Preparing for your Class 10 Science Board Exam or Pre-Board Exam? This comprehensive collection of Acids, Bases and Salts Class 10 Important Questions with Answers is designed for quick revision and exam preparation.
In this chapter, students need to understand important concepts such as acid-base indicators, chemical properties of acids and bases, reactions of acids with metals and metal carbonates, neutralisation reactions, hydrogen ions, hydronium ions, hydroxide ions, pH scale, strong and weak acids, importance of pH in everyday life, salts and their properties.
The chapter also covers the highly important chemistry of common salt, chlor-alkali process, sodium hydroxide, bleaching powder, baking soda, washing soda, water of crystallisation, gypsum and Plaster of Paris. The questions below are organised topic-wise so that you can revise Class 10 Acids, Bases and Salts efficiently before examinations.
THE BUSY BRAINS • BY MANSI SARASWAT
CLASS 10 ACIDS, BASES AND SALTS
Important Questions with Answers
CBSE Science | Pre-Board & Board Exam Preparation
NCERT-Based • Exam-Focused • Quick Revision1. Acids, Bases and Indicators
Q1. What are acids?
Answer: Acids are substances that show acidic properties. They change
blue litmus to red and produce hydrogen ions in aqueous solution.
Q2. What are bases?
Answer: Bases are substances that show basic properties. They change
red litmus to blue and produce hydroxide ions in water.
Q3. What is an indicator?
Answer: An indicator is a dye or a mixture of dyes used to indicate
the presence of an acid or a base by a characteristic change such as colour.
Q4. Name two natural indicators.
Answer: Litmus and turmeric are natural indicators.
Q5. Name two synthetic indicators.
Answer: Methyl orange and phenolphthalein.
Q6. What are olfactory indicators?
Answer: Substances whose odour changes in acidic or basic media
are called olfactory indicators.
Q7. Give examples of substances that can act as olfactory indicators.
Answer: Onion, vanilla essence and clove oil are discussed in the chapter
as substances that can be tested for olfactory indicator behaviour.
Q8. What happens to blue litmus in an acidic solution?
Answer: Blue litmus turns red.
Q9. What happens to red litmus in a basic solution?
Answer: Red litmus turns blue.
Q10. What is litmus?
Answer: Litmus is a natural dye extracted from lichen and is commonly
used as an acid-base indicator.
Q11. How can three test tubes containing distilled water, an acid and a base be identified using only red litmus paper?
Answer: Put a drop of each solution on red litmus paper.
The solution that turns red litmus blue is the base. The solution that
does not change the red litmus can be either water or acid. To distinguish
between them, use the blue litmus made blue by the basic solution:
the acid will turn it red, while distilled water will not produce the acidic
colour change.
2. Chemical Properties of Acids and Bases
Q12. What happens when an acid reacts with a metal?
Answer: An acid reacts with a suitable metal to form a salt and
hydrogen gas.
Acid + Metal → Salt + Hydrogen gas
Q13. Which gas is usually liberated when an acid reacts with a metal?
Answer: Hydrogen gas.
Q14. How can hydrogen gas be tested?
Answer: Bring a burning candle near the gas. Hydrogen burns with
a characteristic pop sound.
Q15. What happens when zinc reacts with dilute sulphuric acid?
Answer: Zinc reacts with dilute sulphuric acid to form zinc sulphate
and hydrogen gas.
Zn + H2SO4 → ZnSO4 + H2
Q16. What happens when zinc reacts with sodium hydroxide solution?
Answer: Zinc reacts with sodium hydroxide on warming to form
sodium zincate and hydrogen gas.
2NaOH + Zn → Na2ZnO2 + H2
Q17. What is the general reaction between a metal carbonate and an acid?
Answer: A metal carbonate reacts with an acid to form a corresponding
salt, carbon dioxide and water.
Metal carbonate + Acid → Salt + CO2 + H2O
Q18. What is the general reaction between a metal hydrogencarbonate and an acid?
Answer: It gives the corresponding salt, carbon dioxide and water.
Q19. How can carbon dioxide be tested?
Answer: Pass the gas through lime water. Lime water turns milky
due to formation of calcium carbonate.
Ca(OH)2 + CO2 → CaCO3 + H2O
Q20. What happens when excess carbon dioxide is passed through lime water?
Answer: The calcium carbonate precipitate reacts with excess carbon
dioxide and water to form soluble calcium hydrogencarbonate.
