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WAEC Chemistry Past Questions & Answers - Page 94

466.

Equal amounts of marble chips are reacted separately with 100cm3 of hydrochloric acid of different concentrations. If all the marble chips reacted; which of the following remained the same in each case?

A.

Average rate of evoluton of gas

B.

Total mass of gas evolved during the reaction

C.

Time taken for the reaction to reach completion

D.

Initial reaction rates

Correct answer is B

The total mass of gas evolved during the reaction will remain the same in each case. This is because the amount of marble chips is the same in each case, and the reaction goes to completion. Therefore, the same amount of gas will be produced in each case, regardless of the concentration of the hydrochloric acid.

467.

What is the expression for the equilibrium constant (Kc) for the following reaction? N2(g) + O2(g) ⇌ 2NO(g)

A.

[NO2][N2]+[O2]

B.

[2NO]2[N2][O2]

C.

[N2]+[O2]2[NO]2

D.

[NO]2[N2][O2]

Correct answer is D

No explanation has been provided for this answer.

468.

What will happen if more heat is applied to the following system at equilibrium?

X2(g) + 3Y2(g) ⇌ 2XY3(g); ∆H = xKJmol1

A.

the yield of XY 3 will decompose

B.

more of XY3 will decompose

C.

More of X2 will react

D.

the forward reaction will remain static

Correct answer is C

Increase in temperature will cause the forward reaction to occur, increasing the amounts of the products and decreasing the amounts of reactants.

469.

Calculate the mass of sodium hydroxide in 5.00 dm3 of a 0.125 mol dm-3 solution. [NaOH = 40 g mol-1]

A.

0.0156 g

B.

0.625 g

C.

1.00 g

D.

25.0 g

Correct answer is D

1 mole of NaOH per dm3 has a mass of 40g.
mass of NaOH in 0.125mole
= 0.125 x 40 = 5g.
mass in 5.00 dm3 of the solution.
= 5 x 5 = 25.0g.

470.

A substance is said to be hygroscopic if it absorbs

A.

water from the atmosphere to form a solution

B.

heat from the surrounding

C.

carbon (IV) oxide from the atmosphere

D.

moisture from the atmosphere without dissolving

Correct answer is D

No explanation has been provided for this answer.