Chemistry: Post your doubts here!

[aalmuhannadi]

For 33 try contemplating on this that the SH can never be negative unless u have negative hydrogen ion attached to the sulfur atom so do this and you will have three lone pairs !

For 11 i need to revise this Cl thing tomorrow ill do it INSHAALLAH

Oh I figured it out now but I believe your explanation is wrong? How can you have a negative hydrogen ion? If it was a negative S ion then S would bond in a single bond with H and still have 3 lone pairs (due to the extra electron gained) is that not right?

 

[scouserlfc]

Oh I figured it out now but I believe your explanation is wrong? How can you have a negative hydrogen ion? If it was a negative S ion then S would bond in a single bond with H and still have 3 lone pairs (due to the extra electron gained) is that not right?

You could look at it either way because u can have H- ions which means H has a complete orbit on its own it can exist but is complex ! It doesnt really matter but your explanation suits it better because it doesnt mention any form of dative bond involved

 

[scouserlfc]

Hey guys !! ive got my exams coming so i was practicing past papers so i came across a qn which i culdnt figure out so i thought you guys could help

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_21.pdf
its qn no 3 d

For this u must have done the parts before and understood them !
3biii) -32.60KJ/mol

3ciii) +23.20 KJ/mol

so now all u have to do is use enthalpy of neutralisations for KHCO3 and K2CO3 and the answers with it ! the other products CO2 + H2O are negated as they are common in the reaction so basically u will end up with
H + (-32.60) =2(23.20 ) (you have to use two as the answer u gave in 3ciii was for one mole and here u have two moles of KHCO3)
H=79.00 KJ/mol

If u still dont get it ill draw the hess cycle for you

 

[1357913579]

please help me solve this doubt which is of paper-5 mayjune 2009
doubt on 1e,g,h and for 2d iam not able to get one point so please help me for that as well
here is the link for other parts which are required for solving the doubts iam posting
thanks and Jazak Allah khairn

 

[aalmuhannadi]

For this u must have done the parts before and understood them !
3biii) -32.60KJ/mol

3ciii) +23.20 KJ/mol

so now all u have to do is use enthalpy of neutralisations for KHCO3 and K2CO3 and the answers with it ! the other products CO2 + H2O are negated as they are common in the reaction so basically u will end up with
H + (-32.60) =2(23.20 ) (you have to use two as the answer u gave in 3ciii was for one mole and here u have two moles of KHCO3)
H=79.00 KJ/mol

If u still dont get it ill draw the hess cycle for you

For q11 do you at least know what chapter this question could be from? like which topic?

 

[aalmuhannadi]

In Q18 here, the examiner report says that after observation X, HCl is made, but then it says that HCl will not react with KI? I thought that it would indeed react as Cl would displace I and therefore no reaction = colourless solution? Or is there something I'm missing...
In Q14, I'd just like to know the reaction because apparently 10Al + 3Ba(NO3)2 > 3BaO + 5Al2O3 + 9N2 is wrong
In q15, I read that group II oxides give stronger alkaline solution going down the group, so why is SrO wrong and A is the right answer?

 

[scouserlfc]

For q11 do you at least know what chapter this question could be from? like which topic?

Oh 11 is supposed to be a part of the grp 7 chapter in the inorganic chem property !!

View attachment 19944View attachment 19945

In Q18 here, the examiner report says that after observation X, HCl is made, but then it says that HCl will not react with KI? I thought that it would indeed react as Cl would displace I and therefore no reaction = colourless solution? Or is there something I'm missing...
In Q14, I'd just like to know the reaction because apparently 10Al + 3Ba(NO3)2 > 3BaO + 5Al2O3 + 9N2 is wrong
In Q15, I read that group II oxides give stronger alkaline solution going down the group, so why is SrO wrong and A is the right answer?

For 18 tell me the year but what i think is happening is that HCl reacts with KI and produces HI and KCl and the result is a colourless solution and for the other reaction with silver nitrate and aqueous ammonia is white so answer should be D

For Q15 you made the most funny error Ba is below Sr so even your reason is correct but u didnt see Sr is above Ba

For 14 i think its correct but tell me the year please ??

 

[aalmuhannadi]

Oh 11 is supposed to be a part of the grp 7 chapter in the inorganic chem property !!



For 18 tell me the year but what i think is happening is that HCl reacts with KI and produces HI and KCl and the result is a colourless solution and for the other reaction with silver nitrate and aqueous ammonia is white so answer should be D

For Q15 you made the most funny error Ba is below Sr so even your reason is correct but u didnt see Sr is above Ba

For 14 i think its correct but tell me the year please ??

