Chemistry Doubts: Paper 1 & 2

[sourov97]

hello! guys...hope chemistry paper 4 (atp) went well for most of us! ...but as the biology paper 2 seemed extremely difficult ...chemistry paper 1 and 2 are likely to be difficult as well
members seems to be distracted from the regular Biology;Chemistry;Physics thread(https://www.xtremepapers.com/commun...try-physics-post-your-doubts-here.9672/unread) so hope this thread can bring only the chemistry mind-sparks as well as confused ones together and help each other so that we all can achieve good grades in Chemistry.
please pray to the Almighty so that we all succeed in our wills and and bring home as many A*s as possible.

 

[achana]

ur wish is really gud but don't be too pessimistic !!!

hello! guys...hope chemistry paper 4 (atp) went well for most of us! ...but as the biology paper 2 seemed extremely difficult ...chemistry paper 1 and 2 are likely to be difficult as well
members seems to be distracted from the regular Biology;Chemistry;Physics thread(https://www.xtremepapers.com/commun...try-physics-post-your-doubts-here.9672/unread) so hope this thread can bring only the chemistry mind-sparks as well as confused ones together and help each other so that we all can achieve good grades in Chemistry.
please pray to the Almighty so that we all succeed in our wills and and bring home as many A*s as possible.

 

[sourov97]

ur wish is really gud but don't be too pessimistic !!!

okay...thanks. but what did u mean by "pessimistic"

 

[Salman Rahman]

my chemistry p4 went super!, xpecting min - 57/60.
yup, it is possible that p1 and p4 might be difficult, my mentors said too.

 

[Shadman Azad]

can anyone please help Q13 of June 04 paper 1 http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s04_qp_1.pdf

 

[Saad Mughal]

can anyone please help Q13 of June 04 paper 1 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s04_qp_1.pdf

Concentration = Moles/Volume.
The unit is mol./dm^3.
Therefore, Volume = 250/1000 = 0.250 dm^3
Moles of Iodine = Mass/Mr = 2.54/(127*2) = 0.01
Concentration = 0.01/0.250 = 0.04 mol./dm^3.
Answer C.

 

[Salman Rahman]

First find the moles of iodine molecules, 2.54/(127*2) = 0.01 mol
then conc = mol/vol ; remember to convert vol in dm3

 

[Salman Rahman]

if aqueous sodium chloride is electrolysed, the OH- ions should move to anode and produce O2 right? Cl2 can only be producd using conc solution?
mark scheme say different, any1 pls explain

 

[sourov97]

yes it is sort of confusing, but chlorine will be formed for both aqueous and conc solutions of NaCl (this is an exception)
oxygen (OH-) comes only when "dilute" is mentioned.

 

[Salman Rahman]

thanks and one more, if i can bug u again, Q15 same year.
thanks in advance

 

[Shadman Azad]

pls explain Q 25 http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_w04_qp_1.pdf​

 

[Snowysangel]

pls explain Q 25 http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_w04_qp_1.pdf​

B? Methyl orange is yellow in alkaline and red with hcl

 

[achana]

okay...thanks. but what did u mean by "pessimistic"

thinking negative !!!

 

[sourov97]

pls explain Q 25 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w04_qp_1.pdf

well, consider the options:
A - cant be true as the concentration of H+ is not increasing but decreasing to form H2O (H+ + OH- = H2O)
D - the reaction produces NaCl which is a soluble salt, so no ppt can be formed
B - consider the moles HCl = (10/1000) * 1 = 0.01 (with methyl orange in beaker)
NaOH = (5/1000) * 1 = 0.005
since the reaction is not complete there will be no colour change
C - as the reaction proceeds, more H+ are reacting with more OH- thus producing more H2O
hope it helps

 

[Saad Mughal]

pls explain Q 25 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w04_qp_1.pdf

The answer could be B or C. Because, Methyl orange COULD change colour AND Water molecules are formed. I guess the key word in the question is 'gradually' which means that in this NEUTRALIZATION reaction, more water molecules are being formed which is a sure enough fact.

 

[sourov97]

B? Methyl orange is yellow in alkaline and red with hcl

sorry...but the answer is C

 

[sourov97]

thinking negative !!!

ohhh! its okay...no offence, just trying to help.

 

[sourov97]

thanks and one more, if i can bug u again, Q15 same year.
thanks in advance

its silmple...note the mole ratio between steam and O2, 2:1
so 2 moles of steam can be produced from 1 mole of O2
hope it helps

 

[achana]

lol take it easy !!

ohhh! its okay...no offence, just trying to help.

 

[Shadman Azad]

thanks for explaining. one more pls: Q 28 http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s07_qp_1.pdf