Ans: Iron displaces hydrogen from HCl. Fe + 2HCl → FeCl₂ + H₂↑. A pale green solution of ferrous chloride is formed and hydrogen gas is evolved.

Ans: Baking soda (NaHCO₃) is heated: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂. Na₂CO₃ is then recrystallised with 10 water molecules to form washing soda (Na₂CO₃·10H₂O).

Ans: Plaster of Paris is CaSO₄·½H₂O. It is a white powder that reacts with water to form gypsum (CaSO₄·2H₂O), a hard solid. Uses: Making casts for fractured bones, making chalk, for decorations and sculptures.

Ans: Hydrogen gas is evolved with bubbles when warmed. 2NaOH + Zn → Na₂ZnO₂ + H₂. Sodium zincate is formed along with hydrogen gas.

Ans: Bleaching powder (calcium oxychloride, Ca(ClO)Cl) is prepared by passing chlorine gas over dry slaked lime: Ca(OH)₂ + Cl₂ → Ca(ClO)Cl + H₂O. Formula: Ca(ClO)Cl. Uses: (1) Bleaching cotton and linen in the textile industry. (2) Disinfecting drinking water (kills bacteria). (3) As an oxidising agent in the chemical industry. (4) Bleaching wood pulp in paper manufacture.

Ans: (a) Strong acids: Completely ionise in aqueous solution to give maximum H⁺ ions. Examples: HCl, H₂SO₄, HNO₃. HCl → H⁺ + Cl⁻ (100% ionisation). Weak acids: Partially ionise in aqueous solution, giving fewer H⁺ ions. Examples: CH₃COOH (acetic acid), H₂CO₃ (carbonic acid), H₃PO₄. CH₃COOH ⇌ CH₃COO⁻ + H⁺ (partial — equilibrium). (b) Dilute acid: Has a small amount of acid dissolved in a large amount of water — low concentration of H⁺ ions. Concentrated acid: Has a large amount of acid with little water — high concentration of H⁺ ions (e.g., conc. H₂SO₄). Note: A concentrated weak acid can still be less corrosive than a dilute strong acid.

Ans: Universal indicator: A mixture of several indicators (phenolphthalein, methyl orange, methyl red, bromothymol blue, thymol blue) that shows a gradual change of colour over a wide pH range (pH 1–14). It gives different colours for different pH values — can measure the approximate pH of a solution. Litmus: A single indicator that only tells whether a substance is acidic (turns red) or basic (turns blue) — it cannot measure the actual pH value. Litmus cannot differentiate between strongly and weakly acidic/basic solutions. Universal indicator is more informative and used when pH measurement is needed.

Ans: When CO₂ is passed through lime water (Ca(OH)₂), it first turns milky due to formation of insoluble calcium carbonate (CaCO₃): Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. When excess CO₂ is passed, the milky precipitate dissolves and the solution becomes clear again, forming soluble calcium bicarbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂ (soluble). This is a confirmatory test for CO₂.

Ans: Acidic solutions have a pH less than 7 (from 0 up to just below 7).

Ans: Washing soda (sodium carbonate decahydrate, Na₂CO₃·10H₂O).

Ans: Mixing acid with water is a highly exothermic process. If water is added to concentrated acid, the heat released can cause the mixture to splash out and cause burns, and may break the glass container. Adding acid slowly to water with constant stirring dissipates the heat safely.

Ans: On dilution, the concentration of H₃O⁺ ions per unit volume decreases because the same number of ions is spread in a larger volume. As a result the acid becomes weaker in concentration and its pH increases.

Ans: X = calcium carbonate (CaCO₃), Y = calcium chloride (CaCl₂), Z = calcium carbonate (CaCO₃). CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The CO₂ evolved turns lime water milky: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. If excess CO₂ is passed, the milkiness disappears due to formation of soluble calcium hydrogencarbonate.

Ans: The reaction will be faster in test tube A with hydrochloric acid. HCl is a strong acid that ionises completely and provides a higher concentration of H⁺ ions, whereas acetic acid is a weak acid that ionises only partly. So more hydrogen gas bubbles are formed per second in A.

Ans: Bleaching powder: calcium oxychloride, CaOCl₂; used for disinfecting drinking water and bleaching fabrics. Baking soda: sodium hydrogencarbonate, NaHCO₃; used in baking powder and as an antacid. Washing soda: sodium carbonate decahydrate, Na₂CO₃·10H₂O; used to remove permanent hardness of water and in glass and soap industries. Plaster of Paris: calcium sulphate hemihydrate, CaSO₄·½H₂O; used for supporting fractured bones and making toys and decorative items.