2008/2009 UNN Chemistry Post-UTME

1. Question

How many molecules are there in 14g of nitrogen gas at S.T.P? (N= 14, Avogadro number= 6.0 x 10²³)

1.2 x 10
3.0 x 10²³
6.0 x 10²³
1.2 x 10²⁴
3.0 x10²³

2. Question

120cm³of hydrogen were sparked with 60cm³of oxygen at 110⁰. What was the volume of steam produced? The equation for the reaction is 2H²O(g) + o₂(g) 2H₂O(g)

$30 {cm}^{3}$
$60 {cm}^{3}$
$90 {cm}^{3}$
$120 {cm}^{3}$
$180 {cm}^{3}$

3. Question

In the purification of town water supply, alum is used principally to

Kill bacteria
Control ph of water
Improve the taste of the water
Coagulate small particles of mud

4. Question

The solubility of Na₃AsO₄(H₂O)12 is 38.9g per 100g H₂O.
What is the mass percentage of Na₃AsO₄ in the ethanol? (As = 75, Na = 23, O = 16, H = 1)

87.2%
38.9%
19.1%
13.7%

5. Question

35cm³of hydrogen was sparked with 12cm of oxygen at 1100C and 760mm Hg to produce. What percentage of the total volume of gas left after the reaction is hydrogen?

11%
31%
35%
69%
80%

6. Question

In the extraction of iron in the blast furnace, limestone is used to

Release CO₂ for the reaction
reduce the iron ore
increase the strength of the iron
remove impurities

7. Question

10.0 dm³ of air containing H₂S as an impurity was passed through a solution of Pb(NO₃)₂ until all the H₂S had reacted. The precipitate of PbS was found to weigh 5.02 g. According to the equation:

Pb(NO₃)₂ + H₂S → PbS + 2HNO₃ the percentage by volume of hydrogen sulphide in the air is?

(Pb= 207, S=32 GMV at S.T.P. = 22.4dm³)

50.2
47.0
4.70
0.47

8. Question

The Avogadro number at 24g of magnesium is the same as that of

1g of hydrogen molecules
16g of oxygen molecules
12g of carbon molecules
35.5g of chlorine molecules

9. Question

Helium atoms are chemically uncreative because

There are no electrons around the neutrons
The number of protons equal the number of electrons
There are equal number of protons and electrons
The outer electron shell is completely filled
The atoms contain only protons

10. Question

How many grams of Hbr would exactly be required to react with 2g of propyne? (C=12, H=1, Br=80)

4.1g
6.1g
8.1g
10g
16.2g

POST-UTME: UNN – CHEMISTRY

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