Question 1

Question 5Elements are broadly classified into metals & non-metals. State six general differences in physical properties of metals & non-metals. State two metals & two non-metals which contradict with the general physical properties — giving reasons. State one difference in property between metalloids & noble gases.

Accepted Answer

Six general differences in physical properties of metals & non-metals:S.No.MetalsNon-metals1.Have lustre shineDo not have lustre2.Have high melting and boiling pointsHave low melting and boiling points3.Have high densityHave low density4.Malleable i.e., can be beaten into sheetsNon-malleable i.e., cannot be beaten into sheets5.Ductile can be drawn into wiresNon-ductile cannot be drawn into wires6.Good conductors of heat & electricityPoor conductors of heat & electricityTwo metals that contradict with the general physical properties:Mercury — It is liquid at room temperature.Zinc — It is non-malleable [beyond certain temperatures].Two non-metals that contradict with the general physical properties:Iodine — It is lustrous.Graphite — It is lustrous and conducts electricity.One difference between metalloids & noble gases:Metalloids are chemically reactive whereas noble gases are chemically inert or inactive.

Question 2

Question 7How does sodium chloride differ from its constituent elements? Explain.

Accepted Answer

The properties of sodium chloride are completely different from those of sodium and chlorine. Sodium is a soft, highly reactive metal. Chlorine is a poisonous greenish yellow gas with choking smell. But sodium chloride is a white crystalline solid which is non-poisonous and useful. It is added to our food as a mineral and also to add taste to it.

Question 3

Question 3Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method.(a) Salt from sea water(b) Ammonium chloride from sand(c) Chalk powder from water(d) Iron from sulphur(e) Water and alcohol(f) Sodium chloride and potassium nitrate(g) Calcium carbonate and sodium chloride

Accepted Answer

(a) Salt from sea water is separated by evaporation method. Evaporation method is used to separate the components of a homogeneous solid-liquid mixture. The liquid is escaped in the form of vapour and the solid is left behind.(b) Sublimation method is used to separate ammonium chloride from sand. This method is used when one of the component is sublime in nature. Ammonium chloride is sublime in nature so when it is heated, ammonium chloride directly changes into vapours and sand is left behind. The vapours of ammonium chloride on cooling changes directly into solid.(c) Chalk powder and water can be separated by filtration method. Filtration method is used for separating insoluble solids from liquids. On filtration, chalk powder gets deposited on filter paper whereas water passes through the filter paper and gets collected in the beaker.(d) Iron from sulphur can be separated by magnetic separation method. This method is used when one of the component is magnetic in nature. Iron gets attracted towards magnet and can easily be separated from sulphur.(e) Water and alcohol can be separated by fractional distillation method using a fractionating column fitted over the distilling flask. Fractional distillation method is used to separate miscible mixtures in which the liquids have different boiling points. Boiling point of alcohol is 78°C and water is 100°C. Hence, this method is the most suitable for separating them. 95.5% pure alcohol is obtained by this method.(f) Sodium chloride and potassium nitrate can be separated by fractional crystallization. This method is used when the solubility of solid components of a mixture is different in the same solvent. Both salts are soluble in water but solubility of potassium nitrate is more than that of sodium chloride in water.(g) Solvent extraction method is used to separate calcium carbonate and sodium chloride mixture. This method is used when one component is soluble in a particular liquid while the other component is insoluble. Sodium chloride is soluble in water but calcium carbonate is insoluble which settles down.

Question 4

Question 4cState four differences between compounds and mixtures.

Accepted Answer

CompoundsMixturesA compound is a pure substance.A mixture is an impure substance.Compounds are always homogeneous.Mixtures may be homogeneous or heterogeneous.Formation of a compound involves a change in energy.Formation of a mixture does not involve any change in energy.Components of compounds can be separated only by complex chemical processes.Components of mixtures can be separated by simple physical methods of separation.

Question 5

Question 5bWhat are the advantages of chromatography?

Accepted Answer

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.It also helps in quantitative estimation of the components of a mixture.

Question 6

Question 5cGive two applications of chromatography.

