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CHEM2 AQA Exam semantics

In doing past papers for the exam tommorow, I have found unusual quirks which I do not understand the most notable being marked down for using C4H10O instead of C4H9OH in the reaction of glucose to form butan-1-ol, carbon dioxide and Water. Since both are both identical why would I be marked down in using this in an equation.

Answers to this and any other wierd semantics you know about please post thanks.

Reply 1

gildartz

14

C4H9OH represents the structure of butanol more clearly since OH is the functional group for an alcohol.

Reply 2

username301959

9

Yes, my teacher said that the board requires a certain degree of structural formula with alcohols. You need to give the -OH functional group separate to the rest of the formula.

Also, stick diagrams are penalised. You must fill in all the hydrogens, bar none. That's about all I can remember. I'll have a look at examiners' report in a minute to help, as well.

Reply 3

QuantumOverlord

OP

16

Thankyou for the help; this is very useful we were never taught about this.

Reply 4

gildartz

14

oh, here's one which catches quite a few people out: when drawing displayed forumlae, whether it's for a mechanism or to just show the structure, you have to show the OH as O-H otherwise you will be penalised, that's what happened for my mock XD

Reply 5

username334839

21

for enthalphy changes you get a mark for just stating the formula used.

Reply 6

QuantumOverlord

OP

16

I've found another one! In a question about the use of barium sulphate. Why it could be used in medicine? (the answer is obviously it is insoluble)

Right? Wrong!
Because you are not allowed to use "it", you have to say "Barium sulphate is insoluable"!

Reply 7

username301959

9

QuantumOverlord

I've found another one! In a question about the use of barium sulphate. Why it could be used in medicine? (the answer is obviously it is insoluble)

Right? Wrong!
Because you are not allowed to use "it", you have to say "Barium sulphate is insoluable"!

You can use "it", because in this case, it is fairly obvious what you're referring to. If there are more than one things you could be writing about, then you'd be correct. It's always wise to get into a rhythm of good practise, mind!

Here's some more tips:

State symbols are GENERALLY ignored, unless specified.

For calculations, a correct answer alone is sufficient to gain full marks, unless the Q asks for working.

Names of functional groups and compounds MUST be spelled correctly to gain credit.

Reply 8

gildartz

14

QuantumOverlord

I've found another one! In a question about the use of barium sulphate. Why it could be used in medicine? (the answer is obviously it is insoluble)

Right? Wrong!
Because you are not allowed to use "it", you have to say "Barium sulphate is insoluable"!

yeah, that's really annoying

Reply 9

QuantumOverlord

OP

16

NAMES MUST BE SPELT CORRECTLY AAAAAAAAAAAAAAAAAAAHHHHH!!!!!!!

This is madness! i'd consider myself very good at chemistry but terrible at spelling!

Reply 10

Ihategcse

10

as good habit.. just write out the structural formulae, that is what I've started doing just in case. Try and use the 'key' words for the short answer questions (ones underlined in ms)
the o-h bond in displayed formula should be shown
try and use stuff they've given you in questions in your explanations [like not using it]
don't bother with state symbols unless mentioned.. in some cases if you get it wrong you might be penalised for 'contradictions' like for BaSO4 if you put (aq) instead of (s) etc etc.

generally just read the question and try to find out exactly what they want, I've noticed during my revision that it REALLY helps :P

CHEM2 AQA Exam semantics

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