Chem Unit 2 (Redox Reactions)

Question 1

Sum on both sides must be…

Answer 1

… equal!

Question 2

Oxidising agents…

Answer 2

gain electrons

so are themselves reduced

Question 3

Reducing agents

Answer 3

lose electrons

so are themselves oxidised

Question 4

What are the rules for half-equations?

Answer 4

1) Work out oxidation states
2) Work out what is oxidising agent and therefore reducing agent.
3) Balance any elements that aren’t O or H
4) Add H20’s for oxygen-deficient side and add H+ for hydrogen-deficient side.
5) Check charges and add correct number of electrons to oxidising side (side that has gained electrons)

Question 5

oxygen never changes…

Answer 5

….from 2- so all the other elements are the ones that change and become reducing or oxidising agents

Question 6

2OH- means that…

Answer 6

…. it’s 2- for that molecule so you have to times the balanced equation by the overall charge

Question 7

What is the rule about the added electrons?

Answer 7

added electrons always go on the oxidising agent (that has gained electrons)

Question 8

What do you do if there is a small number next to the oxidising or reducing agent next to oxygen (e.g. Cr2 07)

Answer 8

You divide by that small number once you have worked out the oxidation number the element should have.

Question 9

4H+ ion instead of 2H+ ions means?

Answer 9

It adds a +4 charge instead of a 2+ charge to whatever side it is on.

Question 10

0 is always 2- except for in peroxides when its -1 and flurodes when its.? 0F2

Answer 10

2+

Question 11

Hydroghen is always 1+ except for in metal hydrides like calcium hydride, magnesium hydride when its..? H202

Answer 11

1-