Chemistry
State your observation in each of the following cases :
(i) When dilute hydrochloric acid is added to sodium carbonate crystals.
(ii) When excess sodium hydroxide is added to calcium nitrate solution.
(iii) At the cathode when acidified aqueous copper sulphate solution is electrolyzed with copper electrodes.
(iv) When calcium hydroxide is heated with ammonium chloride crystals.
(v) When moist starch iodide paper is introduced into chlorine gas.
Answer
(i) Effervescence of a gas are seen which turns lime water milky confirming that the gas is CO2.
Na2CO3 + 2HCl ⟶ 2NaCl + H2O + CO2 ↑
(ii) Milky white precipitate is obtained which is sparingly soluble in excess of NaOH.
Ca(NO3)2 + 2NaOH ⟶ Ca(OH)2 ↓ + 2NaNO3
(iii) Copper, a brownish pink metal is deposited at the cathode when acidified aq. CuSO4 soln. is electrolysed with copper electrodes.
(iv) Pungent smelling gas (ammonia) is given out.
2NH4Cl + Ca(OH)2 ⟶ CaCl2 + 2H2O + 2NH3
(v) Chlorine gas turns moist starch iodide paper blue black.
Cl2 + 2KI ⟶ 2KCl + I2
[Starch + I2 ⟶ blue black colour]
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