Q:
Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution.
A:
Milk and starch solution will show Tyndall effect because they are colloidal solutions.
Q:
Identify the solutions among the following mixtures. (a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water
A:
Sea water, air and soda water are solutions.
Q:
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
A:
Growth of plant, rusting of iron, cooking of food, digestion of food and burning of a candle are chemical changes.
Q:
How would you confirm that a colourless liquid given to you is pure water?
A:
Every liquid has a characteristic boiling point. Pure water has boiling point of 100 °C (373 K) at 1 atmospheric pressure. Hence, the purity of water can be confirmed by determining its boiling point.
Q:
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
A:
|
Element |
Compound |
Mixture |
|
Sodium, Silver, Tin, Silicon |
Calcium carbonate, Methane, Soap, Carbon dioxide |
Soil, Sugar solution, Coal Air, Blood |
Q:
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
A:
Ice, iron, hydrochloric acid, calcium oxide and mercury fall in the category of pure substance.
Q:
Classify each of the following as a homogeneous or heterogeneous mixture. soda water, wood, air, soil, vinegar, filtered tea.
A:
Homogeneous mixtures: Soda water, vinegar, filtered tea
Heterogeneous mixtures: Soil, wood
Air is a homogeneous mixture of different gases. However, if some dust or other particles are also present, then air becomes heterogeneous mixture.
Q:
Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
A:
Tea can be prepared by following steps:
- Take some water as solvent in a kettle and boil it for few minutes.
- Now add one tea spoon sugar, one tea spoon tea leaves and some milk as solute to water. They all together form a solution.
- Now boil the solution again for few minutes so that sugar dissolves in solution as sugar is soluble in water.
- Now filter the solution through a strainer. The insoluble tea leaves remain on the strainer as residue and the filtrate is collected in cup.
Q:
Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension
A:
(a) Saturated solution: A solution in which no more solute can be dissolved at a particular temperature is called as saturated solution. For example: Soft drinks are saturated with carbon dioxide, hence it gives off carbon dioxide through bubbles, the Earth's soil is saturated with nitrogen.
(b) Pure Substance: A substance that shows same characteristics at a given temperature and pressure is called a pure substance. For example distilled water is a pure substance.
(c) Colloid: A colloid is a heterogeneous mixture that consists of particles bigger than that of a solution and smaller than that of suspension. For example: Smoke, butter, milk, etc. are colloids.
(d) Suspension: A suspension is a heterogeneous mixture in which solid is dispersed in liquid. The solute particles in suspension do not dissolve but remain suspended throughout the medium. The particles are large in size and visible to naked eye. For example: Chalk particles, muddy water etc.
Q:
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?
(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?
A:
Q:
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.
A:
(a) Sodium chloride from its solution in water: Evaporation
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride: Sublimation
(c) Small pieces of metal in the engine oil of a car: Filtration
(d) Different pigments from an extract of flower petals: Chromatography
(e) Butter from curd: Centrifugation
(f) Oil from water: Using separating funnel
(g) Tea leaves from tea: Filtration
(h) Iron pins from sand: Magnetic Separation
(i) Wheat grains from husk: Winnowing
(j) Fine mud particles suspended in water: Centrifugation
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