WAEC Chemistry Past Questions & Answers - Page 60

296.

Which of the following electron configurations represents the transition element Chromium \(_{24}Cr\)?

A.

\(1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{4}\)

B.

\(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{6}\)

C.

\(1s^{2}2s^{2}2p^{6}3s^{2}3d^{4} 4s^{1}\)

D.

\(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5}\)

Correct answer is D

Electronic configuration of Chromium: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5}\)

297.

Common Salt (NaCl) is used to preserve foods. Which of the following properties can be used to determine its purity before use?

A.

Solubility in water

B.

Melting point

C.

Relative density

D.

Crystalline nature

Correct answer is B

No explanation has been provided for this answer.

298.

Atoms are electrically neutral because they

A.

do not conduct electricity

B.

contain equal number of protons and electrons

C.

are composed of neutrons and electrons

D.

cannot be attracted by electromagnetic field.

Correct answer is B

Atoms are electrically neutral because they contain equal amount of positive and negative charge. This is because they have equal number of protons and electrons.

299.

What is the relative molecular mass of a compound which has empirical formula \(CH_{2}O\)?   [C= 12, H= 1, O= 16]

A.

42

B.

45

C.

126

D.

180

Correct answer is D

Molecular formula = (empirical formula x n)

where n= (1,2,3,...)

\(CH_{2}O = 12 + (2\times 1) + 16 = 30\)

Relative molecular mass = (30 x n)

From the options, only 180 is a multiple of 30, when n=6.

300.

The law of definite proportions states that

A.

pure samples of the same compound contain the same elements combined in the same proportion by mass

B.

pure samples of substances are in the same proportion by mass

C.

chemical compounds are pure because they contain the same elements

D.

matter can neither be created nor destroyed.

Correct answer is A

The Law of Definite Proportions states that all pure samples of a particular chemical compound contain similar elements combined in the same proportion by mass.