Important Questions for Class 10 Science Chapter 2: Understanding Acids, Bases and Salts is important for Class 10 Science students.
This chapter covers identifying acids, bases, and salts, their reactions, neutralisation, and pH analysis in daily life. Practising CBSE Class 10 Science Acids, Bases and Salts questions and using them for revision helps students strengthen concepts, improve accuracy, and perform better in exams
Class 10 Science Acids, Bases and Salts Important Question Answers
Strengthen your understanding of class 10 science chapter 2 acids, bases, and salts with these high-yield questions.
Practice reactions, neutralisation, pH, and key applications to boost your exam score.
Multiple Choice Questions (1 Mark):
1. The name of the salt used to remove permanent hardness of water is
(A) Sodium hydrogen carbonate (NaHCO3)
(B) Sodium chloride (NaCl)
(C) Sodium carbonate decahydrate (Na2CO3·10H2O)
(D) Calcium sulphate hemihydrate
Ans: (C)
2. Which of the following options in the given table are correct?
| Option | Natural Source | Acid Present |
| (i) | Orange | Oxalic acid |
| (ii) | Sour milk | Lactic acid |
| (iii) | Ant sting | Methanoic acid |
| (iv) | Tamarind | Acetic acid |
(A) (i) and (ii)
(B) (i) and (iv)
(C) (ii) and (iii)
(D) (iii) and (iv)
Ans: (C)
3. Assertion (A): Sodium hydrogen carbonate is used as an ingredient in antacids.
Reason (R): NaHCO3 is a mild, non-corrosive basic salt.
(A) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.
Ans: (A)
4. Sodium hydroxide is termed as an alkali, while ferric hydroxide is not because:
(A) Sodium hydroxide is a strong base, while ferric hydroxide is a weak base.
(B) Sodium hydroxide is a base soluble in water, while ferric hydroxide is a base but insoluble in water.
(C) Sodium hydroxide is a strong base, while ferric hydroxide is a strong acid.
(D) Both are strong bases, but sodium hydroxide is more soluble in water.
Ans: (B)
5. How will you protect yourself from the heat generated while diluting a concentrated acid?
(A) By adding acid to water with constant stirring.
(B) By adding water to acid with constant stirring.
(C) By adding water to acid followed by the base.
(D) By adding base to acid with constant stirring.
Ans: (A)
6. With reference to gases CO2, CO, Cl2 and O2, which option is correct?
| Acidic oxide | Used in water treatment | Product of respiration | Product of incomplete combustion |
| CO | Cl2 | O2 | CO |
| CO2 | Cl2 | CO2 | CO |
| CO2 | O2 | O2 | CO2 |
| CO | O2 | CO2 | CO2 |
Ans: (B)
7. Salt ‘A’ used in food products reacts to produce salt ‘B’ used in kitchen pakoras; salt ‘B’ on heating converts to salt ‘C’ used in glass manufacture. The salts ‘A’, ‘B’, and ‘C’ are respectively:
(A) NaHCO3, NaCl, Na2CO3
(B) Na2CO3, NaHCO3, NaCl
(C) Na2CO3, NaCl, NaHCO3
(D) NaCl, NaHCO3, Na2CO3
Ans: (D)
Very Short Answer Type Questions (1 Mark)
8. Write the chemical equation for the reaction of zinc metal on sodium hydroxide.
Sol: 
9. Three acidic solutions A, B and C have pH = 0, 3, and 5, respectively.
a) Which solution has the highest concentration of H+ ions?
b) Which solution has the lowest concentration of H+ ions?
Sol:
a) Solution with pH = 0 has highest H+ concentration.
b) Solution with pH = 5 has lowest H+ concentration.
10. Define alkalies and give an example.
Sol:
Water-soluble bases are called alkalies, e.g., NaOH.
11. Write the chemical name and formula of washing soda.
Sol: 
12. How will you test the gas liberated when hydrochloric acid reacts with an active metal?
Sol: Bring a burning matchstick near the gas; if it burns with a 'pop' sound, the gas is hydrogen.
13. Why does dry HCl gas not change the colour of dry blue litmus?
Sol: Dry HCl gas does not form ions, thus it does not affect dry blue litmus.
14. Name the chemicals used in an acid fire extinguisher and the gas evolved during its use.
Sol: NaHCO3 (Sodium hydrogen carbonate) and H2SO4 (Sulphuric acid). The gas evolved is carbon dioxide
15. During the summer season, a milkman usually adds a very small amount of baking soda to fresh milk. Given one reason.
Sol. Baking soda is basic in nature; it will not allow milk to turn sour due to the formation of lactic acid.
