WAEC Chemistry Past Questions & Answers - Page 52

256.

If 0.2g of a salt is required to saturate 200\(cm^{3}\) of water at room temperature, what is the solubility of the salt?

A.

0.2\(gdm^{-3}\)

B.

1.0\(gdm^{-3}\)

C.

2.0\(gdm^{-3}\)

D.

5.0\(gdm^{-3}\)

Correct answer is B

Solubility in \(gdm^{-3}\) = \(\frac{mass of salt in gram}{volume of liquid in dm^{3}}\)

200\(cm^{3}\) = \(\frac{200}{1000} dm^{3}  = 0.2dm^{3}\)

Solubility = \(\frac{0.2g}{0.2dm^{3}}\)

= 1.0\(gdm^{-3}\)

257.

Solubility curve can be used in the determination of the

A.

amount of crystals formed

B.

amount of solvent that can be recovered

C.

amount of solid drugs in a given solution

D.

temperature of the solution

Correct answer is C

No explanation has been provided for this answer.

258.

When water was added to a white anhydrous substance X, the colour changed to blue. X is

A.

\(CuSO_{4}\)

B.

\(FeSO_{4}\)

C.

\(Na_{2}SO_{4}\)

D.

\(PbSO_{4}\)

Correct answer is A

When water is added to white coloured anhydrous copper sulphate, its colour changes to blue, indicating that the blue coloured copper sulphate pentahydrate is regenerated. 

259.

Potassium Chloride solid does not conduct electricity because

A.

it is a covalent compound

B.

strong cohesive forces make its ions immobile

C.

strong cohesive force makes its molecule immobile

D.

each of potassium and chlorine structures contain noble gas structure

Correct answer is B

For a substance to conduct electricity, it must have charge particles like electrons and ions within it that are able to move freely throughout it. In its solid state, potassium chloride (like many other ionic compounds) have fixed ions, hence, they are immobile and can't conduct electricity.

260.

Halogens generally react with metals to form

A.

alkalis

B.

acids

C.

bases

D.

salts

Correct answer is D

The word "halogen" is a Greek word meaning salt former, because they form salts when they react with metals eg NaCl.