nmjasdk
Badges: 16
Rep:
?
#1
Report Thread starter 6 years ago
#1
on this paper
http://www.ocr.org.uk/Images/65869-q...d-elements.pdf

how is the answer for q7 d ii obtained?

here is the markscheme
http://www.ocr.org.uk/Images/60302-m...ments-june.pdf
0
reply
nmjasdk
Badges: 16
Rep:
?
#2
Report Thread starter 6 years ago
#2
SOMEONE PLEASE HELP ME! PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE.

that should get enough attention.
0
reply
shahbaz
Badges: 15
Rep:
?
#3
Report 6 years ago
#3
You know the over all equation, try to work out two half equations one for each product. Trial and error.
0
reply
charco
Badges: 17
Rep:
?
#4
Report 6 years ago
#4
(Original post by nmjasdk)
on this paper
http://www.ocr.org.uk/Images/65869-q...d-elements.pdf

how is the answer for q7 d ii obtained?

here is the markscheme
http://www.ocr.org.uk/Images/60302-m...ments-june.pdf
You are told that the electrolyte is aqueous hydroxide ions.
You are told the products.
There must be an oxidation (loss of electrons) and a reduction (addition of electrons).
The electrons must balance to give the overall equation.

2H2O --> 2H2 + O2

4OH- - 4e -> 2H2O + O2
4H2O + 4e --> 4OH- + 2H2

the second half equation can be divided through by 2 to give
2H2O + 2e --> 2OH- + H2

although glancing at the markscheme, the doubled version is allowed ...
0
reply
ChemistryBud
Badges: 0
Rep:
?
#5
Report 6 years ago
#5
(Original post by charco)
You are told that the electrolyte is aqueous hydroxide ions.
You are told the products.
There must be an oxidation (loss of electrons) and a reduction (addition of electrons).
The electrons must balance to give the overall equation.

2H2O --> 2H2 + O2

4OH- - 4e -> 2H2O + O2
4H2O + 4e --> 4OH- + 2H2

the second half equation can be divided through by 2 to give
2H2O + 2e --> 2OH- + H2

although glancing at the markscheme, the doubled version is allowed ...
This.

Another tip and good practice for redox questions is to start by writing the half equation for oxidation above the half equation for reduction. In this case, the half equation for oxidation gives clues as to the reduction step.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (95)
13.91%
I'm not sure (32)
4.69%
No, I'm going to stick it out for now (214)
31.33%
I have already dropped out (16)
2.34%
I'm not a current university student (326)
47.73%

Watched Threads

View All