JAMB Chemistry Past Questions & Answers - Page 98

486.

Given that the molecular mass of iron is 56 and that of oxygen is 16, how many moles of iron(iii)oxide will be contained in 1kg of the compound?

A.

25.0 moles

B.

12.5 moles

C.

6.25 moles

D.

3.125 moles

E.

0.625 moles

Correct answer is C

Fe2O3 = 56 x 2 + 48 = 160 = 1 moles

1000gm will contain \(\frac{1000}{160}\) = 6.25 moles

487.

Hydrogen diffuses through a porous plug

A.

at the same rate as oxygen

B.

at a slower rate than oxygen

C.

twice as fast as oxygen

D.

three times as fast as oxygen

E.

four times as fast as oxygen

Correct answer is E

No explanation has been provided for this answer.

488.

In the experiment, which of the following observations would suggest that a solid sample is a mixture? The

A.

solid can be ground to a fine powder

B.

density of the solid is 2.25gdm-3

C.

solid begins to melt at 573k but is not completely melted until 648k

D.

solid absorbs moisture from the atmosphere and turns into liquid

E.

solid melts at 300k

Correct answer is C

No explanation has been provided for this answer.

489.

0.499g 0f CuSO4.xH2O when heated to constant weight gave a residue of 0.346g. the value of x is? (Cu = 63.5, S = 32.0, O = 16, H = 1)

A.

0.5

B.

2.0

C.

3.0

D.

4.0

E.

5.0

Correct answer is D

No explanation has been provided for this answer.

490.

An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. The empirical formula of the compound is

A.

C8H22O3

B.

C6H10O3

C.

C12H12O

D.

C6H12O

E.

C3H6O

Correct answer is D

carbon = 72%, hydrogen = 12%, 16%

Dividing by the atomic weight we have for C = \(\frac{5}{1}\) = 6

H = \(\frac{12}{1}\) = 12

O = \(\frac{16}{16}\) = 1

Divide by the smallest number, we have = \(\frac{6}{1}\) = 6

H = \(\frac{12}{1}\) = 12

O = \(\frac{1}{1}\) = 1

The formula is C6H12O