Edexcel AS Chemistry Unit 2 Thread

I did the Jan 2010 paper - got 70/80 which scales up to full UMS. Hopefully, the June paper will be similar.

Hey !! Can anyone please enlighten me with some keyfacts to remeber while i am answering such types of questions, i am really clueless about this one as what should i recall while attempting this one.

Q. The ability of a liquid to flow is linked to the strength of its intermolecular forces.
Suggest which of these liquids flows the slowest when poured.
A Propane-1,2,3-triol
B Propane-1,2-diol
C Pentane
D Butane

Ans. A
Please do not ignore me ...i really need your help, i am taking for the first time june 2010 unit 2 exam .
Please answer soon & Thanks alot for your help

It's A because it has more -OH groups, which means that more hydrogen bonds can form between its molecules. Hydrogen bonds are the strongest intermolecular force, so this means the attraction between molecules of A is great and so A wil naturally be the most viscuous.

I agree with the rest but "so A wil naturally be the most viscuous" ??... viscosity is it mentioned any where in thnew new edexcel syll. ?? this question striked me with a shock cause i hadn't been thought by the teacher about it .

So you mean that the most soluble pours out least ?!?!?
thnks for the reply. B-]

do you mean between alcohol molecules so not with the water molecules ??

Dont worry, reading the question makes it seem so confusing but just think: what are the strongest intermolecular forces: hydrogen bonding. Therefore the one with more of these will be stronger. In this case its compound A. More hydrogen bonds means the compound is stronger and its bonds are held tighter (same thing pretty much) and so it will be the most viscous. and yes its the 3 alcohol groups with the hydrogen bonding.

SO i can end this with this that the molecule which has most stronger/more no. of hydrogen bond will be held tightly and so will flow most slowly ( more viscous).

Tbh i think that this question is not covered by any of my teacher notes like i know which has the strongest intermolecular force but didn't that which one should i relate to slowest flow the one with weakest force D which i chose while attempting this paer today or the one with strongest force A ? you are right SK-mar but really i had no idea aftr recognising the types of forces.

ha dont worry about it, even in the exam im sure they will throw a few weird questions like this at us. As long as you give them some 'educated bull' then you'll get most of the marks lol.

B-] hhaha i am usually good at guessing such stuff but thought of understanding this one so is my explaination above fine?

Are you giving unit 2 exam ? how is your prep going on ? B.O.L

4 Which of the following has dipole-dipole interactions between its molecules, but no
hydrogen bonding?

A Methane, CH4
B Methanol, CH3OH
C Ammonia, NH3
D Hydrogen iodide, HI

Why is the answer D?

B and C both have hydrogen bonding. A has no dipole because of the symmetry of the molecule cancelling the dipole moments. Therefore it must be D as there is no hydrogen bonding and there is a dipole moment with I being delta negative and H being delta +.

I think (:

your thinking is indeed correct!!

I think the shapes of compounds and bond angles will have a feature in this paper!! ... other than that just the usual stuff really! ....they always do the usual alcohol/halogenoalkane section tooo!! so much to learnnnn

What I'm predicting;

Really Odd MCQs;

A stupid Question regarding the preperation of a halogenalkane;

A really weird Question regarding Green Chemistry

Maybe a weird Group 7 question too!

yeh i think I agree with most of that.

I think today im just gonna right down each halo/alcohol test on an individual sheet of paper and learn them like that cos when they're seperated its much easier to understand.

Just wanted to ask a question:

Trichloromethane, CHCl3, is a highly polar and so has strong dipole-dipole attractions whereas tetrachloromethane, CCl4, is non-polar and has dispersion forces (London forces) but still the boiling point of CCL4 is higher than that of CHCl3-Why???