# Is Matter Around us Pure? (NCERT Solutions, Class 9)

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(1) What is meant by a substance?

Ans- Substances are those matters that have specific chemical composition and specific properties.

Eg: – Gold, table salt etc.

(2) List the points of differences between homogeneous and heterogeneous mixtures.

Ans– Differences between homogeneous and heterogeneous mixtures are given below –

 SN Homogeneous mixture Heterogeneous mixture 1. mixture has uniform composition of substances throughout mixture has non – uniform composition of substances throughout 2. Has uniform properties throughout Do not have uniform properties throughout

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(1) Differences between homogeneous and heterogeneous mixture with examples.

Ans– Differences between homogeneous and heterogeneous mixtures are given below –

 SN Homogeneous mixture Heterogeneous mixture 1. mixture has uniform composition of substances throughout mixture has non – uniform composition of substances throughout 2. Has uniform properties throughout Do not have uniform properties throughout 3. Eg:- Water, vinegar etc. Eg:- Iron fillings and water, soil etc.

(2) How are sol, solution and suspension different from each other?

Ans- Differences between sol, solution and suspension are given below –

 SN Sol Solution Suspension 1. Heterogeneous mixture Homogeneous mixture Heterogeneous mixture 2. Show tyndall effect Cannot show tyndall effect Show tyndall effect 3. Solute dispersed in solvent Solute dissolves in solvent Solute suspended in solvent 4. Can not separate by filtration Can not separate y filtration Can be filtered 5. Eg:- Mud Eg:- Solution of sugar and water Eg:- chalk in water

(3) To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293K.Find its concentration at this temperature.

Ans-

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(a)Arrange the gases present in the air in increasing order of their boiling points.

Ans – The increasing order of boiling points of gasses are given below –

Nitrogen(- 1960C), Argon (-1860C), Oxygen(-1830C)

(b) Which gas forms the liquids first as the air is cooled?

Ans- The gas which has lowest boiling point will form liquid. Therefore, Nitrogen( -1960C) will form liquid first.

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(1) Classify the following as chemical and physical changes:

(a) cutting of trees

(b) melting of butter in a pan

(c) rusting of almirah

(d) boiling of water to form steam

(e) passing of electric current, through water and the water breaking down into hydrogen and oxygen goes.

(f) dissolving common salt in water

(g) making a fruit salad with raw fruits , and

(h) burning of paper and wood.

Ans-

 SN Activities Physical change Chemical change 1. cutting of trees yes 2. melting of butter in a pan yes 3. rusting of almirah yes 4. boiling of water to form steam yes 5. passing of electric current, through water and the water breaking down into hydrogen and oxygen goes. yes 6. dissolving common salt in water yes 7. making a fruit salad with raw fruits yes 8. burning of paper and wood. yes

(2) Try segregating the things around you as pure substances or mixtures.

Ans- Pure substances – Air, water, iron, dal uncooked etc.

Mixtures – shakes, milk, cook food etc.

Exercises

(1) Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.

(c) Small pieces of metal in the engine oil of a car.

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Iron pins from sand.

(i) What grains from husk.

(j) Fine mud particles suspended in water.

Ans-

 SN Mixture Separation technique a. Sodium chloride from its solution in water Evaporation b. Ammonium chloride from a mixture containing sodium chloride and ammonium chloride Sublimation c. Small pieces of metal in the engine oil of a car Filtration d. Different pigments from an extract of flower petals. Chromatography e. Butter from curd Centrifugation f. Oil from water Separating  funnel g. Tea leaves from tea Filtration h. Iron pins from sand By using magnets i. Wheat grains from husk Winnowing j. Fine mud particles suspended in water. Centrifugation

(2) Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Ans- Take some water in a pan. Put solute milk and sugar in solvent water. Solute sugar dissolves in solvent water. Put tea leaves in this mixture. Tea leaves are insoluble while sugar is soluble. After, boiling this mixture, filter this mixture. Residue will leave in sieve and tea filtrate from the sieve.

(3) Pragya tested the solubility of the three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substances dissolved in 100 grams of water to form a saturated solution).

