C - 2, Is Matter Around Us Pure || NCERT Solution

 PAGE NO.15 

 

Q1. What is meant by a substance? 

Ans. A substance is a pure single form of matter. 


Q2. List the point of differences between homogeneous and heterogeneous mixtures? 

Ans.  

HOMOGENEOUS MIXTURE 

  • Composition is throughout the bulk. For example, sugar dissolved in water has same taste throughout. 
  • It has no distinct boundaries. For example,  we do not see any separate boundaries in sugar solutions. 
HETROGENEOUS MIXTURE 
  • Composition is not same throughout. For example, chalk and water 
  • It has distinct boundaries of separation. For example, if we mix sand and water, the boundary separating sand from water is clearly visible. 



PAGE NO. 18 


Q1. Differentiate between homogeneous and heterogeneous mixtures with examples. 

Ans. 

HOMOGENEOUS MIXTURE 

  • Composition is throughout the bulk. For example, sugar dissolved in water has same taste throughout. 
  • It has no distinct boundaries. For example,  we do not see any separate boundaries in sugar solutions. 
HETROGENEOUS MIXTURE 
  • Composition is not same throughout. For example, chalk and water 
  • It has distinct boundaries of separation. For example, if we mix sand and water, the boundary separating sand from water is clearly visible. 

Q2. How are sol, solution and suspension different from each other? 

Ans.  


Q3. To make a saturated solution, 36g of sodium chloride is dissolved in 100 g of water at 293 k. Find its concentration at this temperature. 



PAGE NO.24 


Q1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25˚C), which are miscible with each other? 

Ans. Mixture containing kerosene and petrol whose boiling point has a difference of more than 25˚C can be separated by distillation. 


Q2. Name the technique to separate, 

  1. Butter from curd, 
  2. Salt from sea- water 
  3. Camphor from salt. 
Ans. 
  1. centrifugation 
  2. crystallisation 
  3. sublimation 


Q3. What type of mixtures are separated by the technique of crystallisation? 

Ans. Crystallisation is used to separate mixtures in which impurities are either insoluble or more soluble than solid in a particular solvent. For example, impure copper sulphate can be easily purified by the technique of crystallisation. 


PAGE NO. 24 


Q1. Classify the following as chemical or physical changes: 

  1. Cutting of trees  
  2. Melting of butter in a pan 
  3. Rusting of almirah 
  4. Boiling water to form steam, 
  5. Passing of electric current through water and the water breaking down into hydrogen and oxygen gases 
  6. Dissolving common salt in water 
  7. Making a fruit salad with raw fruits and 
  8. Burning of paper and wood 

Ans.

  1. chemical change 
  2. physical change 
  3. chemical change 
  4. physical change 
  5. chemical change 
  6. physical change 
  7. physical change 
  8. chemical change 


Q2. Try segregating the things around you as pure substances or mixtures. 

Ans. Pure substances: Distilled water, diamond, graphite, raw rubber 

Mixtures: curd, ice cream, kerosene oil, cooking oil, steel. 

 


EXERCISE 

Q1. Which separation techniques will you apply for the separation of the following? 

 (a) sodium chloride from its solution in water 

Ans. Evaporation 

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

Ans. Sublimation 

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

Ans. Filtration 

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

Ans. Chromatography 

(e) Butter from curd 

Ans. Centrifugation 

(f) Oil from water 

Ans. Separating funnel 

(g) Tea leaves from tea 

Ans. Filtration 

(h) Iron pins from sand 

Ans. Using a sand 

(i) Wheat grains from husk 

Ans. Blowing air 

(j) Fine mud particles suspended in water 

Ans. Using alum 


Q2. 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 kettle and heat it on a burner. Now add some tea leaves and boil. Here, water act as solvent and the solute is caffeine present in tea leaves. Tea leaves dissolves in water to give a brownish black mixture. Now, add some sugar and milk which are soluble and boil again. When sugar and milk dissolves in water properly the tea is ready. Filter the mixture through sieve. The tea leaves being insoluble remain as residue on sieve while a solution of caffeine, sugar and milk in water called tea is obtained as the filtrate. 


Q3. 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). 



(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? 

