WBBSE Class 9 Physical Science Solutions Chapter 4.5 Separation of Mixtures

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 4.5 Separation of Mixtures offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 4.5 Question Answer – Separation of Mixtures

Very short answer type questions

Question 1.
Name a metal and a non-metal which exists in liquid state at room temperature.
Answer:
Mercury is a liquid metal at room temperature.
Bromine is a liquid non-metal at room temperature.

Question 2.
Name a non-mental heavier than water.
Answer:
Iodine is a non-metal heavier than water

Question 3.
What type of change occurs when milk is converted to curd ?
Answer:
Chemical change occurs when milk is converted to curd.

Question 4.
What type of change occurs when quick lime is treated with water ?
Answer:
Chemical change occurs when quick lime is treated with water.

Question 5.
Name a non-metal having lustre.
Answer:
Iodine is a non-metal having lustre.

Question 6.
Name a metal lighter than water.
Answer:
Lithium is a metal lighter than water.

Question 7.
Mention chemical reaction which is influenced by pressure.
Answer:
In crackers, a mixture of potassium chlorate and sulphur explodes under pressure.

Question 8.
Mention chemical reaction which is influenced by contact.
Answer:
Quick lime in contact with water produces slaked lime with evolution of heat.

Question 9.
Which gas has the smell of rotten egg ?
Answer:
Hydrogen sulphide (H₂S) gas has the smell of rotten egg.

Question 10.
Mention a chemical reaction that is influenced by a catalyst.
Answer:
When a mixture of MnO₂ and KClO₃ are heated, oxygen gas is evolved. In this reaction MnO₂ acts as a catalyst.

Question 11.
Name two solids which may be identified by colour.
Answer:
The colour of blue vitriol or hydrated copper sulphate is blue. The colour of chalk powder is white.

Question 12.
Mention a chemical reaction where heat is absorbed.
Answer:
Quick lime in contact with water produces slaked lime with evolution of heat.

Question 13.
Name a non-mental that conducts electricity.
Answer:
Graphite or Gas carbon, a non-metal conducts electricity.

Question 14.
Name two metalloids.
Answer:
Arsenic (As) and Antimony (Sb) are two metalloids.

Question 15.
Sugar is added to
(i) concentrated sulphuric acid and
(ii) water. State whether a physical change occurs or a chemical change during these two incidents.
Answer:
(i) Chemical change occurs when sugar is added to concentrated sulphuric acid.
(ii) Physical change occurs when sugar is added to water.

Question 16.
Name an electropositive metal and an electropositive non-metal.
Answer:
Sodium is an electropositive metal.
Hydrogen is an electropositive non-metal.

Question 17.
Cite one physical change where heat is absorbed.
Answer:
When ammonium chloride or ammonium nitrate is dissolved in water heat is absorbed.

Question 18.
Name a soft metal.
Answer:
Sodium (Na) is a soft metal.

Question 19.
Give an example where physical and chemical changes take place simultaneously.
Answer:
Burning of candle is an example of simultaneous occurrence of both physical and chemical change.

Question 20.
Give an example of a slow reaction.
Answer:
Rusting of iron is an example of a slow reaction.

Question 21.
State one chemical change where heat is absorbed.
Answer:
Heat is absorbed when nitrogen and oxygen combine to form nitric oxide.

Question 22.
Give an example of a metal which reacts both with acid and alkali.
Answer:
Zinc is the metal which reacts both with acid and alkali.

Question 23.
Which type of ion is formed by hydrogen in NaH ?
Answer:
H^(-) ion is formed by hydrogen in NaH.

Question 24.
Give an example of natural physical change.
Answer:
Melting of glacier is an example of natural physical change.

Question 25.
Give an example of a natural chemical change.
Answer:
Forest fire is an example of natural chemical change.

Short Answer Type Question

Question 1.
Define properties of matter ?
Answer:
Properties of matter : Each and every substance has its special characteristics by which we can identify it. These characteristics of matter are known as the properties of matter.

