Question 1

Question 2What is observed on performing the following :  HydrogenOxygenCarbon dioxideChlorineLitmus test        Applying burning splint to the gas        Colour of gascolourlesscolourlesscolourlessgreenish yellowOdour of gas

Accepted Answer

HydrogenOxygenCarbon dioxideChlorineLitmus testNeutral to litmusNeutral to litmusblue litmus turns redblue litmus turns red and finally bleachesApplying burning splint to the gasPure hydrogen burns with a pale blue flame when a burning splinter is brought near itrekindles a glowing splinterburning splint is extinguishedburning splint is extinguishedColour of gascolourlesscolourlesscolourlessgreenish yellowOdour of gasodourlessodourlessodourlesssharp pungent choking smell

Question 2

Question 5What do you observe when(a) CO2 is passed through lime water first and then a little in excess?(b) HCl is passed through silver nitrate solution?(c) H2S is passed through lead nitrate solution?(d) Cl2 is passed through potassium iodide (KI) solution?(e) Cobalt chloride paper is introduced in water vapour?Write the balanced equations for each of the above.

Accepted Answer

(a) When CO2 is passed through lime water first in small amounts it turns lime water milky. This is due to the formation of insoluble calcium carbonate.Ca(OH)2 + CO2 ⟶ CaCO3 ↓ + H2OWhen excess of the gas is passed through the solution, milkiness disappears. This is due to the formation of a soluble bicarbonate.CaCO3 + CO2 + H2O ⟶ Ca(HCO3)2 [soluble](b) When HCl is passed through silver nitrate solution, a white ppt. of silver chloride is formed.HCl + AgNO3 ⟶ AgCl ↓ + HNO3(c) When H2S is passed through lead nitrate solution, black ppt. of PbS is formed.Pb(NO3)2 [colourless] + H2S ⟶ PbS ↓ [black] + 2HNO3(d) Cl2 turns potassium iodide (KI) solution blue blackCl2 + 2KI ⟶ 2KCl + I2(e) Water vapour turns blue cobalt chloride paper pink.CoCl2 + 2H2O ⟶ CoCl2.2H2O

Question 3

Question 1Distinguish by heating the following in dry test tube.(a) Zinc carbonate, copper carbonate and lead carbonate(b) zinc nitrate and copper nitrate(c) copper sulphate and copper carbonate(d) ammonium chloride and iodine

Accepted Answer

(a) zinc carbonate, copper carbonate and lead carbonate :On heating zinc carbonate, light amorphous white solid changes to pale yellow.On heating copper carbonate, light green amorphous powder changes to black.On heating lead carbonate, heavy white crystalline solid crumbles with a crackling sound.(b) zinc nitrate and copper nitrate :On heating zinc nitrate, white solid changes to yellow when hot and white when cold.On heating copper nitrate, bluish green crystalline solid melts to form a bluish green mass and gives off steamy vapours which condense on cooler parts of the test tube.On further heating, the bluish green mass changes to a black residue.(c) copper sulphate and copper carbonate :On heating copper sulphate, blue crystalline solid crumbles to form a white amorphous powder and gives off steamy vapours which condense on cooler parts of the test tube to form a colourless liquid (water).On strong heating, a black solid is formed and a gas is evolved that turns moist blue litmus red and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.On strongly heating copper carbonate, light green amorphous powder changes to black and a colourless odourless gas is evolved that extinguishes a burning wooden splinter and turns lime water milky but has no effect on acidified K2Cr2O7 solution suggesting that it is CO2.(d) ammonium chloride and iodine :On heating ammonium chloride, white crystalline solid sublimates to form a basic gas (NH3) and acidic gas (HCl). The dense white fumes are noticed that form a white mass on the cooler parts of the test tube.On heating iodine, violet crystalline solid sublimates to form violet vapours. These vapours settle down on cooler parts of test tube to form violet crystals.