CaCO3 + H2O + CO2
→ Ca(HCO3)2
3. Acids with Metals – Important Questions
Q21. Why are bubbles formed when zinc is added to dilute sulphuric acid?
Answer: The bubbles are formed because hydrogen gas is evolved
during the reaction of zinc with dilute sulphuric acid.
Q22. Why should the gas produced in the zinc-acid experiment be tested carefully?
Answer: The gas is hydrogen, which is combustible. The NCERT activity
specifically indicates that this experiment needs teacher assistance.
Q23. Write the reaction between magnesium and dilute hydrochloric acid.
Answer:
Mg + 2HCl → MgCl2 + H2
Q24. Write the reaction between iron and dilute hydrochloric acid.
Answer:
Fe + 2HCl → FeCl2 + H2
Q25. Write the reaction between aluminium and dilute sulphuric acid.
Answer:
2Al + 3H2SO4 → Al2(SO4)3 + 3H2
4. Metal Carbonates and Hydrogencarbonates
Q26. What happens when sodium carbonate reacts with hydrochloric acid?
Answer: Sodium carbonate reacts with hydrochloric acid to form
sodium chloride, water and carbon dioxide.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
Q27. What happens when sodium hydrogencarbonate reacts with hydrochloric acid?
Answer: Sodium hydrogencarbonate reacts with hydrochloric acid to
form sodium chloride, water and carbon dioxide.
NaHCO3 + HCl → NaCl + H2O + CO2
Q28. Why does lime water turn milky when carbon dioxide is passed through it?
Answer: Carbon dioxide reacts with calcium hydroxide to form
insoluble calcium carbonate, producing a milky appearance.
Q29. Name three forms of calcium carbonate mentioned in the chapter.
Answer: Limestone, chalk and marble.
Q30. Complete the reaction: Metal hydrogencarbonate + Acid → ?
Answer: Salt + Carbon dioxide + Water.
5. Neutralisation and Oxides
Q31. What is a neutralisation reaction?
Answer: The reaction between an acid and a base to form salt
and water is called a neutralisation reaction.
Acid + Base → Salt + Water
Q32. Give one example of a neutralisation reaction.
Answer:
NaOH + HCl → NaCl + H2O
Q33. What happens when copper oxide reacts with dilute hydrochloric acid?
Answer: Copper oxide dissolves and a blue-green solution of
copper(II) chloride is formed along with water.
CuO + 2HCl → CuCl2 + H2O
Q34. Why are metallic oxides called basic oxides?
Answer: Metallic oxides react with acids to give salt and water,
similar to the reaction of a base with an acid. Therefore, metallic oxides
are considered basic oxides.
Q35. What is the nature of non-metallic oxides?
Answer: Non-metallic oxides are generally acidic in nature.
For example, carbon dioxide reacts with calcium hydroxide to produce
salt and water.
6. Hydrogen Ions, Hydronium Ions and Hydroxide Ions
Q36. Why do acids show acidic character in aqueous solution?
Answer: Acids produce hydrogen ions in aqueous solution.
These hydrogen ions are responsible for their acidic properties.
Q37. What ion is common to all acids in aqueous solution?
Answer: H+(aq), represented in water as hydronium ion H3O+.
Q38. Why do hydrogen ions not exist alone in water?
Answer: Hydrogen ions combine with water molecules to form
hydronium ions.
H+ + H2O → H3O+
Q39. Write the reaction of HCl with water.
HCl + H2O → H3O+ + Cl−
Q40. What ions are produced when sodium hydroxide dissolves in water?
Answer: Sodium ions and hydroxide ions.
NaOH → Na+(aq) + OH−(aq)
Q41. What are alkalis?
Answer: Bases that are soluble in water are called alkalis.
Q42. Why does an aqueous acid conduct electricity?
Answer: An aqueous acid contains ions. The movement of these ions
allows electric current to pass through the solution.
Q43. Why do glucose and alcohol solutions not show acidic character even though they contain hydrogen?
Answer: They do not produce H+(aq) ions in aqueous solution
in the way acids do. Therefore, they do not show acidic behaviour.
Q44. Why does dry HCl gas not change the colour of dry blue litmus paper?
Answer: HCl produces hydrogen ions in the presence of water.
In the absence of water, the separation of H+ ions from HCl molecules
does not occur, so dry HCl gas does not show acidic behaviour on dry litmus.