Accepted Answer

The two applications of chromatography are:It is used to purify many industrial products.It is used to separate pigments from natural colors.

Question 7

Question 6aChoose the most appropriate answer from the options given below:A mixture of sand and ammonium chloride can be separated byfiltrationdistillationsublimationcrystallization

Accepted Answer

sublimationReason — Sublimation method is used when one of the component is sublime in nature. Ammonium chloride is sublime in nature so on heating, it directly changes into vapour leaving behind the sand.

Question 8

Question 6bChoose the most appropriate answer from the options given below:A pair of metalloids are:Na and MgB and SiC and PHe and Ar

Accepted Answer

B and SiReason — Boron(B) and Silicon(Si) are metalloids because they show some properties of metals and some properties of non-metals.

Question 9

Question 6cChoose the most appropriate answer from the options given below:Which of the following property is not shown by compounds?They are heterogeneous.They are homogeneous.They have definite molecular formulae.They have fixed melting and boiling points.

Accepted Answer

They are heterogeneous.Reason — Compounds are always homogeneous because the composition and properties is same throughout.

Question 10

Question 6dChoose the most appropriate answer from the options given below:A solvent of iodine isWaterKerosene oilAlcoholPetrol

Accepted Answer

AlcoholReason — Iodine gets dissolved in ethyl alcohol.

Question 11

Question 6eChoose the most appropriate answer from the options given below:This gas is highly soluble in waterAmmoniaNitrogenCarbon monoxideOxygen

Accepted Answer

AmmoniaReason — Ammonia is highly soluble in water.

Question 12

Question 9Explain the term 'mixture'. Differentiate between homogeneous & heterogeneous mixtures. State why brass is considered as a homogeneous mixture while a mixture of iron & sulphur - heterogeneous. Give an example of two liquids which form (a) homogeneous (b) heterogeneous mixtures.

Accepted Answer

A mixture is made up of two or more substances — elements or compounds or both — mechanically mixed together in any proportion.Difference between homogeneous and heterogeneous mixtures:Homogeneous mixturesHeterogeneous mixturesConstituents - uniformly mixedConstituents - not uniformly mixedProperties & composition - same throughout the mixtureProperties & composition vary throughout the mixtureBrass is considered as a homogeneous mixture because:The constituents are uniformly mixed andProperties and composition are same throughout the mixture.A mixture of iron & sulphur is considered a heterogeneous mixture because:The constituents are not uniformly mixed andProperties and composition vary throughout the mixture.(a) Two liquids forming homogeneous mixture : Alcohol and Water(b) Two liquids forming heterogeneous mixture : Oil and Water

Question 13

Question 5Give reasons for the following statements:Components in a mixture can be separated by physical methods only.Centrifugation can be used for separating an insoluble heavier solid, present in an insoluble solid-liquid mixture.The filter paper made into a cone & placed in a funnel for filtering out the solid particles in a solid-liquid mixture, should be moistened before placing.Brass & bronze are examples of mixtures, while copper sulphate & lead nitrate are examples of compound.Zinc is considered an element, while zinc sulphide is considered a compound.

Accepted Answer

A mixture is made by mixing two or more substances mixed mechanically and the components retain their original properties, hence, components in a mixture can be separated by physical methods only.Centrifugation is used for separating an insoluble heavier solid, present in an insoluble solid-liquid mixture as more dense component migrates away from the axis of the centrifuge and less dense component migrates towards the axis of the centrifuge. Hence, the two components can be separated.On moistening the filter paper cone, it sticks to the walls of the funnel and makes filtration easy.Brass & bronze are examples of mixtures as the components are mixed together mechanically and the components retains their original properties. Copper sulphate & lead nitrate are examples of compounds as the components are combined chemically in fixed proportions and they do not retain their original property.Zinc is considered an element as it is made up of one kind of atoms only, while zinc sulphide is considered a compound as it is made up of two elements [zinc and sulphur] combined in a fixed proportion.

