Class 10 Science – Acids, Bases and Salts: Important Questions

Q1. A solution turns red litmus paper blue. Its pH is most likely to be:

Q2. Which of the following is a natural acid-base indicator?

Q3. Which gas is generally evolved when a dilute acid reacts with a reactive metal?

Q4. When an acid reacts with a metal carbonate, the products are generally:

Q5. Which ion is responsible for the acidic character of an aqueous solution?

Q6. Which medicine is commonly used to neutralise excess acid in the stomach?

Q7. The chemical formula of baking soda is:

Q8. Which salt is used to remove permanent hardness of water?

Q9. Tooth decay starts when the pH of the mouth falls below approximately:

Q10. The fixed number of water molecules present in one formula unit of a salt is called:

Q11. What are acid-base indicators? Name two natural indicators and two synthetic indicators.

Q12. What are olfactory indicators? Give two examples.

Q13. Why does dry HCl gas not change the colour of dry blue litmus paper?

Q14. Why do aqueous solutions of acids conduct electricity? Why do glucose and alcohol solutions not show the same behaviour in the chapter's experiment?

Q15. Define neutralisation. Write one balanced chemical equation to illustrate it.

Q16. What is an alkali? How is it different from a base?

Q17. What is water of crystallisation? Give the chemical formula of hydrated copper sulphate.

Q18. What is the difference between a strong acid and a weak acid? Explain in terms of the hydrogen ions produced in solution.

Q19. Explain the reaction of acids with metals. Write a balanced equation for the reaction of zinc with dilute sulphuric acid and state how the gas evolved can be tested.

Q20. What happens when a metal carbonate reacts with a dilute acid? Write a balanced equation for the reaction of sodium carbonate with hydrochloric acid.

Q21. Explain the reaction of a metallic oxide with an acid. Use copper(II) oxide and hydrochloric acid as an example and write the balanced equation.

Q22. Explain the pH scale. Differentiate between acidic, neutral and basic solutions using their pH values.

Q23. Why should concentrated acid be added slowly to water and not water to concentrated acid? Explain the danger involved.

Q24. Explain why:

1. Tooth decay begins when the pH of the mouth falls below 5.5.
2. Basic toothpaste can help prevent tooth decay.
3. Antacids provide relief from indigestion caused by excess stomach acid.

Q25. What is the chlor-alkali process? Write the balanced chemical equation and name the three products formed during the electrolysis of brine.

Q26. What happens when baking soda is heated? Write the balanced chemical equation and mention two uses of baking soda.

Q27. State three important uses of washing soda. Write its chemical formula.

Q28. Chemical Properties of Acids

Describe the reactions of acids with the following, giving one balanced chemical equation for each:

1. Metals
2. Metal carbonates
3. Metal hydrogencarbonates
4. Bases
5. Metallic oxides

Q29. pH in Everyday Life

Explain the importance of pH in the following situations:

1. Digestion in the stomach
2. Tooth decay
3. Growth of plants and soil treatment
4. Survival of aquatic organisms during acid rain
5. Relief from a bee sting using a mild base

Q30. Common Salt and Its Products

Common salt is an important raw material for several useful chemicals. Explain the preparation, chemical formula and any two uses of each of the following:

1. Sodium hydroxide
2. Bleaching powder
3. Baking soda
4. Washing soda

Q31. Plaster of Paris and Water of Crystallisation

1. What is water of crystallisation?
2. What happens when hydrated copper sulphate crystals are heated?
3. Write the formula of gypsum.
4. How is Plaster of Paris prepared from gypsum?
5. Write the equation for the reaction of Plaster of Paris with water and mention two uses of Plaster of Paris.

Q32. Chemical Equations and Observations

Write balanced chemical equations for the following reactions and mention one important observation wherever applicable:

1. Zinc with dilute hydrochloric acid
2. Sodium carbonate with dilute hydrochloric acid
3. Sodium hydroxide with hydrochloric acid
4. Carbon dioxide with lime water
5. Heating sodium hydrogencarbonate

Q33. Case Study: Identifying Solutions Using pH

A student tests four solutions using a universal indicator and records their pH values as 2, 7, 9 and 12.

1. Which solution is the most acidic?
2. Which solution is neutral?
3. Which solution is the most basic?
4. Which solution has the highest hydrogen-ion concentration?
5. What happens to the pH of an acidic solution when it is diluted with water?

Q34. Case Study: A Metal Carbonate and an Acid

A student adds dilute hydrochloric acid to a white sample of a metal carbonate. Effervescence occurs. The gas produced turns lime water milky.

1. Identify the gas evolved.
2. What does the milky appearance of lime water indicate?
3. Write the balanced equation for the reaction of sodium carbonate with hydrochloric acid.
4. Write the equation for the reaction of carbon dioxide with lime water.
5. What happens when excess carbon dioxide is passed through lime water?

Q35. HOTS: Reasoning and Application

1. Two solutions have pH values of 4 and 6. Which is more acidic? Explain.
2. Why does an aqueous acid solution conduct electricity while dry HCl gas does not show acidic behaviour with dry litmus paper?
3. Why are sour food items not stored in brass or copper vessels?
4. A farmer finds that the soil in a field is too acidic. Name a substance that can be added to treat the soil, as described in the chapter.
5. Why is a salt formed from a strong acid and a strong base generally neutral?

Q36. HOTS: Salts and Their Uses

Identify the substances described below and write their chemical formulae:

1. A salt used to disinfect drinking water.
2. A mild basic salt used in antacids and baking.
3. A salt used for removing permanent hardness of water.
4. A substance used to support fractured bones and make decorative items.
5. A hydrated salt that is blue but becomes white on heating and regains its blue colour on adding water.

Q37. Complete and balance the following equations:

(a) Zinc + dilute sulphuric acid →

(b) Sodium hydroxide + hydrochloric acid →

(c) Sodium carbonate + hydrochloric acid →

(d) Calcium hydroxide + carbon dioxide →

(e) Sodium hydrogencarbonate — heat →

(f) Sodium chloride solution + water — electrolysis →

(g) Calcium hydroxide + chlorine →

(h) Plaster of Paris + water →

Q38. Write balanced chemical equations for the preparation or reactions of the following compounds. Include the required conditions wherever mentioned in your NCERT text.

1. Bleaching powder
2. Baking soda
3. Washing soda from sodium carbonate
4. Plaster of Paris from gypsum