Question 1

Question 1Differentiate between the terms elements, compounds & mixtures with suitable examples.

Accepted Answer

Elements, compounds and mixtures can be differentiated as below:ElementsCompoundsMixturesPure substance made up of one kind of atoms only.E.g., Iron [Fe], Sulphur [S]Pure substance made up of two or more elements.E.g., Iron Sulphide [FeS]Impure substance made up of two or more elements or compounds.E.g., Iron Sulphur mixtureElements i.e., atoms of one kind are present on their own.E.g., Iron & sulphur exist on their own as elements – iron & sulphurComponents in a compound are present in a definite proportion.E.g., Iron and Sulphur are chemically combined in a fixed ratio in iron sulphideComponents in a mixture present in any proportion.E.g., Iron and sulphur are mixed in any ratio in the mixture of iron and sulphur.Elements have a definite set of properties.Elements are classified into metals & non-metals each with its own propertiesCompounds have a definite set of properties.Elements of a compound do not retain their original properties.Mixtures do not have a definite set of properties.Components of a mixture do retain their original properties.Elements occur on their own or as compounds & can be separated by -chemical & physical methods.Elements in a compound are chemically combined and can be separated by chemical methods only.Components in a mixture can be separated by physical methods only.Example:Metal : Iron, copper, silver, goldNon-metal: sulphur, chlorineExample:Iron sulphide, copper oxideExample:Iron + sulphur, Sodium chloride + water

Question 2

Question 3Elements are mainly classified into metals & non-metals. State six properties of metals which differ from non-metals.

Accepted Answer

Six properties of metals which differ from non-metals are as below:S.No.PropertiesMetalsNon-metals1.State of matterMetals are generally solids at room temperature.Non-metals are gases, liquids, and soft solids at room temperature.2.LustrousMetals have lustre i.e., shineNon-metals do not have lustre i.e., do not shine.3.MalleabilityMetals are malleable i.e., can be beaten into sheets.Non-metals are non-malleable i.e., cannot be beaten into sheets.4.DuctilityMetals are ductile i.e., can be drawn into wires.Non-metals are non-ductile i.e., cannot be drawn into wires.5.ConductivityMetals are good conductors of heat and electricity.Non-metals are poor conductors of heat and electricity.6.Melting and boiling pointsMetals have high melting and boiling points.Non-metals have low melting and boiling points.

Question 3

Question 5State what is meant by the term 'activity series of metals'. State the most reactive & the least reactive metal from the following - Zn, Ag, Na, Fe, Cu, Pb.

Accepted Answer

It is a series of metals arranged according to their reactivity in which the most reactive metal i.e., potassium is at the top of the series and the least reactive metal i.e, gold is at the bottom.Amongst the mentioned metals: Zn, Ag, Na, Fe, Cu, & Pb, Sodium (Na) is the most reactive metal and Silver (Ag) is the least reactive metal.

Question 4

Question 6Give three reasons why - carbon dioxide is considered a compound, while carbon - an element.

Accepted Answer

Carbon is an element, whereas carbon dioxide is considered a compound because:Carbon is made up of only one kind of atom, Carbon dioxide is made up of two kinds of atoms i.e., Carbon and Oxygen [CO2].Carbon cannot be broken down into two or more simpler substances by physical or chemical means. Carbon dioxide can be broken down into simpler substances by chemical means only.Carbon has its own set of properties. Properties of Carbon dioxide differ from the properties of carbon and oxygen.

Question 5

Question 10Write the chemical formula of the following -(a) magnesium oxide(b) sodium bromide(c) calcium sulphide(d) magnesium sulphate(e) aluminium chloride(f) zinc oxide(g) calcium carbonate.