7. pH Scale and Strength of Acids and Bases
Q45. What is the pH scale?
Answer: The pH scale is a scale used to indicate the acidic or
basic nature of a solution. It generally ranges from 0 to 14.
Q46. What is the pH of a neutral solution?
Answer: 7.
Q47. What pH values indicate an acidic solution?
Answer: pH values less than 7 indicate an acidic solution.
Q48. What pH values indicate a basic solution?
Answer: pH values greater than 7 indicate a basic solution.
Q49. What is the relationship between hydronium ion concentration and pH?
Answer: Higher hydronium ion concentration corresponds to a lower
pH value.
Q50. What is a universal indicator?
Answer: A universal indicator is a mixture of several indicators
that shows different colours at different hydrogen ion concentrations.
Q51. What is a strong acid?
Answer: An acid that produces a relatively larger amount of
H+ ions in solution is called a strong acid.
Q52. What is a weak acid?
Answer: An acid that produces a relatively smaller amount of
H+ ions in solution is called a weak acid.
Q53. Which has more hydrogen ion concentration: pH 3 or pH 5?
Answer: The solution with pH 3 has higher hydrogen ion concentration.
Q54. Solution A has pH 6 and solution B has pH 8. Which has more hydrogen ion concentration?
Answer: Solution A, because lower pH means higher hydronium/hydrogen
ion concentration.
Q55. Arrange pH values 1, 4, 7, 9 and 11 in increasing order of hydrogen ion concentration.
Answer: 11 < 9 < 7 < 4 < 1.
As pH decreases, hydrogen ion concentration increases.
Q56. What happens to hydronium ion concentration when an acid is diluted?
Answer: The concentration of hydronium ions decreases.
Q57. What happens to hydroxide ion concentration when excess base is dissolved in sodium hydroxide solution?
Answer: The concentration of hydroxide ions increases.
Q58. Why should acid be added to water while diluting it?
Answer: Mixing concentrated acid with water is highly exothermic.
Adding acid slowly to water with constant stirring helps distribute the
heat safely. Adding water to concentrated acid can cause rapid heating
and splashing.
⭐ BOARD EXAM TIP:
Remember the pH relationship:
Lower pH → higher H+/H3O+ concentration → more acidic.
Higher pH → greater OH− concentration → more basic.
Higher pH → greater OH− concentration → more basic.
8. Importance of pH in Everyday Life
Q59. What is the normal pH range of our body mentioned in the chapter?
Answer: Our body works within a pH range of about 7.0 to 7.8.
Q60. What is acid rain?
Answer: Rain water having pH less than 5.6 is called acid rain.
Q61. Why can acid rain be harmful to aquatic life?
Answer: Acid rain can lower the pH of river water, making conditions
difficult for aquatic organisms to survive.
Q62. Why does our stomach contain hydrochloric acid?
Answer: Hydrochloric acid is produced in the stomach and helps in
the digestion of food.
Q63. What are antacids?
Answer: Antacids are mild bases used to neutralise excess acid in
the stomach and provide relief from indigestion.
Q64. Give one example of an antacid mentioned in the chapter.
Answer: Magnesium hydroxide, commonly known as milk of magnesia.
Q65. At what pH does tooth decay begin according to the chapter?
Answer: Tooth decay starts when the pH of the mouth falls below 5.5.
Q66. How do basic toothpastes help prevent tooth decay?
Answer: Basic toothpastes can neutralise excess acid in the mouth,
helping to prevent tooth decay.
Q67. Which acid is present in an ant sting?
Answer: Methanoic acid.
Q68. Why can baking soda provide relief from a bee sting?
Answer: Baking soda is mildly basic and can neutralise the acid
responsible for the irritation.
| Natural Source | Acid |
|---|---|
| Vinegar | Acetic acid |
| Sour milk / Curd | Lactic acid |
| Orange | Citric acid |
| Lemon | Citric acid |
| Tamarind | Tartaric acid |
| Ant sting | Methanoic acid |
| Tomato | Oxalic acid |
| Nettle sting | Methanoic acid |
9. Salts and Family of Salts
Q69. What is a salt?
Answer: A salt is a compound formed in reactions such as
neutralisation and other acid-base reactions.
Q70. What is meant by a family of salts?
Answer: Salts having the same positive or negative radical are said
to belong to the same family.
Q71. NaCl and Na2SO4 belong to which family?
