JAMB Past Questions and Answers - Page 1595

7,971.

The pressure on 100 cm3 of oxygen gas at 35°C is 750mm of Hg.What would be the volume of the gas if the pressure is increased to 1000mm of Hg without changing the temperature?

A.

133.3 cm3

B.

85 cm3

C.

75 cm3

D.

65 cm3

E.

58.3 cm3

Correct answer is C

P1 = 750MHg V1 = 100cm3 l2 = 308k
P2 = 100 mmHg V2 = ?
But (P1V1)/(T1) = ((P2V2)/(T2) i.e (750 x 100)/(308) = (1000 x )/(V2)/(308)
V2 = (750 x 1000 x 308)/(308 x 1000) = 75 cm3

7,972.

0.07g of a hydride of carbon occupies 56.0cm3 at S.T.P. when vaporized and contains 14.29% by mass of hydrocarbon is(C = 12, H = 1)

A.

CH4

B.

C2H2

C.

C2H4

D.

C2H6

E.

C3H8

Correct answer is C

% of H2 = 14.29
% of C = 85.71
Divided by At wts
For H = (14.29)/(1) = 14.29
For C = (85.71)/(12) = 7.14
Dividing by smallest number we have the following:
For H (14.29)/(7.14) = 2
For C = (7.14)/(7.14) = 1
Emperical formula of the comp = CH2
wt of hydride taht will occupy 22400 cm is 22400 x 0.7
56 = 28 = mole wt of hydride
X(CH2) = 28
X(12 + 2) = 28 i.e 14x = 28x = 2
The formula of hydrocarbon is therefore C2H4

7,973.

A mixture contains 20cm3 of hydrogen, 35cm3 of oxygen, 15cm3 of carbon monoxide and 10cm3 of nitrogen at S.T.P. Which of the following gives the mole fraction of hydrogen in this mixture?

A.

0.02

B.

0.16

C.

0.20

D.

0.25

E.

20

Correct answer is D

H2 = 20cm
O2 = 35cm
N2 = 10cm
CO = 15cm
Total vol = 80cm

Mole fraction of H2 = (20)/(80) = 0.25

7,974.

The general formula of an alkyl halide (which represent the halide) is?

A.

CnH2n - 2X

B.

CnH2n + 1X

C.

CnH2n + 2X

D.

CnH2nX

E.

CnH2n - 1

Correct answer is B

No explanation has been provided for this answer.

7,975.

An efflorescent compound is a substance that?

A.

absorbs water froom the air without dissolving in it

B.

is capable of giving off coloured luminosity

C.

gives out water to the atmosphere

D.

absorbs water from the air and dissolves in it

E.

gives out its water of crystallization on heating

Correct answer is C

Efflorescence is a phenomenon where a crystalline salt loses all or part of its water of crystallization when exposed to the atmosphere to form a lower dehydrate or an anhydrous salt.