Summer 2012 paper 11, for q18 I thought the same thing but the answer is C apprently and in the exmainer report it says: "The relevant product of the first reaction is HCl. HCl will not react with KI(aq), so observation X is 'colourless solution'. The second reaction was between KCl and AgNO3 in the presence of ammonia solution. The expected product, AgCl, is soluble in ammonia solution and so observation Y is also 'colourless solution'. So your reasoning for both observations is wrong, and I don't understand their reasoning either...

 

[scouserlfc]

Summer 2012 paper 11, for q18 I thought the same thing but the answer is C apparently and in the examiner report it says: "The relevant product of the first reaction is HCl. HCl will not react with KI(aq), so observation X is 'colourless solution'. The second reaction was between KCl and AgNO3 in the presence of ammonia solution. The expected product, AgCl, is soluble in ammonia solution and so observation Y is also 'colourless solution'. So your reasoning for both observations is wrong, and I don't understand their reasoning either...

Oh i am sorry for the second part of the question its supposed to be colourless too so its C either ways ! but i will check it anyways the first part of the reaction that why HCl wont react with KI !!! but actually my reasoning that HCl reacts with KI is giving a correct answer too now !! ??

 

[scouserlfc]

Summer 2012 paper 11, for q18 I thought the same thing but the answer is C apprently and in the exmainer report it says: "The relevant product of the first reaction is HCl. HCl will not react with KI(aq), so observation X is 'colourless solution'. The second reaction was between KCl and AgNO3 in the presence of ammonia solution. The expected product, AgCl, is soluble in ammonia solution and so observation Y is also 'colourless solution'. So your reasoning for both observations is wrong, and I don't understand their reasoning either...

by the way did u solve 14 ????

 

[aalmuhannadi]

by the way did u solve 14 ????

No because there's something wrong with the reaction I wrote, something stoichiometric or I got some of the products/reactants wrong...

 

[aalmuhannadi]

by the way did u solve 14 ????

So all that's left now is explaining why HCl and KI don't react

 

[scouserlfc]

Minato112 can u help out on Q18 and 14 above ! !!

 

[Minato112]

scouserlfc : Bro is it urgent? Cuz I've got something to do.....

 

[snowbrood]

scouserlfc http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_ir_31.pdf(page 4) http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_31.pdf (page2) the concentration of FA1 is different in both can anyone tell me what concentration of sodium carbonate would be consider ?

 

[aalmuhannadi]

scouserlfc solved q14

 

[Salman Khalid]

I have doubt in q4 of this , paper can someone just give the answer
and does anyone has old pastpapers, if yes then can u plz send them to me or tell me the link

 

[scouserlfc]

scouserlfc solved q14

How was your equation wrong ???

scouserlfc : Bro is it urgent? Cuz I've got something to do.....

Nah its okay

scouserlfc http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_ir_31.pdf(page 4) http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_31.pdf (page2) the concentration of FA1 is different in both can anyone tell me what concentration of sodium carbonate would be consider ?

Yeah this looks interesting both conc. are different but use the one in the question paper probably the chemicals here given in reality were less to save costs and more conc. so try it by doing the calculations with the qp values and check the ms and er ! Otherwise there isnt any other method to decide because i dont have values of it atm

 

[scouserlfc]

I have doubt in q4 of this , paper can someone just give the answer
and does anyone has old pastpapers, if yes then can u plz send them to me or tell me the link

This is a PHYSICS question anyways ill solve it here !
4a(i) Y (ductile materials can undergo plastic deformation too )
ii) X (breaks after reaching UTS or at max stress and doesnt undergo plastic deformation)
iii) Z(because it undergoes varying elastic deformation like a rubber band and then breaks )

X can be glass
Y can be a cooper wire
Z can be any polymeric substance like rubber

4ci) find the area under graph of Y between 0 and 2
Area=strain energy= 0.5*2*40*(1/1000) (divide by the 1000 because convert it to m )
------------------------> u can calculate this !

4cii) similarly find the area under the graph between 20 and 2 using either two trapeziums or one because it wants an estimate so it doesnt want an accurate value !

 

[aalmuhannadi]

How was your equation wrong ???



Nah its okay



Yeah this looks interesting both conc. are different but use the one in the question paper probably the chemicals here given in reality were less to save costs and more conc. so try it by doing the calculations with the qp values and check the ms and er ! Otherwise there isnt any other method to decide because i dont have values of it atm

I just balanced it wrong, should've been 3N2 instead of 9, then it works