Question 1

Question 17Differentiate between an efflorescent, deliquescent & hygroscopic substance with suitable examples.

Accepted Answer

PropertyEfflorescent SubstanceDeliquescent SubstanceHygroscopic SubstanceNatureCrystalline - hydratedCrystalline - water solubleAmorphous - solids or liquidsOn exposure to atmosphereLose moisture - partly or completely to the atmosphereAbsorb moisture- from the atmosphere.Absorb moisture- from the atmosphere.Change in stateChanges into an amorphous powderChanges into a saturated solutionDo not change their original state.ExampleNa2CO3.10H2O washing soda⟶Na2CO3.H2O\underset{	ext{ washing soda} }{	ext{Na}_2	ext{CO}_3.10	ext{H}_2	ext{O}} \longrightarrow {	ext{Na}_2	ext{CO}_3.	ext{H}_2	ext{O}} washing sodaNa2​CO3​.10H2​O​⟶Na2​CO3​.H2​OFeCl3 crystals⟶FeCl3 solution\underset{	ext{ crystals} }{	ext{FeCl}_3} \longrightarrow \underset{	ext{ solution} }{	ext{FeCl}_3} crystalsFeCl3​​⟶ solutionFeCl3​​CaO solid⟶CaO solid\underset{	ext{ solid} }{	ext{CaO}} \longrightarrow \underset{	ext{ solid} }{	ext{CaO}} solidCaO​⟶ solidCaO​

Question 2

Question 6cGive reasons:It is difficult to cook in hills as compared to plains.

Accepted Answer

The boiling point of water decreases with a decrease in pressure. Therefore, water boils at a lower temperature (i.e., less than 100°C) in hilly areas where the atmospheric pressure is lower as compared to the plains. Due to this it takes a longer time to cook food making cooking difficult in hills.

Question 3

Question 4Differentiate between:(a) Solution and suspension(b) Suspension and colloid

Accepted Answer

(a) Difference between Solution and suspension:SolutionSuspensionSolution is a homogeneous mixture.Suspension is a heterogeneous mixture.Particle size less than 10-10 m.Particle size greater than 10-7 m.It is transparent.It is opaque.Particles of solute are invisible.Solute particles are visible.Particles of solute do not settle.Solute particles settle at the bottom of the container.Solute particles cannot be filtered. The solution passes easily through a filter paper.Solute particles do not pass through a filter paper.(b) Difference between Suspension and colloid:SuspensionColloidParticle size greater than 10-7 m.Particle size between 10-10 - 10-7 m.It is opaque.It is translucent.Solute particles are visible.Solute particles can be seen with the help of a powerful microscope.Solute particles settle at the bottom of the container.Solute particles do not settle.Solute particles do not pass through a filter paper.Solute particles pass easily through ordinary filter papers but do not pass through ultra fine filters or nano filters.

Question 4

Question 5Define water of crystallization. Give two examples with formulae.

Accepted Answer

The fixed amount of water which is in a loose chemical combination with one molecule of a substance in its crystal form is called water of crystallization.The two examples are:Common nameChemical nameFormulaBlue vitriolCopper sulphate pentahydrateCuSO4.5H2OWashing sodaSodium carbonate decahydrateNa2CO3.10H2O

Question 5

Question 7What do you observe when:(a) Blue vitriol is heated?(b) Washing soda is exposed to air?(c) Blue litmus solution is added to water?

Accepted Answer

(a) When blue vitriol is heated, it loses its water of crystallisation. The blue crystalline solid of copper sulphate turns into white amorphous (powder) solid and drops of colourless liquid (which is water) condense on the upper cooler parts of the test tube.(b) When washing soda is exposed to air the white crystalline substance changes into white powder.(c) There is no change in colour of blue litmus solution when added to water as pure water is neutral.

Question 6

Question 8bGive reason:Table salt becomes moist during rainy season.

Accepted Answer

Table salt contains impurities like magnesium chloride and calcium chloride which are deliquescent. They absorb water and become moist during rainy season.

Question 7

Question 8cGive reason:On opening a bottle of cold drink, a fizz sound is heard.

