Processing math: 100%

WAEC Chemistry Past Questions & Answers - Page 60

296.

Which of the following methods can be used to seperate blood cells from plasma?

A.

Centrifugation

B.

Filtration

C.

Chromatography

D.

Distillation

Correct answer is A

No explanation has been provided for this answer.

297.

The change in the oxidation state of iron in the reaction represented by the equation:  2FeCl3+H2S2FeCl2+2HCl+S  is

A.

+2 to +3

B.

0 to +2

C.

+3 to +2

D.

+3 to 0

Correct answer is C

The oxidation number of Iron in FeCl3 = +3. The oxidation number in FeCl2 = +2.

298.

The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is    [Cu = 63.5, O = 16]

A.

Cu2O

B.

CuO

C.

CuO2

D.

CuO4

Correct answer is B

    Cu   :   O

0.067   :   0.066

mole ratio   0.0670.066  :  0.0660.066

= 1   :   1

= CuO

299.

When zinc is added to AgNO3 solution, crystals of silver forms on the zinc surface. This indicates that zinc is

A.

oxidised

B.

reduced

C.

decomposed

D.

dissociated

Correct answer is A

Reaction: 2AgNO3+ZnZn(NO3)2+2Ag

The oxidation number of Zn in the reactant is 0, and in the product is +2. Therefor, it is oxidized.

300.

The strength of metallic bonds depends on the 

A.

charge density of the atoms

B.

ductility of the metal

C.

number of valence electrons

D.

total number of electrons in the atom

Correct answer is C

It is determined by the difference in the electron structures of the atoms. These primarily are: The number of outer electrons, i.e the number of valence shell electrons released during a metallic bond.