Daily Practice Problems

📝 SolutionA pure substance consists of a single type of particle throughout. Distilled water is a pure compound ($H_2O$). Air is a mixture of gases, sugar solution is a mixture of sugar and water, and milk is a colloidal mixture. Pure substances have a fixed composition and definite properties.

📝 SolutionSalt dissolves completely in water to form a uniform solution where you cannot distinguish the components — this is a homogeneous mixture. In a heterogeneous mixture (like sand in water) the components remain visibly separate. A solution of salt in water is the classic example of a homogeneous mixture.

📝 SolutionSimple distillation separates two miscible liquids whose boiling points differ by more than about 25 K. The mixture is heated; the liquid with the lower boiling point vaporises first, then condenses in the condenser and is collected separately. Filtration separates insoluble solids, and sublimation separates substances that sublime (like ammonium chloride).

📝 SolutionThe Tyndall effect is the scattering of a light beam by particles in its path, making the path visible. Colloidal particles are large enough to scatter light, so colloids (like milk or fog) show the Tyndall effect. True solutions have particles too small to scatter light, so the beam passes without becoming visible. This effect helps distinguish colloids from true solutions.

📝 SolutionAssertion (A) is true — compounds have fixed composition while mixtures can vary. Reason (R) is also true and states exactly why: in a compound, elements combine chemically in a fixed mass ratio (Law of Definite Proportions), but in a mixture the substances are only physically combined in any ratio. Since R gives the direct reason for A, R correctly explains A. Both true, R explains A.