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Q1: What is meant by a substance?
Ans: A substance is a material whose particles have similar properties.
Q2: List the points of difference between homogeneous and heterogeneous mixtures?
Ans:
|
Homogeneous |
Heterogeneous |
|
The solute is completely dissolved into the solvent |
The solute does not dissolve in the solvent |
|
Homogeneous mixtures do not scatters the light |
Heterogeneous mixtures scatters the light making its path visible |
|
The solute in this mixtures are stable. They do no settle at the bottom |
The solute in this mixtures are unstable. They settle at the bottom. |
|
For example, sugar solution |
For example, mixture of sand and water |
Q3: Differentiate between homogeneous and heterogeneous mixtures with examples.
Ans:
|
Homogeneous mixtures |
Heterogeneous mixtures |
|
The solute is completely dissolved into the solvent |
The solute does not dissolve in the solvent |
|
Homogeneous mixtures do not scatters the light |
Heterogeneous mixtures scatters the light making its path visible |
|
The solute in this mixtures are stable. They do no settle at the bottom |
The solute in this mixtures are unstable. They settle at the bottom. |
|
For example, sugar solution |
For example, mixture of sand and water |
Q4: How are sol, solution, and suspension different from each other?
Ans:
|
Sol (colloidal) |
Solution |
Suspensions |
|
Heterogeneous mixture |
Homogenous mixtures |
Heterogeneous mixtures |
|
Particles cannot be seen with naked eyes but it scatters light. |
Particles cannot be seen with naked eyes and it do not scatters light. |
Particles are seen with naked eyes and scatters the light. |
|
The particles are generally stable. They do no settle at the bottom |
The particles are stable. They do not settle at the bottom. |
The particles are unstable. They settle at the bottom. |
|
They cannot be separated by filtration method. |
They cannot be separated by filtration method. |
They can be separated by filtration method. |
Q5: To make a saturated solution 36g of sodium chloride is dissolved in 100g of water at 293 K. Find its concentration at this temperature.
Ans: Given, mass of solute (sodium chloride) = 36g
Mass of solvent (mass of water) = 100g
Mass of solution = mass of sodium chloride + mass of solvent
= 36g + 100g
= 136g
Now,
Using mass by mass percentage to concentration of solution
= (mass of solute / mass of solution) x 100
= (36/136) x 100
= 0.2647 x 100
= 26.47%
Q6: How will you separate a mixture containing kerosene and petrol (difference in their boiling point is more than 25 degree Celsius) which are miscible with each other?
Ans: Petrol and kerosene, which are miscible with each other, can be separated by fractional distillation.
Q7: Name the technique to separate
Ans: (1) Centrifugation is used to separate butter from curd.
(2) Crystallization is used to obtained salt from sea water.
(3) Sublimation is used to separate camphor from salt.
Q8: What type of mixtures are separated by the technique of crystallization?
Ans: Any homogeneous mixture can be separated by the method of crystallization. For example, obtaining salt from sea water.
Q9: Classify the following as chemical or physical changes
Ans:
|
Cutting of trees |
Physical change |
|
Melting of butter in a pan |
Physical change |
|
Rusting of almirah |
Chemical change |
|
Boiling of water to form steam |
Physical change |
|
Passing of electric current through water and the water breaking down into hydrogen and oxygen gases |
Chemical change |
|
Dissolving common salt in water |
Physical change |
|
Making a fruit salad with raw fruits |
Physical change |
|
Burning of paper and wood |
Chemical change |
Q1: Which separation technique 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: using funnel
(g) Tea leaves from tea
Ans: filtration
(h) Iron pins from sand
Ans: with a magnet
(i) Wheat grains from husk
Ans: winnowing
(j) Fine mud particles suspended in water
Ans: sedimentation
Q2: Write the steps you would use for making tea use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and Residue.
Ans:
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).
(Please refer your textbook for the table)
(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: If 62g of potassium nitrate produces saturated solution in 100g of water.
Therefore, just half the amount of potassium nitrate i.e 31g will be needed to produce saturated solution in 50g 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.
Ans: She will observe crystals of potassium nitrate when it starts to cool at room temperature.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
Ans: The solubility of each salt at 293K is as follows:
(d) What is the effect of change of temperature on the solubility of a salt?
Ans: According to the table if the temperature is increasing the solubility of salt is also increasing.
Q4: Explain the following giving examples
(a) Saturated solution
Ans: When a solution has no more space left to dissolve particles in it, that solution is called saturated solution.
(b) Pure substance
Ans: When the particles of a substance have similar chemical properties it is called pure substance. Example: oxygen.
(c) Colloid
Ans: Colloid is a heterogeneous mixture. Its particles are quite stable and scatter the light making its path visible. Example: Butter and blood.
(d) Suspension
Ans: It is a heterogeneous mixture. Its particles are unstable and scatter the light making its path visible. Example: mixture of sand and water.
Q5: Classify each of the following as a homogeneous or heterogeneous mixture
Soda water, wood, air, soil, vinegar, filtered tea
Ans: Homogeneous mixtures: soda water, vinegar, filtered tea.
Heterogeneous mixture: Wood, air, and soil.
Q6: How would you confirm that a colourless liquid given to you is pure water?
Ans: If the given colourless liquid boils at 1000C and freezes at 00C, then it is a pure water.
Q7: 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: Pure substance: Ice, iron, hydrochloric acid, calcium oxide, mercury
Q8: Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Ans: Sea water and soda water are mixtures.
Q9: Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution.
Ans: Milk and starch solution will show 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 |
Compounds |
Mixtures |
|
Sodium, silver, tin, silicon, coal |
Calcium carbonate, carbon dioxide, methane |
Soil, sugar solution, air, soap, blood |
Q11: 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.
Ans: Following are the chemical changes