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WAEC Chemistry Past Questions & Answers - Page 63

311.

Stainless steel is an alloy comprising of

A.

Fe and C

B.

Fe and Ni

C.

Fe, C and Ni

D.

Fe, C and Al

Correct answer is C

Stainless steel comprises iron (Fe), chromium (Cr), manganese (Mn), silicon (Si), carbon (C) and, in many cases, significant amounts of nickel (Ni) and molybdenum (Mo).

312.

The valence electrons of 12Mg are in the

A.

3s orbital

B.

2px

C.

2s orbital

D.

1s orbital

Correct answer is A

12Mg=2,8,2

=1s22s22p63s2

313.

The preferential discharge of ions during electrolysis is influenced by the 

A.

mechanism of electrolysis

B.

electrolytic reactions

C.

nature of the electrode

D.

type of electrolytic cell

Correct answer is C

The preferential discharge of ions is influenced by:

- The position of the ions in the electrochemical series

- The concentration of the ions in the electrolyte

- The nature of the electrode

314.

When substance X was added to a solution of bromine water, the solution became colourless. X is likely to be

A.

propane

B.

propanoic acid

C.

propyne

D.

propanol

Correct answer is C

Thus bromine water will be decolorized by alkynes due to the presence of two pi bonds available for reaction!

315.

When a salt is added to its saturated solution, the salt

A.

dissolves and the solution becomes super saturated

B.

dissolves and the solution becomes unsaturated

C.

precipitates and the solution remains unchanged

D.

dissolves and crystals are formed

Correct answer is C

The point of saturation is the point it gets to and from thence, the solution can no longer take in the salt anymore. From this point, it begins to form precipitate while the solution remains unchanged.