JAMB Chemistry Past Questions & Answers - Page 239

1,191.

When a pressure cooker is half filled with water, and heated to boiling point, then the pressure inside the cooker will?

A.

decrease, since only a fraction of the water molecules has changed to vapour

B.

remain constant, because the total number of water molecules has not changed

C.

increase, because the water molecules can now reach every part of the sealed tube

D.

decrease, since water boils under reduced pressure

E.

increase, because the water vapour molecules now strike the walls of the tube more frequently because of their increased velocity

Correct answer is E

No explanation has been provided for this answer.

1,192.

Which of the following bonds exist in crystalline ammonium chloride (NH4Cl)?

A.

Ionic and covalent

B.

Ionic and co-ordinate

C.

Ionic covalent and co-ordinate

D.

Covalent , co-ordinate and metalllic

E.

Ionic, covalent and metallic

Correct answer is C

No explanation has been provided for this answer.

1,193.

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

1,194.

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

1,195.

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