Accepted Answer

Please find below the chemical formulas of mentioned compounds:(a)	Magnesium oxide:Step 1 — Write each symbol with its valencyMg2+↗O2−\text{Mg}^{2+} \phantom{\nearrow} \text{O}^{2-}Mg2+↗O2−Step 2 — Interchange the valenciesMg22 ↘↙ O2⇒Mg12 ↘↙ O2\overset{\phantom{2}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{O}} \Rightarrow \underset{\phantom{1}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{O}} \[0.5em]Mg22​ ↘↙ O2⇒12Mg​ ↘↙ 2O​Step 3 — Write the interchanged number, ignore equal numbers & hence the formulaTherefore, we getFormula of Magnesium oxide : MgO\bold{MgO}MgO(b)	sodium bromide:Step 1 — Write each symbol with its valencyNa1+↗Br1−\text{Na}^{1+} \phantom{\nearrow} \text{Br}^{1-}Na1+↗Br1−Step 2 — Interchange the valenciesNa21 ↘↙ Br1⇒Na11 ↘↙ Br1\overset{\phantom{2}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Br}} \Rightarrow \underset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{Br}} \[0.5em]Na21 ↘↙ Br1⇒11Na​ ↘↙ 1Br​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of Sodium bromide : NaBr\bold{NaBr}NaBr(c)	calcium sulphide:Step 1 — Write each symbol with its valencyCa2+↗S2−\text{Ca}^{2+} \phantom{\nearrow} \text{S}^{2-}Ca2+↗S2−Step 2 — Interchange the valenciesCa22 ↘↙ S2⇒Ca12 ↘↙ S2\overset{\phantom{2}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{S}} \Rightarrow \underset{\phantom{1}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{S}} \[0.5em]Ca22 ↘↙ S2⇒12Ca​ ↘↙ 2S​Step 3 — Write the interchanged number, ignore equal numbers & hence the formulaTherefore, we getFormula of Calcium sulphide : CaS\bold{CaS}CaS(d)	magnesium sulphate:Step 1 — Write each symbol with its valencyMg2+↗SO42−\text{Mg}^{2+} \phantom{\nearrow} \text{SO}_4^{2-}Mg2+↗SO42−​Step 2 — Interchange the valenciesMg22 ↘↙ SO42⇒Mg12 ↘↙ SO42\overset{\phantom{2}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{1}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{SO}_4} \[0.5em]Mg22​ ↘↙ SO4​2​⇒12Mg​ ↘↙ 2SO4​​Step 3 — Write the interchanged number, ignore equal numbers & hence the formulaTherefore, we getFormula of Magnesium sulphate : MgSO4\bold{MgSO_4}MgSO4​(e)	aluminium chloride:Step 1 — Write each symbol with its valencyAl3+↗Cl1−\text{Al}^{3+} \phantom{\nearrow} \text{Cl}^{1-}Al3+↗Cl1−Step 2 — Interchange the valenciesAl23 ↘↙ Cl1⇒Al11 ↘↙ Cl3\overset{\phantom{2}{3}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{1}{1}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{Cl}} \[0.5em]Al23 ↘↙ Cl1⇒11Al​ ↘↙ 3Cl​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of Aluminium chloride : AlCl3\bold{AlCl_3}AlCl3​(f)	zinc oxide:Step 1 — Write each symbol with its valencyZn2+↗O2−\text{Zn}^{2+} \phantom{\nearrow} \text{O}^{2-}Zn2+↗O2−Step 2 — Interchange the valenciesZn22 ↘↙ O2⇒Zn12 ↘↙ O2\overset{\phantom{2}{2}}{\text{Zn}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{O}} \Rightarrow \underset{\phantom{1}{2}}{\text{Zn}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{O}} \[0.5em]Zn22 ↘↙ O2⇒12Zn​ ↘↙ 2O​Step 3 — Write the interchanged number, ignore equal numbers & hence the formulaTherefore, we getFormula of Zinc oxide : ZnO\bold{ZnO}ZnO(g) calcium carbonate:Step 1 — Write each symbol with its valencyCa2+↗CO32−\text{Ca}^{2+} \phantom{\nearrow} \text{CO}_3^{2-}Ca2+↗CO32−​Step 2 — Interchange the valenciesCa22 ↘↙ CO32⇒Ca12 ↘↙ CO32\overset{\phantom{2}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{CO}_3} \Rightarrow \underset{\phantom{1}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{CO}_3} \[0.5em]Ca22 ↘↙ CO3​2​⇒12Ca​ ↘↙ 2CO3​​Step 3 — Write the interchanged number, ignore equal numbers & hence the formulaTherefore, we getFormula of Calcium carbonate : CaCO3\bold{CaCO_3}CaCO3​

Question 6

Question 11Give the formulas of the following acids:(a) hydrochloric(b) nitric(c) sulphuric(d) carbonic - acid.

