Chemistry
JAMB 1990
10.0 dm
3 of air containing H
2S as an impurity was passed through a solution of Pb(NO
3)
2 until all the H
2S had reacted. The precipitate of PbS was found to weigh 5.02 g. According to the equation:
Pb(NO
3)
2 + H
2S → PbS + 2HNO
3 the percentage by volume of hydrogen sulphide in the air is?
(Pb = 207, S = 32, GMV at s.t.p = 22.4dm
3)
-
A.
50.2
-
B.
47.0
-
C.
4.70
-
D.
0.47
Correct Answer: Option C
Explanation
Pb(NO3)2 + H2S → PbS + 2HNO3
34 g H2S → 239 g pbs
5.02g pbs → (34)/(237g) χ 5.02 g = 0.714 g
34g → 22.4 dm3
=0.714 → (22.4)/34g) χ 100 = 4.70
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