Topic outline

  • Chapter 2 - Is Matter Around Us Pure - 9

    • Is Matter Around Us Pure - Questions Page

      Is Matter Around Us Pure 

      Q107. 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) Wheat grains from husk.

      (j) Fine mud particles suspended in water.

      Ans. The following separation techniques are used for the separation of the following:

      (a) Sodium chloride from its solution in water. By Evaporation

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

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

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

      (e) Butter from curd. By Centrifugation

      (f) Oil from water. By Separating Funnel

      (g) Tea leaves from tea. By Filtration

      (h) Iron pins from sand. By Magnetic Separation

      (i) Wheat grains from husk. By Winnowing/Sedimentation

      (j) Fine mud particles suspended in water. By Decantation and Filtration

       

      Q108. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

      Substance Dissolved

      Temperature in K

      283

      293

      313

      333

      353

      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 to 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. (a) Mass of potassium nitrate to produce a saturated solution in 100g of water at 313 K = 62g 

      Therefore, mass of potassium nitrate in 50 g of water at 313K 

      = 62 x 50/100 

      = 31g

      (b) Pragya would observe crystals of potassium chloride  as the solution cools. 

      (c) The solubility of each salt at 293K is

      • Potassium nitrate = 32g

      • Sodium chloride = 36g

      • Potassium chloride = 35 g

      • Ammonium chloride = 37g

      Ammonium chloride has the highest solubility at this temperature.

      (d) Solubility is directly proportional to the temperature, thus, on increasing the temperature, the solubility of salt increases.

       

      Q109. Explain the following giving examples.

      (a) saturated solution

      (b) pure substance

      (c) colloid

      (d) suspension 

      Ans. Saturated solution - At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution.

      Pure substance - A pure substance consists of a single type of particles. Example: gold, silver, copper etc.

      Colloid – A colloid or colloidal solution is a heterogeneous mixture, for example: milk. Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light.

      Suspension - A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye.

       

      Q110. What is a colloid? Write its properties.

      Ans. A colloid or colloidal solution is a heterogeneous mixture, for example, milk. Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light. This scattering of a beam of light is called the Tyndall effect.

      Properties of a colloid

      1. A colloid is a heterogeneous mixture.

      2. The size of particles of a colloid is too small to be individually seen by naked eyes.

      3. Colloids are big enough to scatter a beam of light passing through it and make its path visible.

      4. They do not settle down when left undisturbed, that is, a colloid is quite stable. 

      5. They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation, can be used to separate the colloidal particles.

       

      Q111. List the points of differences between homogeneous and heterogeneous mixtures.

      Or

      Differentiate between homogeneous and heterogeneous mixtures with examples.

      Ans. Difference between homogeneous and heterogeneous mixtures

      Homogeneous mixtures

      Heterogeneous mixtures

      1. Those mixtures in which the substances are completely mixed together and are indistinguishable from one another are called homogeneous mixtures.

      1. Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles are called heterogeneous mixtures.

      2. It has a uniform composition throughout.

      2. It does not have a uniform composition throughout.

      3. It has no visible boundaries of separation between the various constituents.

      3. It has visible boundaries of separation between the various constituents.

      4. Example: soda water, lemonade, air, petrol, sugar solution, salt solution, soft drinks etc.

      4. Example: ink, milk, coal, soil, sugar and sand mixture, soap solution, dyes etc.

       

      Q112. How are sol, solution and suspension different from each other?

      Ans.

      Sol. (Colloid)

      Solution

      Suspension

      1. A colloid is a heterogeneous mixture.

      1. A solution is a homogeneous mixture.

      1. Suspension is a heterogeneous mixture.

      2. The size of particles of a colloid is too small to be individually seen by naked eyes.

      2. The particles of a solution are smaller than 1 nm (10-9 metre) in diameter. So, they cannot be seen by naked eyes.

      2. The particles of a suspension can be seen by the naked eye.

      3. Colloids are big enough to scatter a beam of light passing through it and make its path visible.

      3. Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.

      3. The particles of a suspension scatter a beam of light passing through it and make its path visible.

      4. They do not settle down when left undisturbed, that is, a colloid is quite stable.

      4. The solute particles do not settle down when left undisturbed, that is, a solution is stable.

      4. The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable.

      5. Example: fog, clouds, smoke, milk, cheese, butter, rubber etc.

      5. Example: air, soda water, vinegar, sugar solution, salt solution etc.

      5. Example: muddy water, milk of magnesia, chalk water mixture etc.