Ans: The Tyndall effect is the scattering of a beam of light by colloidal particles, making the path of light visible. It is used to distinguish colloids from true solutions.

Ans: Centrifugation is used to separate cream from milk. Spinning forces the denser particles (milk) to settle, and the lighter cream rises to the top.

Ans: A saturated solution is one in which no more solute can dissolve at a given temperature. As temperature increases, solubility of most solid solutes increases (e.g., sugar in water), because more kinetic energy helps dissolve more solute. For gases, solubility decreases with rising temperature (e.g., less CO₂ dissolves in warm soda water).

Ans: Step 1: Add water — camphor does not dissolve but salt does; sand also does not dissolve. Step 2: Filter the mixture — sand is left on filter paper; camphor floats. Step 3: Sublimation — heat the filtrate to sublime camphor (it turns directly to vapour and is collected on a cold surface). Step 4: Evaporate the salt solution to get salt crystals. This uses filtration, sublimation, and evaporation/crystallisation.

Ans: Solutions: homogeneous, particle size <1 nm, transparent, no Tyndall effect, do not settle, cannot be filtered, e.g., salt water, sugar water. Colloids: appear homogeneous, particle size 1–100 nm, translucent, show Tyndall effect, do not settle, cannot be filtered by ordinary paper, e.g., milk, fog, blood. Suspensions: heterogeneous, particle size >100 nm, opaque/cloudy, settle on standing, can be filtered, e.g., chalk in water, muddy water. Key distinguishing test: shine a beam of light — colloids scatter it (Tyndall effect) while solutions do not.

Ans: Distilled water is a pure substance. Air, milk and brass are mixtures.

Ans: Chromatography. The dyes travel different distances on the paper because of different solubility, so they separate into bands.

Ans: When a mixture is spun rapidly, the denser particles are forced to the bottom and the lighter particles stay at the top. Applications: separating cream from milk, separating blood components in a diagnostic lab, squeezing water out of wet clothes in a dryer.

Ans: The particles of a true solution are smaller than 1 nm and too small to scatter light, so the beam is not visible. Colloidal particles (1–1000 nm) are large enough to scatter light, so the path of the beam becomes visible.

Ans: Mass of solution = 5 + 45 = 50 g. Mass percentage = (5 ÷ 50) × 100 = 10%.

Ans: Air is first cleared of dust, water vapour and carbon dioxide, then compressed and cooled to get liquid air. The liquid air is warmed slowly and fractionally distilled in a fractionating column. Nitrogen (boiling point about 77 K) boils off first, argon (about 87 K) next and oxygen (about 90 K) last, and each gas is collected separately.

Ans: Crystallisation is the process of obtaining pure solid crystals from a saturated solution by slow cooling. It is preferred to evaporation because evaporation may leave impurities, some solids decompose or get charred on heating to dryness, and crystals give a purer product. Application: purification of salt obtained from sea water, getting pure copper sulphate or alum crystals.

Ans: (1) Mixture: components are mixed in any proportion; compound: elements are combined in a fixed ratio by mass. (2) Mixture: components keep their original properties; compound: properties differ from the constituent elements. (3) Mixture: can be separated by physical methods; compound: can be broken down only by chemical methods. Also, a mixture forms without energy change, while a compound usually forms with a heat change.

Ans: Take a strip of filter paper, draw a pencil line near one end and put a small drop of black ink on it. Dip the end of the strip in water so that the ink spot stays above the water level. Water rises up the paper by capillary action and carries the dyes. Different dyes rise to different heights and separate into coloured bands. Principle: the components differ in solubility in the solvent and in their attraction to the paper, so they move at different rates. Chromatography is used to separate pigments, dyes, drugs and to detect adulterants.

Ans: A colloid is a heterogeneous mixture in which particles of size 1–1000 nm are spread in a medium. Properties: (1) Particles are too small to be seen individually and form a seemingly homogeneous mixture. (2) They show the Tyndall effect, i.e. scatter light. (3) They do not settle on standing because of Brownian motion. (4) They cannot be separated by ordinary filtration, but can be separated by centrifugation. Examples: milk (emulsion), fog (aerosol), butter (gel), smoke (aerosol), jelly (gel).