Chemistry: Post your doubts here!

[manya]

y must it belong from Group 3 because all atoms do not have 3 electrons in there outer shells. it must belong to period 3

 

[manya]

Asslamoalikum,
I have some problems with the following questions can someone help me as soon as possible. Thanks in advanceView attachment 50731 View attachment 50731 View attachment 50731 View attachment 50732 View attachment 50731 View attachment 50732 View attachment 50733 View attachment 50731 View attachment 50731 View attachment 50731

question regarding reduction of chromium, the answer is D because in Cr2O3, u have to do +6/2 for the oxidation no. of chromium

 

[manya]

Asslamoalikum,
I have some problems with the following questions can someone help me as soon as possible. Thanks in advanceView attachment 50731 View attachment 50731 View attachment 50731 View attachment 50732 View attachment 50731 View attachment 50732 View attachment 50733 View attachment 50731 View attachment 50731 View attachment 50731

for identification of P, Q and R, SiO2 will not conduct in a liquid state so it can not be P

 

[princess Anu]

why do period 3 group 2 metals not show variable oxidation states but sulphur , phosphorus do?

 

[princess Anu]

why is A the right answer?
why would C decolourise AQueous BRomine?
Haven't we learnt that only alkene ( out of all the homologous series) decolourises aq bromine and it is a universal test for alkene as well:/

 

[shazmina]

Here's why it'll never be either of those answers

View attachment 50730

Thanks alot sis May God bless u immensely

 

[princess Anu]

can somebody do this?

answer is E

 

[Liv2Stdy]

Thanks alot sis May God bless u immensely

You're welcome !

 

[Bba321]

Hi please tell me why have we used the equation Fe 3+ + e -----> Fe 2+ in this question and not the equation of fe3+ given in data booklet?
Thanks

 

[Abdel Moniem]

Hi, how can I prepare for my chemistry A-level exams? Iam currently revising the chapters of the book. I am worried because I haven't yet started solving past papers.

 

[Hassan Ali Abid]

Hi, how can I prepare for my chemistry A-level exams? Iam currently revising the chapters of the book. I am worried because I haven't yet started solving past papers.

AS level or A2 ? Without making any delays , start solving the past papers...Refer the mark scheme .....Keep revising the organic part cz majority of the paper is based from that part so make sure you dont lose much of the marks from those questions.
Once you're done with these ,then start practising P5.

 

[Hassan Ali Abid]

Hi please tell me why have we used the equation Fe 3+ + e -----> Fe 2+ in this question and not the equation of fe3+ given in data booklet?
Thanks
View attachment 50786

Bcz in the question its clearly given that the final colour of the solution is Blue which means , at the end we are left up with fe+2....definately then we'll use the equ in which iron +3 will reduce to iron +2 rather then using the other equ....
Hope you have got it ..ryt!

 

[Abdel Moniem]

AS level or A2 ? Without making any delays , start solving the past papers...Refer the mark scheme .....Keep revising the organic part cz majority of the paper is based from that part so make sure you dont lose much of the marks from those questions.
Once you're done with these ,then start practising P5.

I am taking both AS level and A2, my major problems are with the practical papers. I am retaking chemistry AS level this year, along with the A2. Last year I scored 2 A's in my theory papers and a U grade on my practical paper. Have you got any suggestions on how I study both P3 and P5?

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s05_qp_4.pdf\
4bii)

 

[robinhoodmustafa]

why is A the right answer?
why would C decolourise AQueous BRomine?
Haven't we learnt that only alkene ( out of all the homologous series) decolourises aq bromine and it is a universal test for alkene as well:/

Question says "Will NOT de-colorized bromine..

Does Chlorine overtake Bromine gas O-o? strange!

 

[Bba321]

Bcz in the question its clearly given that the final colour of the solution is Blue which means , at the end we are left up with fe+2....definately then we'll use the equ in which iron +3 will reduce to iron +2 rather then using the other equ....
Hope you have got it ..ryt!

Isn't the colour of Fe 2+ green?

 

[Hassan Ali Abid]

Isn't the colour of Fe 2+ green?

when one will reduce the other will oxidise so cu+ will oxidise to +2..ie cu+ ----> cu+2 which is responsible for the blue colour ...

 

[Bba321]

when one will reduce the other will oxidise so cu+ will oxidise to +2..ie cu+ ----> cu+2 which is responsible for the blue colour ...

Ohh tnx

 

[Excellence]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Question 2c

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Question 2c

Kc=[Products]^n/[Reactants]^n
Kc is only affected by temperature temperature in the question is the same and therefore the value of kc is the same.
Suppose x moles of ethanoic acid have been used up at equilibrium. The number of moles of ethanoic acid left will be 0.5-x.For every mole of ethanoic acid that is used up, the same number of moles of ethanol will have gone, because they react 1 to 1. There will be 1.0 - x moles of ethanol left as well. For each mole of ethanoic acid that gets used up 1 mole of ethyl ethanoate and 1 mole of water are formed. So if x moles of ethanoic acid are used up, x moles of ethyl ethanoate and x moles of water will be formed but be careful we already have initial moles of both products,add them up.
now use the expression above.
Kc=[CH3CH2CO2C2H5][H2O]/[CH3COOH][C2H5OH]=[0.1+x/v]^2/[0.5-x/v]^2=4 V cancels out and take the square root of both sides.
o.1+x/0.5-x=2 2(0.5-x)=(0.1+x) 1-2x=0.1+x 3x=0.9 x=0.3
0.1+0.3=0.4
0.5-0.3=0.2