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EDEXCEL UNIT 2 (RESIT) 2016 Answers

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That's weird. Loads of people at my school got that BF3 bonded to NF3 via a dative covalent bond and quite a few people got like around 40 for the iodine question at the end.

oh yeah considering that, thats correct because the NF3 donates its lone pain to the BF3 to for a dative covalent bond, that was hard to spot but you're correct my bad :smile:

Reply 21

RUNSran

Original post by Fmathslad

C was a tertiary halogenoalkane and they for precipitate almost instantaneously, then they secondary halogenoalkane is slight slower, leading to the primary which is much slower

oh is it? **** then.
how did you guys get 80 for the iodine mass? how and what did you get for the moles of thiosuphate that reacted in the blank titration?

Reply 22

scrlk

Original post by srg101

What did people get for the last question? the mass of iodine

i got 80 something :s-smilie:

Original post by Crespo0008

Think like 80.6?

Same, around 80g.

Original post by RUNSran

oh is it? **** then.how did you guys get 80 for the iodine mass? how and what did you get for the moles of thiosuphate that reacted in the blank titration?

2*10^-3 moles for the blank -> 1*10^-3 moles -> 1*10^-3 - whatever reacted = moles in 0.2g
(0.2*1000)/2 = moles in 100g (I think it's ~0.3 moles?). Then ~0.3 * (126.7 * 2) giving ~ 80g.

Screwed up the BF3 question, wrote down trigonal planar and 120*, came back to it and had a panic, switched it to tetrahedral (lone pair on the B). :frown:

Really kicking myself over that totally stupid mistake, but it's only 2 marks overall.

Apart from that I thought it was a pretty decent paper.

(edited 7 years ago)

Reply 23

setarcos

what did people draw for the setup for alcoholic ammonia with the halogenoalkane?

Reply 24

ToxicPhantom007

Original post by setarcos

what did people draw for the setup for alcoholic ammonia with the halogenoalkane?

Dialkylamine

Reply 25

RUNSran

Original post by scrlk

Same, around 80g.
2*10^-3 moles for the blank -> 1*10^-3 moles -> 1*10^-3 - whatever reacted = moles in 0.2g
(0.2*1000)/2 = moles in 100g (I think it's ~0.3 moles?). Then ~0.3 * (126.7 * 2) giving ~ 80g.

Screwed up the BF3 question, wrote down trigonal planar and 120*, came back to it and had a panic, switched it to tetrahedral (lone pair on the B). :frown:

Really kicking myself over that totally stupid mistake, but it's only 2 marks overall.

Apart from that I thought it was a pretty decent paper.

the question said 20 cm^3 of thiosuphate reacted with 10cm3 of the wijs soln so isn't the total volume of the reaction 30cm3? and why did they highlight the word" blank"? what do yyou reckon the grade boundaries will be?

(edited 7 years ago)

Reply 26

srg101

Original post by setarcos

what did people draw for the setup for alcoholic ammonia with the halogenoalkane?

What was the reaction name and type swell?

Reply 27

ToxicPhantom007

Original post by scrlk

Really kicking myself over that totally stupid mistake, but it's only 2 marks overall.

Apart from that I thought it was a pretty decent paper.

The number of moles you got is right. Though they asked that thses moles are in 0.2 g of oil so in 100 g of oil we had to multiply moles by 500 and the moles came were 0.45 something
0.45 x 2(126.9)= 114.8 g
80 is wrong

Reply 28

ToxicPhantom007

The answer wasC B A because C--I bond is weakest so it breaks first similarly c--cl bond is strongest so it reacts at last

Reply 29

setarcos

Original post by srg101

What was the reaction name and type swell?

so it was nucleophilic substitution and then a reflux setup for the diagram?

Reply 30

ToxicPhantom007

Original post by srg101

What was the reaction name and type swell?

Nucleophilic substitution

Reply 31

ToxicPhantom007

Original post by setarcos

so it was nucleophilic substitution and then a reflux setup for the diagram?

There was no question like that
I think you guys did gce i did IAL

(edited 7 years ago)

Original post by ToxicPhantom007

The answer wasC B A because C--I bond is weakest so it breaks first similarly c--cl bond is strongest so it reacts at last

yeah but they all had bromine in it no iodine or chlorine so that doesn't make sense

Reply 34

Lewmid

Did people say smaller concentration of unsaturated hydrocarbon leads to a smaller titre so greater error

Reply 35

dpoojaraa

Is this IAL paper or normal?

Reply 36

scrlk

Original post by RUNSran

When you want to calculate the no of moles of thiosulfate reacting you want to use the volume of thiosulfate, not the total volume of the reaction mixture.

Blank titration = no sample added

Grade boundaries will be similar to last year, around 60 for an A.

Original post by dpoojaraa

Is this IAL paper or normal?

Normal

Reply 37

Crespo0008

Original post by Fmathslad

was bonded by hydrogen bonding from the F-N, the first question i put original pyramidal and BA was 102? not sure

Wasn't it 107?

Reply 38

RUNSran

Original post by scrlk

Oh I get it .. do you think i will the marks that follows if i carry my error forward?

Reply 39

iasilva

Original post by setarcos

so it was nucleophilic substitution and then a reflux setup for the diagram?

Well, there was a similar question in a previous paper where the product is a gas -
in that paper, the correct setup was to Distill off the product and collect the gaseous product under water in a testube. So I assumed the setup would be the same for this question as well. Im not sure if it's right though