Answer: Neutralisation is the chemical reaction between an acid and a base that produces a salt and water, often releasing heat. For example, hydrochloric acid reacting with sodium hydroxide forms sodium chloride and water: HCl + NaOH → NaCl + H₂O. In a titration experiment, a measured volume of acid is placed in a flask with an indicator (like phenolphthalein), and a base of known concentration is added from a burette until the end point (colour change) shows neutralisation. Applications include determining concentrations of unknown solutions, manufacturing salts, treating acidic soils with lime, and neutralising acidic industrial effluents.

Answer: Strength refers to the degree of ionisation of an acid or base in water: strong acids/bases ionise almost completely (e.g., HCl, NaOH) while weak ones ionise partially (e.g., CH₃COOH, NH₄OH). Concentration refers to the amount (moles) of substance present per litre of solution (molarity). A concentrated weak acid may contain more molecules but still produce fewer ions than a dilute strong acid. pH depends on [H⁺] — strong acids at the same concentration yield lower pH. Conductivity depends on ion concentration: more ions → higher conductivity. Thus both properties affect observable behaviour but describe different qualities.

Answer: Acids react with metals (above hydrogen in reactivity series) to produce salts and hydrogen gas, e.g., Zn + 2HCl → ZnCl₂ + H₂. With metal oxides (basic oxides), acids form salt and water: CuO + 2HCl → CuCl₂ + H₂O. With carbonates/bicarbonates acids yield salt, CO₂ and water: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. Practical uses include metal extraction, acid cleaning of surfaces, laboratory tests (CO₂ effervescence to detect carbonates), and antacid chemistry where carbonates neutralise stomach acid producing CO₂.

Answer: pH is a logarithmic measure of hydrogen ion concentration in solution. By definition, pH = −log₁₀[H⁺]. This arises because [H⁺] in aqueous solutions spans many orders of magnitude; the negative log compresses the scale to convenient numbers (0–14). For [H⁺] = 3.16×10⁻⁴, pH = −log(3.16×10⁻⁴) = −(log 3.16 + log 10⁻⁴) ≈ −(0.5 − 4) = 3.5. Thus the solution is acidic. Remember: lower pH → higher [H⁺].

Answer: Indicators are substances that change colour at specific pH ranges due to differing ionic forms. Litmus is a general indicator: red in acidic and blue in basic solutions. Phenolphthalein is colourless in acidic/neutral media and turns pink in basic solutions (transition ~pH 8.2–10), making it suitable for titrations involving strong acid with strong/weak base. Methyl orange changes from red in acid to yellow in base (transition ~pH 3.1–4.4), useful for titrations of strong acid with weak base. Selection depends on equivalence point pH of the titration so the endpoint matches the indicator's transition range.

Answer: Salt hydrolysis is the reaction of ions from a dissolved salt with water that produces H⁺ or OH⁻ ions, altering the pH. NH₄Cl dissociates to NH₄⁺ and Cl⁻; NH₄⁺ can donate a proton to water: NH₄⁺ + H₂O ⇌ NH₃ + H⁺, making the solution acidic. Na₂CO₃ gives CO₃²⁻ that reacts: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻, producing OH⁻ and making the solution basic. Thus salts can be acidic, basic or neutral based on parent acid/base strengths.

Answer: Amphoteric substances react with both acids and bases. ZnO reacts with acid: ZnO + 2HCl → ZnCl₂ + H₂O, and with base forming complex ions: ZnO + 2NaOH + H₂O → Na₂[Zn(OH)₄]. Aluminium hydroxide behaves similarly: Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O (with acid), and Al(OH)₃ + NaOH → Na[Al(OH)₄] (with base). Amphoterism is important for refining metals and waste treatment.

Answer: Prepare Na₂SO₄ by neutralising dilute H₂SO₄ with NaOH: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. Procedure: add NaOH solution slowly to measured H₂SO₄ with stirring; check pH with indicator until neutral (pH 7). Filter any impurities, evaporate the filtrate to concentrate, then cool to crystallise Na₂SO₄. Observations: on evaporation, salt crystals appear; cooling yields well-formed crystals. Dry and collect crystals for use.

Answer: Electrical conduction in liquids requires mobile charged particles (ions). Acids ionise in water producing H⁺ and corresponding anions; for example HCl → H⁺ + Cl⁻. These ions move under an electric field and carry charge, causing current. Pure water has very low [H⁺] and [OH⁻] (10⁻⁷ M), so it is a poor conductor. Strong acids produce many ions and conduct well; weak acids produce fewer ions and conduct poorly compared to strong acids at the same concentration.

Answer: Acid rain forms when sulfur dioxide (SO₂) and nitrogen oxides (NO_x) from combustion react with water vapour and oxygen in the atmosphere to form sulfuric (H₂SO₄) and nitric acids (HNO₃): SO₂ + H₂O + ½O₂ → H₂SO₄. Acid rain lowers soil and water pH, damages vegetation, corrodes buildings and monuments (particularly limestone and marble), and harms aquatic life. Mitigation includes reducing emissions (scrubbers, cleaner fuels) and liming acidic soils and lakes to restore pH balance.

