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1990 - WAEC Chemistry Past Questions and Answers - page 2

11

How many molecules are there in 14g of nitrogen gas at s.t.p? (n = 14, Avogadro Number = 6. 0 x 1023 mol-1)

A
1.2 x 10 23
B
3.0 x 1023
C
6.0 x1023
D
1.2 x 1024
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12

Which of the following correctly explains entropy?

A
the natural tendency for a system to achieve a greater disorder
B
a balance of two driving forces between free energy and enthalpy changes
C
the cause of spontaneity of a reaction
D
a measure of the enthalpy of a reaction
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13

The gas that is liberated when iron is heated with concentrated tetraoxosulphate (VI)acid is

A
H2S
B
\(SO_{2}\)
C
HCI
D
SO3
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14

Which of the following salts in aqueous solution will have a pH greater than 7?

A
NaCl
B
ACI3
C
FeCI3
D
Na 2SO4
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15

The compound of copper which is used in electroplating dyeing, printing, wood preservation and as a fungicide is

A
copper (ll) hydroxide
B
copper (ll) trioxonitrate (V) pentahydrate
C
copper (ll) tetraoxosulphate (VI) pentahydrate
D
copper (ll) oxide
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16

What is the molecular formula of a compound whose empirical formula is CH2O and molar mass is 180? (H = 1, C = 12, O = 16)

A
C 4H 8O2
B
C 4H 8O3
C
C 6H 10O5
D
C 6H 12O6
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17

MO and X 2O represent the formula of oxides of elements M and X respectively . If M and X should combine to form a separate compound, what would be the formula of the compound?

A
MX2
B
M2X
C
MX
D
M3X2
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18

Which of the following pollutants is biodegradable ?

A
Sewage
B
Plastics
C
Metal scrape
D
Lead compounds
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19

In the reaction represented by the equation; 2FeCI3 + SO2 + 2H2O → 2FeCL2 + H2SO4 + 2HCI the oxidation number of sulphur changes from

A
+2 to + 6
B
+ 4 to + 6
C
0 to + 6
D
- 2 to + 4
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20

Which of the following equations represents the reaction leading to the removal of permanent hardness of water?

A
Ca(HCO 3)2 → CaCO3 + H2O + CO2
B
MgSO4 + Na 2CO3 + Na 2SO
C
Ca(OH) 2 + 2HCI → CaCI 2 + 2H 2O
D
Ca(HCO3)2 + Ca(OH)3 → 2CaCO3 + 2H2O
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