WAEC Chemistry Past Questions & Answers - Page 50

246.

Which of the following pairs of gases are pollutants from car exhaust?

A.

Nitrogen(II) oxide and Carbon(IV) oxide

B.

Carbon(IV) oxide and Nitrogen

C.

Carbon(II) oxide and Sulphur(IV) oxide

D.

Carbon(II) oxide and oxygen

Correct answer is C

No explanation has been provided for this answer.

247.

The name of the compound \(C_{4}H_{9}COOC_{3}H_{7}\) is

A.

propyl pentanoate

B.

pentyl propanoate

C.

butyl propanoate

D.

propyl butanoate

Correct answer is A

The alkyl group is attached to the parent chain being a carboxylic acid. The name of the compound is gotten by writing the name of the attached alkyl group first and then the parent carboxylic acid is written but you change the -oic acid to -oate. 

The alkyl group in this case is \(C_{3}H_{7}\)

The parent carboxylic acid is \(C_{4}H_{9}COOH\) which is pentanoic acid. 

Hence, the name is propyl pentanoate.

248.

Classification of alkanols is based on the 

A.

number of carbon atoms present in the compound

B.

molecular mass of the compound

C.

molecular formula of the compound

D.

number of alkyl groups bonded to the carbon having the hydroxyl group

Correct answer is D

Alkanols can be classified as primary, secondary or tertiary, according to the number of alkyl groups attached to the carbon which bears the -OH group. 

249.

Calculate the mass of copper deposited if a current of 0.45A flows through \(CuSO_{4}\) solution for 1hour 15mins.   [Cu=64.0, S= 32.0, O =16.0, 1F= 96500C]

A.

6.40g

B.

0.67g

C.

0.64g

D.

0.45g

Correct answer is B

\(Cu^{2+} + 2e^{-}  \to  Cu_{(s)}\)

\( 2 \times 96500C = 193000C  deposits 64g of Cu\)

\(M \propto It\)

\(Q = It = 0.45A \times 1hr15mins\)

= \( 0.45 \times 75 \times 60\) [converting the time to seconds]

Quantity of electricity passed = 2025C

\(193000C \to 64g Cu\)

\(1C \to \frac{64}{193000}\)

\(2025C \to \frac{64}{193000} \times 2025\)

\(= 0.6715g  \approxeq  0.67g\)

250.

Which of the following factors characterize members of the same homologous series?

A.

The chemical property change gradually throughout the series

B.

physical properties of members are similar

C.

They have the same molecular formular

D.

Successive members undergo changes in molecular formula by \(CH_{2}\)

Correct answer is D

The difference between every successive member of the same homologous series is always \(CH_{2}\) eg methane is \(CH_{4}\) and ethane is \(C_{2}H_{6}\), difference being \(CH_{2}\).