Question 2.
What do you mean by physical properties of matter ?
Answer:
Physical properties of matter : Physical properties of matter are those which are observed externally and can be determined without changing the composition of matter.

Question 3.
What are the different forms of matter ?
Answer:
Matters can exist normally in three forms.
These forms are :

• solid
• liquid
• gas or vapour

Question 4.
Define melting point of a solid.
Answer:
Melting point of a solid: Melting point of a solid is the temperature at which the solid begins to transform to liquid under normal pressure, the temperature remains constant till the whole mass of the solid converts to liquid.

Question 5.
Define boiling point of a liquid.
Answer:
Boiling point of a liquid: Boiling point of a liquid is the temperature at which the liquid begins to transform rapidly to its vapour state under normal atmospheric pressure and the temperature remains constant until whole mass of the liquid converts to its vapour.

Question 6.
What do you mean by chemical properties of matter ?
Answer:
Chemical properties of matter: Chemical properties of matter are those which are manifested when the matter undergoes chemical changes involving the change of its composition.

Question 7.
What do you mean by physical change ?
Answer:
Physical change : The physical change is a temporary change in which internal structure of the molecules of the component remains unchanged, only physical state of matter is changed.

Question 8.
What do you mean by chemical change ?
Answer:
Chemical change : A chemical change is a permanent change in which the substance gives rise to one or more new substances with different compositions and properties.

Question 9.
Which of the following are physical changes and which are chemical changes ? Give one reason for each answer.
(i) Lime is treated with water
(ii) Water is boiled to steam
(iii) Rice is converted to puffed rice
(iv) Sugar is dissolved in water
(v) Iron is magnetised
(vi) Souring of milk
(vii) Coal is burnt in air
(viii) A platinum wire is heated
(ix) Rusting of iron
(x) Burning of magnesium wire
(xi) Melting of ice
(xi) Burning of candle.
Answer:
(i) Lime is treated with water: This is a chemical change.
When quick lime is added to water, it boils and ultimately slaked lime is formed. It is heavier than quick lime having different properties also. So it is a chemical change.
CaO + H₂O → Ca (OH)₂ + heat

(ii) Water is boiled to steam: This is a physical change.
After some time steam returns to water, so it is a temporary change.

(iii) Rice is converted to puffed rice: This is a chemical change. Puffed rice cannot be converted to rice again, so it is a permanent change.

(iv) Sugar is dissolved in water: This is a physical change. A lump of sugar breaks into tiny pieces while it dissolves in water. If the solution is now heated to boil off water, sugar is again obtained. So it is a temporary change.

(v) Iron is magnetised: This is a physical change. An iron bar acquires magnetism when it is rubbed with a magnet several times. There has been only a rearrangement of its molecules. The new property acquired by the iron is temporary because when it is heated strongly, its magnetic property is removed.

(vi) Souring of milk: Souring of milk is a chemical change. In this process, milk is converted to curd which is sour in taste. The sour taste is due to the conversion of fat molecules of milk to sour lactic acid. Curd thus produced cannot be converted back to milk.

(vii) Coal is burnt in air: Burning of coal in air is a chemical change. When coal is burnt in air, carbon dioxide gas and some ashes produce from which the original substance cannot be recovered. So it is a permanent change.

(viii) A platinum wive is heated: This is a physical change. When platinum wire is heated it burns becoming white hot and radiates light but there is no change in the composition of the matter. It regains its initial state on cooling.

(ix) Rusting of iron: This is a chemical change. Rusting is nothing but hydrated ferric oxide which is formed by the reaction of iron, oxygen and water. It is heavier than iron. Iron and rusting of iron are different in composition. So, it is a permanent change.

(x) Burning of magnesium wire : This is a chemical change.
When magnesium burns in air or oxygen, magnesium oxide is produced.
2Mg + O₂ = 2MgO.

When magnesium is burnt in air, Mg₃ N₂ also produces. Magnesium cannot be recovered from these new substances. So, this is a permanent change.

