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### Topic: Electrochemistry Question  (Read 1627 times)

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#### readerstudent

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• Mole Snacks: +0/-0 ##### Electrochemistry Question
« on: December 05, 2011, 08:12:02 AM »
Hi there, I'm a new member here! I've attempted the following two questions and even tried Googling for answers but I still don't quite get what the question is asking for.

Q1)

A student sets up an electrolytic circuit using graphite electrodes and sulfuric acid as the electrolyte.

(a) One of the gases (A) produced is more than twice the vol. of the other (B). If the volume of B is 10cm3, what is the expected volume of the (A).

I'm assuming (A) is hydrogen here, so my answer was 20 cm3.

Here's the real question:
(b) It is found out that the volume of A is 2.5cm3 greater than what is the expected value. With appropriate equations, suggest why this is so.

What could this answer be? Did the hydrogen redissolve or something?

Qns 2)

Note: I'm quite new to the topic and I don't quite get how to do the relevant calculations. I tried using mole calculations but my answer always turns out wrong somehow.

Two voltaic cells: Cell A uses Mg and Cu and Cell B uses Zn and Cu. The electrolyte is dilute sulfuric acid.

-Assuming that the rate of electron flow is the same for both cells, which cell will have a greater loss in mass at one of the electrodes and why?

-Calculate the loss in mass of the electrode in cell B when the loss in mass in cell A is 1.2g.

I do appreciate it in advance! #### readerstudent

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• Mole Snacks: +0/-0 ##### Re: Electrochemistry Question
« Reply #1 on: December 05, 2011, 08:15:41 AM »
Ok, I forgot to post my attempt for the second one.

For my 2nd question:

- Cell B (Although I don't know why.)
- Number of moles of Magnesium lost
= 1.2/24.3
=0.4938271

Mass of Zinc lost:
0.4938271 x 65.4
=32.29629

I'm not sure if this is correct. Would appreciate if someone points out my mistake.

#### UG

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• Gender:  ##### Re: Electrochemistry Question
« Reply #2 on: December 05, 2011, 06:34:24 PM »
- Cell B (Although I don't know why.)
- Number of moles of Magnesium lost
= 1.2/24.3
=0.4938271
You forgot to add a zero, it should be 0.04938 mol. Mass of zinc then = 3.2296 grams.
Cell B would have the greater mass loss. Can you think of a reason why based on their molar masses?