Elements, Compounds and Mixtures — Important Questions

Sand and stone

Step 1: A heterogeneous mixture has components that are NOT uniformly distributed — you can see the components separately. Step 2: Sand and stone is heterogeneous because you can easily see and identify the sand particles and stones separately. Step 3: Salt solution is homogeneous — salt dissolves uniformly in water, you cannot see separate particles. Step 4: Air is a homogeneous mixture of gases — the gases are uniformly mixed. Step 5: Brass is an alloy (solid-solid homogeneous mixture) — copper and zinc are uniformly distributed. Only sand and stone shows non-uniform composition.

Common salt and water (recovering both components)

Step 1: Distillation is the process of heating a liquid to form vapour and then condensing the vapour back into a liquid — this allows BOTH solid and liquid to be recovered. Step 2: When salt water is heated, water evaporates and passes through a condenser where it is cooled and collected as pure distilled water. Salt remains in the flask. Step 3: This is different from evaporation, where only the solid (salt) is recovered and the liquid is lost as vapour. Step 4: Sand and water is separated by sedimentation/filtration, not distillation. Step 5: Iron and sulphur use magnetic separation; kerose

Silicon (Si)

Step 1: Metalloids are elements that show properties of BOTH metals and non-metals. Step 2: Silicon (Si) is a classic metalloid — it has some metallic properties (lustrous, hard solid) and some non-metallic properties (semiconductor, brittle). Step 3: Sodium (Na) is a metal — it is soft, reactive, and a good conductor of electricity. Step 4: Sulphur (S) is a non-metal — it is a yellow solid, bad conductor of electricity, and non-lustrous. Step 5: Argon (Ar) is a noble gas — it is inert, monoatomic, and does not react with other elements. Other examples of metalloids include Boron (B), Germaniu

Sublimation

Step 1: Sublimation is the process where a solid directly converts to vapour on heating, without passing through the liquid state. Step 2: Ammonium chloride (NH₄Cl) is a substance that sublimes — it converts directly to vapour when heated. Step 3: Common salt (NaCl) does NOT sublime — it remains as a solid in the dish when heated. Step 4: When the mixture is heated in a covered dish with an inverted funnel, ammonium chloride vapours rise and condense on the cooler neck of the funnel as a solid. Common salt remains in the dish. Step 5: Filtration works for insoluble solids in liquids; magnetic