Acid, Base and Salt
Q1. Define acids.
A. Acids are substances that produce hydrogen ions (H⁺) in aqueous solution.
Q2. Define bases.
A. Bases are substances that produce hydroxide ions (OH⁻) in aqueous solution.
Q3. Give two examples of strong acids.
A. Hydrochloric acid (HCl) and Sulphuric acid (H₂SO₄).
Q4. Give two examples of strong bases.
A. Sodium hydroxide (NaOH) and Potassium hydroxide (KOH).
Q5. What are indicators?
A. Indicators are substances which change their colour in acidic or basic solutions.
Q6. Give one natural and one synthetic indicator example.
A. Natural – Litmus, Synthetic – Phenolphthalein.
Q7. What colour does blue litmus turn in acid?
A. It turns red.
Q8. What colour does red litmus turn in base?
A. It turns blue.
Q9. Define pH.
A. pH is the negative logarithm of hydrogen ion concentration in a solution.
Q10. State pH range of acids.
A. Less than 7.
Q11. State pH range of bases.
A. Greater than 7.
Q12. What is the pH of pure water at 25°C?
A. pH = 7 (neutral).
Q13. What is neutralisation reaction?
A. A reaction in which an acid reacts with a base to form salt and water.
Q14. Write a neutralisation reaction equation.
A. HCl + NaOH → NaCl + H₂O
Q15. Give the chemical formula of baking soda.
A. NaHCO₃ (Sodium bicarbonate).
Q16. Give the formula of washing soda.
A. Na₂CO₃·10H₂O (Sodium carbonate decahydrate).
Q17. Give the formula of bleaching powder.
A. CaOCl₂ (Calcium oxychloride).
Q18. What is the common name of Ca(OH)₂?
A. Slaked lime.
Q19. What happens when an acid reacts with a metal?
A. Salt and hydrogen gas are produced.
Q20. Write an example of acid-metal reaction.
A. Zn + H₂SO₄ → ZnSO₄ + H₂↑
Q21. What happens when an acid reacts with a carbonate?
A. Salt, water, and carbon dioxide gas are produced.
Q22. Give an example of acid-carbonate reaction.
A. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑
Q23. Why is HCl not stored in metal containers?
A. Because it reacts with metals producing hydrogen gas.
Q24. Why should acids be diluted by adding acid to water and not water to acid?
A. Adding water to acid can cause violent splashing due to heat released.
Q25. Give one use of baking soda.
A. Used in making cakes and as an antacid.
Q26. Give one use of washing soda.
A. Used in softening hard water.
Q27. Give one use of bleaching powder.
A. Used for disinfecting drinking water.
Q28. Why do acids conduct electricity?
A. Because they produce ions in aqueous solution which carry electric current.
Q29. Why are concentrated acids diluted before use?
A. To reduce their corrosive nature and make them safe for handling.
Q30. Why does tooth decay start when pH of mouth falls below 5.5?
A. Because the acidic environment dissolves the enamel made of calcium phosphate.