State one observation for each of the following:
(i) Concentrated nitric acid is reacted with sulphur.
(ii) Ammonia gas is passed over heated copper (II) oxide.
(iii) Copper sulphate solution is electrolysed using copper electrodes.
(iv) A small piece of zinc is added to dilute hydrochloric acid.
(v) Lead nitrate is heated strongly in a test tube.
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(i) Reddish brown nitrogen dioxide gas is evolved.
S + 6HNO3 [conc.] ⟶ H2SO4 + 2H2O + 6NO2
(ii) Black copper [II] oxide is reduced to brown copper.
2NH3 + 3CuO ⟶ 3Cu + 3H2O + N2 [g]
(iii) A brownish pink deposit of copper metal is seen at the cathode when copper solution is electrolyzed using copper electrodes. The blue colour of Copper Sulphate solution does not fade and Copper anode diminishes in mass.
(iv) Effervescence of H2 gas can be seen.
Zn + 2HCl ⟶ ZnCl2 + H2
(v) White precipitate of PbCl2 is formed which is soluble in hot water.
Pb(NO3)2 + 2HCl ⟶ PbCl2 + 2HNO3