Accepted Answer

Please find below the chemical formulas of mentioned acids:(a) Hydrochloric acid:Step 1 — Write each symbol with its valencyH1+↗Cl1−\text{H}^{1+} \phantom{\nearrow} \text{Cl}^{1-}H1+↗Cl1−Step 2 — Interchange the valenciesH21 ↘↙ Cl1⇒H11 ↘↙ Cl1\overset{\phantom{2}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{1}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{Cl}} \[0.5em]H21 ↘↙ Cl1⇒11H​ ↘↙ 1Cl​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of hydrochloric acid: HCl\bold{HCl}HCl(b) Nitric acid:Step 1 — Write each symbol with its valencyH1+↗NO31−\text{H}^{1+} \phantom{\nearrow} \text{NO}_3^{1-}H1+↗NO31−​Step 2 — Interchange the valenciesH21 ↘↙ NO31⇒H11 ↘↙ NO31\overset{\phantom{2}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{NO}_3} \Rightarrow \underset{\phantom{1}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{NO}_3} \[0.5em]H21 ↘↙ NO3​1​⇒11H​ ↘↙ 1NO3​​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of nitric acid: HNO3\bold{HNO}_3HNO3​(c) Sulphuric acid:Step 1 — Write each symbol with its valencyH1+↗SO42−\text{H}^{1+} \phantom{\nearrow} \text{SO}_4^{2-}H1+↗SO42−​Step 2 — Interchange the valenciesH21 ↘↙ SO42⇒H12 ↘↙ SO41\overset{\phantom{2}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{1}{2}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{SO}_4} \[0.5em]H21 ↘↙ SO4​2​⇒12H​ ↘↙ 1SO4​​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of Sulphuric acid : H2SO4\bold{H}_2\bold{SO}_4H2​SO4​(d) Carbonic acid:Step 1 — Write each symbol with its valencyH1+↗CO32−\text{H}^{1+} \phantom{\nearrow} \text{CO}_3^{2-}H1+↗CO32−​Step 2 — Interchange the valenciesH21 ↘↙ CO32⇒H12 ↘↙ CO31\overset{\phantom{2}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{CO}_3} \Rightarrow \underset{\phantom{1}{2}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{CO}_3} \[0.5em]H21 ↘↙ CO3​2​⇒12H​ ↘↙ 1CO3​​Step 3 — Write the interchanged number & hence the formulaTherefore, we getFormula of Carbonic acid : H2CO3\bold{H}_2\bold{CO}_3H2​CO3​

Question 7

Question 12Give the formulas of the following gases:(a) hydrogen chloride(b) ammonia(c) carbon monoxide(d) nitric oxide(e) nitrous oxide(f) nitrogen dioxide(g) nitrogen(h) sulphur dioxide.

Accepted Answer

(a) hydrogen chloride — HCl(b) ammonia — NH3(c) carbon monoxide — CO(d)	nitric oxide — NO(e) nitrous oxide — N2O(f) nitrogen dioxide — NO2(g) nitrogen — N2(g)	sulphur dioxide — SO2

Question 8

Question 13Explain the term mixture. Differentiate between a homogeneous & heterogeneous mixture with one example of each in the(a) solid-solid(b) solid-liquid(c) liquid-liquid state of the mixture.

Accepted Answer

A mixture is an impure substance containing more than one element or compound, mechanically mixed together in any proportion. The mixture retains the properties of its constituents (elements or compounds) and it can be separated into its components by simple mechanical or physical means.Homogeneous mixturesHeterogeneous mixtureThey have the same composition and properties throughout the mixture and components of the mixture are uniformly mixed throughout.These are mixtures which have different composition and properties throughout the mixture and components of the mixture are not uniformly mixed throughout.Examples:(a) Solid-solid mixture: Alloys e.g., Brass [Cu,Zn](b) Solid-liquid mixture: Iodine and alcohol [tincture of Iodine-antiseptic](c) Liquid-liquid mixture: Petrol & Kerosene,Examples:(a) Solid-solid mixture: Soil(b) Solid- liquid mixture: Chalk and water(c) liquid-liquid mixture: Kerosene and water.

Question 9

Question 14State four differences between - elements, compounds & mixtures with suitable examples.

Accepted Answer

S.No.PropertiesElementsCompoundsMixtures1.TermPure substance made up of one kind of atoms only.E.g., Iron [Fe], Sulphur [S]Pure substance made up of two or more elements.E.g., Iron Sulphide [FeS]Impure substance made up of two or more elements or compounds.E.g., Iron Sulphur mixture2.ExistenceElements i.e., atoms of one kind are present on their own.E.g., Iron & sulphur exist on their own as elements – iron & sulphurComponents in a compound are present in a definite proportion.E.g., Iron and Sulphur are chemically combined in a fixed ratio in iron sulphideComponents in a mixture present in any proportion.E.g., Iron and sulphur are mixed in any ratio in the mixture of iron and sulphur.3.PropertiesElements have a definite set of properties.Elements classified into metals & non-metal each with its own propertiesCompounds have a different set of properties.Elements of a compound do not retain their original properties.Mixtures do not have a definite set of properties.Components of a mixture do retain their original properties.4.SeparationElements occur on their own or as compounds & can be separated by -chemical & physical methods.Elements in a compound are chemically combined and can be separated by chemical methods only.Components in a mixture can be separated by physical methods only.

