Kaplan FL-11 Question

[Tonino]

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Hi, this is a question out of Kaplan FL11, Physical Sciences question #8.

The total amount of gold to be deposited onto a pair
of glasses made of aluminum is 0.5 grams. How long
should the plating process be performed to deposit
this amount of gold?
A. 73 seconds
B. 146 seconds
C. 24 seconds
D. 48 seconds

The passage didn't provide any useful information other than a table of reduction potentials.

Here was the answer:
Time to plate = 0.5 g Au  (1 mol Au / 197 g Au)  (3 mol e– / 1 mol Au) (96500 C / 1 mol e– ) (1 sec / 10 C) = 73.4 seconds.

I understood every part of the answer except for "1sec/10C."

Why would you have to divide by 10?

Thank you.

 

[RogueUnicorn]

I'm not 100% on this, but let me take a crack at it -

The equation I believe simply takes advantage of I * t = Q, where I=current, t=time, Q=charge. The current itself is not given in the information you have given us, so it's either in the passage somewhere or you have to calculate it with some other info. For example, is the resistance of the wires given at all?

 

[chemtopper]

you want to calculate time
or t(time )= Q/I
and I is the current which is charge per unit time
they must have given you I = 10C/sec
Now you can use all these conversions to get the answer
Au3+ + 3e ----> Au
1mole of Au = 197 g
1mole of Au = 3 moles of electrons
1 mole of electrons = 96500C
I = 10 C/sec
plug in all these values to get the answer .

 

[bostoncollegepremed]

SAME QUESTION!? why the 10C/s???

This is the exact passage:

Electroplating allows for an efficient cost-effective means of applying a thin veneer of an expensive substance such as gold onto a metallic item. This can be done for aes- thetic purposes, such as in jewelry. It can also be used to coat items for protective purposes, such as corrosion pre- vention. A variety of materials can be used as a plating material, and a variety of materials have properties which allow them to be plated easily.

In a certain electroplating apparatus used to plate alu- minum eyeglass frames, a bar of gold or copper is placed in an acidic solution and attached via a battery to the item to be plated. The eyeglasses to be plated are also placed in the solution. A voltage is applied to create an electrolytic cell, which plates the material onto the eyeglass frames.

Au3++ 3e → Au


1.50 V

Fe3+ + 1e → Fe2+


0.70 V

Cu2+ + 2e → Cu


0.34 V

Zn2+ + 2e → Zn


0.76 V

Cr2+ + 2e → Cr


0.91 V

Al3+ + 3e → Al


1.66 V

Ca2+ + 2e → Ca


2.87 V

Table 1–Standard reduction potentials

(Note: Faraday’s constant is 96,487 C / 1 mol e–)

THAT'S IT! WHERE IS THAT NUMBER COMING FROM?

 

[Karinede91]

I was extremely confused by this as well. Also, the answer reads as D but after the calculation they say its 73 seconds... I feel like this question is just out of whack. I think I'm going to stick to aamc tests because the Kaplan full lengths are 1: not the correct length and 2: too difficult to a fault