Answer: They belong to the family of sodium salts because both contain
the sodium ion.
Q72. NaCl and KCl belong to which family?
Answer: They belong to the family of chloride salts.
Q73. What is the pH of a salt formed from a strong acid and a strong base?
Answer: Such a salt is neutral with pH 7.
Q74. What is the nature of a salt formed from a strong acid and a weak base?
Answer: It is acidic and has pH less than 7.
Q75. What is the nature of a salt formed from a strong base and a weak acid?
Answer: It is basic and has pH greater than 7.
10. Common Salt and Chlor-Alkali Process
Q76. What is common salt?
Answer: Common salt is sodium chloride, NaCl.
Q77. What is rock salt?
Answer: Large deposits of solid salt found in several parts of the
world are called rock salt. They may appear brown due to impurities.
Q78. Why is common salt an important raw material?
Answer: Common salt is used as a raw material for producing
sodium hydroxide, baking soda, washing soda, bleaching powder and
other useful substances.
Q79. What is brine?
Answer: Brine is an aqueous solution of sodium chloride.
Q80. What is the chlor-alkali process?
Answer: The process in which electricity is passed through aqueous
sodium chloride solution (brine), producing sodium hydroxide, chlorine
and hydrogen, is called the chlor-alkali process.
2NaCl(aq) + 2H2O(l)
→ 2NaOH(aq) + Cl2(g) + H2(g)
Q81. What are the three products of the chlor-alkali process?
Answer: Sodium hydroxide, chlorine gas and hydrogen gas.
Q82. Where is chlorine gas produced in the chlor-alkali process?
Answer: Chlorine gas is given off at the anode.
Q83. Where is hydrogen gas produced in the chlor-alkali process?
Answer: Hydrogen gas is given off at the cathode.
Q84. What is bleaching powder?
Answer: Bleaching powder is produced by the action of chlorine
on dry slaked lime, Ca(OH)2. It is represented as Ca(ClO)2
in the chapter.
2Ca(OH)2 + 2Cl2
→ Ca(ClO)2 + CaCl2 + 2H2O
Q85. Give three uses of bleaching powder.
Answer:
1. Bleaching cotton, linen, wood pulp and washed clothes.
2. Used as an oxidising agent in chemical industries.
3. Used to make drinking water free from germs.
1. Bleaching cotton, linen, wood pulp and washed clothes.
2. Used as an oxidising agent in chemical industries.
3. Used to make drinking water free from germs.
11. Baking Soda – Important Questions
Q86. What is the chemical name of baking soda?
Answer: Sodium hydrogencarbonate.
Q87. Write the chemical formula of baking soda.
Answer: NaHCO3.
Q88. Why is baking soda called a mild basic salt?
Answer: Sodium hydrogencarbonate is a mild, non-corrosive basic salt
and can neutralise acids.
Q89. What happens when baking soda is heated?
Answer: Sodium hydrogencarbonate decomposes into sodium carbonate,
water and carbon dioxide.
2NaHCO3
→ Na2CO3 + H2O + CO2
Q90. What is baking powder?
Answer: Baking powder is a mixture of baking soda and tartaric acid,
a weak edible acid.
Q91. Why does bread or cake rise when baking powder is used?
Answer: Carbon dioxide produced during the reaction causes the
bread or cake to rise, making it soft and spongy.
Q92. Give three uses of baking soda.
Answer:
1. Used in baking powder.
2. Used as an ingredient in antacids.
3. Used in soda-acid fire extinguishers.
1. Used in baking powder.
2. Used as an ingredient in antacids.
3. Used in soda-acid fire extinguishers.
12. Washing Soda – Important Questions
Q93. What is the chemical formula of washing soda?
Answer: Na2CO3·10H2O.
Q94. How is washing soda obtained from sodium carbonate?
Answer: Recrystallisation of sodium carbonate gives washing soda.
Na2CO3 + 10H2O
→ Na2CO3·10H2O
Q95. Give two important uses of washing soda.
Answer: It is used in glass, soap and paper industries and for
removing permanent hardness of water. It can also be used as a domestic
cleaning agent.
Q96. What is another important industrial use of sodium carbonate?
Answer: It is used in the manufacture of sodium compounds such as borax.
13. Water of Crystallisation
Q97. What is water of crystallisation?
Answer: Water of crystallisation is the fixed number of water molecules
present in one formula unit of a salt.
