WAEC Chemistry Past Questions & Answers - Page 24

116.

What is the empirical formula of a hydrocarbon containing 0.160 moles of carbon and 0.640 moles of hydrogen

A.

CH\(_{2}\)

B.

CH\(_{3}\)

C.

CH\(_{4}\)

D.

C\(_{2}\)H\(_{4}\)

Correct answer is C

No explanation has been provided for this answer.

117.

What is the concentration of a solution which contains 0.28g of potassium hydroxide in 100 cm\(^{3}\) of solution [KOH = 56]

A.

0.01 mol dm\(^{-3}\)

B.

0.05 mol dm\(^{-3}\)

C.

0.10 mol dm\(^{-3}\)

D.

0.50 mol dm\(^{-3}\)

Correct answer is B

No explanation has been provided for this answer.

118.

Student X titrated 25 cm\(^{3}\) of Na\(_{2}\)CO\(^{3}\) with 0.1 mol dm\(^{-3}\) HCI, using methyl orange as indicator. Student Y carried out the same exercise but used phenolphthalein as an indicator. Which of the following statements about the titration is true

A.

hydrogen chloride gas was released in the reactions in both titrations

B.

the titer values obtained from the titration are equal

C.

the tirer value obtained by X is twice that of Y

D.

the titer value obtained by Y is twice that of X

Correct answer is B

No explanation has been provided for this answer.

119.

The 25°C evaporation of a 100 cm\(^{3}\) solution of K\(_{2}\)CO\(_{3}\) to dryness gave 14g of the salt. What is the solubility of K\(_{2}\)CO\(_{3}\) at 25°C? [K\(_{2}\)CO\(_{3}\) = 138]

A.

0.01 mol dm\(^{-3}\)

B.

0.101 mol dm\(^{-3}\)

C.

1.01 mol dm \(^{-3}\)

D.

10.0 mol dm\(^{-3}\)

Correct answer is C

solubility( in mol/dm^3) = \(\frac{ mass  of salt}{ Molar Mass of salt} = \frac{ 1000cm^3}{ volume of solution in cm^3}\)

                                         \(\frac{14}{138 } = \frac{ 1000cm^3}{ 100}\)

                                           \(\frac{14000}{13800}  = 1.01 mol/dm^3\)

120.

The Bohr model of the atom proposed the existence of? 

A.

the nucleus

B.

electron shells

C.

nucleons

D.

neutrons

Correct answer is B

Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets .