WAEC Chemistry Past Questions & Answers - Page 90

446.

An oxidation state of Cr in K2Cr2O7

A.

7

B.

6

C.

5

D.

4

Correct answer is B

The oxidation state of K2Cr2O7 is +6. option A,C,D are the oxidation state of other elements like O7,C14, etc.

\(+2 + 2x + (-2\times7) =0\)

\(2x=12\)

\(x = +6\)

447.

A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. If the molar mass of the compound is 180, Find the molecular formula [H = 1, C = 12, O = 16)

A.

CH2O

B.

C3H6O3

C.

C6H12O6

D.

C6H12O3

Correct answer is C

C = 40%, 40/12 = 3.33
H = 6.7%, 6.7/1 = 6.7
O = 53.3%, 53.3/16 = 3.33
C = 3.33/3.33 = 1
H = 6.7/3.33 = 2
O = 3.33/3.33 = 1
(CH2O)n = 180
(12 + 2 + 16)n = 180
30n = 180
n = 6
= C6H12O6

448.

The energy value of petrol can be determined by

A.

Bomb calorimeter

B.

Catalytic cracker

C.

Fractionating column

D.

Thermometer

Correct answer is C

Fractionating column contains petrol with different densities.

449.

The basic particles from which matter could be made up of are as follow, except?

A.

Salt

B.

Atom

C.

Ion

D.

Molecule

Correct answer is A

Salt is a chemical used for varieties of purposes, so it’s not part of matter, Atom being the smallest part of molecule and ion are charge which are part of matter

450.

The number of isomers formed by C6H14 is

A.

4

B.

5

C.

2

D.

3

Correct answer is B

The number of isomers C6H14 cm is 5. it will not form options A,C, D