Chemistry Paper One Problems

[Zizu1992]

I had some problems in May June 2010, Paper 11:
Please help me with my queries,

First Problem:
6. Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this reaction proceeds?
A –2, –4 B +2, +6 C +4, –6 D +4, –4

 

[sweetiepie]

itx D

 

[Zizu1992]

Yes, but please explain how?

 

[Zizu1992]

Please can anybody answer!!!

 

[xHazeMx]

I had some problems in May June 2010, Paper 11:
Please help me with my queries,

First Problem:
6. Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this reaction proceeds?
A –2, –4 B +2, +6 C +4, –6 D +4, –4

the initial oxidation numbers of the nitrogen atoms is -3 and +5, now the new oxidation number of N atom is +1 so the change is +4, -4

 

[Zizu1992]

7 The Haber process for the manufacture of ammonia is represented by the following equation.
N2(g) + 3H2(g) 2NH3(g) ∆H = –92 kJ mol–1

Which statement is correct about this reaction when the temperature is increased?

A Both forward and backward rates increase.
B The backward rate only increases.
C The forward rate only increases.
D There is no effect on the backward or forward rate.

How can both the rates increase? Since the answer is A.

 

[Zizu1992]

And,
10 The table gives the concentrations and pH values of the aqueous solutions of two compounds, X
and Y. Either compound could be an acid or a base.
X Y
concentration 2mol dm–3 2 mol dm–3
pH 6 9

Student P concluded that X is a strong acid.
Student Q concluded that the extent of dissociation is lower in X(aq) than in Y(aq).
Which of the students are correct?
A both P and Q
B neither P nor Q
C P only
D Q only

Please explain why the answer is D in this case?

 

[Zenzenzen]

7 The Haber process for the manufacture of ammonia is represented by the following equation.
N2(g) + 3H2(g) 2NH3(g) ∆H = –92 kJ mol–1

Which statement is correct about this reaction when the temperature is increased?

A Both forward and backward rates increase.
B The backward rate only increases.
C The forward rate only increases.
D There is no effect on the backward or forward rate.

How can both the rates increase? Since the answer is A.

At first glance, the answer APPEARS to be B, as the reaction is exothermic and so the backward reaction would be favoured. However, you need to keep in mind that a temperature change increases the average kinetic energy of the particles in the reaction -- therefore, the speed of the forward reaction would increase as well (not as much as the backwards however). Therefore, the answer is A

Hope you understood

 

[Zenzenzen]

And,
10 The table gives the concentrations and pH values of the aqueous solutions of two compounds, X
and Y. Either compound could be an acid or a base.
X Y
concentration 2mol dm–3 2 mol dm–3
pH 6 9

Student P concluded that X is a strong acid.
Student Q concluded that the extent of dissociation is lower in X(aq) than in Y(aq).
Which of the students are correct?
A both P and Q
B neither P nor Q
C P only
D Q only

Please explain why the answer is D in this case?

Acids = pH 1-6
Neutral = pH 7
Basic = pH 8-14

Student P:
Is INCORRECT because strong acids must have a pH around 1-3. The acid X has a pH of 6, which is only very slightly acidic.

Student Q:
Keep this in mind: Extent of dissociation is greater when an acid or base have a pH further away from 7. Stronger bases and Stronger acids have larger extents of dissociation.

The compound Y has a pH of 9
The compound X has a pH of 6.

9-7 =2
7-6 = 1

Therefore compound X has a lower extent of dissociation that compound Y. So student Q is correct

 

[Zizu1992]

I do But what about the second MCQ?

 

[Zizu1992]

Thank you so much <3

 

[Zizu1992]

20 When gaseous chemicals are transported by road or by rail they are classified as follows.
flammable non-flammable poisonous
Which commonly transported gas is non-flammable?
A butane
B hydrogen
C oxygen
D propene

Why is oxygen non-flammable?

 

[sweetiepie]

because oxygen relights the glowing splint..

 

[Zizu1992]

How does that even make sense here? :/

 

[MHHaider707]

because oxygen relights the glowing splint..

I didn't get it...if oxygen relights glowing splint then it should be flammable!!!

 

[sweetiepie]

ooopss sorrieee itx rong i did a mistakee n i dont know....

 

[Zizu1992]

Exactly :/

 

[sweetiepie]

hmm

 

[Zizu1992]

Oh I got it. It says Oxygen cannot burn on its own, it can only spread the fire hence non-flammable.

 

[sweetiepie]

okay thankss...