Question 4

Question 3Distinguish by dilute sulphuric acid.(a) Sodium sulphite and sodium carbonate.(b) Copper and magnesium.(c) Sodium sulphide and sodium sulphite.

Accepted Answer

(a) Sodium sulphite and sodium carbonate :On adding dilute sulphuric acid to sodium sulphite and warming, a colourless gas with suffocating smell of burning sulphur is evolved. The evolved gas turns lime water milky and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.Na2SO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + SO2↑On adding dilute sulphuric acid to sodium carbonate and warming, a colourless gas is evolved with brisk effervescence. The evolved gas extinguishes a burning wooden splinter and turns lime water milky but has no effect on acidified K2Cr2O7 solution suggesting that it is CO2.Na2CO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + CO2↑(b) Copper and magnesium :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.(c) Sodium sulphide and sodium sulphite :When dil. sulphuric acid is added to sodium sulphide and heated, hydrogen sulphide gas is evolved which has the smell of rotten eggs.Na2S + H2SO4 ⟶ Na2SO4 + H2S ↑On adding dilute sulphuric acid to sodium sulphite and warming, a colourless gas with suffocating smell of burning sulphur is evolved. The evolved gas turns lime water milky and changes the colour of acidified K2Cr2O7 solution from orange to green suggesting that it is SO2.Na2SO3 + H2SO4 (dil.) ⟶ Na2SO4 + H2O + SO2↑

Question 5

Question 4Write your observation and a balanced equation in the case of the following substances being heated.(a) Ammonium dichromate(b) Copper nitrate(c) Copper carbonate(d) Zinc carbonate(e) Ammonium chloride

Accepted Answer

(a) Ammonium dichromate — Orange red crystalline solid, on heating, swells up and decomposes violently with flashes of light leaving greenish residue. It also gives off steamy fumes, which condense on the cooler parts of the test tube to form tiny droplets of water.(NH4)2Cr2O7[Ammonium dichromate (orange)]→ Δ Cr2O3 [Chromic oxide(green)]+4H2O+N2\underset{	ext{[Ammonium dichromate (orange)]}}{(	ext{NH}_4)_2	ext{Cr}_2	ext{O}_7} \xrightarrow{\space \Delta \space} \underset{	ext{ [Chromic oxide(green)]}}{	ext{Cr}_2	ext{O}_3} + 4	ext{H}_2	ext{O} + 	ext{N}_2[Ammonium dichromate (orange)](NH4​)2​Cr2​O7​​ Δ ​ [Chromic oxide(green)]Cr2​O3​​+4H2​O+N2​(b) Copper nitrate — Bluish green crystalline solid, on heating, melts to form a bluish green mass and gives off steamy vapours that condense on the cooler parts of test tube.Cu(NO3)2.6H2O→ Δ Cu(NO3)2+6H2O{	ext{Cu(NO}_3)_2}.6	ext{H}_2	ext{O} \xrightarrow{\space \Delta \space} {	ext{Cu(NO}_3)_2} + 6	ext{H}_2	ext{O}Cu(NO3​)2​.6H2​O Δ ​Cu(NO3​)2​+6H2​OOn further heating, the bluish green mass changes to a black residue of copper (II) oxide and brown coloured nitrogen dioxide gas is evolved along with oxygen gas.2Cu(NO3)2[Copper nitrate (blue)]→ Δ 2CuO[copper oxide - black]+4NO2↑[Nitrogen dioxide]+O2↑[Oxygen]\underset{	ext{[Copper nitrate (blue)]}}{2	ext{Cu(NO}_3)_2} \xrightarrow{\space \Delta \space} \underset{	ext{[copper oxide - black]}}{2	ext{CuO}} + \underset{	ext{[Nitrogen dioxide]}}{4	ext{NO}_2\uparrow} + \underset{	ext{[Oxygen]}}{	ext{O}_2\uparrow}[Copper nitrate (blue)]2Cu(NO3​)2​​ Δ ​[copper oxide - black]2CuO​+[Nitrogen dioxide]4NO2​↑​+[Oxygen]O2​↑​(c) Copper carbonate — Light green amorphous powder changes to black. Carbon dioxide gas is given off which turns lime water milky.CuCO3[Copper carbonate (light green)]⟶ΔCuO[copper oxide - black]+CO2↑[Carbon dioxide]\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\uparrow}[Copper carbonate (light green)]CuCO3​​⟶Δ​[copper oxide - black]CuO​+[Carbon dioxide]CO2​↑​(d) Zinc carbonate — On strong heating, light amorphous white solid changes to pale yellow. Carbon dioxide gas is given off which turns lime water milky.The residue, on cooling, changes to a white colour. i.e., residue is yellow when hot and white when cold.ZnCO3→ΔZnO+CO2↑[Zinc[Zinc oxide][Carboncarbonate][yellow - hot]dioxide][white][white - cold]\begin{matrix} 	ext{ZnCO}_3 &\xrightarrow\Delta & 	ext{ZnO} & + & 	ext{CO}_2\uparrow \ 	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]​(e) Ammonium chloride — On heating ammonium chloride, white crystalline solid sublimates to form a basic gas (NH3) and acidic gas (HCl). The dense white fumes are noticed that form a white mass on the cooler parts of the test tube. No residue is left behind.NH4Cl⇌coolheatNH3↑+HCl↑	ext{NH}_4	ext{Cl} \xrightleftharpoons[	ext{cool}]{	ext{heat}} 	ext{NH}_3 \uparrow + 	ext{HCl} \uparrowNH4​Clheatcool​NH3​↑+HCl↑