16. Curd is not kept in copper and brass utensils. Why?
Sol. Curd contains Lactic acid, which can make poisonous compounds with brass and copper vessels.
17. A white chemical compound becomes hard on mixing proper quantity of water. It is also used to maintain joints in fixed position. Name the chemical compound and write its chemical formula. Write the chemical equation to show what happens when water is added to this compound in a proper quantity.
18. Write the chemical equation to describe how baking soda is produced on a large scale. Also, write the chemical name of the products formed in the reaction.
19. What is meant by the term water of crystallisation? How would you show that copper sulphate crystals contain water of crystallisation?
Sol. The molecules of water associated with a crystalline substance are called the water of crystallisation. When hydrated copper sulphate is heated, its colour changes from blue to dirty white and water droplets are formed.
20. Equal lengths of magnesium ribbon are taken in test tubes ‘A’ and ‘B’. Hydrochloric acid (HCl) is added to test tube ‘A’ while acetic acid (CH3COOH) is added to test tube ‘B’. In which test tube, will fizzing occur more vigorously and why?
Sol. The fizzing will occur more vigorously in test tube ‘A’ because HCl is a strong acid and reacts faster than acetic acid, which is a weak acid.
21. What is a neutralisation reaction? Given one example
Sol. The reaction in which an acid reacts with a base to form a salt and water is called a neutralisation reaction, e.g.,
22. What is the colour of FeSO4 7H2O crystals? How does this colour change upon heating? Give a balanced chemical equation for the change.
Sol. FeSO4.7H2O is pale green in colour. It becomes dirty white on heating.
23.
(a) Why does aqueous solution of an acid conduct electricity?
(b) How does the concentration of H3O+ ions change when a solution of an acid is diluted?
(c) Which one has a higher pH, a concentrated or a dilute solution of hydrochloric acid?
(d) What would to be the gas evolved on adding dilute hydrochloric acid to
(i) Solid sodium carbonate placed in a test tube?
(ii) Zinc metal in a test tube?
a. It contains ions which carry current.
b. H3O+ ions per unit volume decrease when it is diluted.
c. Dilute solution has a higher pH than a concentrated one.
25. Name the products formed in each case when:
(a) Hydrochloric acid reacts with caustic soda.
(b) Granulated zinc reacts with caustic soda.
(c) Carbon dioxide is passed through lime water.
26. Write balanced chemical equations for the following:
a. Bleaching powder is kept open in the air.
b. Blue crystals of copper sulphate are heated.
c. Chlorine gas is passed through dry slaked lime.
d. Carbon dioxide gas is passed through lime water.
e. NaOH solution is heated with zinc granules.
27. Identify the acid and the base whose combination forms the common salt that you use in your food. Write its chemical formula and the chemical name of the salt.
b. What is rock salt? Mention its colour and the reason due to which it has this colour.
c. What happens when electricity is passed through brine? Write a chemical equation for it.
Sol: NaOH (Sodium hydroxide) and HCl (Hydrochloric acid) from common salt. NaCl is common salt, sodium chloride.
b. Rock salt is sodium chloride found in the form of rocks. It is yellowish in colour due to the presence of impurities.
c. Sodium hydroxide, H2 gas and chlorine gas will be formed:
28. Explain why is hydrochloric acid a strong acid and acetic acid, a weak acid. How can it be verified?
b. Explain why an aqueous solution of an acid conducts electricity.
c. You have four solutions: A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7.
(1) Identify the most acidic and most basic solutions, respectively.
(2) Arrange the above four solutions in increasing order of H+ ion concentration.
(3) State the change in colour of pH paper on dipping in solution C and D.
Sol.
a. Hydrochloric acid is a strong acid because it is completely ionised in its aqueous solution. Acetic acid is only partially ionised. HCl reacts with Mg vigorously whereas acetic acid reacts less vigorously.
b. Aqueous solution of an acid contains ions which carry current; it conducts electricity.
c.
(1) With pH = 6, A is most acidic and C with pH= 12, (C) 1.5 Most basic.
(2) C < B < D < A is the increasing order of H+ ion concentration
(3) pH paper will turn blue in ' C ' with pH = 12, basic pH paper will turn green in D with pH = 7, neutral.