Q98. What happens when hydrated copper sulphate crystals are heated?
Answer: The water of crystallisation is removed and the blue
copper sulphate crystals turn white.
Q99. How can the blue colour of heated copper sulphate be restored?
Answer: Adding water restores the blue colour.
Q100. Write the formula of hydrated copper sulphate.
Answer: CuSO4·5H2O.
Q101. How many water molecules are present in one formula unit of hydrated copper sulphate?
Answer: Five water molecules.
Q102. What is the formula of gypsum?
Answer: CaSO4·2H2O.
14. Plaster of Paris – Very Important
Q103. What is Plaster of Paris?
Answer: Plaster of Paris is calcium sulphate hemihydrate,
CaSO4·½H2O.
Q104. How is Plaster of Paris prepared?
Answer: Gypsum is heated at 373 K. It loses water molecules and
forms calcium sulphate hemihydrate, called Plaster of Paris.
CaSO4·2H2O
→ CaSO4·½H2O + 1½H2O
Q105. What happens when Plaster of Paris is mixed with water?
Answer: It changes back into gypsum and forms a hard solid mass.
CaSO4·½H2O + 1½H2O
→ CaSO4·2H2O
Q106. Why should Plaster of Paris be stored in a moisture-proof container?
Answer: Plaster of Paris reacts with moisture and changes into gypsum.
Therefore, it should be protected from moisture.
Q107. Give two uses of Plaster of Paris.
Answer: It is used for supporting fractured bones and for making
toys, decorative materials and smooth surfaces.
15. NCERT Exercise-Based Questions with Answers
Q108. A solution turns red litmus blue. Its pH is likely to be:
(a) 1
(b) 4
(c) 5
(d) 10
Answer: (d) 10
Q109. A solution reacts with crushed egg-shells to give a gas that turns lime water milky. The solution contains:
(a) NaCl
(b) HCl
(c) LiCl
(d) KCl
Answer: (b) HCl
Q110. 10 mL NaOH solution is neutralised by 8 mL HCl solution. How much of the same HCl solution is needed for 20 mL of the same NaOH solution?
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL
Answer: (d) 16 mL
Q111. Which type of medicine is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Answer: (c) Antacid
Q112. Write the balanced equation for dilute sulphuric acid reacting with zinc granules.
Answer:
Zn + H2SO4 → ZnSO4 + H2
Q113. Write the balanced equation for dilute hydrochloric acid reacting with magnesium ribbon.
Answer:
Mg + 2HCl → MgCl2 + H2
Q114. Why does distilled water not conduct electricity whereas rain water does?
Answer: Distilled water contains very few ions. Rain water contains
dissolved substances that provide ions, enabling it to conduct electricity.
Q115. Why does dry HCl gas not show acidic behaviour without water?
Answer: HCl produces H+ ions in the presence of water.
Without water, H+ ions are not produced in the required aqueous form.
Q116. Equal magnesium ribbons are placed in HCl and CH3COOH of the same concentration. In which test tube will fizzing be more vigorous?
Answer: Fizzing will be more vigorous with HCl because, for the same
concentration, HCl produces more hydrogen ions than acetic acid.
Q117. Fresh milk has pH 6. What happens to its pH as it turns into curd?
Answer: Its pH decreases because lactic acid is produced as milk
turns into curd.
Q118. Why does adding a small amount of baking soda to fresh milk make it slightly alkaline?
Answer: Baking soda is a mild basic salt, so it raises the pH of the milk.
Q119. Why does milk containing a small amount of baking soda take longer to set as curd?
Answer: Baking soda makes the milk slightly alkaline. More acid needs
to be produced before the milk reaches the conditions required for setting
into curd.
Q120. Give two examples of neutralisation reactions.
Answer:
1. HCl + NaOH → NaCl + H2O
2. Acidic soil can be treated with suitable basic substances such as lime compounds to reduce excess acidity.
1. HCl + NaOH → NaCl + H2O
2. Acidic soil can be treated with suitable basic substances such as lime compounds to reduce excess acidity.
Q121. Give two important uses of washing soda.
Answer: It is used in glass, soap and paper industries and for
removing permanent hardness of water.
Q122. Give two important uses of baking soda.
Answer: It is used in baking powder and antacids. It is also used
in soda-acid fire extinguishers.
16. Important Diagrams & Activity-Based Questions
Q123. Draw and label the apparatus used to test hydrogen gas evolved when zinc reacts with dilute sulphuric acid.
