2 - Is Matter Around Us Pure

PAGE NO - 15

Q1 - What is meant by pure substance ?
Ans - A pure substance is the one that consists of a single type of particles. Pure substance can be classified a s elements of compounds.

Q2 - List the points of differences between homogeneous and heterogeneous mixtures.
Ans - A HOMOGENEOUS Mixture - It is a mixture having a uniform composition throughout the mixture.  Ex - salt in water, sugar in water etc.
 A HETEROGENEOUS Mixture - It is a mixture having non-uniform composition throughout the mixture.   Ex - oil in water, sodium chloride in iron fillings etc.

PAGE NO - 18

Q1 - Defferentiate between homogeneous and heterogeneous mixtures with examples.
Ans - 

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

Q3 - To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Ans - Mass of solute ( sodium chloride ) = 36 g
          Mass of solvent ( water ) = 100 g
         Mass of solution = Mass of solute + Mass of solvent
                                = 36 g + 100 g = 136g

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 misscible with each other ?
Ans - We can seperate a mixture containing kerosene and petrol by distillation process, As the boiling temperature difference is 25°C.

Q2 - Name the tehnique to separate :
 (i) butter from curd.
 (ii) salt from sea-water.
 (iii) camphor from salt.
Ans -
(i) Centrifugation method.
(ii) Vaporization method.
(iii) Sublimation method.

Q3 - What type of mixtures are separated by the technique of crystallisation ?
Ans - From impure samples of solids, pure solid crystals can be obtained by the method of crystallization. Ex - pure sugar from impure sample, pure salt from impure sample etc.

PAGE - 24

Q1 - Classify the following as chemical or physical changes:
        *Cutting of trees,
        *melting of butter in a pan,
        *rusting of almrah,
        *boiling of water to form steam,
        *passing of electric current, through water and the water breaking down into hydrogen and oxygen gases,
        *dissolving common salt in water,
        *making a fruit salad with raww fruits and
        *burning of paper and wood.
Ans - CHEMICAL CHANGES - Cutting the trees, Rusting of almirah, passing of electric current through water and the water breaking down into hydrogen and oxygen gases, Burning of paper and wood.
PHYSICAL CHANGES - Melting of butter in a pan, Boiling of water to form steam, Dissolving common salt in water, Making a fruit salad with raww fruits.

Q2 - Try segregating the things around you as pure substances or mixtures.
Ans - PURE - Distilled water, diamond, graphite, raww rubber etc.
                Mixture - Ice cream, curd, cooking oil etc.


Q1 - 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 and 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 –
(a) Evaporation.
(b) Sublimation.
(c) Filtration.
(d) Chromatography.
(e) Centrifugation.
(f) Separating Funnel.
(g) Filtration.
(h) By magnet.
(i) Blowing air and Sieving.
(j) Alum Using

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 amount of solvent (water) in a pan and after heating it add little amount of solute (sugar) to the solvent. Solute will dissolve completely in the solvent forming true solution, then add tea leaves that are insoluble along with another soluble liquid milk. After boiling allow filtration with a sieve so the filtrate you obtain is tea while the residue has tea leaves that are thrown away.

Q3 – Pragya tested the solubility of three different substances at different temperatures and collected the data as given blow (results are given in the following table, as frams 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 313K ?
(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) At 313 K temperature 62 grams of Potassium nitrate dissolved in 100 grams of water. So to produce a saturated solution of potassium nitrate in 50 grams of water,
we need 62 x 50/100 = 31 grams of potassium.
(b) Some soluble potassium chloride will separate out in the form of crystals at room temperature because the solubility of potassium chloride decreases with decrease in temperature.
(c) Solubility of salts at 293 K :-
Potassium nitrate = 32 grams
Sodium Chloride =36 grams
Potassium Chloride = 35  grams
Ammonium chloride = 37 grams
Solubility of Ammonium chloride is highest at this temperature.
(d) The solubility of salts increases with increase in temperature.

Q4 – Explain the following giving examples :
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Ans –
(a) Saturated Solution – It is a solution in which no more solute particles can be dissolved at a particular temperature.
(b) Pure Substance – Those substance consisting of a single type of particles called pure substance. Ex – salt, sugar, water etc
(c) Colloid – It is a kind of heterogeneous mixture in which particle size is between 1nm to 100nm. Colloids have dispersion medium and dispersed phase. Ex – smoke, milk, shaving cream etc.
(d) Suspension – It is heterogeneous mixture in which insoluble solid particles remain suspended in medium and dispersion particles are visible to the unaided eyes. Ex – muddy water, chalk powder in water, dust storm etc.

Q5 – Classify each of the following as a homogeneous or heterogeneous mixture. Soda water, wood, air, soil, vinegar, filtered tea.
Ans – Homogeneous mixture – Soda water, air, vinegar, filtered tea.
Heterogeneous mixture – Wood, soil.
Air is homogeneous mixture if dust and other suspended particles are excluded.

Q6 – How do you confirm that a colourless liquid given to you is pure water ?
Ans – If the boiling point and freezing point of the given liquid comes out to be 100 degree Celsius or 0 degree Celsius under atmospheric pressure. Then it confirm that it is water.

Q7- Which of the following 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 – Pure substance are – Ice, Iron, Hydrochloric acid, Calcium oxide, Mercury.

Q8 – Identify the solutions among the following mixtures.
(a) Soil
(b) Air
(c) Coal
(d) Soda water
Ans – Sea water, air and Soda water are solutions.

Q9 – Which of the following show ‘’Tyndall effect’’ ?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
Ans – Milk and Starch solution show the ‘’Tyndall effect’’.

Q10 – 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 – Elements -  Sodium, silver, tin, silicon
Compounds – Calcium carbonate, methane, carbon dioxide
Mixtures – Soil, sugar solution, coal, air, soap, blood.

Q11 – Which of the following changes are chemical changes ? (a)
(a) Growth of plant
(b) Rusting of iron
(c) Mixing of iron fillings and sand
(d) Cooking of food 
(e) Digestion of food
(f) Freezing of water
(g) Burning of candle
Ans – The following changes are chemical changes : -
(a) Growth of plant
(b) Rusting of iron
(d) Cooking of food
(e) Digestion of food
(g) Burning of candle.

Post a Comment