Is Matter Around Us Pure
Class: 9 | Chapter: 2
Intext Questions with Answer
1. What is meant by a pure substance ?Answer:A pure substance has a fixed chemical composition and it consists of a single type of particles.
2. List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
| Homogeneous mixture | Heterogeneous mixture |
|---|---|
| Uniform composition | Non - uniform composition |
| Clear bondaries of separation | No Boundaries of seperation among the consituents |
| example : air, alloys | example : sugar & sand, oil & water |
3. How are sol, solution and suspension different from each other ?
Answer:
| Sol | Solution | Suspension |
|---|---|---|
| A sol is a heterogeneous mixture | A solution is a homogenous mixture | Suspension is a heterogeneous mixture |
| Colloid is stable mixture | Solution is stable, solute particles don't settle down when left undisturbed | Suspension is unstable means particles settle down. |
| They scatter a beam of light and make it's path visible | JSolutions can't scatter beam of light due to very small size of particles | They also scatter a beam of light |
| They can't be seen by naked eyes | They are not visible to naked eyes | They can be seen by naked eyes |
4. 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.
Answer: Given-
Mass of solute (sodium chloride) = 36g
Mass of solvent ( water) = 100g
As we know, Concentration = Mass of solute / Mass of solution × 100
Here, Mass of solution = Mass of solute + Mass of solvent 36 + 100 = 136 g
Concentration = 36/136 × 100 = 26.5%
5. 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 ?
Answer: Here temperature difference is more than 25°C so, we can separate by simple distillation method.
1. First we will take mixture to be separated in a distillation flask.
2. Then we need to arrange the apparatus and it's parts which are required to do this separation technique.
3. We need to heat the mixture by watching at the thermometer.
4. Petrol will vaporise first as it is having less boiling point and condenses and then after can be collected.
5. Kerosene will be left behind in distillation flask.
6. Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
Answer: (i) Centrifuge
(ii) Evaporation
(iii) Sublimation
7. What type of mixtures are separated by the technique of crystallisation ?
Answer: This technique is used when there is a difference in solubilities of components in a given solvent.
8. Classify the following as chemical or 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 gas,
(f)dissolving common salt in water,
(g)making a fruit salad with raw fruits and
(h) burning of paper and wood.
Answer: Physical change: (a) cutting of trees, (b) melting of butter in a pan, (d) boiling of water to form steam, (f) dissolving commonnsalt in water, (g) making a fruit salad with fruits Chemical change: (c) rusting of almirah, (e) passing of electric current through water and water breaking down into hydrogen and oxygen gases, (h) burning of paper and wood.
9. Try segregating the things around you as pure substances or mixtures.
Answer: Pure substances: sugar, salt, diamond, water
Mixtures: air, mixture of sugar & water, mixture of salt & water
Exercise Questions with Answer
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) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer: (a) Evaporation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Separating funnel
(g) Filtration
(h) By magnet
(i) Winnowing
(j) Filtration
2. Write the steps you would use for making tea. Use the words, solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer: Steps : (1) First of all, we take some water as solvent and boil it.
(2) Add insoluble tea leaves into boiling water.
(3) Now, we filter and collect in filtrate in a cup. Tea leaves are residue on the sieve.
(4) we can add some sugar and milk as solutes and dissolve all together to get tea as solution.
3. 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 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 us 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 ?
Answer: (a) From the table, it is given that Mass of potassium nitrate ( KNO3) needed to produce a saturated solution of KNO3 in 100g of water at 313 k is 62g So, Mass of potassium nitrate ( KNO3) required to produce a saturated solution of potassium nitrate in 50g of water at 313 would be half means 62×50/100 = 31g
(b) On cooling this solution, some amount of solute ( potassium chloride) will be seaparated out and crystallisation occurs.
(c) Ammonium chloride ( NH4Cl) has the highest solubility ( 37g) at 293K.
(d) Generally, solubility of salt increases with increase in temperature.
4. Explain the following giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Answer: (a) Saturated solution : solution in which no more quantity of solute can be dissolved at a given temperature. example- soda water.
(b) Pure substance : A pure substance has a fixed chemical composition and it consists of a single type of particles. example : Silver, diamond.
(c) Colloid : A solution which has particles larger than true solution but smaller than suspension. example : milk, blood.
(d) Suspension : A solution in which solute particles don't dissolve but get suspended throughout solvent. example : sand and water mixture, paints.
5. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air. soil, vinegar, filtered tea.
Answer: Homogeneous mixture: Soda water, vinegar, filtered tea Heterogeneous mixture: Air, soil, wood.
6. How would, you confirm that a colourless liquid given to you is pure water ?
Answer: Water has fixed Boiling point equal to 100°C and freezing point equal to 0°C. If the given liquid boils and freezes on these fixed values then it is confirmed that a colourless 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) Back (h) Wood (i) Air.
Answer: Pure substances : (c) Iron, (d) Hydrochloric acid, (e) Calcium oxide, (f) Mercury
8. Identify the solutions among the following mixtures.
(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.
Answer: Mixtures : (b) Sea water, (c) air and (e) soda water
9. Which of the following will show 'Tyndall effect'?
(a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution
Answer: (b) Milk, (d) Starch solution will show Tyndal effect.
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
Answer: Elements: Sodium, silver, tin, silicon
Mixtures: Soil, sugar solution, coal, air, blood, soap
Compounds: Calcium carbonate, methane, carbon dioxide
11. Which of the following are chemical changes ?
(a) Growth of a plant (b) Rusting of iron (c) Mixing of iron filings and sand (d) Cooking of food (e) Digestion of food (f) Freezing of water (g) Burning of a candle.
Answer: Chemical changes are : (a) Growth of a plant (b) Rusting of iron (d) Cooking of food (e) Digestion of food ( g) Burning of a candle