Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

what exactly do you mean by synoptic by the way? :P I am new to A2 :/

Like they'll do a bit of a back ground check on you

Anything from previous units can come up... from what I've seen mostly unit 4 organic

So if you have a burette that measures to 0.1cm3, you uncertainty is +/- 0.05, so 0.05*2=0.1

I have attached qsn and answer, How is the answer that? Why does product B show different structure, as if the CL is joined onto CH3? and Why cant chlorine join onto all 5 positions including the CH3 group?

I have attached qsn and answer, How is the answer that? Why does product B show different structure, as if the CL is joined onto CH3? and Why cant chlorine join onto all 5 positions including the CH3 group?

what exactly do you mean by synoptic by the way? :P I am new to A2 :/

Could someone please explain this question from Unit 4? I know the answer cannot be C or D...
Sorry, the Unit 4 thread is not so active atm

Q) The mass spectrum of CH3CH2Br will have:

A a peak at m/e = 109
B peaks at m/e = 108 and 110
C peaks at m/e = 93, 94 and 95
D peaks at m/e = 79, 80 and 81

Could someone please explain this question from Unit 4? I know the answer cannot be C or D...
Sorry, the Unit 4 thread is not so active atm

Q) The mass spectrum of CH3CH2Br will have:

A a peak at m/e = 109
B peaks at m/e = 108 and 110
C peaks at m/e = 93, 94 and 95
D peaks at m/e = 79, 80 and 81

Hi, could anybody explain why the answer here is D and not the others?

The acid used in a standard Hydrogen electrode to provide a 1 mol dm^-3 solution of Hydrogen ions is
A - Ethanoic acid
B - Phosphoric(V) acid
C - Sulfuric acid
D - Hydrochloric acid

I can't find my notes on this but it's because sulfuric acid gives 2mol of hydrogen ions so you would need to use 0.5moldm-3 of sulfuric acid in order to give 1moldm-3 of hydrogen ions. The electrode needs to be under standard conditions with all concentrations at 1moldm-3. Phosphoric acid gives 3mol so you'd need 0.33moldm-3. Then ethanoic acid is too weak.

I doubt this was helpful but I can't find my notes on this lol.

I think the answer is B (for the parent ion peak at least) because the RAM of bromine is 80, this however is an average resulting from the mass of the two most common stable isotopes of Bromine; one being Br-79, and the other being Br-81.
Br-80 is much less common and only has a half life of about 18 minutes so it won't appear in the mass spectrum.
Therefore there will be one peak for the bromoethane with Br-79 in it (29 + 79 = 108) and one peak for the bromoethane with Br-81 in it (29 + 81 = 110).

Wow we need to know all this ???

Yeah you need to know from unit 1 or 2 that RAM is just the average mass of the isotopes rather than the actual mass of the atom, that's why they're all decimals. You also need to be able to calculate RAM when given values.
Then you need to know that Bromine and Chlorine in particular have a different pattern since Bromine's main isotopes are 79 and 81 which average at 80 and chlorines main ones are 35 and 37 which average at 36.
If you want more information then look over here:
http://www.chemguide.co.uk/analysis/masspec/mplus2.html

Thanks, yeah I see what you mean, the reason it confused me though is that surely using the correct concentrations and volumes, any of them could give a 1 moldm^-3 solution of H+ ions.
I guess it must just be that for standard conditions it all has to be 1 moldm^-3.

This is bit of a rookie question but how do you know which group attached to the ring is the starting number (when naming whole compound), if I was going to use the Benzene prefix rather than Phenol, btw the bonds dont show in the picture , would 1,3 dimethyl,2-chloro,5-hydroxybenzene be correct?