WAEC Chemistry Past Questions & Answers - Page 62

306.

When zinc is added to AgNO\(_{3}\) 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: \(2AgNO_{3} + Zn \to Zn(NO_{3})_{2} + 2Ag\)

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

307.

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.

308.

How many atoms are contained in 0.2moles of nitrogen? \([N_{A} = 6.02 \times 10^{23}]\)

A.

\(1.20 \times 10^{23}\)

B.

\(2.41 \times 10^{23}\)

C.

\(3.62 \times 10^{23}\)

D.

\(4.82 \times 10^{23}\)

Correct answer is A

\(1 mole = 6.02 \times 10^{23} atoms\)

\(0.2 moles = 6.02 \times 10^{23} \times 0.2\) atoms

= \(1.204 \times 10^{23}\)

\(\approxeq 1.2 \times 10^{23}\)

309.

When chlorine is passed through a sample of water, the pH of the water sample would be

A.

< 7

B.

> 7

C.

= 7

D.

0

Correct answer is A

\(Cl_{2} + H_{2}O \to HCl + HOCl\)

The two compounds in the product end are acidic and hence, their mixture is acidic. Hence, the pH is < 7

310.

One of the criteria for confirming the purity of benzene is to determine its

A.

heat capacity

B.

boiling point

C.

mass

D.

colour

Correct answer is B

Any pure substance will have a specific melting and boiling point. The presence of impurities alters the boiling point of benzene.