JAMB Chemistry Past Questions & Answers - Page 83

411.

For a general equation of the nature xP + yQ → mR + nS, the expression for the equilibrium constant is

A.

k [P]x [Q]y

B.

\(\frac{[P]^x [Q]^y}{[R]^m [S]^n}\)

C.

\(\frac{[R]^m [S]^n}{[P]^x [Q]^y}\)

D.

\(\frac{m[R] n[S]}{x[P] y[Q] }\)

Correct answer is C

Expression for equilibrium constant

k = \(\frac{\text{concentration of product}}{\text{concentration of reactant}}\)

412.

The constituent of air necessary in the rusting process are

A.

O2 and H2O

B.

Ar and CO2

C.

CO2 and H2O

D.

O2 and CO2

Correct answer is A

Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.

413.

In the laboratory preparation of ethyl ethanoate, the water present in the mixture is removed using ?

A.

Anhydrous CaCl2

B.

concentrated NaCO4

C.

dilute NaOH

D.

concentrated H2SO4

Correct answer is A

To purify the distillate of impurities like unreacted ethanol, acids, water and ethoxyethane.

Adding anhydrous calcium chloride and leave it to stand for a day to remove any water present

in the mixture.

414.

When element \(_{20}\)Y combines with element \(_8\)Z, it forms

A.

A covalent compound , YZ is formed

B.

A covalent compound, ZY is formed

C.

An ionic compound, YZ is formed

D.

An ionic compound, ZY is formed

Correct answer is C

Y = 2,8,8,2 and Z = 2,6.

Y will readily give off its 2 valence electrons and Z will accept the 2 electrons in order to achieve octet configuration. Hence, the compound YZ is formed by ionic bonding.

415.

How many electrons are present in \(^9_4Be^{2+}\)?

A.

2

B.

4

C.

5

D.

6

Correct answer is A

Neutral Be has 4 electrons but \(Be^{2+}\) means it has lost two electrons from possible four and became a positive ion. 

\(\therefore\) the number of electrons left will be equal to two.