CH02: Is Matter Around Us Pure?
Intext Questions NCERT
Questions (Page - 15)
- What is meant by a substance?
- List the points of differences between homogeneous and heterogeneous mixtures.
A substance is defined as matter that has a specific composition and properties. It cannot be separated into other kinds of matter by physical methods, without breaking chemical bonds.
Homogeneous mixtures have uniform composition throughout, whereas heterogeneous mixtures have visibly different phases or components that can be distinguished by the naked eye or under a microscope.
Questions (Page - 18)
- Differentiate between homogeneous and heterogeneous mixtures with examples.
- How are sol, solution, and suspension different from each other?
- 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.
Homogeneous mixtures include solutions like saltwater, where the solute (salt) is evenly distributed in the solvent (water). Heterogeneous mixtures include substances like trail mix, where different components can be easily distinguished.
Sol is a colloidal suspension of a solid dispersed in a liquid. A solution is a homogeneous mixture of two or more substances. A suspension is a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase some time after their introduction.
Concentration is determined by dividing the mass of solute (36 g) by the mass of solvent (100 g), then multiplying by 100 to express it as a percentage: (36 / 100) * 100 = 36%.
Questions (Page - 19)
- Classify the following as chemical or physical changes:
- 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
- Try segregating the things around you as pure substances or mixtures.
Analyze each item based on its composition and properties to determine if it is a pure substance (elements or compounds) or a mixture (homogeneous or heterogeneous).
Exercises
- Which separation techniques will you apply for the separation of the following?
- Sodium chloride from its solution in water - Evaporation
- Ammonium chloride from a mixture containing sodium chloride and ammonium chloride - Sublimation
- Small pieces of metal in the engine oil of a car - Filtration
- Different pigments from an extract of flower petals - Chromatography
- Butter from curd - Decantation and filtration
- Oil from water - Separating funnel technique
- Tea leaves from tea - Filtration
- Iron pins from sand - Magnetic separation
- Wheat grains from husk - Winnowing
- Fine mud particles suspended in water - Centrifugation
- Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
- Boil water (solvent).
- Add tea leaves (solute) to the boiling water.
- Let the tea leaves dissolve in the water.
- Filter the tea leaves (residue) using a strainer to obtain the tea solution (filtrate).
- Add sugar (solute, soluble) to the tea solution and stir until it dissolves.
- Enjoy your tea!
- Pragya tested the solubility of three different substances at different temperatures...
- (a) Mass of potassium nitrate needed for 50 g of water at 313 K: Calculate using given solubility data.
- (b) Observation when potassium chloride solution cools: Crystals of potassium chloride will precipitate out as the solution becomes supersaturated.
- (c) Solubility of each salt at 293 K: Compare solubility values provided.
- (d) Effect of temperature on solubility of a salt: Generally, solubility increases with temperature for most salts.
- Explain the following giving examples.
- Saturated solution - A solution that contains the maximum amount of solute that can dissolve at a given temperature, e.g., sugar in water at room temperature.
- Pure substance - A substance that has a fixed composition and cannot be separated into simpler substances by physical methods, e.g., gold.
- Colloid - A heterogeneous mixture where one substance is dispersed evenly throughout another substance at the microscopic level, e.g., milk.
- Suspension - A heterogeneous mixture where solid particles do not dissolve but remain suspended in a liquid or gas, e.g., muddy water.
- Classify each of the following as a homogeneous or heterogeneous mixture.
- soda water - Homogeneous mixture
- wood - Heterogeneous mixture
- air - Homogeneous mixture
- soil - Heterogeneous mixture
- vinegar - Homogeneous mixture
- filtered tea - Homogeneous mixture
- How would you confirm that a colorless liquid given to you is pure water?
- Which of the following materials fall in the category of a “pure substance”?
- Ice - Pure substance (solid water)
- Milk - Mixture
- Iron - Pure substance
- Hydrochloric acid - Pure substance
- Calcium oxide - Pure substance
- Mercury - Pure substance
- Brick - Mixture
- Wood - Mixture
- Air - Mixture
- Identify the solutions among the following mixtures.
- Soil - Not a solution
- Sea water - Solution
- Air - Not a solution
- Coal - Not a solution
- Soda water - Solution
- Which of the following will show “Tyndall effect”?
- Salt solution - No
- Milk - Yes
- Copper sulphate solution - No
- Starch solution - Yes
- Classify the following into elements, compounds and mixtures.
- Sodium - Element
- Soil - Mixture
- Sugar solution - Mixture
- Silver - Element
- Calcium carbonate - Compound
- Tin - Element
- Silicon - Element
- Coal - Mixture
- Methane - Compound
- Carbon dioxide - Compound
- Blood - Mixture
- Which of the following are chemical changes?
- Growth of a plant - Chemical change
- Rusting of iron - Chemical change
- Mixing of iron filings and sand - Physical change
- Cooking of food - Chemical change
- Digestion of food - Chemical change
- Freezing of water - Physical change
- Burning of a candle - Chemical change
Check its boiling point and freezing point to ensure they are at 100°C and 0°C respectively, which are characteristic properties of pure water.
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