Question 1

Question 1Give a chemical test to distinguish between the following gases:(a) Hydrogen and oxygen(b) Carbon dioxide and sulphur dioxide(c) Hydrogen chloride and hydrogen sulphide(d) Chlorine and nitrogen dioxide(e) Ammonia and hydrogen chloride(f) Sulphur dioxide and chlorine

Accepted Answer

(a) Hydrogen and oxygenBurning wooden splinter is extinguised in hydrogen whereas Oxygen rekindles a glowing wooden splinter.(b) Carbon dioxide and sulphur dioxideCarbon dioxide has no effect on acidified KMnO4 or K2Cr2O7.Sulphur dioxide turns KMnO4 from pink to clear colourless and K2Cr2O7 from orange to clear green.2KMnO4 + 2H2O + 5SO2 ⟶ K2SO4 + 2MnSO4 + 2H2SO4K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O(c) Hydrogen chloride and hydrogen sulphideHydrogen chloride — Forms a curdy white precipitate on passage through AgNO3 solution.AgNO3 [aq.] + HCl ⟶ AgCl ↓ [curdy white ppt.] + HNO3Hydrogen sulphide — Turns moist lead acetate paper silvery black.Pb(CH3COO)2 [colourless] + H2S ⟶ PbS ↓ [black] + 2CH3COOH(d) Chlorine and nitrogen dioxideChlorine reacts with silver nitrate solution to form a white precipitate of silver chloride.4AgNO3 [aq.] + 2Cl2 (g) ⟶ 4AgCl ↓ [curdy white ppt.] + 2N2O5 (g) + O2 (g)Nitrogen dioxide does not react with silver nitrate solution, hence, no white precipitate is formed.(e) Ammonia and hydrogen chlorideAmmonia turns Nessler's reagent from colourless to pale brown.Hydrogen chloride shows no action with Nessler's reagent. It forms a curdy white ppt. on passage through AgNO3 solution.AgNO3 [ag.] + HCl ⟶ AgCl ↓ [curdy white ppt.] + HNO3The ppt. of AgCl is soluble in NH4OH but insoluble in dil. HNO3(f) Sulphur dioxide and chlorineOn passing Sulphur dioxide gas through lime water, it turns lime water milky.Ca(OH)2 + SO2 ⟶ CaSO3 ↓ [white ppt.] + H2OChlorine gas does not turn lime water milky. It turns moist starch iodide paper blue black.Cl2 + 2KI ⟶ 2KCl + I2Starch + I2 ⟶ Blue black colour

Question 2

Question 2On heating which of the following substances i.e., copper carbonate, zinc carbonate, washing soda, copper sulphate, zinc nitrate, copper nitrate, lead nitrate, ammonium chloride and ammonium dichromate - relate to the reactions given below.(a) A white substance which leaves an amphoteric oxide as a residue [whose colour varies in the heated and in the cold state] and evolves a gas which turns lime water milky.(b) An efflorescent substance which leaves a residue having the same colour as the substance and evolves a gas which changes the colour of cobalt chloride paper.(c) A white solid which evolves two colourless gases which on cooling combine and condense on the cooler parts of the test tube.(d) A coloured substance which decomposes violently leaving a coloured residue and evolving two neutral gases one of which is unreactive or inert in nature.(e) A coloured substance which leaves a black residue and evolves two gases one of which is acidic and the other neutral and colourless.(f) A coloured substance which leaves on strong heating a black residue and evolves two colourless gases one of which is acidic and other neutral.(g) A white crystalline solid which decrepitates on heating leaving a residue which fuses with the glass and evolves two gases one of which is coloured and acidic.(h) An amorphous substance which turns from pale green to black on strong heating evolving a colourless, acidic gas as the only gaseous product.

