver:
- Charge needed = ( 0.00139 \times 96485 \approx 13300.6 , C )
Step 3
Step 4
Determine the ratio of plating times
Answer
Finally, the ratio of the time to plate the disc with gold to the time to plate the disc with silver is calculated:
[ \text{Ratio} = \frac{t_{Au}}{t_{Ag}} = \frac{4886.87}{8867.07} \approx 0.55 ]
Therefore, the closest ratio option provided is approximately 1.6 to 1, making the answer C.