Aqa chem 4/ chem 5 june 2016 thread

Can someone help me with q9? It's about percentage error, and they've said in the answer that the titre will be 24.4 so you can use that.
I've forgotten what the formulae for percentage error is ://
http://filestore.aqa.org.uk/subjects...T-P10-TEST.PDF

Thanks

For enthalpy questions, in the mark scheme it shows that one mark is awarded for saying "∆H = Σ(enthalpies formation products) – Σ(enthalpies formation reactants)" etc... if you were to get the correct answer, would that score all the marks or is it required to state, like above what formula you are using? Just wondering because I always seem to get the correct answer for Born-Haber cycle questions but never write it out in words, for example the june 2015 mark scheme for question 1C.) says: "–∆Hf(MgCl2) + ∆Ha(Mg) + 1st IE(Mg) + 2nd IE(Mg) +2∆Ha(Cl)= –2EA(Cl) – LE(MgCl2)" Would I need to write this out even if I got the correct answer to score full marks?

Hope that makes sense!!

Is there anything in the margin saying things along the line or "or correct cycle"?

For this specific question, the born haber cycle was already done, I just had to work out one of the missing values, In the margin it says "Allow Enthalpy of Formation = sum of other enthalpychanges (incl lattice formation)" instead of saying "–∆Hf(MgCl2) + ∆Ha(Mg) + 1st IE(Mg) + 2nd IE(Mg) +2∆Ha(Cl)= –2EA(Cl) – LE(MgCl2)" I guess they may just one you to write it down so they can see what you're doing with all the values maybe?? To be on the safe side I may just start including the little formula bit before, just incase the correct answer alone doesn't get full marks.

Hi guys I need to attain a grade C and tbh that's all I want as I do struggle with chemistry but enjoy learning it hence why I took it but im not good at exams. What tips do you have so I can get my C im struggling with unit 5.

Hi guys I need to attain a grade C and tbh that's all I want as I do struggle with chemistry but enjoy learning it hence why I took it but im not good at exams. What tips do you have so I can get my C im struggling with unit 5.

Can someone please help me work out the splitting pattern for 2,3 dichlorobutane?

It says that it should be one quartet and one doublet...Can someone please explain this.
I understand that there will only be two splitting patterns since there are only two different environments, but I don't get how to work out the patterns.

Thanks

Draw out the molecule first, I find that always makes it easier.

It's a 4 carbon chain and the two middle carbons both have 1 chlorine and 1 hydrogen attached. This gives the first environment as they are also both attached to 1 methyl group. The splitting pattern is a qaurtet as for both hydrogens, they are attached to a carbon that is adjacent to a carbon with 3 hydrogens (3+1 if you follow the N+1 rule).

The second environment is for both the methyl groups being attached to a carbon that has 1 chlorine and 1 hydrogen attached. The splitting pattern is a doublet as the hydrogens in both methyl groups are attached to a carbon that is adjacent to a carbon with only 1 hydrogen attached (1+1 as per N+1).

Hopefully that helps somewhat

So the hydrogens in the middle, even though there are two separate ones since they are have the same environment do you just consider them as 1 c-h group when figuring out the splitting pattern and the same with the ch3 group since they are both the same environment it's actually like one ch3 group?

If anyone can be arsed...Is it possible to run me through why there is a 3:5 ratio of manganate(VII): Iron(II) ethanedioate as opposed to the 2:5 ratio that I managed to get after cancelling out the electrons etc on June 2012 6(d)(i) ? I managed to get 4/5 for working through with my ratio but am a bit irritated at not being able to work out the right ratio.
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN12.PDF
Ta

Why does aluminium oxide have a lower melting point than magnesium oxide but a higher melting point than sodium oxide?

you know when they ask you to draw the repeating unit of a poly(alkene). does the monomer need to have brackets at the end ??

Can someone explain why (e)(ii) has the answer (R)OCH3?
When using the integration information from the first part, we identified that there are six hydrogens (two methyl groups) at delta = 3.3. Can anyone explain why the answer is (R)OCH3 for (ii), as there is only one methyl group attached here!