Question 14

Question 12Explain with diagrams the process used to separate the following substances from the given mixtures.(a) Ammonium chloride from a mixture of ammonium chloride and potassium chloride.(b) Iron from a mixture of iron & copper.(c) Sulphur from a mixture of sulphur & copper.(d) Potassium nitrate from a mixture of potassium nitrate & potassium chlorate.(e) Lead carbonate [insoluble] from a mixture of lead carbonate & water.(f) Lead nitrate [soluble] from a mixture of lead nitrate & water i.e lead nitrate solution.(g)	Carbon tetrachloride from a mixture of carbon tetrachloride [heavier component] & water.(h) Benzene from a mixture of benzene [b.p. 80°C] & toluene [b.p. 110°C].(i) Different dyes in their liquid constituent ink.

Accepted Answer

(a) Sublimation can be used to separate Ammonium chloride from a mixture of ammonium chloride and potassium chloride.Process — Take a mixture of ammonium chloride and potassium chloride in an evaporating dish, covered with a funnel plugged with cotton. Heat it slowly as shown below:Ammonium chloride collects on the inner side of the funnel and is scrapped out easily.Potassium chloride remains in the evaporating dish and is separated out easily.(b) Magnetic separation can be used to separate iron from a mixture of iron & copper.Process — Take a mixture of iron & copper in a flat dish. Move a magnet over the mixture as shown below:Magnetic solid 'Iron' is attracted to the magnet.Non-magnetic solid 'copper' remains in the dish.(c) Solvent extraction can be used to separate Sulphur from a mixture of sulphur & copperProcess — Add the mixture to a beaker containing the solvent carbon disulphide. Stir well till sulphur dissolves. Filter the contents.Soluble component [sulphur] is obtained on slow evaporation of the filtered solution.Insoluble component [copper] remains on the filter paper.(d) Fractional crystallization can be used to separate potassium nitrate from a mixture of potassium nitrate & potassium chlorate.Process — Add the mixture of potassium nitrate & potassium chlorate to a beaker of water & heat to obtain, hot saturated soln. Cool the hot saturated soln. when crystals of less soluble 'potassium chlorate' crystallize out.Less soluble [potassium chlorate] is filtered out from the hot saturated soln. recrystallized from hot water and dried.More soluble [potassium nitrate] is obtained from the filtrate by heating the filtrate followed by cooling. The crystals of the more soluble solid crystallize out.(e) Filtration can be used to separate insoluble lead carbonate from a mixture of lead carbonate & water.Process — Place a wet folded filter paper in a funnel, clamped above a beaker. Pour the mixture carefully through it.Insoluble lead carbonate remains on filter paper, it is dried and recovered.Water remains in the beaker.(f) Distillation can be used to separate lead nitrate [soluble] from a mixture of lead nitrate & water i.e lead nitrate solution.Process — Add the mixture to the flask 'X' of the distillation apparatus. The flask is then carefully heated and the mixture evaporates and later condenses.Soluble lead nitrate remains in the flask 'X' after evaporation.Water collects in receiver after condensation.(g)	Separating funnel can be used to separate carbon tetrachloride from a mixture of carbon tetrachloride [heavier component] & water.Process — Pour the mixture from the top of a separating funnel and allow the mixture to stand till the heavier layer [carbon tetrachloride] and lighter layer [water] separate.Water remains in the separating funnel and carbon tetrachloride collects in the flask on opening the tap.(h) Fractional distillation can be used to separate benzene from a mixture of benzene [b.p. 80°C] & toluene [b.p. 110°C]Process — Mixture is kept in a distillation flask 'X' with a fractionating column. The flask is then heated as shown and the mixture evaporates and later condenses.Higher boiling point liquid [toluene] remains in the flask X, after condensation.Lower boiling point liquid [benzene] collects in the receiver Y, after condensation in Leibigs condenser.(i) Chromatography can be used to separate different dyes - in their liquid constituent ink.Process — Place the ink spot containing different dyes on the filter paper.The filter paper is hung with its lower end completely dipped in the solvent.The solvent flows over the ink spot and the dyes separate out as shown below.

Elements, Compounds and Mixtures

Elements

Exercise 3(A)

Exercise 3(B)

Mixtures

Objective Type Questions

Separation of mixtures