(xi) Melting of ice: This is a physical change. No new substance produces during this change. Water can be cooled back to ice. So, this is a temporary change.

(xii) Burning of Candle: This is a chemical change. New substances like carbon dioxide and water vapour are produced during this change. Original substance cannot be obtained from these new substances. So, this is a permanent change.

Question 10.
Explain one natural physical change.
Answer:
Natural physical change (Melting of Glacier): Ice exists in the peak of a mountain but in summer it flows down as water in the plane surface or earth. Glacier, a slowly moving mass of ice is transformed into water when pressure, temperature and other geographical conditions change.

Water thus produced is ultimately mixed with sea. In summer, water from river, sea and other sources are again transformed to vapour and is condensed to ice in peak of mountain in cold. So melting of glacier is a temporary change. So, melting of glacier is an example of natural physical change.

Question 11.
Explain one natural chemical change.
Answer:
Natural chemical change (Forest fire) : Far from seaside, in summer or any hot condition fire is formed in the forest due to friction of woods. The fire spreads quickly in the forest. As a result the trees and the bushes burn forming carbon dioxide and the wood charcoal with some other organic materials. So, forest fire is a permanent change.For this reason, forest fire is considered as natural chemical change.

Question 12.
Physical and chemical changes take place simultaneously when a candle burns — Explain.
Answer:
Simultaneous occurrence of physical and chemical change: When a candle burns in air, a portion of it melts. The molten part when cooled returns to solid wax, the material of candle. So this part is a physical change.

Major part of the candle converts into water vapour and carbon dioxide gas. Original portion of the candle cannot be obtained from these water vapour and carbon dioxide. So this is a chemical change.
So, in this case, physical and chemical changes occur at the same time.

Question 13.
Give an example where physical and chemical changes take place simultaneously.
Answer:
When water is sprayed over quick lime, and much heat generates and quick lime converts to slaked lime. The produced heat converts a part of water to steam which is a physical change since steam may be cooled to water again.

The conversion of quick lime to slaked lime is a chemical change as the slaked lime thus formed cannot be converted to its original form (quick lime) easily. So, both the physical and chemical changes occur simultaneously.

Question 14.
Give the example of a slow reaction.
Answer:
Slow reaction: The reaction in which the amount of activation energy is high, is called slow reaction.
Example : Organic compounds or some of the covalent compounds undergo chemical reactions slowly.

Question 15.
Give the example of a fast reaction.
Answer:
Fast reaction : The reaction in which the amount of activation energy is low, called fast reaction at given temperature. The time required for the completion of such reactions is about 10^-14 to 10^-15 second.

Example : Ionic compounds which are inorganic in nature normally undergo fast reaction.

• NaCl + AgNO₃ → AgCl ↓ + NaNO₃
• BaCl₂ + H₂SO₄ → BaSO₄ ↓ + 2HCl

Question 16.
What do you mean by catalyst and catalysis?
Answer:
Catalyst and catalysis : A catalyst is a substance that alters the rate of a chemical reaction without itself being used up and can be recovered unchanged chemically at the end of a chemical reaction. The phenomenon of acceleration or retardation of chemical reactions by the presence of a catalyst is called catalysis.

Question 17.
Explain positive catalyst with example.
Answer:
Positive catalyst: Catalyst which can accelerate the rate of chemical reaction is called positive catalyst.
Example:

Question 18.
Explain negative catalyst with example.
Answer:
Negative catalyst: Catalyst which can retard the rate of the themical reaction is called negative catalyst.

(ii) Antifreezes like glycerol which retard the rusting of the machines.

Question 19.
What do you mean by exothermic change?
Answer:
Exothermic change: Exothermic change is one in which a substance undergoing a physical change or a chemical change releases heat into its surroundings.

