OCR AS Salters Chemistry F332 - Wednesday 23rd May 2012 1:30pm

Hey!

OK so the way displacement reactions work when it comes to the halogens is that the higher up elements displace the lower down ones. This is because the higher up elements are better oxidising agents, therefore they oxidise the other halogen and essentially 'steal' their electrons, becoming reduced themselves.

So in the case of your reactions:

Cl₂ + 2KBr ---> Br₂ + 2KCl This is because Cl is a better oxidising agent that Br so Br is oxidised and Cl is reduced, taking its place in the compound.

Cl₂ + 2KI ----> I₂ + 2KCL
Br₂ + 2KI ----> I₂ + 2KBr

Both these reactions work on the same principle.

Now as for colours in cyclohexane you just have to see which halogen is oxidised for it is this one which will dissolve in the cyclohexane.

Chlorine in cyclohexane is virtually colourless
Bromine in cyclohexane is an orange/red colour.
Iodine in cyclohexane is a pink/violet colour.


From this information you should be able to figure out that the first equation Bromine is oxidised, so the cyclohexane would be orange/red, and the 2nd and 3rd equations Iodine is oxidised so the cyclohexane would be pink/violet.


Hope this helps
S

What one is the bottom layer and which is the top? Please, give an example.
Thanks in advance

Cyclohexane is immiscible in water and less dense and therefore floats on top of water. Therefore in this reaction

Cl₂ + 2KI ---> I₂ + 2KCl

the top layer (being the cyclohexane and Iodine mixture) will go purple and the bottom layer (water + KCl) will remain colourless.

I would think the bottom layer would be a bit brown as the Iodine partitioned itself between the layers.

june 2011, question 1) b) i)



thanks, that makes sense


for these types of questions where it asks you to show the overall equation for the reaction, what do you do?
equation 2.1: NO(g) + ½ O2(g) --> NO2(g)
equation 2.2: NO2(g) --> NO(g) + O(g)
equation 2.3: O2(g) + O(g) --> O3(g)

i don't understand how the overall equation ends up being 1½ O2 --> O3, since you start with just ½ O2

Anyone have the jan 2012 f332 paper? would be very grateful if they could upload it

My chemistry teacher explained these questions really well. She said to write all the reactants on one side and then all the products on the other and then cross out all the ones that are on both sides to get the overall reaction. For this example:
NO(g) + ½ O2(g)+NO2(g)+O2(g) + O(g) --> NO2(g) +NO(g) +O(g)+O3(g)
This would simplify to:
1.5 O2 --> O3

Could some kind soul please walk me through the ionic equation for
Write the ionic equation for the reaction of sodium chlorate(V) with HCl.

For the love of me I can't do it, any help is greatly apprecuated.

OK I don't know the context of the question so I can't figure out which ionic equation you need so I will out line both.



Does this help?

S

The markscheme says 2ClO3 – + 4H+ + 2Cl –  2ClO2 + Cl2 + 2H2O
That is why I am so confused, but thanks for teh quick reply man.

Can you let me know the past paper and question number please?

F332 Jan 2012 Question 5b, thanks.

OK the confusion has arisen because you have to use the pre release material for this question which tells you that:


2NaClO₃(aq) + 4HCl(aq) ---> 2ClO₂(aq) + Cl₂(aq) + 2NaCl (aq) + 2H₂O(l)

So for the ionic equation all you have to do is remove the spectator ions (i.e the ions that dont change and aren't invovled) which in this case is the Na+ from NaCLO3 and the NaCl from the other side. You are only interested in the reaction between ClO3 and HCl so are only writing that equation out.

ahhh ok thanks so much man