Question 6

Question 3(a) What are soaps and detergents?(b) Why do they differ in their actions ?(c) Explain their cleansing actions.

Accepted Answer

(a) Soap — It is the sodium or potassium salt of an organic fatty acid. It reacts with hard water forming scum, which is why ordinary soap is wasted.CaSO4 + 2NaSt (soap) ⟶ CaSt2 (scum) + Na2SO4Detergents — They are the sodium salts of alkyl sulphonic acids. Detergents contain a sulphonic acid group (-SO3H) instead of a carboxylic group (-COOH).(b) Soaps reacts with hard water forming scum, which is why ordinary soap is wasted.Detergents can lather even with hard water. Due to the solubility of their calcium and magnesium salts in water, they do not form scum.(c) Soap or detergent molecules form clusters called micelles when dissolved in water. The molecules arrange themselves with their tails inward and their heads outward. During the cleansing process, the hydrocarbon tail of the detergent attaches to oil and dirt. When water is stirred, the oil and dirt separate into smaller fragments. This allows other tails to attach to the fragmented oil and dirt. The detergent molecules surround these small oil and dirt globules. The negatively charged heads in the water prevent the globules from recombining into larger aggregates. As a result, when clothes are rinsed with water, the oil and dirt are effectively removed.

Question 7

Question 4Compare the effect of soap and detergent on hard water.

Accepted Answer

Soaps react with hard water forming scum which is why ordinary soap is wasted whereas detergents can lather even with hard water. Due to the solubility of their calcium and magnesium salts in water, they do not form scum.

Question 8

Question 5Copy and complete the following table that refers to the action of heat on some carbonates:CarbonateColour of residue on coolingZinc carbonate  Lead carbonate  Copper carbonate

Accepted Answer

CarbonateColour of residue on coolingZinc carbonateYellow when hot, white when coldLead carbonateYellowCopper carbonateBlack

Question 9

Question 6Complete the following table and write your observations.  Hydrogen sulphideAmmoniaSulphur dioxideHydrogen chlorideShake the gas with red litmus solution        Shake the gas with blue litmus solution        Apply a burning splint to the gas

