Unit 4 questions

[Collin Li]

Yeah, pretty much

You have to remember that this is just a "prediction" tool, and that in reality you might get a tiny bit of another reaction happening (especially if they are close-by on the electrochemical series, and you're at non-SLC).

But when you have a question on these things, you just use the prediction and don't have to worry about empirical findings. For a prac, you may find that empirical results don't match up with this prediction.

[bec]

Great, got it. thanks!

[bec]

Are these right?

1. What mass of copper is produced if copper (II) nitrate solution is electrolysed for 10 minutes using a current of 2.0 amps? 0.95g

2. What time is needed if a current of 1.0 amp is passed through a solution of nickel(II) nitrate and 0.50g of metallic nickel is produced? 27min24sec

3. A fixed amount of electricity is passed between inert electrodes dipping into solutions of each of these metal ions.

ION    RAM
W+     65
X2+    210
Y3+    140
Z4+    120

Metal was deposited on the negative electrode in each solution.
Which metal would deposit the greatest number of atoms? W+
Which metal would deposit the greatest mass? X2+

4. A square iron plate of dimensions 6x6 is required to be plated with 0.1cm of copper on both sides. Copper has a density of 7.9g/cm3.
An electrolytic cell is set up using 1M CuSO4 as electrolyte, and the anode is made of copper.
Calculate the time taken to plate the iron plate using a constant current of 35A. 1min 19sec

Thanks!

[Collin Li]

For Question 1, I got 0.39 g. Show us your working. I had of copper.

I agree with your Question 2, but I'm not sure if they would have just preferred it in seconds.

I agree with your Question 3. Yep, you divide the RAM by the charge to figure out which one gives you the most mass.

Question 4

of copper required

of copper required





Using

[bec]

1. What mass of copper is produced if copper (II) nitrate solution is electrolysed for 10 minutes using a current of 2.0 amps? 0.95g

       



...I wrote the whole thing out then realised that my mistake was calculating the mass from no. mols.....

[Collin Li]

Hahaha, hmm, but I was even nice enough to show you how many moles I had:

Show us your working. I had of copper.

[bec]

Lithium metal is used extensively in lithium batteries. It is obtained by electrolyising LiCl found naturally as an ore. LiCl in molten form is electrolysed in an electrolytic cell using graphite electrodes.
a) Why is electrolysis a suitable method for extracting lithium metal from ore?
- Lithium is highly reactive so Li+ + e- -> Li reaction wouldn't naturally occur ?

b) At what electrode is lithium formed?
Cathode, since it's a reduction reaction

c) Calculate the mass of lithium metal that can be formed from a cell operating at 9V, 4000A and 700^oC for a period of 12 hours assuming 100% efficiency.
Not sure how to do this...

[Collin Li]

a) Why is electrolysis a suitable method for extracting lithium metal from ore?

Also because it's a redox reaction. That's fundamental to electrolysis.

c) Calculate the mass of lithium metal that can be formed from a cell operating at 9V, 4000A and 700^oC for a period of 12 hours assuming 100% efficiency.

They are giving you irrelevant information to throw you off (voltage and temperature). Efficiency is important, but since it's at 100%, there is no change to our calculation.

[bec]

c) Calculate the mass of lithium metal that can be formed from a cell operating at 9V, 4000A and 700^oC for a period of 12 hours assuming 100% efficiency.

They are giving you irrelevant information to throw you off (voltage and temperature). Efficiency is important, but since it's at 100%, there is no change to our calculation.






[/quote]

Really! I worked it out like that, treating the volts etc as extraneous info but then I was so sure I was wrong because me teacher's given me several pages of questions like this, with the volts and temperature included.

Thanks coblin - finally finished the course now wooo

[Collin Li]

No problems

(celebration time!)

[bec]

A student uses electrolysis to experimentally determine Faraday’s constant. She electrolyses a 1 M Sn(NO3)2 solution using Sn electrodes. Using a constant current of 8.0 A for a time period of 10 minutes, the student finds that the mass decrease of the positive tin electrode after electrolysis is 3.02 g.

Give a half equation for the reaction occurring at the positive electrode.

The solution is Sn --> Sn2+  + 2e-

And...that confuses me because I thought that the positive electrode was the ANODE in electrolytic cells, and at the anode, reduction occurs... doesn't it? So I would've thought it'd be Sn2+ + 2e- --> Sn

What've I got wrong?

[Collin Li]

And...that confuses me because I thought that the positive electrode was the ANODE in electrolytic cells, and at the anode, reduction occurs... doesn't it? So I would've thought it'd be Sn2+ + 2e- --> Sn

What've I got wrong?

Anode is where oxidation occurs (always).

AN OIL RIG CAT

[bec]

gahhh
I knew that, and yet I kept staring at it trying to figure out what was wrong with it. I think I need a day off...

[Collin Li]

gahhh
I knew that, and yet I kept staring at it trying to figure out what was wrong with it. I think I need a day off...

* coblin patpats

[Collin Li]

c) Calculate the mass of lithium metal that can be formed from a cell operating at 9V, 4000A and 700^oC for a period of 12 hours assuming 100% efficiency.

They are giving you irrelevant information to throw you off (voltage and temperature). Efficiency is important, but since it's at 100%, there is no change to our calculation.

Oops, this is off by a factor of 60, because it was 12 hours. I didn't convert it to seconds. I only converted it to minutes.

Thanks to unknown id for pointing it out.