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NECO Chemistry Past Questions & Answers - Page 17

81.

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.

82.

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 250cm3 of its solution is about molar concentration.

using n = cv 

c = nv

where c = molar concentration, n = number of moles and v = volume in dm3

number of mole of NaHCO3 = mass of NaHCO3 / molar mass of NaHCO3 = 8.484 = 0.1moles

but v = 250cm3 = 250/1000 = 0.25dm3

therefore c = 0.25 x 0.1 = 0.025moldm3

83.

In the reaction 2H2S(g) + SO2(g) → 2H2SO(I)+3S(s)SO2is acting as _agent

A.

a bleaching

B.

a dehydrating

C.

an oxidizing

D.

a precipitating

E.

a reducing

Correct answer is C

No explanation has been provided for this answer.

84.

What is the change in the oxidation number of phosphorus in the following reaction?

4P(s) + 5O2(ag) → 2P2O5(s)

A.

0 to 2

B.

0 to 5

C.

4 to 2

D.

4 to 5

E.

4 to 10

Correct answer is B

No explanation has been provided for this answer.

85.

Chlorine displaces bromine from aqueous potassium bromide because

A.

bromine is a liquid at room temperature

B.

bromine is weakly acidic.

C.

bromine has a greater atomic radius than chlorine

D.

chlorine is a stronger oxidising agent than bromine.

E.

the density of chlorine is less than the density of bromine.

Correct answer is D

No explanation has been provided for this answer.