Examples :
(j) Exothermic physical changes: When caustic soda (NaOH) dissolves in water or when concentrated sulphuric acid (H₂SO₄) is mixed in water, plenty of heat evolves in each of the physical change 8.
(ii) Exothermic chemical changes:

• C + O₂ = CO₂ + heat (94,000 cal)
• CaO + H₂O = Ca(OH)₂ + heat

Question 20.
What do you mean by endothermic change?
Answer:
Endothermic change: Endothermic change is one where a substance undergoing physical or chemical change takes heat from its surroundings.

Examples :
(i) Endothermic physical changes : In the dissolution process of ammonium chloride (NH₄Cl) or ammonium nitrate (NH₄NO₃) in water, heat is absorbed.
(ii) Endothermic chemical changes:

• C + 2S = CS₂ — heat (25,000 cal)
• N2 + O₂ = 2NO — heat (43,000 cal)

Question 21.
What is fractional distillation?
Answer:
Fractional distillation : The process by which two or more miscible liquids are separated by distillation using the difference in their boiling point is known as fractional distillation. When the boiling points of two or more miscible liquids differ by about 15°C — 20°C, these are separated by simple fractional distillation.

Question 22.
How two immiscible liquids are separated?
Answer:
Separation of two immiscible liquids: When two different liquids do not mutually dissolve in each other but remain floating one above the other, it is called a mixture of two immiscible liquids. They are separated with the help of a separating funnel.

Question 23.
What is chromatography?
Answer:
Chromatography : It is a modern technique by which mixture of different substances are separated. In this method due to difference in adsorption of different substances in solid phase (adsorbent) and the difference in migration of the substances in the mobile phase (liquid or gas) various substances are separated.

Question 24.
What do you mean by paper chromatograpny?
Answer:
Paper chromutographv : This is a very easy technique to separate the various organic dyes present in the writing ink or printing ink.

Question 25.
What are the advantages of chromatography?
Answer:
Advantage of chromatography :

• A small amount of the compound present in the mixture can be separated.
• The properties of the individuals present in the mixture do not alter.
• This is very easier method to separate the different components present in the mixture.

Question 26.
What do you mean by sublimation?
Answer:
Sublimation: There are some solids which on heating directly transform into vapour phase without transforming through the intermediate liquid state. This phenomenon is known as sublimation. Using this method two different solids ammonium chloride (NH₄Cl) and sand (SiO₉) can be separated.

Question 27.
What are metals?
Answer:
The elements having lustre, normally solid and heavy, which conduct heat and electricity, electro-positive in nature producing metallic sound on striking are called metals.
Example : Fe, Al, Zn, Na, Ag etc.

Question 28.
What do you mean by non-metals
Answer:
Non -Metals: The elements which do not possess any lustre, normally exist in liquid and gaseous state, poor conducting ability of heat and electricity, electronegative in character are called non metals.
Example : H₂, O₂, Cl₂, N₂, C, S, P etc.

Question 29.
What is a metalioid ?
Answer:
Metalloids : The elements which have both metallic and non metallic characters are known as metafloids. Arsenic (As), antimony (Sb).

Question 30.
What are reasons for separting the components of mixture?
Answer:
The components of a mixture are separated because of the following reasons :

• To get a pure sample of a substance.
• To remove any undesirable or harmful components.
• To obtain the useful components of a mixture.

Question 31.
What is distillation?
Answer:
Distillation: The process of converting a liquid into its vapour by heating and the subsequent condensation of the vapour back into the original liquid is known as distillation.

Question 32.
What is separatory funnel?
Answer:
It is an apparatus used for sepating immiscible liquids. The liquids do not mix with each others and due to the difference in densities, the liquids remain in separate layers in the sepratory funnel.

Broad answer type questions 

Question 1.
Give an example for each of the chemicaì changes influenced by
(a) Contact
(b) Heat
(c) Pressure
(d) Light
Answer:
(a) Contact: Quick lime (CaO) in contact with water produces slaked lime [Ca(OH)₂] with generation of heat.
(b) Heat: When mercury is heated in air, red mercuric oxide is formed.”
2Hg + O₂ = 2HgO (red)
(c) In Haber’s process nitrogen combines with hydrogen at 200 atmospheric pressure forming ammonia.