Answer: Baking soda (NaHCO₃) is prepared industrially by the Solvay process and can be produced by passing CO₂ into concentrated Na₂CO₃ solution: Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃. It is a white crystalline solid, mildly alkaline, decomposes on heating to produce Na₂CO₃, CO₂ and H₂O. Uses: as a leavening agent in baking (CO₂ release), an antacid to neutralise stomach acid, and in cleaning and fire extinguishers due to CO₂ release.

Answer: Plaster of Paris (POP) is obtained by heating gypsum (CaSO₄·2H₂O) to about 373 K to remove water of crystallisation: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O. When mixed with water, POP undergoes hydration to reform gypsum, setting to a hard mass: 2(CaSO₄·½H₂O) + 3H₂O → 2CaSO₄·2H₂O. Uses include casts for broken bones, moulds, sculptures, and building materials. The setting is exothermic and forms interlocking crystals that harden quickly.

Answer: Sea water is channelled into shallow ponds where solar evaporation concentrates salts. As water evaporates, different salts precipitate; NaCl crystallises out when concentration is suitable. Crude salt contains impurities and is dissolved in water, filtered to remove insolubles, and recrystallised by controlled evaporation to obtain purified NaCl. Further washing and drying yield food-grade salt. Rock salt (halite) is another source. Salt is used for cooking, preservation, and as a raw material in chemical industries (NaOH, Cl₂ production).

Answer: NaCl is formed from a strong acid (HCl) and a strong base (NaOH); its ions (Na⁺, Cl⁻) do not hydrolyse significantly, so solution remains neutral (pH ~7). NH₄Cl comes from a strong acid (HCl) and a weak base (NH₃). The NH₄⁺ ion hydrolyses: NH₄⁺ + H₂O ⇌ NH₃ + H⁺, increasing [H⁺] and making solution acidic. Thus nature of parent acid and base determines salt hydrolysis and final pH.

Answer: Titration is a technique to find unknown concentration by reacting with a solution of known concentration. Procedure: Pipette a measured volume of HCl into a conical flask, add a few drops of phenolphthalein indicator, and place standard NaOH in a burette. Add NaOH slowly while swirling until a persistent faint pink appears (end point). Record volume of NaOH used. Use formula M₁V₁ = M₂V₂ (for 1:1 reaction) to calculate unknown acid concentration. Ensure accuracy by repeating and taking average volumes.

Answer: Concentrated acids and bases are corrosive and can cause severe burns, respiratory harm, and damage to materials. Precautions: wear goggles, gloves and lab coat; work in a fume hood or well-ventilated area; always add acid to water slowly to dilute (never water to acid) to prevent violent splattering; use appropriate containers and labels; neutralise spills with suitable reagents and dispose of waste correctly. These measures protect skin, eyes, and breathing and prevent accidents from exothermic dilution or violent reactions.

Answer: Chlorine reacts with cold dilute NaOH to form sodium hypochlorite (NaOCl), sodium chloride and water: Cl₂ + 2NaOH → NaCl + NaOCl + H₂O. NaOCl is a bleaching and disinfecting agent. With hot, concentrated NaOH, chlorine gives sodium chlorate (NaClO₃) and NaCl: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O. Sodium chlorate is used in herbicides and bleaching. These reactions are fundamental to chlor-alkali industry and water treatment.

Answer: Acids and bases maintain conditions necessary for biological processes. Example 1: Stomach acid (HCl, pH ~2) helps denature proteins and activate pepsin for digestion; excess acid causes heartburn and is treated with antacids. Example 2: Blood pH is tightly regulated (~7.35–7.45); enzymes and metabolic processes depend on this range. Buffers (bicarbonate system) resist pH changes; deviation leads to acidosis or alkalosis, impairing organ function. Thus acid–base balance is crucial for digestion, enzyme activity and homeostasis.

Answer: Salts form by various routes: (a) Neutralisation — acid + base → salt + water (HCl + NaOH → NaCl + H₂O). (b) Precipitation — mixing soluble salts to form an insoluble salt: AgNO₃ + NaCl → AgCl(s) + NaNO₃. (c) Acid–metal reaction — metal + acid → salt + H₂ (Zn + 2HCl → ZnCl₂ + H₂). Each method is used depending on desired salt solubility and purity; purification often follows via crystallisation or filtration.

Answer: (a) Universal indicator is a mixture that shows a spectrum of colours across pH 0–14, allowing approximate pH determination (red for strong acid, green ~7, purple for strong base). (b) Salts are vital: NaCl in food, NaHCO₃ in baking and medicine, CaCO₃ in building; industrially salts are raw materials for NaOH, Cl₂, fertilizers and detergents. (c) Basicity of an acid is the number of replaceable H⁺ per molecule: HCl is monobasic (1), H₂SO₄ is dibasic (2), H₃PO₄ is tribasic (3); basicity affects salt types formed.