(a)(i) List three characteristic properties of transition metals
(ii) 0.45g of a metal M was deposited when a current of 1.8 amperes was passed for 12.5 minutes through a solution containing M(^{2+}). Calculate the relative atomic mass of M. [1 Faraday = 96500 C]
(iii) Give the reason why copper-plated iron corrodes easily when the surface is scratched.
(b)(i) State the law of definite proportions (constant composition).
(ii) Describe in outline, an experimental procedure for determining the proportion of oxygen in a given sample of copper(II) oxide.
(iii) Write an equation to show how copper (II) oxide can be obtained directly from copper (II) trioxonitrate (V)
Explanation
(a)(i) – They formed coloured ions in solution
– They exhibit variable oxidation
– They exhibit very high catalytic activity
(ii) Quantity of electricity (Q) = current x time Q = 1.8 x 12.5 x 60 = 1350 coulombs
M(^{2+}) + 2e(^-) M;
2 x 96500 will liberate one mole of the metal but 1350 liberatrate 0.45
2 x 96500 (to) X;
X = (frac{2 times 96500}{1350}) x 0.45 = 64.33
The relative molecular mass of m is 64.33
(iii) copper – plated iron corrodes easily when scratched because the iron is exposed to moisture, which readily reacts with iron to form iron(iii) oxide (rust). Copper has high resistance to corrosion but iron does not
(b)(i) The law of definite proportion states that all pure sample of a particular chemical compound contain similar elements combined in the same proportion by mass
(ii) – weigh the sample of copper (II) oxide in boat
– place the boat inside a hard glass tube
– Heat the sample strongly while passing a stream of dry hydrogen gas through the glass tube
– Remove the flame, but continue to pass hydrogen gas as the sample cools down
– Weigh the residue, the difference in mass is the quantity of oxygen in the sample
(b)(iii) 2Cu(NO(_3))(2) (to) 2CuO + O(_2) + 4NO(_2)