Answer: Practise the NCERT Figure 2.1. Important labels include
test tube, zinc granules, dilute sulphuric acid, delivery tube, soap solution
and the burning candle used for testing hydrogen.
Q124. Draw the pH scale and mark acidic, neutral and basic regions.
Answer: Mark 0–6 as acidic, 7 as neutral and 8–14 as basic.
Also indicate that hydrogen ion concentration decreases as pH increases.
Q125. Draw the chlor-alkali process diagram and identify the products.
Answer: Practise the NCERT Figure 2.8 showing brine, anode,
cathode, chlorine, hydrogen and sodium hydroxide.
Q126. Explain the copper sulphate crystallisation activity.
Answer: On heating blue copper sulphate crystals, water of
crystallisation is removed and the salt becomes white. Adding water
restores the blue colour.
17. Important MCQs for Class 10 Board Exam
Q127. Which ion is responsible for acidic character?
(a) Na+
(b) H+/H3O+
(c) OH−
(d) Cl−
Answer: (b)
Q128. A solution with pH 2 is:
(a) Strongly acidic
(b) Neutral
(c) Basic
(d) Alkaline
Answer: (a)
Q129. Which substance is used as an antacid?
(a) Magnesium hydroxide
(b) Hydrochloric acid
(c) Sodium chloride
(d) Sulphuric acid
Answer: (a)
Q130. Which gas turns lime water milky?
(a) Hydrogen
(b) Oxygen
(c) Carbon dioxide
(d) Nitrogen
Answer: (c)
Q131. The pH of a neutral solution is:
(a) 0
(b) 5
(c) 7
(d) 14
Answer: (c)
Q132. Which compound is commonly known as baking soda?
(a) NaCl
(b) NaHCO3
(c) Na2CO3
(d) CaCO3
Answer: (b)
Q133. Which compound is washing soda?
(a) NaHCO3
(b) NaCl
(c) Na2CO3·10H2O
(d) CaSO4·2H2O
Answer: (c)
Q134. Which process produces sodium hydroxide, chlorine and hydrogen?
(a) Neutralisation
(b) Chlor-alkali process
(c) Crystallisation
(d) Dilution
Answer: (b)
Q135. Plaster of Paris is:
(a) CaSO4·2H2O
(b) CaSO4·½H2O
(c) Na2CO3·10H2O
(d) NaHCO3
Answer: (b)
Q136. Tooth decay starts when the pH of the mouth is:
(a) Below 5.5
(b) 7
(c) Above 10
(d) 14
Answer: (a)
Q137. Which acid is present in vinegar?
(a) Citric acid
(b) Acetic acid
(c) Lactic acid
(d) Methanoic acid
Answer: (b)
Q138. Which acid is associated with curd?
(a) Lactic acid
(b) Acetic acid
(c) Tartaric acid
(d) Methanoic acid
Answer: (a)
Q139. Which substance is used for removing permanent hardness of water?
(a) Baking soda
(b) Washing soda
(c) Common salt
(d) Bleaching powder
Answer: (b)
Q140. Which substance contains five molecules of water of crystallisation?
(a) Gypsum
(b) CuSO4·5H2O
(c) NaCl
(d) NaHCO3
Answer: (b)
18. Case-Based Questions
Case Study 1 – pH of Solutions
Five solutions A, B, C, D and E have pH values 4, 1, 11, 7 and 9 respectively. Use the pH scale to analyse their nature.
(a) Which solution is neutral?
Answer: D, pH 7.
(b) Which solution is strongly acidic?
Answer: B, pH 1.
(c) Which solution is strongly alkaline?
Answer: C, pH 11.
(d) Which solution is weakly acidic?
Answer: A, pH 4.
(e) Which solution is weakly alkaline?
Answer: E, pH 9.
Case Study 2 – Acid and Metal Reaction
Zinc granules are added to dilute sulphuric acid. Bubbles are produced and the evolved gas is tested using a burning candle.
(a) Which gas is evolved?
Answer: Hydrogen.
(b) Write the balanced equation.
Answer: Zn + H2SO4 → ZnSO4 + H2
(c) How can the gas be identified?
Answer: It burns with a characteristic pop sound when tested
with a burning flame.
Case Study 3 – Baking Soda and Curd
Fresh milk has a pH of 6. A small amount of baking soda is added to it. The milk takes longer to set as curd.