Ans. Mass of potassium nitrate present in 100 g of water in a saturated solution at 313 k= 62 g 

Shape∴ Mass of potassium nitrate in 50 g of water in saturated solution at


(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 

Ans. When a saturated solution of potassium chloride at 353k cools down, the solubility of potassium chloride decreases. As a result, some amount of potassium chloride which exceeds its solubility at lower temperature separates out as crystals. 

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

Ans. Solubility of potassium nitrate at 293 k= 32g 

Solubility of sodium chloride at 293k = 36g 

Solubility of potassium chloride at 293 k = 35g 

Solubility of ammonium chloride at 293k = 37g 

So, ammonium chloride has the highest solubility at 293 k 

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

Ans. The solubility of salt increases with change in temperature. It is different for different salts.  


Q4. Explain the following giving examples. 

  1. Saturated solution 

(b)Pure substance 

(c) colloid  

(d) suspension 

Ans. (a) saturated solution- A solution in which no more solute can be dissolved at a given temperature is called saturated solution. The concentration of solution cannot be increased beyond a certain limit. 

For example, when we add copper sulphate to water, the crystals of copper sulphate keep on going into solution in the beginning to form a clear solution but after some times copper sulphate stops dissolving instead of temperature is kept constant. 

(b) pure substance- A pure substance can be defined as a material which contains only one kind of particles (atoms or molecules). 

For example, elements like iron, silver, copper etc. and compounds like water, sugar, sodium chloride etc. 

(c) Colloid- A colloidal solution is a heterogeneous mixture in which solute particles having size between 1 nm to 100 nm are evenly distributed throughout the bulk of the medium. Due to small size of particles, the colloidal solutions may appear to be homogeneous. Examples of colloidal solution are, milk, gum solution, blood, milk-cream, ink, smoke etc. 

(d) Suspension- suspension is a heterogeneous mixture in which solute particles having size greater than 100nm (diameter) re spread or distributed throughout the bulk of the medium. The particles of suspension are visible to the naked eyes. 

Examples of suspension are: 

Muddy water, paints, milk of magnesia, lime water etc. 


Q5. Classify each of the following as a homogeneous and heterogeneous mixture. 

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

Ans. Homogeneous mixture: soda water, air, vinegar, filtered tea. 

Heterogeneous mixture: water and soil. 


Q6 Hoe would you confirm that a colourless liquid given to you is pure water? 

Ans. If the boiling point and freezing point of the given liquid is 100˚C and 0˚C under one atmospheric pressure than we can say that given liquid is a pure water. 


Q7. Which of the following materials fall in the category of a ̎pure substance”? 

  1. Ice 

(b)Milk 

(c)Iron 

(d) Hydrochloric acid  

(e) Calcium oxide 

(f) Mercury 

(g) Brick 

(h) Wood 

(i) Air 

Ans. Materials which fall under pure substances are, ice, iron, calcium oxide and mercury. 


Q8. Identify the solutions among the following mixtures. 

  1. Soil 

  1. Sea water 

  1. Air 

  1. Coal 

  1. Soda water 

Ans. Sea water, Air and Soda water are solutions. 


Q9. Which of the following will show ̎Tyndall effect”? 

  1. Salt solution 

  1. Milk 

  1. Copper sulphate solution 

  1. Starch solution 

Ans. Milk and starch solution shows Tyndall effect as they are colloids and Tyndall effect is shown by colloidal solutions. 


Q10. Classify the following into elements, compounds and mixtures. 

  1. Sodium 

  1. Soil 

  1. Sugar solution 

  1. Silver 

  1. Calcium carbonate 

  1. Tin silicon 

  1. Silicon 

  1. Coal 

  1. Air 

  1. Soap 

  1. Methane 

  1. Carbon dioxide 

  1. Blood 

Ans. Elements: sodium, silver, tin, silicon. 

Compounds: calcium carbonate, methane, carbon dioxide. 

Mixtures: soil, sugar solution, coal, air, soap, blood. 


Q11. Which of the following are chemical changes? 

  1. Growth of a plant 

  1. Rusting of iron 

  1. Mixing of iron filings and sand 

  1. Cooking of food 

  1. Digestion of food 

  1. Freezing of water 

  1. Burning of a candle 

Ans. Growth of a plant, rusting of iron, cooking of food, digestion of food and burning of candle are chemical changes. 

 

 

 

 

. 












Tags
Reactions