1993 - JAMB Chemistry Past Questions and Answers - page 2

Topic is Impurities of Crude-oil

Anhydrous CuSO₄ will turn blue with water

Topic is Salts With Water of Crystallization.

Unit of concentration = (moles)/(dm³)

If 250 cm³ solution NaOH contains 4.0 g NaOH

i.e -1cm³ solution NaOH (4.0)/(250) g

∴ 1000 cm³ (1 dm³) will contain (40 x 1000) / (250 x 1) = 16 g/dm³

16 g/dm³ = 16g/dm³ + molar mass NaOH

because no of moles = (mass of substance given) / (molar mass)

∴ (16 g) / (40 g) dm³ = (16 g)/(dm³ x (1 mole)/ (40g) = 0.4 (moles)/(dm³)

Ampere = (Coulomb) x (Sec) x 1930 secs = 965 coulombs (unit of current)

But quantity of electricity = current x time = (Coulomb)/(Sec) x time

If 0.5 A for 32 mins 10 secs; Quantity of electricity = (0.5 coulomb)/(Sec x 1930) secs

= 965 coulombs

Since 965 coulombs give 0.325 g M

i.e1 coulombs = (0.325)/(965) g

∴96500 coulombs = (0.30)/(965) x 96500 =32.5 g

∴(65 g)/(32.5) = 2

inference: it takes 2 Faraday of electricity to deposit 1 mole of M. Therefore, the change on M ion = 2.