Edexcel Chemistry A2 Unit 4- 14th January

An A for jan 10 was 56 But no thats not even close, 67-70 ould get you an a*, 67 just about more like. You will need at least about 83-85 at least to get maximum ums.

oh that's not good at all! I wonder who got full ums in jan 2010!
so it will only be the case if paper is hard and if paper is hard you will loose more mark too! well lets just hope paper will be good bt grade boundaries less

lol as, dont we all want that, but it wont happen will it Generally, look at about 65-68 for an A*

Goodness me, this isnt on the syllabus is it? Lol, I wouldnt worry on this stuff, have never ever seen it in a paper before.
...

Jojo

for solven you need the one that doesn't interact with radio waves so in other word the one that doesn't have odd number of protons or neutrons and odd mass number.
I think detecting the amount of radio frequency absorbed and emitted is just done by computer lol. I don't know about this

Just reject . Thats in relation to entropy. In the mark scheme it talks about describing in terms of disorder, and then just reject "entropy decreases". I have an explanation, but didnt really talk about order, just entropy :/.

And yes, I thought water as well.The question is in relation to converting a hydroxynitrile to a hydroxycarboxylic acid (lactic acid). In the cgp book it says HCl to two molecules of H2O

thanks though



thank you as01

ahh i always forget what the solvent has to be ... thank you

haha i'll just remember computer then !

haha might be if you try harder you will see my post

Guys so sorry about this. I tried uploading to Scribd but I don't think it's the best way as you cannot group all the past papers together. So I've managed to validate my account and now the link should be working http://www.mediafire.com/?za2a1a0c88zt6al,2sryxfiu6gfhwbf,qlf4t9b1z50rel6,57g9s0jww2yt0k7,i9ndc7esyivjnfj,bcbi656878zr8ls,cdjke1io83tthh2,o47s1i4eqz1sys8,9zqyt9t06y7t8zc,7dw7x4k855la8x5,d3uxctxys0o1eex,9x59jk3n5dab3t4,rwkpq8hejqjwbne,6jq7bheu15uqt5a,4h1nov1v61330na,392hv8853eynkrf,79j822b46y6b17p,7w8f975r88rll58,c583c9pm1ueoave,1uf0rr27i4frksn,mv4cevyobwbrhxz,85fsks0vmcobve2,rfj74ymps1i9ap5,8wkkpl5lrrtnfav,80wo3a31l2dp6mm,b0mfdl087i0pnud,jyn9cfzzo4p8e4f,vafnimn1489oqfd,cy92iyhigsa9w2t,ci7cz5jahb78c8b,92urros2jqoruhc,46z6j64iovlqq4h,itvox29qc9t3qb5,ok0w4svt8iqhv51,bs3jbf3zac5k8se,wbc1bcc8dbdlxza,vobqq243r2fy2fu

If you still have problems then contact me and I will email the files as a RAR document. The reason I want to post a link is so that even those without TSR accounts can get a hold of the papers...

huh? ... i saw the stuff about it has to have an even mass no
are you talking about another post/something else?

Acidic hydrolysis of nitriles

The nitrile is heated under reflux with dilute hydrochloric acid. Instead of getting an ammonium salt as you would do if the reaction only involved water, you produce the free carboxylic acid.

For example, with ethanenitrile and hydrochloric acid you would get ethanoic acid and ammonium chloride.

Why is the free acid formed rather than the ammonium salt? The ethanoate ions in the ammonium ethanoate react with hydrogen ions from the hydrochloric acid to produce ethanoic acid. Ethanoic acid is only a weak acid and so once it has got the hydrogen ion, it tends to hang on to it

The above is from chemguide, I dont think its important to know if the hcl is dilute or not.

Why does adding acid or alkali to buffer (ie,ethanoic acid and salt) mean no change in ph? I understand what is needed for the marks but dont understand the full reason, and how do i show this with equations, i only know(but dont understand) in words

So it says dilute :P. The mark scheme says aqueous. Suppose its just one of those things I need to remember.

When you add h+, they form with the ethanoate salt which causes ethaoic acid to form, and this makes eq shift left. So the ph will remain essentialy the same as before, because your h+ conc has fallen.

When you add oh- to the acid, it forms h20 and the ethanoate. The oh- form with the h+ ions in the solution to form h20, and so essentialy, the h+ ions need to be replaced. This is done by the ethanoic acid, which dissociates to SUPRESS the fall in h+ due to forming h20 with oh- So again, the h+ balance is restored, and ph doesnt alter much.

Another common phrase is saying that there are large reseviors of ethanoic acid and sodium ethanoate relative to any addition of h+ or oh-, so the ratio of acid to salt remains relatively unchanged, so ph change is minimal.

Does that help?

chromotography could easily be a 6 marker, lol. Nmr is so boring . Entropy is the best. I dont actually know what the paper could be on.

Yes that has helped thanks, But this is the part I dont understand in mark schemes Another common phrase is saying that there are large reseviors of ethanoic acid and sodium ethanoate relative to any addition of h+ or oh-, so the ratio of acid to salt remains relatively unchanged, so ph change is minimal.

Why does the ratio mean ph unchanged??

entropy is best !!!

am talking about that that solvent one

I believe its dilute. I have read this somewhere before. Just put whatever, aq if thats what the ms says.

OH right thanks



hi, could you pls tell me what a free carboxylic acid is ?

is this the right reaction for hydrolysis of nitrile ? -

---CH3CN+ 2H20 + HCl(aq) = CH3COOH +CH4Cl ?

WHAT IS THE OTHER REACTION PRODUCING NOT A FREE CARBOXYLIC ACID ?

nh4cl, not ch4. I am not sure what a free carb acid means, Im assuming it means when there are also ammonium ions in the solution rather than a separate product forming, like nh4cl. But anyway, your equation boveis probably the most you will need to know