29. Complete and balance the following chemical equation:
(i) NaOH(aq) + Zn(s) →
(ii) CaCO3(s) + H2O(l) + CO2(g) →
(iii) HCl(aq) + H2O(l) →
Sol.
Q.30
(a) Identify the gases evolved at the anode and cathode in the above experimental set-up.
(b) Name the process that occurs. Why is it called so?
(c) Illustrate the reaction of the process with the help of a chemical equation.
Sol.. (a) At anode: Chlorine; At cathode: Hydrogen
(b) Chlor-alkali process, as the products obtained alkali, chlorine gas and hydrogen gas.
31. Case Study-I:
The pH scale measures how acidic or basic a substance is by making use of hydrogen ion concentrations in them.
Based on the above table, answer of the following questions:
(i) Which of the following is/are true about substance B?
I. It is the strongest base among the given substance.
II. It is used in antacids.
III. It turns blue litmus paper to blue.
IV. None of the above.
(A) I and II
(B) II and III
(C) I, II and III
(D) Only IV
Sol. (A) I and II
(ii) What happens when a solution of substance D is mixed with a solution of substance E in a test tube?
I. Salt formation takes place
II. Temperature of solution remains the same
III. Temperature of solution decreases
IV. Temperature of solution increases
(A) Only I
(B) I and II
(C) II and IV
(D) I and IV
Sol. (D) I and IV
Base (D) + Acid (E) → salt + water.
During this reaction, the temperature of the
solution increases.
(iii) Arrange the substances A, C and E in
increasing order of their acidic strength.
(A) C < E < A
(B) A < E < C
(C) A < C < E
(D) E < C < A
Sol. (B) A < E < C
(iv) Equal volumes of hydrochloric acd and sodium hydroxide solutions of same concentration are mixed, and the pH of the resulting solution is checked with a pH paper.
What would be the colour obtained?
(A) Blue
(B) Red
(C) Yellowish green
(D) Orange
Sol. (C) Yellowish green
(v) Study the table given below and select the row that has the incorrect information.
Sol. (C) Action with phenolphthalein No change. They turn phenolphthalein pink in solution B & D as they are basic in nature.
Case Study-II:
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions. Group A Lemon juice, vinegar, colourless aerated drink. Group B - Tomato juice, coffee, ginger juice. Group C - Sodium hydroxide, sodium chloride, lime water. Read the above passage carefully and give the answer of the following questions:
(i) For the solutions provided, which group is/ are likely to have pH value
(a) less than 7,
(b) greater than 7?
Sol.
(a) Group A
(b) Group C
(ii) List two ways of determining pH of a solution.
Sol.
(a) using litmus paper
(b) using universal indicator
(iii) Explain why the sour substances, such as lemon juice, are effective in cleaning the tarnished copper vessels?
Or
"pH has great importance in our daily life." Justify this statement by giving two examples.
Sol. Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface, forming a green layer of copper carbonate. The citric acid present in the lemon juice neutralises the basic copper carbonate and dissolves the layer. That is why, tarnished Copper vessels are cleaned with sour substances like lemon juice to give the surface of the copper vessel its characteristic lustre.
(i) Tooth decay starts when the pH of the mouth is lower than 5.5.
(ii) Our body works within the pH range of 7.0 to 7.8
33. Case Study-III:
The Salt Story From: The New Indian Express 9 March, 2021. The salt pans in Marakkanam, a port town about 120 km from Chennai are the third largest producer of salt in Tamil Nadu. Separation of salt from water is a laborious process and the salt
obtained is used as raw materials for manufacture of various sodium compounds. One such compound is sodium hydrogen carbonate, used in baking, as an antacid and in soda acid firextinguishers. The table shows the mass of various
compounds obtained when 1litre of sea water is evaporated.
Read the above passage carefully and give the answer of the following questions:
(i) Which compound in the table reacts with acid to release carbon dioxide?
(A) NaCl (B) CaSO4
(C) CaCO3 (D) MgSO4
Sol. (C) CaCO3
(ii) How many grams of magnesium sulphate are present in 135g of solid left by evaporation of
sea water?
(A) 6 g
(B) 12 g
(C) 18 g
(D) 24 g
(iii) What is the saturated solution of Sodium Chloride called?
(A) Brine
(B) Slaked lime
(C) Lime water
(D) Soda water
Sol. (A) Brine
(iv) What is the pH of the acid which is used in the formation of common salt?
(A) