O Level Chemistry – Products of Electrolysis of Molten Compound

20 Sep

Posted by: sean in: Chemistry Notes & Tips

We have learned that cations are attracted towards the -ve cathode and being discharged, and the anions are attracted towards the +ve anode and being discharged. Questions with Molten Electrolyte will then be easy to solve since there is only one type of cations and one type of anions.

Try this questions out to see how much you understand.

Question 1:

(i) Name the ions present in molten copper (II) bromide and the products at the electrodes.

(ii) Write equations, including states symbols, to represent the reaction at the cathode and the anode.

(iii) Finally, write the overall reaction that occurs when molten copper(II) bromide is electrolysed.

PS: Leave your suggested answers in the “Comments Section” below. We will discuss on it very soon.

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12 Responses

hartati
20|Sep|2008 1

(i) Cu2+ + Br2- —>CuBr

(ii) K: Cu2+ + 2e- —-> Cu
A: Br2- —-> Br + 2e-

(iii)

Reply
Gary Reply:
September 21st, 2008 at 5:42 pm
Your answer seem very wrong.Probably my answer is wrong or I’m reading the question wrongly

(i)Ions present -Copper(II) ions,Bromide ion
Products- Copper solid,Bromine gas

(ii)Cathode:Cu2+(aq) + 2e ->Cu(s)
Anode:2Br(aq)- ->Br2(g) + 2e

(iii)CuBr2 ->Cu +Br2

Reply
hartati
24|Sep|2008 2

i thought that anode always give its electron
and cathode receive the electron?

and yes.. i think my answer is very wrong…

Reply
Gary Reply:
September 25th, 2008 at 2:23 pm
You’re right.If you have problem remembering,remember it this way:

OA RC

Oxidation Anode Reduction Cathode
(Oxidation means loss of electron and Reduction means gaining of electrons)

I think you have to be more careful.In (i) they asked for name.

Anyway, are you from Singapore?

Reply
sean Reply:
September 30th, 2008 at 4:55 pm
Hi Gary,

Good to see you helping out others here.

I hope you are learning something as you contribute here, and improve your chemistry grades in an exponential rate.

Keep up the good work!

To Your Academic Success in Chemistry,
Sean Chua
Master Trainer
http://www.SimpleChemConcept.com

PS: I am launching the ebook “Up Your Chemistry Grades Nows!” before it is being published into hardcopy. There is a major section that have a comprehensive discussion of major / common mistakes made by students.

Reply
hartati
26|Sep|2008 3

oo..
ok thank you for the easy step to remember.

i’m from Indonesia

Reply
sean Reply:
September 30th, 2008 at 4:53 pm
Hi Hartati,

I hope you are learning something from this chemistry blog-site, especially these interactions with fellow students.

Stay tuned to this blog and hope to see you contributing more! and learn even MORE!

What type of examination system are you taking in Indonesia?

In Singapore, we subscribe to GCE O Levels.

To Your Academic Success in Chemistry,
Sean Chua
Master Trainer
http://www.SimpleChemConcepts.com

PS: I am launching the ebook “Up Your Chemistry Grades Nows!” before it is being published into hardcopy. There is a major section that have a comprehensive discussion of major / common mistakes made by students.

Reply
laav
28|Dec|2008 4

Can you tell me the difference in products of electrolysis of molten NaCl and aq. NaCl?
Also, can you tell me about which ion will get reduced/oxidized depending on the std. electrode (reduction) potential? And also about the ‘overpotential factor’ to be considered.

Thanks for helping me!

Reply
sean Reply:
February 9th, 2009 at 2:40 pm
Hi Laav,

For electrolysis of molten NaCl, products are:
@ Cathode: Sodium Metal
@ Anode: Chlorine Gas

For electrolysis of dilute aqueous NaCl, products are:
@ Cathode: Hydrogen Gas
@ Anode: Oxygen Gas

Above products will be liberated/produced when electrolysis are carried out using Inert Electrodes such as Carbon or Platinum electrodes.

Hope you will find the above information useful towards your learning.

To Your Academic Success in Chemistry,
Sean
Master Trainer
Author

Reply
spicy
25|Apr|2009 5

Question 1:

(i) Name the ions present in molten copper (II) bromide and the products at the electrodes.

(ii) Write equations, including states symbols, to represent the reaction at the cathode and the anode.

(iii) Finally, write the overall reaction that occurs when molten copper(II) bromide is electrolysed.

(i) ions present: Cu2+, Br-
Products:
at anode: Br2 (g)
at cathode: Cu (s)
(ii) equations:
At anode: Br- (aq) – e- ?Br, 2Br(aq) ? Br2(g)
At cathode: Cu2+ (aq) + 2e- ?Cu(s)
(iii) overall equation: CuBr2 (aq)?Cu(s)+Br2(aq)

Reply
Ang
20|Oct|2009 6

Erm can anyone guide me on how to write the overall reaction for electrolysis questions?

Reply
sean Reply:
November 1st, 2009 at 12:27 am
Hi Ang,

There is always a half-equation on the Cathode and another half-equations at the Anode.

Both half equations consists of electrons. Use Simultaneous Equations technique to balance off the electrons and you will end up with the Overall Reaction Equation for electrolysis.

Hope this information helps. =)

Reply