Chemistry
The following materials are provided – solutions of cobalt chloride, ammonia, potassium permanganate, lime water, starch-iodide, sodium hydroxide, lead acetate, potassium iodide. Also provided are litmus and filter papers, glowing splinters and glass rods. Using the above how would you distinguish between :
(a) a neutral, acidic and a basic gas
(b) oxygen and hydrogen gas
(c) carbon dioxide and sulphur dioxide gas
(d) chlorine and hydrogen chloride gas
(e) hydrogen sulphide and nitrogen dioxide gas
(f) ammonia and carbon dioxide gas
(g) zinc carbonate and potassium nitrate
(h) hydrated copper sulphate and anhydrous copper sulphate
(i) ammonium sulphate and sodium sulphate.
Practical Chemistry
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Answer
(a) Litmus paper test is done to distinguish between neutral, acidic and basic gas. Neutral gas does not effect litmus paper. Acidic gas will turn blue litmus paper red and basic gas will turn red litmus blue.
(b) A burning wooden splinter is extinguished in hydrogen whereas oxygen gas rekindles a glowing wooden splinter. Hence, the two gases can be distinguished using a wooden splinter.
(c) There is no effect of carbon dioxide (CO2) gas on potassium permanganate soln. whereas sulphur dioxide (SO2) turns acidified potassium permanganate from pink to clear colourless.
(d) Chlorine turns moist blue litmus red and then bleaches it.
Cl2 + H2O ⟶ HOCl + HCl
HOCl ⟶ HCl + [O]
Colouring matter + [O] ⟶ Colourless or bleached product.
Whereas, HCl gas only turns moist blue litmus paper red and does not bleach it.
(e) Nitrogen dioxide (NO2) liberates iodine [violet vapours] with potassium iodide KI soln., and turns potassium iodide paper brown.
2KI + 2NO2 ⟶ 2KNO2 + I2
Hydrogen sulphide (H2S) gas turns potassium permanganate (KMnO4) from pink to colourless.
2KMnO4 + 3H2SO4 + 5H2S ⟶ K2SO4 + 2MnSO4 + 8H2O + 5S
(f) In the presence of ammonia moist red litmus turns blue and carbon dioxide turns moist blue litmus faint red.
(g) If we heat the given salts, zinc carbonate turns yellow, evolving carbon dioxide gas which turns lime water milky and has no effect on potassium permanganate solution.
Whereas, potassium nitrate emits oxygen gas on heating. Oxygen gas rekindles a glowing wooden splinter.
2KNO3 ⟶ 2KNO2 + O2
Hence, the two salts can be distinguished.
(h) Hydrated copper sulphate is bright blue in colour, whereas anhydrous copper sulphate appears as a white powder. Hence, the two can be distinguished by their colour and appearance.
(i) When ammonium sulphate is heated with NaOH, ammonia gas will be produced which turns red litmus blue whereas, sodium sulphate will not react with sodium hydroxide.
(NH4)2SO4 + 2NaOH ⟶ Na2SO4 + 2H2O + 2NH3
Na2SO4 + NaOH ⟶ no reaction.
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Related Questions
Distinguish between the following pairs of compounds using a reagent as a chemical test:
(i) Calcium nitrate and Zinc nitrate solution
(ii) Magnesium chloride and Magnesium nitrate solution
Identify the salts P, Q, R from the following observations:
(i) Salt P has light bluish green colour. On heating, it produces a black coloured residue. Salt P produces brisk effervescence with dil. HCl and the gas evolved turns lime water milky, but no action with acidified potassium dichromate solution.
(ii) Salt Q is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt Q produces chalky white insoluble ppt. with excess of ammonium hydroxide.
(iii) Salt R is black in colour. On reacting with conc. HCl, it liberates a pungent greenish yellow gas which turns moist starch iodide paper blue black.
Give a chemical test to distinguish between the following:
(i) Sodium carbonate and sodium sulphate
(ii) Potassium chloride and potassium nitrate
(iii) Copper carbonate and copper sulphite
(iv) Lead chloride and lead sulphide
(v) Iron (II) sulphate and iron (III) sulphate
(vi) Calcium sulphate and zinc sulphate
(vii) Lead nitrate and zinc nitrate
(viii) Copper sulphate and calcium sulphate
(ix) Manganese dioxide and copper (II) oxide
(x) dil. HCl, dil. HNO3, dil. H2SO4.
[explain the procedure for the preparation of the solutions for the above tests wherever required]
Identify the cation [positive ion] and anion [negative ion] in - A, B and C. Also identify P, Q, R, S, T, U, V, W.
(a) Substance 'A' is water soluble and gives a curdy white precipitate 'P' with silver nitrate solution. 'P' is soluble in ammonium hydroxide but insoluble in dil. HNO3. Substance 'A' reacts with ammonium hydroxide solution to give a white precipitate 'Q' soluble in excess of NH4OH.
(b) A solution of substance 'B' is added to barium chloride solution. A white ppt. 'R' is formed, insoluble in dil. HCl or HNO3. A dirty green ppt. 'S' is formed on addition of ammonium hydroxide to a solution of 'B' and the precipitate is insoluble in excess of ammonium hydroxide.
(c) Substance 'C' is a coloured, crystalline salt which on heating decomposes leaving a black residue 'T'. On addition of copper turnings and conc. H2SO4 to 'C' a coloured acidic gas 'U' is evolved on heating. A solution of 'C' is added to NaOH soln. until in excess. A pale blue ppt. 'P' is obtained insoluble in excess of NaOH. A solution of 'C' is then added to NH4OH soln. in excess to give an inky blue solution 'V'. A solution of 'C' is warmed and hydrogen sulphide gas is passed through it. A black ppt. 'W' appears.