Chemistry: Post your doubts here!

[MysteRyGiRl]

Omg thankyoooou!!
that helped a lot!! :')

for temperature its easier to learn just 1 variable lyk if rctn is exo,increacing temperature shifts equ. 2 da reactnats syd... if its endo, increasing temp shifts equ 2 da products syd and vice versa for decreasing temp
^^ could you please tell me why though? isnt exothermic bond formaton? so then why does it shft to the reactants side :/

no i dont think theres dis sort of explanation for dis...we just need 2 learn which syd is favoured by increasing or decreasing da temperature...btw i edited my post for concentration..plz chck

 

[MysteRyGiRl]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_4.pdf

What are they talkin about in d(i)?

u should ask in da A2 section

can ny1 tell me what are the important aspects or topics should i cover for the Bio-chemistry?
nd plz dont say me the syllabus just some of the most frequently asked sections!! pls

u mean da organic chemistry part ryt?? learn all da reactions and try solving as many pastpapers as u can..btw u shouldnt ask what 2 learn u cant leave any topic

 

[mr_perfect]

how did chem paper go for y'all ? it sucked for me . will proly get a C. . plz pray 4 me . tnx

 

[MysteRyGiRl]

how did chem paper go for y'all ? it sucked for me . will proly get a C. . plz pray 4 me . tnx

umm which variant and which ppr?

 

[mr_perfect]

umm which variant and which ppr?

Chem Paper 42 M/J 12 CIE

 

[MysteRyGiRl]

Chem Paper 42 M/J 12 CIE

post it in da A2 section

 

[Jaf]

Can this thread be locked and thrown away now that all the Chemistry exams are over? ^_^ Thanks.

 

[MysteRyGiRl]

Can this thread be locked and thrown away now that all the Chemistry exams are over? ^_^ Thanks.

particular reason? was waiting for somebody 2 disccuss da chm ppr

 

[Jaf]

particular reason? was waiting for somebody 2 disccuss da chm ppr

If you notice, this thread is about chemistry doubts.

Only the 'Mendeleev ka bacha' will ask doubts now.

 

[MysteRyGiRl]

If you notice, this thread is about chemistry doubts.

Only the 'Mendeleev ka bacha' will ask doubts now.

hey i just wanted 2 check my answers n dis thread wont hurt anywayz

 

[smzimran]

Can this thread be locked and thrown away now that all the Chemistry exams are over? ^_^ Thanks.

No dear, haven't you heard a quote:
"After every june, there is a november"

 

[user]

Can this thread be locked and thrown away now that all the Chemistry exams are over? ^_^ Thanks.

aoa wr wb!

we DID finish our chem exams, but the next batch is out there...they'll replace us
so no point in locking the thread

 

[alphabravocharlie]

No dear, haven't you heard a quote:
"After every june, there is a november"

 

[anishh]

plz help.
1.on heating,0.02 mol of the element M reacts with 0.025 mol of oxygen gas.what is the empirical formula of the oxide of M?
2.Br,extracted from dead sea,is transported as a 52%solution(by mass)of CaBr2.what mass of bromine,in tonnes,is contained in 100 tonnes of solution?(the use of data booklet is relevant)
3.when an evacuated glass bulb of 1 dm^3 capacity was filled with another sample of krypton at a pressure of 1 x 10^5pa and a temp of 300k,its mass increase by 3.32g.calculate the average Ar.

 

[Amy Bloom]

For num. 1
You have already been given the number of moles of each component, simply divide by the smallest number, that is, M=(0.025/0.02) = 0.8 while with O2, u'll get 1. Multiply by 10 on each side to obtain whole numbers, ull get M8O10, simplify further u shall get M4O5, is that the answer?
For num 2, i got 41.6 tonnes but i'm not sure of the answer. if it is good, confirm with me and i'll post my workings.
Sorry I didn't have much time to complete with the other number today, maybe by the end of this week i shall give u the explanations.

 

[JulyMei]

Hi.. I'm a newbie in A2.. This is is my today's homework.. I'm kinda lost in this question. Can anyone help??
The answer is 4.02 by the way.

Thanks in advance.

 

[Amy Bloom]

Hi! Well i've got 4.01 as answer correct to 2 decimal places but i think is close enough. Here is the explanation:
C6H5COOH -> C6H5COO- + H+(ion)
1 mol of benzoic acid diss. to give 1 mole of benzoate and hydrogen ion
You have to find the [H+].

So, number of moles of benzoic acid from 0.25 moldm-3 = (30 x 0.25)/1000 = 7.5 x 10^-3 moles
and number of moles of NaOH which neutralised the acid = (20 x 0.15)/1000 = 3 x 10^-3 moles

The reaction of benzoic acid with NaOH is shown in the eqn:
C6H5COOH + NaOH -> C6H5COONa + H2O
from the eqn. 1 mol of benzoic acid reacts with one mole of NaOH, so, the number of moles of C6H5COOH which dissociated was 3 x 10^-3
hence, the number of moles of benzoic acid that remained in the solution was = 7.5 x 10^-3 - 3 x 10^-3 = 4.5 x 10^-3 moles

Plug ur values into the equation:
Ka = [C6H5COO-] x [H+] / [C6H5COOH]
6.4 x 10^-5 = (3x10^-3) [H+]/4.5 x 10^-3
[H+] = 9.75 x 10^-5

pH = -lg [H+] = -lg( 9.75 x 10^-5) = 4.02

Hope my answer has been helpful

 

[johnsth]

Hi.. I'm a newbie in A2.. This is is my today's homework.. I'm kinda lost in this question. Can anyone help??
The answer is 4.02 by the way.

Thanks in advance.

View attachment 13674

well seems lyk sum1 has already solved it..

 

[bia awan]

Whats the equation for the reaction between calcium hydroxide and tartaric acid????????
please jaldo btao koi

 

[Amy Bloom]

Whats the equation for the reaction between calcium hydroxide and tartaric acid????????
please jaldo btao koi

According to me its:
HO2CCH(OH)CH(OH)CO2H + Ca(OH)2 --> HO2COOCCH(OH)CH(OH)COO-Ca2+ plus water