1997 - JAMB Chemistry Past Questions and Answers - page 1

1
35 cm3 of hydrogen was sparked with 12 cm3 of oxygen at 110°C and 760mm Hg to produce steam. What percentage of the total volume of gas left after the reaction is hydrogen?
A
11%
B
31%
C
35%
D
69%
correct option: b
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2
2.85g of an oxide of copper gave 2.52g of copper on reduction and 1.90g of another oxide gave 1.52g of copper on reduction. The data above illustrates the law of?
A
constant composition
B
conservation of mass
C
reciprocal proportions
D
multiple proportions
correct option: d
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3
An element, X, forms a volatile hydride XH3 with a vapour density of 17.0. The relative atomic mass of X is?

(H = 1)
A
34.0
B
31.0
C
20.0
D
14.0
correct option: b
Molecular Mass = Vapour density x 2 = 17.0 x 2 = 34.0
∴ Relative Atomic Mass of X in XH3 = 34 - 3
= 31.0 ∴ x = 31.0
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4
A mixture of 0.20 mole of Ar, 0.20 mole of N2 and 0.30 mole of He exerts a total pressure of 2.1 atm. The partial pressure of He in the mixture is?
A
0.90 atm
B
0.80 atm
C
0.70 atm
D
0.60 atm
correct option: a
Total no mole = 0.2 + 0.2 + 0.3 = 0.7
Partial pressure of He = (0.3)/(0.7) x 2.1 =0.90
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5
The temperature of a body decreases when drops of liquid placed on it evaporate because?
A
the atmospheric vapour pressure has a cooling effect on the body
B
a temperature gradient exists between the drops of liquid and the body causing the latter to vaporate
C
the heat of vapourization is drawn from the body causing it to cool
D
the random motion of the liquid molecules causes a cooling effect on the body
correct option: c
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6
The electron configuration of two elements with similar chemical properties are represented by?
A
1s22s22p5 and 1s22s22p4
B
1s22s22p4 and 1s22s22p63s1
C
1s22s22p63s1 and 1s22s1
D
1s22s22p4 and 1s22s1
correct option: c
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7
In the periodic table, what is the property that decreases along the periodic and increases down the group?
A
Atomic number
B
Electron affinity
C
Ionization potential
D
Atomic radius
correct option: d
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8
Two elements, P and Q with atomic numbers 11 and 8 respectively , combine chemically to form the compound PxQY. The respective values of x and y are?
A
1 and 1
B
1 and 2
C
2 and 1
D
3 and 1
correct option: c
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9
Oxygen is a mixture of two isotopes O and O with relative abundances of 90% and 10% respectively. The relative atomic mass of oxygen is?
A
16.0
B
16.2
C
17.0
D
18.0
correct option: b
816O, 818O
90% 10%
R.A.M = (90)/(100) x 16 + (10)/(100) x 18 = 14.4 + 1.8 = 16.2
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10
If 30cm3 of oxygen diffuses through porous plug in 7s, how long will it take 60 cm3 of chlorine to diffuse through the same plug?
A
12s
B
14s
C
21s
D
30s
correct option: c
(R)o/(R)a √(M)a/(MO (30/7)/(60/t) = √ (35.5)/(16)
(60/t) (30/7)/ √(35.5)/(16) t = (60/30)/(7) x (4)√35.5
t = (60 x 7 x √35.5)/(30 x 4) = 21s
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