Accepted Answer

(a) A white substance which leaves an amphoteric oxide as a residue [whose colour varies in the heated and in the cold state] and evolves a gas which turns lime water milky — Zinc carbonate.(b) An efflorescent substance which leaves a residue having the same colour as the substance and evolves a gas which changes the colour of cobalt chloride paper — Washing soda.(c) A white solid which evolves two colourless gases which on cooling combine and condense on the cooler parts of the test tube — Ammonium chloride.(d) A coloured substance which decomposes violently leaving a coloured residue and evolving two neutral gases one of which is unreactive or inert in nature — Ammonium dichromate.(e) A coloured substance which leaves a black residue and evolves two gases one of which is acidic and the other neutral and colourless — Copper nitrate.(f) A coloured substance which leaves on strong heating a black residue and evolves two colourless gases one of which is acidic and other neutral — Coper sulphate.(g) A white crystalline solid which decrepitates on heating leaving a residue which fuses with the glass and evolves two gases one of which is coloured and acidic — Lead nitrate.(h) An amorphous substance which turns from pale green to black on strong heating evolving a colourless, acidic gas as the only gaseous product — Copper carbonate.

Question 3

Question 3Give balanced equations for the following conversions affected by heat alone on the substances:(a) Copper carbonate to copper oxide(b) Hydrated copper sulphate to sulphur dioxide(c) Copper nitrate to nitrogen dioxide(d) Ammonium dichromate to nitrogen(e) Zinc carbonate to zinc oxide(f) Zinc nitrate to nitrogen dioxide

Accepted Answer

(a) Copper carbonate to copper oxideCuCO3[Copper carbonate (light green)]⟶ΔCuO[copper oxide - black]+CO2[Carbon dioxide][g]\underset{	ext{[Copper carbonate (light green)]}}{	ext{CuCO}_3} \overset{\Delta}{\longrightarrow} \underset{	ext{[copper oxide - black]}}{	ext{CuO}} + \underset{	ext{[Carbon dioxide]}}{	ext{CO}_2} [	ext{g}][Copper carbonate (light green)]CuCO3​​⟶Δ​[copper oxide - black]CuO​+[Carbon dioxide]CO2​​[g](b) Hydrated copper sulphate to sulphur dioxideCuSO4.5H2O[Copper sulphate (hydrous - blue)]⟶CuSO4 [Copper sulphate (anhydrous - white)]+5H2O [water vapour]\underset{	ext{[Copper sulphate (hydrous - blue)]}}{	ext{CuSO}_4.5	ext{H}_2	ext{O}}\longrightarrow \underset{	ext{ [Copper sulphate (anhydrous - white)]}}{	ext{CuSO}_4} + \underset{	ext{ [water vapour]}}{5	ext{H}_2	ext{O}}[Copper sulphate (hydrous - blue)]CuSO4​.5H2​O​⟶ [Copper sulphate (anhydrous - white)]CuSO4​​+ [water vapour]5H2​O​On strong heating2CuSO4⟶2CuO[ Copper oxide - black] +2SO2[Sulphur dioxide]+O2 [oxygen]2	ext{CuSO}_4 \longrightarrow \underset{	ext{[ Copper oxide - black] }}{2	ext{CuO}} + \underset{	ext{[Sulphur dioxide]}}{2{	ext{SO}_2}} + \underset{	ext{ [oxygen]}}{	ext{O}_2}2CuSO4​⟶[ Copper oxide - black] 2CuO​+[Sulphur dioxide]2SO2​​+ [oxygen]O2​​(c) Copper nitrate to nitrogen dioxide2Cu(NO3)2[Copper nitrate (blue)]⟶Δ2CuO[copper oxide - black]+4NO2[Nitrogen dioxide]+O2[Oxygen]\underset{	ext{[Copper nitrate (blue)]}}{2	ext{Cu(NO}_3)_2} \overset{\Delta}{\longrightarrow} \underset{	ext{[copper oxide - black]}}{2	ext{CuO}} + \underset{	ext{[Nitrogen dioxide]}}{4	ext{NO}_2} + \underset{	ext{[Oxygen]}}{	ext{O}_2}[Copper nitrate (blue)]2Cu(NO3​)2​​⟶Δ​[copper oxide - black]2CuO​+[Nitrogen dioxide]4NO2​​+[Oxygen]O2​​(d) Ammonium dichromate to nitrogen(NH4)2Cr2O7[Ammonium dichromate (orange)]⟶Cr2O3 [Chromic oxide(green)]+H2O+N2\underset{	ext{[Ammonium dichromate (orange)]}}{(	ext{NH}_4)_2	ext{Cr}_2	ext{O}_7} \longrightarrow \underset{	ext{ [Chromic oxide(green)]}}{	ext{Cr}_2	ext{O}_3} + 	ext{H}_2	ext{O} + 	ext{N}_2[Ammonium dichromate (orange)](NH4​)2​Cr2​O7​​⟶ [Chromic oxide(green)]Cr2​O3​​+H2​O+N2​(e) Zinc carbonate to zinc oxideZnCO3→ΔZnO+CO2[Zinc[Zinc oxide][Carboncarbonate][yellow - hot]dioxide][white][white - cold]\begin{matrix} 	ext{ZnCO}_3 &\xrightarrow\Delta & 	ext{ZnO} & + & 	ext{CO}_2 \ 	ext{[Zinc} & & 	ext{[Zinc oxide]} & & 	ext{[Carbon} \ 	ext{carbonate]} & & 	ext{[yellow - hot]} & & 	ext{dioxide]} \ 	ext{[white]} & & 	ext{[white - cold]} \end{matrix}ZnCO3​[Zinccarbonate][white]​Δ​​ZnO[Zinc oxide][yellow - hot][white - cold]​+​CO2​[Carbondioxide]​(f) Zinc nitrate to nitrogen dioxide2Zn(NO3)2[zinc nitrate (white)]⟶Δ2ZnO[yellow - hot, white - cold]+4NO2[Nitrogen dioxide]+O2[Oxygen]\underset{	ext{[zinc nitrate (white)]}}{2	ext{Zn(NO}_3)_2} \overset{\Delta}{\longrightarrow} \underset{	ext{[yellow - hot, white - cold]}}{2	ext{ZnO}} + \underset{	ext{[Nitrogen dioxide]}}{4	ext{NO}_2} + \underset{	ext{[Oxygen]}}{	ext{O}_2}[zinc nitrate (white)]2Zn(NO3​)2​​⟶Δ​[yellow - hot, white - cold]2ZnO​+[Nitrogen dioxide]4NO2​​+[Oxygen]O2​​

