P1 MCQ's preparation thread for chemistry ONLY!!!!

[Lyfroker]

Q28 2002 NOVhttp://www.freeexampapers.com/#A Level/Chemistry/CIE/2002 Nov WHY NOT C?

its not a substitution reaction
CN will get attach to carbon and the O will attach to H, thee anwer should be CH3CH(OH)CN

check this for explanation:
http://www.chemguide.co.uk/mechanisms/nucadd/hcntt.html

 

[sagystu]

can someone help s10 : 6 and 7

answers D and A

 

[h4rriet]

in question no 9,at equilibrium moles of p will be (2-x),R will be (x).adding them togather & putting them equal to (2+x).still confused!!

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf .kindly also tell these qusetions.2(why not B),10,33.thanks alot!!!

2. Number of electrons = 10 (it's a negative ion) which also = the number of neutrons.
10. In symmetrical molecules, dipoles cancel out.
33. 1 is true because H2SO4 will dissociate lots since it's a strong acid. For 2, you'll have to check and see where the SO42- ion comes from. It comes from the dissociation of HSO4- ions, which are weak, so they don't dissociate much. Hence obviously 3 is wrong.

 

[magnesium]

is there any need of doing very old pastpapers??? 1990's?

 

[Lyfroker]

is there any need of doing very old pastpapers??? 1990's?

if u r done wid the recent ones then u cn gv it a try, they do repeat ques

 

[MaboroshI_I]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf
Q 3, Q 14 and Q 15. If anyone could explain these please.

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf
Q 3, Q 14 and Q 15. If anyone could explain these please.

3. Use pV=nRT.
14. The moles of metal nitrate and metal oxide are the same (you can find that by constructing a balanced equation for he decomposition of a Group II metal nitrate). The mass of metal nitrate is given; 3-1.53=mass of metal oxide. n=mass/Mr. mass/Mr of metal oxide = mass/Mr of metal nitrate. Cross multiply and find x in each Mr.

 

[snowbrood]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf
Q 3, Q 14 and Q 15. If anyone could explain these please.

for Q3 use the formula PV=nRT
(95*10^3)*(4.32*10^-5)=n*8.13*(40+273)
n is the number of moles mr of NH3 is 17
n/17 u get the mass

for Q14
for any group 2 metal nitrate decomposition equation is


2M(NO3)2 yields 2MO+4NO2+O2

let the molecular mass of metal nitrate be X
as the mass is conserved so mass of the oxide is 3-1.53 as oxide is solid.
number of moles of nitrate and oxide are the same
3/X number of moles of nitrate
X is mr of that metal nitrate here comes the tricky part
u want to find the mr of metal oxide
this will give u mass of 2*mr as there are 2 moles of oxide
2X-(32+4(14+32)
we want mr so divide it by 2
(3/X)=1.47/(X-108)
3*(X-108)=1.47X
1.53X=324
X=211.76
211.8-108
103.8-16
87.8 only strontium fits in so it is correct

for Q15 u know down the group halogens become reducing agents
iodine is a reducing agent this means it will reduce the sulfuric acid
hydrogen has +2 charge in hydrogen sulfide water and sulfuric acid no change in hydrogen's oxidation number
oxygen is oxidized only sulfur is reduced
it has charge of -2 in H2S it has a charge of +6 in sulfuric acid the change is 8 right

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_s07_qp_1.pdf

Q no 9 10 12 13 14 16 18 20 22 26 34 37 39 n 40 pleasee

9. Since the reaction is reversed, the Kc will become the reciprocal of the forward reaction. So 1/2. Since all the moles are divided by two, the new Kc will be the root of 1/2.
10. Study the graph. L shows the number of molecules with the least energy, M with the average energies and N with the highest energies. What'll happen to the numbers of molecules with the least energy when the temperature increases?
12. AlCl3 is ionic; Al2Cl6 is covalent. MgCl2 is very slightly acidic in solution.
13. Draw the compound.
14. Bonds broken - endothermic. Bonds made - exothermic.
16. Draw a Hess cycle.
18. An ammonium compound will release ammonia upon reaction with an alkali.
20. Draw both compounds.
22. A carbocation is a positive ion.
26. Tertiary alcohols resist oxidation.
34. Use Le Chatelier's principle.
37. Bond energy doesn't have anything to do with the reaction actually taking place, only with how much energy is required for bonds to be made or broken.
39. ?
40. Esters get hydrolysed by acids.

 

[fizzah96]

Q 20(C).if anyone can explain this?

 

[mehranshaikh]

Can some please explain Winter 2005 Q24 to me?

 

[mehranshaikh]

Q 20(C).if anyone can explain this?

Check the second step. When CH3CHO converts to CH3CH(OH)OCH2CH3. Aldehydes and Ketones go through Nucleophillic Addition so Neuclophillic addition is involved.

 

[h4rriet]

Can some please explain Winter 2005 Q24 to me?

Draw the alkenes you get when you dehydrate all those alcohols. Count them. Look out for cis-trans isomers.

 

[itallion stallion]

Can someone tell what happens to electronegativity when we down the group and across the period.thanks

 

[mehranshaikh]

Draw the alkenes you get when you dehydrate all those alcohols. Count them. Look out for cis-trans isomers.

Oh thankyou so much! Was mising the cis-trans isomer!

 

[mehranshaikh]

Can someone tell what happens to electronegativity when we down the group and across the period.thanks

Electronegativity increases with decreased ionic radius. So as we go across a period electronrgativity increases. Down a grp electronegativity decreases.

 

[mehranshaikh]

Why can we not oxidise this compound? It has OH group so it should be oxidised which is written in 2. Summer 2005, Q39.

 

[magnesium]

Why can we not oxidise this compound? It has OH group so it should be oxidised which is written in 2. Summer 2005, Q39.
View attachment 28630

when k2cr2o7 is used in oxidation product is always aldehyde not carboxlic acid

 

[mehranshaikh]

when k2cr2o7 is used in oxidation product is always aldehyde not carboxlic acid

I think you're wrong because we do use K2Cr2O7 to oxidise alcohols and aldehydes to Carboxylic acids.

 

[Aries_95]

Why can we not oxidise this compound? It has OH group so it should be oxidised which is written in 2. Summer 2005, Q39.
View attachment 28630

Primary alcohols are oxidised to aldehyde and then carboxylic acid. if you make a displayed formula of the compound, you will see that the OH groups represent a secondary alcohol. Since secondary alcohols are oxidised to ketones and not carboxylic acids, 2 is a wrong option.