AQA CHEM4 - 13th June 2012

Scroll to see replies

Can someone go through step by step how we work out the Moles, I know h2 is 1M because there is 0.25 CO2, but what about the others?

Per 0.25mol of CO2 produced, the reactants have to use that amount to create it, therefore 1-0.25=0.75 mol and with water there has to be two mols used up therefore 2-(2x0.25)=1.5mol

Reply 701

Casshern1456

Original post by TheRenaissanceMan

Can someone Please Help me.

On January 2011,

Question 5i, it says Deduce the number of C-13 NMR Peaks, I don't understand why it is 6, and not 5? Do you include TMS?

Please someone explain:

Link as well : http://postimage.org/image/5ztmsnxm9/

6 different C environments but the attached group is symmetry so 3 c groups. Then the benzene have 3 Carbon groups in different environment.

Reply 702

shuaib786

Original post by lamalas600

For nitrobenzene you use Sn/HCl, for preparing primary amines you use Ni/H2

You know for Primary amines cant you use LiAlH4???

Reply 703

Saphire_93

Original post by TheRenaissanceMan

Can someone Please Help me.

On January 2011,

Question 5i, it says Deduce the number of C-13 NMR Peaks, I don't understand why it is 6, and not 5? Do you include TMS?

Please someone explain:

Link as well : http://postimage.org/image/5ztmsnxm9/

There are 6 different C types; 3 in the R group, and 3 in the Benzene atom.

Reply 704

Glacier

Original post by shuaib786

You know for Primary amines cant you use LiAlH4???

Yes, reduction of nitriles to primary amines can be done with LiAlH₄.

Reply 705

lamalas600

Original post by shuaib786

You know for Primary amines cant you use LiAlH4???

I think so yes, you will probably get marks for either. Though I only remembered the Sn one from my notes :smile:

Reply 706

excell

Original post by Doctor.

Yeah nuc substitution occurs. Lone pair on N to the +ve C atom on the haloalkane

Thanks a lot!

Reply 707

TheRenaissanceMan

Original post by Casshern1456

6 different C environments but the attached group is symmetry so 3 c groups. Then the benzene have 3 Carbon groups in different environment.

Thank you but I don't understand the two you circled on the far left.

I drew it out, and wouldn't the Left Carbons be attached to 2 carbons and 1 hydrogen.

Then the middle Carbons (in the Benzene), be attached to 2 Carbons and 1 Hydrogen as well???/

Original post by Saphire_93

There are 6 different C types; 3 in the R group, and 3 in the Benzene atom.

I don't understand why there are 3 in the R group and not 2 (repeat of what I said above)

(edited 11 years ago)

Reply 708

mrshinyshoes

Jan 10 q1 (i), just wondering why the water is plus 0.54 of moles rather than minus? :/

Reply 709

lamalas600

Original post by mrshinyshoes

Jan 10 q1 (i), just wondering why the water is plus 0.54 of moles rather than minus? :/

Because the reactants are being used up creating more products, therefore more water is created as well

Reply 710

mrshinyshoes

Original post by lamalas600

Because the reactants are being used up creating more products, therefore more water is created as well

oh yeah, oops :colondollar:

Reply 711

Bright.Inspiration.

Good luck for tomorrow guys :smile:

Reply 712

lamalas600

http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM4-W-QP-JUN10.PDF
Why is question 4B. number of Mr peaks 5 again?

Reply 713

mrshinyshoes

If you can find patterns in the colours it's so much easier :smile:

I've just turned over to a huge buffer question and a little piece of me died inside :frown:

Reply 714

mrshinyshoes

Anyone got a link to the examiners report for jan 2010, i can't find it anywhere :frown:

Reply 715

rss.914

whats the answer to

Calculate the concentration, in mol dm–3, of an aqueous solution of sulfuric acid that has a pH of 0.25...

i get that h2so4 is diprotic but dont understand why you have to divide by two when you do log10-0.25

Reply 716

lamalas600

Original post by mrshinyshoes

Anyone got a link to the examiners report for jan 2010, i can't find it anywhere :frown:

http://store.aqa.org.uk/qual/pdf/AQA-CHEM4-W-WRE-JAN10.PDF

Reply 717

shuaib786

Original post by Bright.Inspiration.

Good luck for tomorrow guys :smile:

Same to you. :wink:

Reply 718

lamalas600

Original post by rss.914

Calculate the concentration, in mol dm–3, of an aqueous solution of sulfuric acid
that has a pH of 0.25

10^-0.25=0.56moldm^-3 to get [H+]
However, H2SO4 is diprotic, therefore to get the conc. of [H+] in H2SO4, you will have to to do 0.56/2= 0.28moldm^-3

H2SO4 --> 2H+ + SO42-

(edited 11 years ago)

Reply 719

Casshern1456