Question 4

Question 4Using dilute sulphuric acid how would you differentiate between :(a) Copper and magnesium(b) Sodium carbonate, sodium sulphide and sodium sulphiteHow would you identify the gaseous product evolved.

Accepted Answer

(a) Magnesium on reaction with dil. sulphuric acid produces a colourless, odourless gas with brisk effervescence.The gas evolved is hydrogen as it burns with a pale blue flame producing a pop sound.Mg+H2SO4 dil.⟶MgSO4+H2	ext{Mg} + \underset{	ext{ dil.}}{	ext{H}_2	ext{SO}_4}\longrightarrow 	ext{MgSO}_4+ 	ext{H}_2Mg+ dil.H2​SO4​​⟶MgSO4​+H2​Copper does not react with dil. sulphuric acid liberating hydrogen as it is lower in metal reactivity series than hydrogen.(b) Sodium carbonate — When dil. sulphuric acid is added to sodium carbonate, the gas evolved turns lime water milky but has no effect on potassium permanganate solution or potassium dichromate solution. This confirms that the gas evolved is Carbon dioxide.Na2CO3+H2SO4 [dil.]⟶Na2SO4+H2O+CO2	ext{Na}_2	ext{CO}_3 + \underset{	ext{ [dil.]}}{	ext{H}_2	ext{SO}_4}\longrightarrow 	ext{Na}_2	ext{SO}_4+ 	ext{H}_2	ext{O} + 	ext{CO}_2Na2​CO3​+ [dil.]H2​SO4​​⟶Na2​SO4​+H2​O+CO2​2NaHCO3+H2SO4 [dil.]⟶Na2SO4+2H2O+2CO22	ext{NaHCO}_3 + \underset{	ext{ [dil.]}}{	ext{H}_2	ext{SO}_4}\longrightarrow 	ext{Na}_2	ext{SO}_4+ 2	ext{H}_2	ext{O} + 2	ext{CO}_22NaHCO3​+ [dil.]H2​SO4​​⟶Na2​SO4​+2H2​O+2CO2​Sodium sulphide — When dil. sulphuric acid is added to sodium sulphide, colourless gas is evolved with a rotten egg smell that turns moist lead acetate paper silvery black. This confirms that the gas evolved is hydrogen sulphide.Na2S+H2SO4 [dil.]⟶Na2SO4+H2S	ext{Na}_2	ext{S} + \underset{	ext{ [dil.]}}{	ext{H}_2	ext{SO}_4}\longrightarrow 	ext{Na}_2	ext{SO}_4+ 	ext{H}_2	ext{S}Na2​S+ [dil.]H2​SO4​​⟶Na2​SO4​+H2​SSodium sulphite — When dil. sulphuric acid is added to sodium sulphite, colourless gas is evolved with a suffocating odour. It turns lime water milky and pink potassium permanganate solution colourless. It also turns orange potassium dichromate solution clear green, confirming the presence of sulphur dioxide.Na2SO3+H2SO4 [dil.]⟶Na2SO4+H2O+SO2	ext{Na}_2	ext{SO}_3 + \underset{	ext{ [dil.]}}{	ext{H}_2	ext{SO}_4}\longrightarrow 	ext{Na}_2	ext{SO}_4+ 	ext{H}_2	ext{O} + 	ext{SO}_2Na2​SO3​+ [dil.]H2​SO4​​⟶Na2​SO4​+H2​O+SO2​

Question 5

Question 5Using a platinum wire, conc. hydrochloric acid and a bunsen burner how would you distinguish between the three salts i.e., sodium chloride, potassium chloride and calcium chloride. Explain in brief the method used for the same.

Accepted Answer

We can distinguish between the three salts with the help of flame test as described below:MethodThin platinum wire is thoroughly cleaned and then heated in a non-luminous flame of a burner.When the wire imparts no colour it is dipped in conc. HCl and then into the substance to be identified.The wire is then reintroduced into the non luminous flame and the colour imparted is noted.Observation —The golden yellow flame confirms the presence of sodium [Na1+] ion.Lilac colour of flame confirms the presence of Potassium [K1+]Brick red colour of flame, confirms the presence of Calcium [Ca2+] ion.

Question 6

Question 6Using given samples of temporary and permanent hard water, soft water, ordinary soap, detergent and washing soda how would you:(a) Distinguish between hard and soft water.(b) Distinguish between temporary hard water and permanent hard water.(c) Remove temporary hardness from water without using a chemical compound.(d) Remove temporary hardness and permanent hardness from water using a chemical compound.(e) Prove the advantage of detergent over soap.

