Please help with Chemistry redox Reactions

So I thought this topic was quite easy until I did some questions where you had to identify the species oxidized and reduced and the reducing agent and oxidizing agent.
I'm confused about question 4 and question 11.
In Question 4 why is the species oxidised Br- instead of KBR or would this also be acceptable?
Similarly, in question 11 why have the oxidised and reduced species been split into ions whereas in the other questions the answers are the compounds which contain the ions?
I'm a bit confused because I missed the lesson on this so any help would be greatly appreciated.

REDOX REACTIONS.JPG42.3KB

REDOX REACTIONS 2.JPG18.4KB

Reply 1

lloydmynumber

13

Original post by 11plusboy

So I thought this topic was quite easy until I did some questions where you had to identify the species oxidized and reduced and the reducing agent and oxidizing agent.
I'm confused about question 4 and question 11.
In Question 4 why is the species oxidised Br- instead of KBR or would this also be acceptable?
Similarly, in question 11 why have the oxidised and reduced species been split into ions whereas in the other questions the answers are the compounds which contain the ions?
I'm a bit confused because I missed the lesson on this so any help would be greatly appreciated.

for question 4 , KBr is the ionic compound so it has 0 charge and in order for Br- to go back to being Br2 it needs to lose the electron it had gained in the beginning. K+ needs to gain electrons to form K(s) as it lost electrons in the beginning when forming the ion.

Reply 2

username5019056

3

K is not oxidised as it does not lose electrons. It is still an ion as it reacts with fluorine. Br is only oxidised as it loses electrons to from a neutral Br2 atom.

The reason why some are written as ions is because oxidation means either loss of electrons or gaining oxygen. S02 reacts with oxygen to form SO3 so it is oxidised.

I hope this makes sense

Reply 3

kubes_04

13

The easiest way for me is OIL RIG ==> Oxidised is a loss, Reduction is Gain. So if the oxidation number goes up then something has been oxidised and if it goes down then something has been reduced. Also, an oxidising agent oxidises another species but it gets reduced itself and a reducing agent is vice versa.

Good luck remembering this, it seems hard at first but after a while it seems like second nature

Please help with Chemistry redox Reactions

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