JAMB Past Questions and Answers - Page 1291

6,451.

Calculate the pH of 0.05 moldm\(^{-3}\) H\(_2\)SO\(_4\)

A.

1.30

B.

1.12

C.

1.00

D.

0.30

Correct answer is C

Recall from pH formula pH = -Log [H+]

  H2SO4 → 2H+ + SO42-

  2H+ → 2 X0.05 = 0.1

  pH= -Log [0.1] = 1

6,452.

What mass of Cu would be produced by the cathodic reduction of Cu\(^{2+}\)  when 1.60A of current passes through a solution of CuSO\(_4\) for 1 hour. (F=96500Cmol\(^{-1}\) , Cu=64)

A.

7.64g

B.

3.82g

C.

1.91g

D.

0.96g

Correct answer is C

M = \(\frac{MmIT}{96500n}\)

  Where

  M=mass

  Mm = Molar mass = 64g/mol

  I = current = 1.6A

  T= Time  =1h r=3600s

  N= No of Charge = +2

  M = \(\frac{64x \times 1.6 \times 3600}{96500 \times 2}\)

  M=1.91g

6,453.

The solubility of the solids that dissolves in a given solvent with the liberation of heat will

A.

increase with an increase in temperature

B.

decrease with an increase in temperature

C.

decrease with a decrease in temperature

D.

not be affected by changes in temperature

Correct answer is B

Increasing temperature in exothermic reaction favors the left/reactant side and decreasing temperature will favor the right/product side.

6,454.

Diamond is a bad conductor of electricity because its bonding electrons are used in

A.

crystal lattice formation

B.

covalent bond formation

C.

metallic bond formation

D.

coordinate bond formation

Correct answer is B

Diamond is a covalent macromolecule, and typical of a covalent substance is an insulator. All valence electrons are localized in well-defined covalent bonds and hence are not free to move through the structure

6,455.

To what volume must 300cm\(^3\) of 0.60M sodium hydroxide solution be diluted to give a 0.40M solution?

A.

450cm\(^3\)

B.

300cm\(^3\)

C.

200cm\(^3\)

D.

150cm\(^3\)

Correct answer is A

From the dilution law

  C\(_1\)V\(_1\) = C\(_2\)V\(_2\)

  C\(_1\) = Initial Concentration of NaOH = 0.6M

  V\(_1\) = Initial Volume of NaOH = 300cm3

  C\(_2\) = Final Concentration of NaOH = 0.4M

  V\(_2\) = Final Volume of NaOH = ?

  V\(_2\) = \(\frac{C_1V_1}{C_2}\)

  V\(_2\) = \(\frac{0.6 \times 300}{0.4}\)

  V\(_2\) = 450 cm\(^3\)

Correct Computation as it follows the equation specified