Chemistry: Post your doubts here!

[Jinosupreme]

A solution of Sn2+ ions will reduce an acidified solution of MnO – ions to Mn2+ ions. The Sn2+ ions
are oxidised to Sn4+ ions in this reaction.
How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is
added to an excess of acidified KMnO4 solution?
A 0.010
B 0.020
C 0.050
D 0.125

How to do? Answer is B

 

[x-gamer-x]

A solution of Sn2+ ions will reduce an acidified solution of MnO – ions to Mn2+ ions. The Sn2+ ions
are oxidised to Sn4+ ions in this reaction.
How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is
added to an excess of acidified KMnO4 solution?
A 0.010
B 0.020
C 0.050
D 0.125

How to do? Answer is B

Sn2+ + MnO4- –––––> Sn4+ + Mn2+
ox. no. of sn is increased by 2 (it is oxidized to Sn4+) which means 2 electrons are removed Sn2+ ----> S24+ + 2e
ox. no. of Mn in MnO4- is +7 and in Mn2+ is 2+ so it is reduced means 5 e are added MnO4- + 5e ----> Mn2+
to balance mult. with 5 to the Sn2+ equ.
and 2 wtih MnO4- equ.
u will get 5Sn2+ ----> 5Sn4+ + 10e
2MnO4- + 10e ----> 2Mn2+
adding equtions u will get
5Sn2+ + 2MnO4- ----> 2Mn2+ + 5Sn4+
from equ. Ratio is 5 : 2 so 9.5g which is (0.05moles) of Sn2+ will reduce 0.05 * 2 / 5 = 0.02
Ans B

 

[Jinosupreme]

Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications
are described below.
Compound W is used as a refractory lining material in kilns.
Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils.
Which statements about these compounds are correct?
1 More acid is neutralised by 1g of W than by 1g of X.
2 The metallic element in W reacts with water more quickly than the metallic element in Y.
3 Adding Z to a soil decreases the pH of the soil.

Answer is 1 only why?

 

[Jinosupreme]

An organic compound, Z, will react with calcium metal to produce a salt with the empirical formula
CaC4H6O4.
What could be the identity of Z?
1 ethanoic acid
2 butanedioic acid
3 methylpropanedioic acid

Answer is 1 only. Why?

 

[x-gamer-x]

An organic compound, Z, will react with calcium metal to produce a salt with the empirical formula
CaC4H6O4.
What could be the identity of Z?
1 ethanoic acid
2 butanedioic acid
3 methylpropanedioic acid

Answer is 1 only. Why?

no
ans is 2 and 3
so its C

 

[snowbrood]

An organic compound, Z, will react with calcium metal to produce a salt with the empirical formula
CaC4H6O4.
What could be the identity of Z?
1 ethanoic acid
2 butanedioic acid
3 methylpropanedioic acid

Answer is 1 only. Why?

 

[snowbrood]

An organic compound, Z, will react with calcium metal to produce a salt with the empirical formula
CaC4H6O4.
What could be the identity of Z?
1 ethanoic acid
2 butanedioic acid
3 methylpropanedioic acid

Answer is 1 only. Why?

 

[snowbrood]

no
ans is 2 and 3
so its C

ans will be C if CaC4H4O4 here it is CaC4H6O4

 

[Trevor Jts]

Hi, anybody can help me?
Nov 2011-13 Q28

A reaction between chlorine and propane in ultraviolet light produces two isomeric
monochloropropanes, C3HCl, as products. Which information about this reaction is correct?

expected ratio of 1-chloropropane to 2-chloropropane produced
A 3:1
B: 1:1

 

[*MK*skydiver :D]

you guys , i have some questions ​

​

#33 in June 12 Variant 2 : why isn't the concentration of SO4 high? ​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf​

​

​

In Al2Cl6 , how many non-bonded electron pairs are there ? ​

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#35 I found , online, that the products of this reaction are N2 ,BaO, and MgO , but how am i expected to deduce this in an exam ?​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf​

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#3 I figured it out using the data booklet , but i can't think of a logical explanation!​

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#12 isnt it 1 mol , 1.5 mol and 2 mol (MgO Al2O3 and SO2 respectively) how is it not A then?​

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w05_qp_1.pdf​

 

[*MK*skydiver :D]

I hope you understand from me . If 50% of the nitrogen tetraoxide dissociate then 0.5 moles remain if it was one mole , if 0.5 remains from nitogen tetraoxide then 1 mole of the product is formed because the ratio of moles is 1:2 . so the pressure constant would be the partial pressure of the product which is 1/1.5 multiplied with one , raised to the power 2 because that's the number of moles from the equation. the answer is then divided into the partial pressure of the reactant which is 0.5/1.5 x 1 , thus the answer is 4/3 ... any one correct me if I'm wrong please

Finally found an answer ! *sigh of relief*
Quite convincing , thanks !

