How will you identify?
(a) Chloride ion
(b) Chlorine gas
(c) Sulphur dioxide gas
(d) A soluble carbonate
(e) An amphoteric hydroxide
(a) Chloride ion
(b) Chlorine gas
(c) Sulphur dioxide gas
(d) A soluble carbonate
(e) An amphoteric hydroxide
Disclaimer: More than one test can be used to identify the given substances. Any one of the given tests can be used to answer the given question.
(a) A salt containing chloride ion is hygroscopic or deliquescent in nature. The following tests can also be used to identify a salt containing chloride ion:
(1) Formation of dense white fumes when a glass rod dipped in ammonia solution is brougth near the mouth of test tube in which small amount of salt was warmed with conc. sulphuric acid.
Cl− + H2SO4 → 2HCl + SO42−
HCl + NH3 → NH4Cl
Dense white fumes
(2) Heat the salt with a pinch of manganese dioxide and conc. sulphuric acid. Evolution of greenish yellow coloured gas that turns starch iodide paper blue.
2Cl− + MnO2 + 3H2SO4 → MnSO4 + 2HSO4− + Cl2 + 2H2O
Greenish yellow gas
(3) Formation of white precipitate that dissolves in excess of ammonium hydroxide solution, when salt is treated with silver nitrate solution in presence of nitric acid.
Cl− + AgNO3 → AgCl + NO3−
White precipitate
AgCl + 4NH4OH → [Ag(NH3)4]Cl + 4H2O
(b) Chlorine gas is greenish yellow in colour and has a sharp pungent odour. It turns moist blue litmus red finally bleaching it. Chlorine also turns moist starch iodide paper blue.
(c) Sulphur dioxide gas is colourless and has a smell of burnt sulphur. It turns blue litmus red. Orange solution of acidified potassium dichromate is turned green and purple colour of acidified potassium permanganate solution is discharged by sulphur dioxide gas.
K2Cr2O7 + H2SO4 + 3SO2 → Cr2(SO4)3 + K2SO4 + H2O
Orange Green
2KMnO4 + 5SO2 + 2H2O → 2MnSO4 + K2SO4 + 2H2SO4
Pink
(d) Gas containing carbonate turns lime water milky when it is passed through it. When excess dilute nitric acid is added to the precipitate, the latter dissolves completely to form a colourless liquid.
CO32− + Ca(OH)2 → CaCO3 + H2O
Milky precipitate
2HNO3 + CaCO3 → Ca(NO3)2 + CO2 + H2O
(e) Amphoteric hydroxide reacts with strong acids like HCl to give salt and water. It does the same in the presence of a strong base.
Disclaimer: More than one test can be used to identify the given substances. Any one of the given tests can be used to answer the given question.
(a) A salt containing chloride ion is hygroscopic or deliquescent in nature. The following tests can also be used to identify a salt containing chloride ion:
(1) Formation of dense white fumes when a glass rod dipped in ammonia solution is brougth near the mouth of test tube in which small amount of salt was warmed with conc. sulphuric acid.
Cl− + H2SO4 → 2HCl + SO42−
HCl + NH3 → NH4Cl
Dense white fumes
(2) Heat the salt with a pinch of manganese dioxide and conc. sulphuric acid. Evolution of greenish yellow coloured gas that turns starch iodide paper blue.
2Cl− + MnO2 + 3H2SO4 → MnSO4 + 2HSO4− + Cl2 + 2H2O
Greenish yellow gas
(3) Formation of white precipitate that dissolves in excess of ammonium hydroxide solution, when salt is treated with silver nitrate solution in presence of nitric acid.
Cl− + AgNO3 → AgCl + NO3−
White precipitate
AgCl + 4NH4OH → [Ag(NH3)4]Cl + 4H2O
(b) Chlorine gas is greenish yellow in colour and has a sharp pungent odour. It turns moist blue litmus red finally bleaching it. Chlorine also turns moist starch iodide paper blue.
(c) Sulphur dioxide gas is colourless and has a smell of burnt sulphur. It turns blue litmus red. Orange solution of acidified potassium dichromate is turned green and purple colour of acidified potassium permanganate solution is discharged by sulphur dioxide gas.
K2Cr2O7 + H2SO4 + 3SO2 → Cr2(SO4)3 + K2SO4 + H2O
Orange Green
2KMnO4 + 5SO2 + 2H2O → 2MnSO4 + K2SO4 + 2H2SO4
Pink
(d) Gas containing carbonate turns lime water milky when it is passed through it. When excess dilute nitric acid is added to the precipitate, the latter dissolves completely to form a colourless liquid.
CO32− + Ca(OH)2 → CaCO3 + H2O
Milky precipitate
2HNO3 + CaCO3 → Ca(NO3)2 + CO2 + H2O
(e) Amphoteric hydroxide reacts with strong acids like HCl to give salt and water. It does the same in the presence of a strong base.