(d) Light induces and regulates the chemical reactions involved in photography.

Question 2.
Explain with examples how matter is identified with the help of physical properties.
Answer:
Matters are identified by physical properties :
(a) Physical State: At ordinary conditions all matters do not exist in the same state.
e.g. at ordinary temperature, gold, silver, iron all are solid.

Water, milk, oil are liquid.
Hydrogen, oxygen, carbon dioxide etc. are gaseous.

(ii) Touch: Many substances may be identified by touching.
e.g. Slippery nature of graphite is easily distinguished with the coarse nature of chalk.

(iii) Smell : Different substances have different smell.
e.g. Ammonia gas has pungent smell, hydrogen suiphide has the distinctive smell of rotten egg and oxygen gas is odourless.

(iv) Colour : Some substances have distinctive colours which help us to identity them.
e.g. Blue vitriol (hydrated copper sulphate) has blue colour while gold has a bright yellow colour.

(v) Solubility : Different substances have different solubilities in different solvents.
e.g. Sugar is soluble in water but not in petrol. On the other hand sulphur is not soluble in water but soluble in carbon disuiphide.

(vi) Magnetic property : Different substances may be distinguished with their different magnetic properties.
e.g. Iron, cobalt, nickel and some of their alloys may be magnetised or attracted by a magnet while gold, copper etc. have no such property.

(vii) Melting point and boiling point: Different crystalline solids have different melting points and they are identified by their melting points or freezing point. Again different pure liquids have different boiling point and they are identified by their boiling point.
e.g. At 1 atm. pure ice has melting point 0°C while pure water has boiling point 100°C.

Question 3.
Explain with examples how matter is identified with the help of chemical properties.
Answer:
Matters are identified by chemical properties:
(i) Action of heat:

But sugar when treated with water, it simply dissolves without producing any chemical change.

(iii) Action with acid:
Zn (Zinc) + (dilute) H₂SO₄ → ZnSO₄ + H₂ ↑
But the same acid in ordinary condition has no action on copper.

(iv) Action with alkalis:
NH₄Cl + NaOH → NaCl + NH₃ ↑ + H₂O
But sodium chloride does not react with alkali.

Question 4.
Compare between physical change and chemical change.
Answer:
Difference between physical and chemical change:

Question 5.
What are the characteristics of catalyst?
Answer:
Characteristics of catalyst :

• The catalyst is unchanged chemically at the end of the reaction.
• Only a small quantity of the catalyst is generally needed.
• The catalyst does not alter the position of equilibrium in a reversible reaction.
• The catalyst does not initiate the reaction.
• The catalyst is generally specific in its action.
• The catalyst cannot alter the nature of the products of the reaction.
• A catalyst has an optimum temperature at which the efficiency of the catalyst is maximum.
• A catalyst is poisoned by certain substances.
• The activity of a catalyst is enhanced by the presence of substances called promoters.

Question 6.
Describe how two miscible liquids may be seperated by fractional distillation.
Answer:
Separation of two miscible liquids by fractional distillation:
When the boiling points of two or more miscible liquids differ by about 15°C — 20°C, these are separated by simple fractional distillation.

Procedure: The liquid mixture is kept in a distilation flask fitted with a Leibig’s condenser. The other end of the condenser is connected with a receiving flask for collection of the distillate. Now the liquid mixture is heated. The volatile liquid i.e. liquid having lower boiling point through the condenser in the form of vapour.

The vapour is condensed to liquid and collected in a receiver. Liquid having higher boiling point is left in the distillation flask. By controlling rate of heating and temperature of the fractionating column, a good separation of the components is possible.

Question 7.
Discuss the method of separation of two immiscible liquids by separating funnel.
Answer:
Separation of two immiscible liquids by separating funnel:
A mixture of two immiscible liquids are easily separated by using separating funnel. Each liquid forms its own liquid layer due to difference in density.

