Below are 30 short answer questions with concise, exam-focused answers for quick revision. Chemical formulas use _{and ^{tags for accuracy.}}

1. 1. What ion is released by acids in aqueous solution?
   Acids release hydrogen ions, H⁺, in aqueous solution which are responsible for acidic properties.
2. 2. What ion do bases produce in water?
   Bases produce hydroxide ions, OH⁻, in aqueous solution, giving them alkaline properties.
3. 3. Define a salt.
   A salt is an ionic compound formed when an acid reacts with a base, consisting of cations and anions (e.g., NaCl).
4. 4. Give one physical property common to most acids.
   Many acids taste sour and conduct electricity in aqueous solution due to the presence of ions.
5. 5. Give one physical property common to bases.
   Bases often feel slippery to touch and can be bitter; soluble bases conduct electricity in solution.
6. 6. Write the neutralisation reaction between HCl and NaOH.
   HCl + NaOH → NaCl + H₂O — an acid and a base react to form salt and water.
7. 7. What gas evolves when an acid reacts with a carbonate?
   Carbon dioxide (CO₂) is released when an acid reacts with a carbonate (e.g., CaCO₃ + 2HCl).
8. 8. State the pH of a neutral solution.
   The pH of a neutral solution (pure water) is 7 at 25°C.
9. 9. How is pH related to hydrogen ion concentration?
   pH = −log₁₀[H⁺]; a tenfold change in [H⁺] changes pH by 1 unit.
10. 10. What colour change does blue litmus show in acid?
    Blue litmus turns red in acidic solutions.
11. 11. What does phenolphthalein indicate in a basic solution?
    Phenolphthalein turns pink in basic solutions (around pH > ~8.2).
12. 12. Define strong and weak acids briefly.
    Strong acids ionise almost completely in water (e.g., HCl); weak acids ionise partially (e.g., CH₃COOH).
13. 13. Why do acids conduct electricity?
    Because they ionise in water to produce ions (H⁺ and anions) which carry electric current.
14. 14. Give one use of sodium chloride.
    Sodium chloride (NaCl) is used as table salt and preservative and as a raw material in chemical industries.
15. 15. What is an amphoteric substance?
    An amphoteric substance reacts with both acids and bases, e.g., zinc oxide (ZnO) and aluminium hydroxide (Al(OH)₃).
16. 16. Give the reaction of zinc with hydrochloric acid.
    Zn + 2HCl → ZnCl₂ + H₂ (hydrogen gas is liberated and zinc chloride forms).
17. 17. How is copper(II) sulfate (CuSO₄) prepared from copper and sulphuric acid?
    Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O (reaction with concentrated acid gives copper sulfate and SO₂).
18. 18. What happens when a strong acid reacts with a strong base?
    They neutralise each other to form a neutral salt and water; the reaction is generally exothermic.
19. 19. Explain why NaCl solution is neutral.
    NaCl comes from a strong acid (HCl) and a strong base (NaOH); neither ion hydrolyses significantly, so the solution is neutral (pH ~7).
20. 20. What is salt hydrolysis?
    Salt hydrolysis is reaction of salt ions with water causing the solution to become acidic or basic depending on parent acid/base strengths.
21. 21. Give one example of natural indicator and its source.
    Red cabbage extract is a natural indicator; it shows different colours across pH range and is used in experiments.
22. 22. How does antacid relieve acidity? Give one chemical example.
    Antacids neutralise excess stomach acid; e.g., Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O, reducing acidity and relieving heartburn.
23. 23. What is Plaster of Paris and how is it prepared?
    Plaster of Paris (CaSO₄·½H₂O) is made by heating gypsum (CaSO₄·2H₂O) to remove part of its water of crystallisation.
24. 24. State one industrial use of sodium hydroxide (NaOH).
    NaOH is used in soap and detergent manufacture, paper production, and in chemical processes such as saponification and neutralisation.
25. 25. Why is it advised to add acid to water, not water to acid?
    Adding water to concentrated acid can cause violent exothermic splashing; adding acid to water ensures heat is absorbed by the larger volume, reducing risk.
26. 26. How is baking soda (NaHCO₃) useful in everyday life?
    Baking soda is used in baking as a leavening agent, as an antacid, and for cleaning due to its mild alkaline and buffering properties.
27. 27. What colour change does methyl orange show in an acidic solution?
    Methyl orange turns red in acidic solutions and yellow in basic solutions.
28. 28. Give the equation for reaction of hydrochloric acid with calcium carbonate.
    2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂ (effervescence due to CO₂ evolution).
29. 29. What is the basicity of H₂SO₄ and what salts can it form?
    H₂SO₄ is dibasic (two replaceable H⁺). It can form salts like NaHSO₄ (acidic salt) and Na₂SO₄ (neutral salt).
30. 30. How does rain become acidic and what is one major effect?
    Rain becomes acidic when SO₂ and NO_x gases oxidise to form H₂SO₄ and HNO₃; acid rain lowers soil and water pH, harming ecosystems and corroding buildings.