HKDSE-onward Chemistry Question Review

學術區
21

Question:

Give the word equations for the thermal decomposition of the following compounds:

(a) KNO_3

(b) Pb(NO_3)_2

(c) Au(NO3)_3

22

Solution:

(a) Potassium Nitrate(III) + Oxygen
(b) Lead(II) Oxide + Nitrogen Dioxide + Oxygen
(c) Pure Gold + Nitrogen Dioxide + Oxygen

23

Question:

For the reaction below:

2NO_2(g) \rightleftharpoons N_2O_4(g)

(a) Is the foward reaction exothermic or endothermic? Why?
(b) What favors the forward reaction?

24

Solution:

(a) Exothermic. Bond formation is exothermic.

(b) Higher pressure or cooler condition.

25

Question:

Consider the following reaction:

2N_2O (g) \rightarrow 2N_2 (g)+ O_2(g)

Write down the catalyst required.

26

Solution:

Hot Copper

27

Question:

Is NH_3 denser than air?

28

Solution:

No. The molecular mass of ammonia is just about 17g/mol,
which is much lighter than air:

image
image1617×1080 164 KB

29

Question:

An acid anhydride reacts with NaOH to form NaNO_2 and N_2O. Write out its chemical formula.

30

Solution:

N_2O_3

or

NO + NO_2

31

Question:

NO_2 will disproportionate when dissolved in water. Write down the products formed.

32

Solution:

HNO_3 + NO

33

Question:

What are formed when we burn NH_3?

34

Solution:

NO(g) + H_2O (g)

35

Question:

Write down the active ingredients of nitrogenous fertilizers in ion forms.

36

Solution:

NO_3^-, NH_4^+, SO_4^{2-}, PO_4^{3-}

37

Question:

What are the differences when Copper is reacted with HNO_3 of different concentrations?

38

Solution:

The Hydrogen gas liberated will react wiith NO_3^- ions to form water vapor and NO in low concentration (or NO_2 in high concentration).

39

Question:

Will SO_2 be liberated when a mole of sulphur is immersed in a concentrated HNO_3 solution?

40

Solution:

No, Sulphur will be completely oxidized to H_2SO_4 (aq) where the nitrate(V) ions will be reduced to NO_2 (g). Water vapor is also produced.