Question 10

Question 15State the correct technique for separation of the following mixtures.(a) a sublimable solid & a non-sublimable solid.(b) a liquid component from soluble impurities in the liquid component.(c) a lighter liquid from a heavier liquid.(e) a low boiling point liquid from a high boiling point liquid.(f) solid constituents in a liquid constituent by adsorption.

Accepted Answer

(a) a sublimable solid & a non-sublimable solid — sublimation(b) a liquid component from soluble impurities in the liquid component — distillation(c) a lighter liquid from a heavier liquid — separating funnel(d) a low boiling point liquid from a high boiling point liquid — fractional distillation(e) solid constituents in a liquid constituent by adsorption — chromatography

Question 11

Question 16Give —(a) the principle involved in separation of the mixture(b) the technique of separation for each of the following mixtures.(i) naphthalene & sodium chloride(ii) common salt from a solution of common salt in water(iii) pure water from impure water(iv) kerosene & water(v) methyl alcohol & water(vi) dyes of an ink

Accepted Answer

(i)	Naphthalene & sodium chloride:(a)	Principle involved: Based on the difference in sublimable and non-sublimable nature of solids.(b)	Technique of separation: The mixture of the sublimable solid and non-sublimable solid is heated in an evaporating dish covered with funnel plugged at one end with cotton.Sublimable solids on heating sublimes and the vapours condense and collect in the pure form on the inner side of the funnel, from where the sublimable solid is scrapped off.(ii) Common salt from a solution of common salt in water :(a)	Principle involved: Based on evaporation of the liquid component in a soluble solid-liquid mixture.(b)	Technique of separation: The soluble solid can be separated from its liquid component by allowing the liquid component to evaporate either on its own or by heating. On heating, water is lost to the atmosphere and common salt remains behind in the evaporating dish.(iii) Pure water from impure water:(a)	Principle involved: Based on the distillation of the liquid component in a soluble solid-liquid mixture.(b)	Technique of separation: The soluble impurity can be separated from its liquid component or pure water from impure water by placing the mixture, i.e., impure water in the distillation flask. On heating the distillation flask, the solid or solid impurities in water remains behind in the distillation flask. The liquid or water vaporizes, condenses in the Leibig’s condenser and is collected in the receiver.(iv) Kerosene & water:(a)	Principle involved: Based on the separation of two immiscible liquids (one heavy, one light) through separating funnel.(b)	Technique of separation: The kerosene & water mixture is added to the separating funnel and the funnel is kept aside for some time.The heavier immiscible liquid i.e., water settles down in the separating funnel and is then removed from below on opening the tap and collected out separately.The lighter immiscible liquid i.e., kerosene remains above the heavier liquid.(v)	Methyl alcohol & water:(a)	Principle involved: Based on the separation of mixture of two miscible liquids with different boiling points.(b)	Technique of separation: The mixture of two miscible liquids e.g., methyl alcohol and water having different boiling points is taken in the distillation flask and heated slowly till it boils. The component with the higher boiling point i.e., water remains behind in the distillation flask after condensation. The component with the lower boiling point i.e., methyl alcohol collects in the receiver after condensation in the Leibig's condenser.(vi) Dyes of an ink:(a)	Principle involved: Chromatography is a method by which the various components of a mixture e.g., dyes in an ink, are separated due to their difference in the rate of flow over an adsorbent medium.(b)	Technique of separation:Stationary phase in chromatography, the adsorbent medium is known as the stationary phase e.g., filter paper made of cellulose.Mobile phase the solvent or the solution that moves due to capillary action is known as the mobile phase.Separation of dyes in ink by paper chromatography. Ink prepared by dissolving different dyes e.g. A, B, C, D in a suitable solvent, is taken.A line is drawn with a pencil over a long strip of a filter paper.Place the ink spot containing the different dyes on the filter paper.The filter paper is then hung with its lower end dipped in a suitable solvent.The paper strip with the spot of ink at its end is dipped into the solvent in a way that the spot itself remains above the liquid surface.The solvent flows over the ink spot & the various components of the mixture, of dyes in the ink are separated.

Question 12

Question 7Select elements and compounds from the following list:Iron, plaster of paris, chalk, common salt, copper, aluminium, calcium oxide, cane sugar, carbon, silica, sodium sulphate, uranium, potassium carbonate, silver, carbon dioxide.