Procedure: Two immiscible liquids are kept in a separating funnel and are shaken for few minutes keeping the stop-cock closed. The liquid mixture is allowed to stand for half an hour. The immiscible liquids separate into two distinct layer.

The liquid with lower density remains in the upper layer and the liquid with higher density will be deposited in the lower layer. The denser liquid in the lower layer can be easily run out by opening the stop-cock lying in the bottom of the funnel and collected in a conical flask. Later, the liquid in the upper layer may be collected in another flask.

Question 8.
Briefly describe how the colouring matters of ink can be separated by paper chromatoqraphy.
Answer:
Separation of colouring matters of ink by paper chromatography:
Paper chromatography: It is a very easy technique to separate the colouring matters present in the ink.

Materials required :

• Adsorbent. : Filter paper
• Solvent : Water, ethanol, acetone etc.
• Chroniatographic chamber : A glass jar fitted with a tightly fitting lid.

Procedure :

• A spot of ink is applied on and near the lower edge of a long strip of filter paper. The spot is allowed to dry.
• The paper is hung in an airtight container that does not absorb solvent vapour.
• A glass jar fitted with a tightly fitting lid may serve the purpose as a chromatographic chamber.
• Enough quantity of a solvent (water, ethanol, acetone etc.) is introduced in the flask, so that the level of solvent almost, but not quite, reaches the spot.
• The solvent rises in the porous paper by capillary action. The components of the ink also travel along with it. The various components in the ink lie at different heights in the paper for their differences of speeds in the solvent on the paper.
• The different components of different colours are visible at different levels on the filter paper.
• The colourless substance may be detected by spraying with a substance that reacts to give a coloured spot.
• Different coloured portions of the paper are cut off which are then treated separately in suitable solvents and the components of ink are recovered.

Question 9.
How will you separate ammonium chloride and sand by the method of sublimation?
Answer:
Separation of ammonium chloride and sand by the method of sublimation:
Procedure :

• A small quantity of a mixture of ammonium chloride and sand is taken in a flat basin.
• A funnel is inverted over it. The outer surface of the funnel is wrapped with a water-soaked filter paper. The end portion of the funnel is plugged with a piece of cotton wool to prevent the vapours from escaping.
• The basin is then gently heated on a sand bath. The vaporised ammonium chloride is coming in contact with the colder wall of the funnel condenser kept there as powdered ammonium chloride.
• The sand remains in the flat basin, ammonium chloride is scrapped off. In this way ammonium chloride and sand are separated.

Question 10.
State three basic characteristics of metal and non-metal with respect to
(a) ion formation
b) reaction with oxygen
(c) conduction of electricity and heat.
Answer:
(a) Ion formation : Metals form positive ions by loss of electron.
e.g. Na – e → Na⁺ ; Mg – 2e → Mg²⁺ ; Al – 3e → Al³⁺

Non-metals form negative ions by gaining electron.
e.g. Cl + e → Cl^– ; O + 2e → O^2- ; N + 3e → N^3-

(b) Reaction with oxygen : Almost all metals (except Ag, Au) react with oxygen to produce metallic oxides; aqueous solution of some of these like Na₂O, K₂O are alkali.
Na + O₂ → Na₂O; Na₂O + H₂O = 2 NaOH
K + O₂ → K₂O ; K₂O + H₂O = 2 KOH

Oxides of non-metals are usually acidic in nature. Aqueous solution of oxides of C, S, P etc. are acidic.
C + O₂ → CO2 ; CO₂ + H₂O = H₂CO₃ (Carbonic acid)
S + O₂ → SO₂ ; SO₂ + H₂O = H₂SO₃ (Sulphurous acid)

(c) Conduction of electricity : Metals are good conductors of heat and electricity.
Non-metals are usually bad conductors of heat and electricity.
Exception: Graphite, though a non-metal is a good conductor of heat and electricity.