(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)
(a)(i) Three characteristic properties of transition metals: they show variable oxidation states; they form coloured ions/compounds; they act as catalysts. (They also form complex ions.)
(ii) Current = 1.8 A, time = 12.5 min = 750 s, M2+ (so 2 electrons per atom).
\[ Q=1.8\times750=1350\ \text{C};\quad n(e^-)=\frac{1350}{96500}=0.01399\ \text{mol} \]
\[ n(M)=\frac{0.01399}{2}=6.995\times10^{-3}\ \text{mol} \]
\[ \text{Relative atomic mass}=\frac{0.45}{6.995\times10^{-3}}=64.3\approx 64 \]
(iii) When the copper coat is scratched, the more reactive (more electropositive) iron is exposed. Iron then acts as the anode and copper as the cathode in an electrochemical cell, so the iron loses electrons and corrodes faster than it would on its own.
(b)(i) Law of definite proportions: A given chemical compound always contains the same elements combined together in the same fixed proportion by mass, whatever its source or method of preparation.
(ii) Weigh a known mass of dry copper(II) oxide in a weighed boat/tube. Pass dry hydrogen over it while heating; the hydrogen reduces the oxide to copper (CuO + H2 → Cu + H2O). Heat to constant mass, cool in the stream of hydrogen, and reweigh. The loss in mass is the mass of oxygen, so the percentage of oxygen = (loss in mass / mass of CuO) × 100.
(iii) 2Cu(NO3)2 → 2CuO + 4NO2 + O2
(a)(i) Three characteristic properties of transition metals: they show variable oxidation states; they form coloured ions/compounds; they act as catalysts. (They also form complex ions.)
(ii) Current = 1.8 A, time = 12.5 min = 750 s, M2+ (so 2 electrons per atom).
\[ Q=1.8\times750=1350\ \text{C};\quad n(e^-)=\frac{1350}{96500}=0.01399\ \text{mol} \]
\[ n(M)=\frac{0.01399}{2}=6.995\times10^{-3}\ \text{mol} \]
\[ \text{Relative atomic mass}=\frac{0.45}{6.995\times10^{-3}}=64.3\approx 64 \]
(iii) When the copper coat is scratched, the more reactive (more electropositive) iron is exposed. Iron then acts as the anode and copper as the cathode in an electrochemical cell, so the iron loses electrons and corrodes faster than it would on its own.
(b)(i) Law of definite proportions: A given chemical compound always contains the same elements combined together in the same fixed proportion by mass, whatever its source or method of preparation.
(ii) Weigh a known mass of dry copper(II) oxide in a weighed boat/tube. Pass dry hydrogen over it while heating; the hydrogen reduces the oxide to copper (CuO + H2 → Cu + H2O). Heat to constant mass, cool in the stream of hydrogen, and reweigh. The loss in mass is the mass of oxygen, so the percentage of oxygen = (loss in mass / mass of CuO) × 100.
(iii) 2Cu(NO3)2 → 2CuO + 4NO2 + O2