 Substance Dissolved Temperature in K 283                   293                     313               333                 353                                  Solubility Potassium nitrate 21 32 62 106 167 Sodium chloride 36 36 36 37 37 Potassium chloride 35 35 40 46 54 Ammonium chloride 24 37 41 55 66

(a) What mass of potassium nitrate would be needed produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

(d) What is the effect of change of temperature on the solubility of a salt?

Ans-

(b) Crystal of the potassium chloride will be obtained after cooling at room temperature.

(c) The solubility of each salt at 293 K are given below –

Potassium nitrate – 32

Sodium chloride – 36

Potassium chloride – 35

Ammonium chloride – 37

Ammonium chloride has the highest solubility at 293 k.

(d)The increase of the temperature will increase the solubility of the salt and decrease of the temperature will decrease the solubility of the salt.

(4) Explain the following giving example.

(a) saturated solution

(b) pure substances

(c) colloid

(d) suspension

Ans-

(a) A solution in which the maximum amount of the solute is dissolved in solvent at a particular temperature is known as saturated solution.

Eg:- If 100 g of salt dissolved in 200 g of water at certain temperature. The solution is said saturated if no amount of solute salt can be dissolved.

(b) When all the particles of the matter are of same chemical nature, is called pure substance or pure matter.

Eg:- Water , salt etc.

(c) A heterogeneous mixture of very small particles which cannot be seen by naked eyes but particles can scatter light beam easily, is called colloidal solution.

Eg:- Milk, jelly, smoke etc.

(d) A suspension is unstable (suspension settle down when left undisturbed). Therefore, they can be separated by the filtration. When particles of suspension settle down they can not scatter light.

Eg:- Mixture of chalk and water

(5) Classify each of the following as a homogeneous or heterogeneous mixture.

Soda water, wood, air, soil, vinegar, filtered tea.

Ans-

 Mixture Homogeneous Mixture Heterogeneous  Mixture Soda water Yes Wood Yes air Yes soil Yes vinegar Yes Filtered tea Yes

(6) How would you confirm that a colourless liquid given to you is pure water?

Ans-  Pure water boils at 1000C and 1 atmospheric pressure. If given liquid boils at 1000c and 1 atmospheric pressure than given liquid is pure water.

(7) Which of the following materials fall in the category of a “pure substance”?

(a) Ice

(b) Milk

(c) Iron

(d) Hydrochloric acid

(e) Calcium oxide

(f) Mercury

(g) Brick

(h) Wood

(i) Air

Ans-

Ans-

 Material Pure Substance Ice Yes Milk No Iron Yes Hydrochloric acid Yes Calcium Oxide Yes Mercury Yes Brick No Wood No Air No

(8) Identify the solutions among the following mixtures.

(a) Soil

(b) Sea water

(c) Air

(d) Coal

(e) Soda water

Ans-

 SN Mixture Tyndall effect a. Salt solution No b. Milk Yes c. Copper sulphate solution No d. Starch solution Yes

(10) Classify the following into elements compounds and mixtures.

(a) Sodium

(b) Soil

(c) Sugar solution

(d) Silver

(e) Calcium carbonate

(f) Tin

(g) Silicon

(h) Coal

(i) Air

(j) Soap

(k) Methane

(l) Carbon dioxide

(m) Blood

Ans-

 SN Name Elements Compounds Mixtures a. Sodium Yes b. Soil Yes c. Sugar solution Yes d. Silver Yes e. Calcium carbonate Yes f. Tin Yes g. Silicon yes h. coal Yes i. Air Yes j soap Yes K Methane Yes l. Carbon dioxide Yes m. Blood Yes

(11) Which of the following are chemical changes?

(a) Growth of a plant

(b) Rusting of Iron

(c) Mixing of Iron fillings and stand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of a candle

Ans-

 SN Name Chemical changes a. Growth of a plant Yes b. Rusting of iron Yes c. Mixing of Iron fillings and stand No d. Cooking of food Yes e. Digestion of food Yes f. Freezing of water No g. Burning of a candle Yes

Helping Topics –

Is Matter pure around us pure?

Practice sheet, class 9

Differences betwen mixture and compound

Differences between element and compound