Chemistry unit 6 June 2016

Ahhh so it is in the dichloromethane, I got so confused because I thought the mark scheme was saying that each one will form a layer, okay thanks!

Ah another question, how shall I know that it forms the bottom layer ?

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Get the specification first.

From these, you have to learn: (where each number below is a point on the specification - read through the specification and you'll understand)
Unit4:
4.3c, 4.3e, 4.4g, 4.8.2c, 4.8.3d, 4.8.4.b, 4.4.4c.
Unit5:
5.3.1d, 5.3.1g, 5.3.2g, 5.3.2j, 5.4.1d, 5.4.2b, 5.4.2d, 5.4.2i, 5.4.3f.

that is a lot.
And it helps to know to know background theory too. According to my teacher edexcel likes to test theory through practicals.

ninja edit: I got these from an old mapping document when the syllabus changed. I'm so grateful i decided to highlight them on my copy of the specification, because i lost the file.

Could someone answer this please?

well, when we add a quenching agent to the reaction mixture the reaction slows down but doesn't stop. As mentioned in step 4 (The propanone slows but does not completely stop the reaction.) so the reaction is still going on but at a slower rate, now if we don't titrate them immediately, more reaction would have occured and more NaOH used up, so lesser NaOH remains than we expected and hence lesser HCl is needed to react with it, so the titre would be too low!
Makes sense?

well, when we add a quenching agent to the reaction mixture the reaction slows down but doesn't stop. As mentioned in step 4 (The propanone slows but does not completely stop the reaction.) so the reaction is still going on but at a slower rate, now if we don't titrate them immediately, more reaction would have occured and more NaOH used up, so lesser NaOH remains than we expected and hence lesser HCl is needed to react with it, so the titre would be too low!
Makes sense?

January 16 was not nice.

The density is given (1.32 gcm^-3) which is greater than water's density, which is 1 gcm^-3, so more dense layers settle to the bottom!

Haven't solved it yet but the grade boundaries were way low for this paper

Do it, it's really different. I managed 60/60 UMS but my raw marks were horrendous.

Yes!! Thank you!! But could we get asked to name any quenching agents??

January 16 was not nice.

Well I was very worried about this so I asked my teacher, he says "anything that would react with one of the reactants would work, because another reaction would occur"
The most common is NaHCO3 for Iodine-thiosulfate titration!

what apparatus do we use for boiling point determination?

Well I was very worried about this so I asked my teacher, he says "anything that would react with one of the reactants would work, because another reaction would occur"
The most common is NaHCO3 for Iodine-thiosulfate titration!

Do it, it's really different. I managed 60/60 UMS but my raw marks were horrendous.

There are other ways of quenching e.g. removing catalysts cooling it down adding alkali/acid then back titrating etc etc

Yea I've been reading most of these but cooling just slows, not really stops!

Here you go!