(a) What is the nature of baking soda?
Answer: Mildly basic.
(b) What happens to the pH after adding baking soda?
Answer: The pH shifts towards the alkaline side.
(c) Why does the milk take longer to set?
Answer: More acid has to be produced before the milk reaches the
conditions needed to set as curd.
Case Study 4 – Common Salt
An aqueous solution of sodium chloride, called brine, is subjected to electrolysis.
(a) Name the process.
Answer: Chlor-alkali process.
(b) Name the three products.
Answer: Sodium hydroxide, chlorine and hydrogen.
(c) Where is chlorine produced?
Answer: At the anode.
(d) Where is hydrogen produced?
Answer: At the cathode.
Case Study 5 – Water of Crystallisation
Blue copper sulphate crystals are heated in a dry boiling tube. After heating, the substance becomes white. Water is then added.
(a) Why does the blue salt become white?
Answer: Water of crystallisation is removed during heating.
(b) What happens when water is added again?
Answer: The blue colour is restored.
(c) Write the formula of hydrated copper sulphate.
Answer: CuSO4·5H2O.
⚡ Quick Revision – Acids, Bases and Salts
| Concept | Remember |
|---|---|
| Acidic solution | Produces H+/H3O+ ions in water |
| Basic solution | Produces OH− ions in water |
| Acid + Metal | Salt + Hydrogen |
| Acid + Carbonate | Salt + CO2 + Water |
| Acid + Base | Salt + Water |
| Metal oxide + Acid | Salt + Water |
| pH = 7 | Neutral |
| pH < 7 | Acidic |
| pH > 7 | Basic |
| Baking soda | NaHCO3 |
| Washing soda | Na2CO3·10H2O |
| Gypsum | CaSO4·2H2O |
| Plaster of Paris | CaSO4·½H2O |
| Common salt | NaCl |
| Bleaching powder | Ca(ClO)2 as represented in NCERT |
| Chlor-alkali products | NaOH + Cl2 + H2 |
19. Class 10 Board Exam Checklist
Before your exam, make sure you can:
- ✔ Define acids, bases and indicators.
- ✔ Explain natural, synthetic and olfactory indicators.
- ✔ Write reactions of acids with metals.
- ✔ Identify hydrogen gas.
- ✔ Explain reactions of metal carbonates and hydrogencarbonates.
- ✔ Explain neutralisation reactions.
- ✔ Explain why metallic oxides are basic.
- ✔ Explain why non-metallic oxides are acidic.
- ✔ Explain H+, H3O+ and OH− ions.
- ✔ Explain why dry HCl does not show acidic behaviour without water.
- ✔ Draw and understand the pH scale.
- ✔ Compare strong and weak acids/bases.
- ✔ Explain the importance of pH in everyday life.
- ✔ Learn important natural acids and their sources.
- ✔ Explain family of salts and pH of salts.
- ✔ Explain the chlor-alkali process.
- ✔ Learn uses of bleaching powder.
- ✔ Learn preparation, reaction and uses of baking soda.
- ✔ Learn preparation and uses of washing soda.
- ✔ Understand water of crystallisation.
- ✔ Learn gypsum and Plaster of Paris reactions.
- ✔ Practise all important balanced chemical equations.
- ✔ Solve NCERT exercise questions.
- ✔ Practise pH-based MCQs and case-based questions.
🎯 Exam Strategy for Acids, Bases and Salts
1. Learn the reaction patterns.
Remember the general patterns for acid + metal, acid + carbonate, acid + base and metal oxide + acid.
2. Practise chemical equations.
Do not only memorise names. Practise writing and balancing equations.
3. Master the pH scale.
Questions involving pH, hydrogen ion concentration, acidic/basic nature and everyday applications are important for revision.
4. Do not skip salts.
Common salt, chlor-alkali process, bleaching powder, baking soda, washing soda and Plaster of Paris are major scoring areas.
5. Revise NCERT activities and diagrams.
Pay special attention to the zinc-acid experiment, pH scale, chlor-alkali process and copper sulphate crystallisation activity.
📌 Ready for Your Class 10 Science Exam?
Revise these Acids, Bases and Salts Important Questions with Answers, then practise chemical equations, MCQs and case-based questions. For stronger preparation, revise the other Class 10 Science chapters as well.
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Class 10 Science Important Questions With Answers | All Chapters | CBSE Board Exam - The Busy Brains
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