 

[*MK*skydiver :D]

At a total pressure of 1.0 atm dinitrogen tetraoxide is 50% dissociated at a temperature of 60 degree Celcius. according to the following equation:
N2O4-------------2NO2( reversible reaction)
what is the value of the equilibrium constant Kp, for this reaction at 60 degree Celcius?
A:1/3 atm
B:2/3 atm
C: 4/3 atm
D:2 atm
Common Guyz Someone reply please

https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-191#post-466313

 

[*MK*skydiver :D]

At a total pressure of 1.0 atm dinitrogen tetraoxide is 50% dissociated at a temperature of 60 degree Celcius. according to the following equation:
N2O4-------------2NO2( reversible reaction)
what is the value of the equilibrium constant Kp, for this reaction at 60 degree Celcius?
A:1/3 atm
B:2/3 atm
C: 4/3 atm
D:2 atm
Common Guyz Someone reply please

https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-191#post-466313

 

[*MK*skydiver :D]

At a total pressure of 1.0 atm dinitrogen tetraoxide is 50% dissociated at a temperature of 60 degree Celcius. according to the following equation:
N2O4-------------2NO2( reversible reaction)
what is the value of the equilibrium constant Kp, for this reaction at 60 degree Celcius?
A:1/3 atm
B:2/3 atm
C: 4/3 atm
D:2 atm
Common Guyz Someone reply please

https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-191#post-466313

 

[hope4thebest]

Why doesn't Sodium metal react with Ethanal(aldehyde) to produce hydrogen?

 

[Jinosupreme]

8 Which compound is the only gas at room temperature and pressure?
A CH3CH2CH2NH2 Mr = 59.0
B CH3CH2CH2OH Mr = 60.0
C CH2OHCH2OH Mr = 62.0
D CH3CH2Cl Mr = 64.5

Answer is D. Why?

 

[Jinosupreme]

35 Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications
are described below.
Compound W is used as a refractory lining material in kilns.
Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils.
Which statements about these compounds are correct?
1 More acid is neutralised by 2.0 g of X than by 2.0 g of W.
2 TheMrofXisgreaterthantheMrofYby44.0.
3 The metallic element in Y reacts with cold water more quickly then the metallic element in W.

Answer is 2 and 3, why is 1 wrong?

 

[Trevor Jts]

Hi M

you guys , i have some questions ​

​

#33 in June 12 Variant 2 : why isn't the concentration of SO4 high? ​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf​

​

​

In Al2Cl6 , how many non-bonded electron pairs are there ? ​

​

​

#35 I found , online, that the products of this reaction are N2 ,BaO, and MgO , but how am i expected to deduce this in an exam ?​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf​

​

​

​

​

​

​

#3 I figured it out using the data booklet , but i can't think of a logical explanation!​

​

​

​

#12 isnt it 1 mol , 1.5 mol and 2 mol (MgO Al2O3 and SO2 respectively) how is it not A then?​

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w05_qp_1.pdf​

Hi Mk driver, I'm not good in explaining but I can at least do Q12 in Nov 2005 for you.
Equation being formed is:
2Mg + O2 --> 2MgO
4Al +3O2 ---> 2Al2O3
S + O2 ---> SO2
Simplifying them since you need one mole of reactant, you'll get:
Mg + 0.5O2 ---> MgO
Al + 0.75O2 ---> 0.5Al2O3
S + 1O2 ---> SO2
Hence the trend in option D

For your Nov 2011-12 question,
Ba(NO3)2 ----> BaO + 2NO2 + 0.5O2
and Mg will b oxidised also to MgO because it says barium nitrate is oxidising agent.
I also dono this question at first, but my teacher solved it just in a matter of seconds haha. Good luck if youre taking A LEvels tomoro!

 

[Trevor Jts]

N

How to do? Answer is D

Hi Jinosupreme;
Next time do check out examiner's remarks from xtremepapers. This time I copy and paste for u
The correct answer was D. The most commonly chosen incorrect answers were A and B.
These answers, A and B, both have compound X having a cyclopentane ring which would have to be
opened by the reaction with ammonia. This will not occur. Compound X must be 1,5-dibromooctane. The
reaction of 1,5-dibromooctane with ammonia takes place by nucleophilic substitution in two steps. In the first
step of the reaction an –NH2 group substitutes for one of the bromine atoms. Since this –NH group has a
lone pair it can attack the δ+ carbon atom of the second C-Br by the same nucleophilic mechanism, giving
coniine as the organic product.
BTW, IF POSSIBLE, help me out with POST 6757!

 

[periyasamy]

Hai guys,why is y in this question has an observation of colourless solution?Thanks