Accepted Answer

ElementsCompoundsIronplaster of parisCopperchalkaluminiumcommon saltcarboncalcium oxidesilvercane sugar, silicauraniumsodium sulphate, potassium carbonate, carbon dioxide

Question 13

Question 2What are the characteristic properties of a pure substance? Why do we need them?

Accepted Answer

The characteristic properties of a pure substance are:They have a definite composition and a definite set of properties like boiling point, melting point, density etc.They are all homogeneous i.e. their composition is uniform throughout the bulk.We need pure substances to:Prepare medicines.Maintain good health of human beings.Prepare chemicals in laboratories.

Question 14

Question 8(a) What is chromatography?(b) Why is it named so?(c) What are the advantages of chromatography?(d) Name the simplest type of chromatography?(e) On what principle is this method based?(f) What is meant by stationary phase and mobile phase in chromatography?

Accepted Answer

(a) The process of separating different dissolved constituents of a mixture by their adsorption(particles getting adhered to a surface) on an appropriate material is called chromatography.(b) The word chromatography means colour writing. It is named so because earlier it was used to separate mixtures containing coloured components only.(c) The advantages of chromatography are:A very small quantity of the substance can be separated.Components with very similar physical and chemical properties can be separated.It identifies the different constituents of a mixture.(d) Paper chromatography.(e) Chromatography separates the components of a mixture on the basis of differences between two phases, one of which is stationary while the other is mobile.(f) The stationary phase is made up of common adsorbents like filter paper, silica gel as they are stationary and the mobile phase is made up of common solvents like water, ethyl alcohol, acetic acid etc. which moves or spreads on the stationary phase.

Question 15

Question 9On what principle are the following methods of separation based? Give one example of a mixture for each of the methods mentioned in which they are used(a) sublimation(b) filtration(c) sedimentation and decantation(d) solvent extraction method(e) magnetic separation(f) by using a separating funnel(g) fractional distillation

Accepted Answer

(a) This method is used for solid mixtures in which one of the components can sublime on heating. It is used to separate a mixture of common salt and ammonium chloride.(b) This method is used for separating the components of a heterogeneous solid-liquid mixture in which solids are insoluble in liquids. A mixture of chalk and water can be separated by this method.(c) This method is used when the solid component is insoluble and heavier than the liquid component. A mixture of sand and water can be separated by this method.(d) This method is used when one component is soluble in a particular liquid while the other component is insoluble. A mixture of sand and salt can be separated by this method.(e) This method is used when one of the components of the mixture is magnetic in nature. A mixture of iron and sulphur can be separated by this method.(f) It is used to separate components of liquid-liquid heterogeneous mixture when one of the liquid components is heavier than the other. Kerosene oil and water can be separated by this method.(g) It is used to separate components of homogeneous liquid-liquid mixture on the basis of their difference in boiling points. A mixture of water and alcohol can be separated by this method.

Question 16

Question 4Give reasons for the following statements:If fractional distillation is carried out using a liquid-liquid mixture, one liquid will remain in the flask & the other will be collected in the receiver.Evaporation of a common salt solution or sea water, leaves behind common salt inside the evaporating dish after heating.Components in a mixture are present in varying proportions and not in a fixed proportion.Gunpowder is an example of a heterogeneous mixture.In chromatography the absorbent medium e.g. Whatman filter paper is known as the - stationary phase.

Accepted Answer

Fractional distillation separates two miscible liquids with different boiling points. The fractionating column traps and condenses the higher boiling point component, allowing only the lower boiling point component to enter the condenser and be collected.During evaporation of common salt solution or sea water, common salt is left behind inside the evaporating dish on heating because water, i.e., the liquid component is lost to the atmosphere as it gets converted into water vapour.Mixture is an impure substance formed by mixing two or more elements or compounds in any proportion. Mixtures do not have a definite set of properties. If the components are mixed in a fixed proportion then it will form a compound and not a mixture.Gunpowder is considered as a heterogeneous mixture because its components charcoal, sulphur, and potassium nitrate are not uniformly mixed throughout, and it has different properties and composition throughout the mixture.In chromatography the absorbent medium e.g., Whatman filter paper is known as the stationary phase because the filter paper made up of cellulose binds the water tightly to the paper whereas in mobile phase, the solvent or the solution moves due to capillary action.

Elements, Compounds and Mixtures

Elements, Compounds & Mixtures

Exercise I

Exercise II

Objective Type Questions