CHEM AND BIO HELP AND TIPS HERE

[DEGO]

ok the ORGANIC    i understand the alkane and alkenes part   when it comes to he next i cnt study these u hv notes for the organic (u can skip alkanes and alkenes)

[nid404]

Be a a lil specific plz....
cuz i don't remember what comes after that...I gave my igz a yr back.....syllabus not very fresh in my memory...
Thanks

[DEGO]

alcohols,carboxylic acid,esters,polymerization

[nid404]

http://www.docbrown.info/

nice site....verything pertaining to organic for igz

[DEGO]

Thank You man ur the best

[Baladya]

http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2009%20Jun/0620_s09_qp_3.pdf
Question number: 9) b)
I'm good in chemistery but my biggest nightmare is statiochemtry, so plz can u explain how to do in a baby-simple way  
thx

[holtadit]

SO write the equation out :

Al4C3 + H2O = Al(OH)3 + CH4              We know that H2O was in excess so ignore it for now and compare the moles of each substance
   l                     l           l
   l                     l           l
0.03 moles    0.12 moles   0.09 moles


then look at the ratio of moles i.e.    0.03:0.12 (which can be simplified to 1:4)  and 0.03:0.09 (which can be simplified to 1:3)

Thus u now have    1Al4C3 + ?H20 = 4Al(OH)3 + 3CH4

Now compare the no. of atoms as per the new balancing an we just need to add a 12 before H20 to balance everything out. DONE !!

[holtadit]

Okay Nid need your help again.

2008 Summer Paper 6 Question 4 e ii

I think the MS is wrong. If you use a greater volume of a solution shouldnt the conc. of that particular solution be LOWER ?


I keep getting questions regarding changes in concentration & volume wrong. Is there a formula/principle linking these two. Is there anything in your AS/A level textbook that can help me out with this stuff.

[nid404]

Twice as much soln of KMNO4 ws used for A ws as compared with B.

More the amount of KMNO4 required to complete the react means more no of moles of the substance(that is more conc )
More of it required for A, so A is more concentrated...

Get this right....conc of KMNO4 used is same for both....so the greater the volume of KMNO4 used, greater the conc of te conc of the substance

[holtadit]

Thanks I got it !


But is there any principle/formula for all of this. Even if it a level stuff I am willing to learn and understand it.

[nid404]

Actually ari, it's more like logic

see consider this

A+ KMNO4

25cm3  + 26cm3
conc x      conc z
B + KMNO4

25cm3 + 13cm3
conc y     conc z   

no of moles of a KMNO4 in 13cm3= vol X con
                                     = 13z
no of moles of KMNO4 in 26cm3= 26 Xconc
                                          =26z
more no of moles in 26cm3
implies more no of moles of A 26z> 13z of B
vol of A n B are same....conc=mol/vol
therefore conc A > conc B

[nid404]

If you still don't get it....ill use numericals...
lemme knw

[holtadit]

Hmmmm... nice analogy.

But this is nt my real problem.

Okay heres an example.

If 50 cm3 of HCl are added to 1 g of CaO we get a temp change of +1

Now if we double the volume of acid how is the temp change affected. I know it would go down but WHY ??

Another example.

 
If 50 cm3 of HCl 1 mol/dm3 conc. are added to 1 g of CaCO3. We get a max. CO2 volume of 60 cm3

 If 50 cm3 of HCl 0.5 mol/dm3 conc. are added to 1 g of CaCO3. We get a max CO2 volume of 30 cm3 BUT WHY

[nid404]

I'll be back after dinner.....I'll explain the concept

[holtadit]

I'll be back after dinner.....I'll explain the concept

LOL even I  m having dinner now. Take your time...