Accepted Answer

Hydrogen sulphideAmmoniaSulphur dioxideHydrogen chlorideShake the gas with red litmus solutionNo changeRed litmus becomes blueNo changeNo changeShake the gas with blue litmus solutionBlue litmus becomes redNo changeBlue litmus becomes redBlue litmus becomes redApply a burning splint to the gasBurning splint is extinguishedBurning splint is extinguishedBurning splint is extinguishedBurning splint is extinguished

Question 10

Question 7A series of experiments were performed as shown below to prepare certain gases in the laboratory.(i) Name the gas A. What do you observe when gas A is passed through AgNO3 solution ?(ii) Name the gas B. What test will you perform to identify gas B.(iii) What is the similarity between gas B and gas C ?(iv) Give a test to distinguish between gases B and C.(v) In experiment IV, gas D is :P — HClQ — Cl2R — O2Only POnly QOnly RBoth P and Q(vi) Write the equations for when gas B and gas C are separately passed in lime water first in little quantities and then in excess.(vii) When a rod dipped in ammonium hydroxide solution is brought near gas ............... dense white fumes are seen.P — Gas AQ — Gas BR — Gas DOnly POnly QOnly RBoth P and R

Accepted Answer

(i) Gas A is HCl, When the HCl is passed through silver nitrate solution, a white precipitate of silver chloride is formed.AgNO3 (aq) + HCl ⟶ AgCl ↓ + HNO3(ii) Gas B is SO2 , it decolorises purplish pink acidified potassium permanganate solution.(iii) Gas B is SO2 and Gas C is CO2, they are colourless, acidic gases which can turn lime water milky (turbid).(iv) Gas B (SO2) decolorises purplish pink acidified potassium permanganate solution and it can change orange/yellow solution of acidified potassium dichromate green. Gas C (CO2) has no effect on acidified potassium permanganate solution and acidified potassium dichromate solution.(v) Only Q,MnO2 + 4HCl ⟶ MnCl2 + H2O + Cl2(vi)CO2 in limited Quantity:Ca(OH)2+CO2⟶CaCO3↓+ H2O	ext{Ca(OH)}_2 + 	ext{CO}_2 \longrightarrow 	ext{CaCO}_3 \downarrow + 	ext{ H}_2	ext{O}Ca(OH)2​+CO2​⟶CaCO3​↓+ H2​OCO2 passed in excess:CaCO3ppt+CO2+H2O⟶Ca(HCO3)2soluble\underset{	ext{ppt}}{	ext{CaCO}_3}+{	ext{CO}_2}+{	ext{H}_2{	ext{O}}}\longrightarrow \underset{	ext{soluble}}{{	ext{Ca(HCO}_3)_2}}pptCaCO3​​+CO2​+H2​O⟶solubleCa(HCO3​)2​​SO2 in limited Quantity:Ca(OH)2+SO2⟶CaSO3↓+ H2O	ext{Ca(OH)}_2 + 	ext{SO}_2 \longrightarrow 	ext{CaSO}_3 \downarrow + 	ext{ H}_2	ext{O}Ca(OH)2​+SO2​⟶CaSO3​↓+ H2​OSO2 passed in excess:CaSO3ppt+SO2+H2O⟶Ca(HSO3)2soluble\underset{	ext{ppt}}{	ext{CaSO}_3}+{	ext{SO}_2}+{	ext{H}_2{	ext{O}}}\longrightarrow \underset{	ext{soluble}}{{	ext{Ca(HSO}_3)_2}}pptCaSO3​​+SO2​+H2​O⟶solubleCa(HSO3​)2​​(vii) Only PWhen a glass rod dipped in ammonia solution and brought near the gas A i.e., HCl, dense white fumes of ammonium chloride are formed.NH3 (aq) + HCl ⟶ NH4Cl

Practical Work

Exercise 9A

Exercise 9B

Exercise 9C Structuredapplication Skill Type