Language of Chemistry — Important Questions

Green to black

Step 1: Copper carbonate is a green-coloured solid compound. Step 2: When it is heated, a chemical reaction takes place – this is a thermal decomposition reaction. Step 3: The green copper carbonate breaks down into copper oxide (a black solid) and carbon dioxide gas (which escapes). Step 4: Word equation: Copper carbonate → Copper oxide + Carbon dioxide. Step 5: The change in colour from green to black is a characteristic sign that a chemical reaction has occurred. White, blue, and red are incorrect because none of the products of this reaction have those colours.

A strong effervescence (bubbles) is observed due to CO₂ gas

Step 1: Baking soda (sodium bicarbonate) is a compound commonly used in cooking and baking. Step 2: When it reacts with acetic acid (vinegar), a chemical reaction takes place. Step 3: One of the products of this reaction is carbon dioxide (CO₂) gas. Step 4: This CO₂ gas escapes rapidly from the liquid, causing strong effervescence (bubbling). Step 5: The word equation is: Sodium bicarbonate + Acetic acid → Sodium acetate + Water + Carbon dioxide. A yellow precipitate would form in a different reaction (like potassium iodide + lead acetate), and pungent smell is associated with ammonia, not CO₂

A yellow precipitate of lead iodide

Step 1: When two solutions are mixed and an insoluble solid forms, that solid is called a precipitate. Step 2: Potassium iodide solution (KI) and lead acetate solution are both clear liquids. Step 3: When they are mixed, a chemical reaction takes place and lead iodide is formed. Step 4: Lead iodide is an insoluble yellow solid, so it appears as a bright yellow precipitate at the bottom of the solution. Step 5: The word equation is: Potassium iodide + Lead acetate → Lead iodide (yellow precipitate) + Potassium acetate. A white precipitate forms in other reactions like barium chloride + sodium s

Heating of calcium carbonate to form calcium oxide and CO₂

Step 1: Chemical reactions can be classified based on energy change. Step 2: Exothermic reactions release energy (heat or light) to the surroundings – examples include burning of coal, magnesium burning, and adding water to quick lime. Step 3: Endothermic reactions absorb energy from the surroundings – heat must be supplied for the reaction to proceed. Step 4: Heating calcium carbonate to form calcium oxide and carbon dioxide requires continuous supply of heat, so it is endothermic. Step 5: Word equation: Calcium carbonate → Calcium oxide + Carbon dioxide (heat is absorbed). The other three op