NECO Chemistry Past Questions & Answers - Page 18

86.

The most efficient absorber of ultraviolet radiation in the atmosphere is

A.

CO2

B.

H2

C.

H2O

D.

02

E.

O3

Correct answer is E

No explanation has been provided for this answer.

87.

Chlorine atom forms Cl- by

A.

donating lone pair of electrons

B.

gaining an electron

C.

losing an electron

D.

sharing an electron

E.

sharing a lone pair of electrons.

Correct answer is B

Chlorine is a non-metal and non-metals ionize by gaining electron(s) 

88.

Which of the following laws is obeyed If at constant temperature, 200cm of hydrogen at 1.5 × 10m5Nm-2pressure becomes 300cm3 at 1.0 × 105Nm-2 pressure?

A.

Avogadro’s

B.

Boyle’s

C.

Charles’

D.

Faraday’s

E.

Graham’s

Correct answer is B

No explanation has been provided for this answer.

89.

The type of reaction ethyne mainly undergoes is

A.

addition

B.

carboxylation

C.

esterification

D.

saponification

E.

substitution

Correct answer is A

No explanation has been provided for this answer.

90.

What is the number of moles of NaHCO3in 250cm3 of its solution if the solution contains 8.4 g of NaHCO3 in 1 dm3 of the solution. [Na = 23, 0 = 16, C = 12, H = 1)

A.

1

B.

0.25

C.

0.05

D.

0.025

E.

0.01

Correct answer is D

no of mole in 250\(cm^3\) of its solution is about molar concentration.

using n = cv 

c = \(\frac{n}{v}\)

where c = molar concentration, n = number of moles and v = volume in \(dm^3\)

number of mole of NaHCO3 = mass of NaHCO3 / molar mass of NaHCO3 = \(\frac{8.4}{84}\) = 0.1moles

but v = 250\(cm^3\) = 250/1000 = 0.25\(dm^3\)

therefore c = 0.25 x 0.1 = 0.025mol\(dm^3\)