Accepted Answer

Cold drinks bottles contain dissolved carbon dioxide under high pressure. On opening the bottle, the pressure decreases and the gas releases out producing a fizz sound.

Question 8

Question 9Give balanced chemical equations for the reaction of water with:(a) Sodium(b) Iron(c) Carbon dioxide(d) Sodium oxide

Accepted Answer

(a) 2Na + 2H2O ⟶ 2NaOH + H2 (g)(b) 3Fe + 4H2O ⇌ Fe3O4 + 4H2 (g)(c) CO2 + H2O ⟶ H2CO3(d) Na2O + H2O ⟶ 2NaOH

Question 9

Question 10What is metal activity series?

Accepted Answer

The reaction of metals with water under different conditions indicates the reactive nature of metals and enables us to arrange the metals on the basis of their reactivity which is called metal activity series.

Question 10

Question 11Name the gas produced when:(a) steam is passed over hot coke.(b) chlorine is dissolved in water and exposed to sunlight.(c) a piece of calcium is added to water.(d) when fossil fuel is burnt.

Accepted Answer

(a) Water gas [CO + H2](b) Oxygen gas (O2)(c) Hydrogen gas (H2)(d) Carbon dioxide gas (CO2)

Question 11

Question 20Differentiate between -(a) Hard & soft water(b) Temporary & permanent hard waterwith examples.

Accepted Answer

(a) Differences between Hard and soft water:Hard waterSoft waterWater is said to be hard when it does not lather readily with ordinary soap.Water is said to be soft when it lathers readily with ordinary soap.Hard water contains dissolved calcium & magnesium salts, e.g. calcium and magnesium bicarbonates, sulphates and chlorides.Soft water does not contain dissolved calcium & magnesium salts.Sources of hard water include natural water i.e., water from springs and rivers.Sources of soft water include rain water and distilled water.(b) Differences between temporary and permanent hard water:Temporary hard waterPermanent hard waterTemporary hard water is one whose hardness can be removed by boiling.Permanent hard water is one whose hardness cannot be removed by boiling.It is due to the presence of calcium & magnesium bicarbonates Ca(HCO3)2, Mg(HCO3)2.It is due to the presence of calcium, magnesium, chlorides and sulphates [CaCl2, MgCl2, CaSO4, MgSO4].

Question 12

Question 21Give balanced equations to show how -(a) Temporary hardness enters into water.(b) Temporary hardness in water can be removed by boiling.(c) Permanent hardness in water can be removed by addition of washing soda.

Accepted Answer

(a) CaCO3 + H2O + CO2 ⟶ Ca(HCO3)2MgCO3 + H2O + CO2 ⟶ Mg(HCO3)2(b) Ca(HCO3)2 →boil\xrightarrow{	ext{boil}}boil​ CaCO3 ↓ + H2O + CO2 [g]Mg(HCO3)2 →boil\xrightarrow{	ext{boil}}boil​ MgCO3 ↓ + H2O + CO2 [g](c) Na2CO3 washing soda+CaSO4 calcium sulphate⟶CaCO3↓+Na2SO4\underset{	ext{ washing soda} }{	ext{Na}_2	ext{CO}_3} + \underset{	ext{ calcium sulphate}}{	ext{CaSO}_4} \longrightarrow 	ext{CaCO}_3 ↓ + 	ext{Na}_2	ext{SO}_4 washing sodaNa2​CO3​​+ calcium sulphateCaSO4​​⟶CaCO3​↓+Na2​SO4​

Question 13

Question 14State how a 'supersaturated' solution differs from a 'saturated solution'. State briefly how you would prepare a supersaturated solution using potassium chloride and water.

Accepted Answer

Supersaturated solutionSaturated solutionThe solution which can hold or contains more of the solute at a given temperature than that present in a saturated solution is called supersaturated solution.When the solvent cannot dissolve more of the solute at that temperature, the solution that is formed is called a saturated solution at that temperature.A saturated solution of potassium chloride is prepared in boiling water. If this solution is cooled excess potassium chloride separates out from the hot saturated solution. The hot solution therefore contains more of the solute dissolved in than it can hold at that given temperature and is thus called a supersaturated solution.

Water

Crystals

Exercise I

Exercise II

Hard & soft water

Solutions