AQA Chemistry AS Paper 1 June 2018 Question 07.2

I'm Stuck understanding what I've done wrong for the first part of this question:

So it's the oxidation half equation which I'm Puzzled on:

I started on Cl2 = ClO^-

Then I balenced out the Chlorines:

Cl2 = 2ClO-

Then I added 2 Moles of water to the RHS:

2H20 + Cl2 = 2ClO-

Then I Balenced out the charges:

2H20 +Cl2 = 2CLO- + 4H+ +2e-

on the RHS of the mark scheme it says: "Allow Cl2 + 2H2O  2ClO– + 2e"

But I have no clue on why they didn't add 4 protons onto the other side to balance the charges

Please help.

Reply 1

TypicalNerd

18

Original post by Vinisman

I'm Stuck understanding what I've done wrong for the first part of this question:

So it's the oxidation half equation which I'm Puzzled on:

I started on Cl2 = ClO^-

Then I balenced out the Chlorines:

Cl2 = 2ClO-

Then I added 2 Moles of water to the RHS:

2H20 + Cl2 = 2ClO-

Then I Balenced out the charges:

2H20 +Cl2 = 2CLO- + 4H+ +2e-

on the RHS of the mark scheme it says: "Allow Cl2 + 2H2O  2ClO– + 2e"

But I have no clue on why they didn't add 4 protons onto the other side to balance the charges

Please help.

I think it’s just a typo on the MS, which is really bad for something sat as a live examination paper.

2H2O + Cl2 —> 2ClO^- + 4H^+ + 2e^- is perfectly correct.

Reply 2

Vinisman

OP

3

Thank you so much

phew, I got worried for a second.

Reply 3

TypicalNerd

18

Original post by Vinisman

Thank you so much

phew, I got worried for a second.

I mean, if you just look at the equation in the additional guidance, it’s not even balanced, which is just silly.

Both charge and mass are conserved, so you’d expect both the total of the charges on both sides to be the same and the numbers of each different element to be the same on both sides.