Accepted Answer

(a) Differentiating hard water from soft water —Two unknown samples 'X' and 'Y' containing hard water and soft water are taken separately in a trough or beaker.Ordinary soap is rubbed by the hands inside each sample.Observation —One sample of water 'X' lathers with soapThe sample of water 'Y' does not lather with soap.Result —The sample 'X' which lathers with soap is soft water.The sample 'Y' which does not lather with soap is hard water.(b) Distinguish between temporary hard water and permanent hard water —Two unknown samples 'A' and 'B' containing temporary and permanent hard water are taken separately in a trough or beaker.The water is boiled slowly, gases allowed to escape out and then the water is filtered.Ordinary soap is rubbed by the hands inside each filtered sample.Observation —One sample of water 'A' lathers with soap.The sample of water 'B' does not lather with soap.Result —The boiled and filtered sample 'A' which lathers is temporary hard water whose hardness is removed by boiling.Sample 'B' is permanent hard water whose hardness cannot be removed by boiling.(c) Remove temporary hardness from water without using a chemical compound.Temporary hard water is taken in a beaker and heated slowly.After the gases escape out, the water is filtered through a filter paper.Ordinary soap is rubbed inside the filtered solution.Observation — The boiled and filtered sample of temporary hard water lathers readily with soap.Result — Temporary hard water can be softened by heating.Ca(HCO3)2[in temporary hard water]⟶CaCO3↓[ppt. filtered out]+CO2+H2O [filtered water is soft]\underset{	ext{[in temporary hard water]}}{	ext{Ca(HCO}_3)_2} \longrightarrow \underset{	ext{[ppt. filtered out]}}{	ext{CaCO}_3\downarrow} + 	ext{CO}_2 + \underset{	ext{ [filtered water is soft]}}{{	ext{H}_2	ext{O}}}[in temporary hard water]Ca(HCO3​)2​​⟶[ppt. filtered out]CaCO3​↓​+CO2​+ [filtered water is soft]H2​O​(d) Remove temporary hardness and permanent hardness from water using a chemical compound.Temporary and permanent hard water are taken in separate beakers and washing soda is added in it. Then the solutions are filtered to remove the precipitate.Ordinary soap is rubbed inside the filtered solution.Observation — The filtered sample of temporary and permanent hard water lathers readily with ordinary soap.Result — Temporary hard water and permanent hard water can be softened by using washing soap.(e) Advantage of detergent over soapA sample of hard water 'X' is taken and ordinary soap is rubbed inside the water.Another sample of hard water 'Y' is taken and detergent is rubbed inside the water. [Detergents are sodium salts of sulphonic acid and do not form scum].Observation — Lather forms in 'Y' but not in 'X'.Result — Detergents form lather even with hard water, while ordinary soap is wasted due to formation of scum.Ca(HCO3)2[in hard water]+2NaSt[soap]⟶Ca(St)2[scum]+2NaHCO3\underset{	ext{[in hard water]}}{	ext{Ca(HCO}_3)_2} + \underset{	ext{[soap]}}{2	ext{NaSt}} \longrightarrow \underset{	ext{[scum]}}{	ext{Ca(St)}_2} + 2	ext{NaHCO}_3[in hard water]Ca(HCO3​)2​​+[soap]2NaSt​⟶[scum]Ca(St)2​​+2NaHCO3​

Question 7

Question 7State the meaning of the term 'water pollution'. State how would you find out the different sources of pollution of water bodies in the locality.AnswerWater pollution is an undesirable change in the chemical, physical and biological conditions of water due to the presence of foreign substances in water.It leads to degradation in the quality of water and makes it unsuitable for it's designated use.The main sources of pollution of water bodies in the locality are:Household Detergents — Household chemical cleaning organic compounds used for laundering and dish washing contain phosphates, mainly sodium triphosphate. Phosphates are a major source of water pollution.Domestic Sewage — It is the waste water generated from household activities. Domestic sewage water contains organic materials from food and vegetables and inorganic materials like phosphates and nitrates from soaps and detergents.

Accepted Answer

Answer: Household Detergents, Domestic Sewage

Question 8

Question 8State in brief, the preventive steps to control the pollution of water bodies in the locality.AnswerThe following preventive steps can control the pollution of water bodies in the locality —Collection and disposal of domestic sewage — A typical waste water system for sewage consists of a network of waste water pipes.Sewer Lateral Pipes — These waste water pipes collect sewage from household.Sewer Main Pipe — It is the larger pipe on the main street which connects from sewer lateral pipe. The waste water from this pipe is then led to the Water treatment plant.Water treatment plant — In a water treatment plant, the waster water goes through the below stages to remove the pollutants and impurities from it, thereby controlling water pollution:ScreenCoagulationSedimentationFiltrationDisinfection

Accepted Answer

Answer: Collection and disposal of domestic sewage, Water treatment plant

Practical Chemistry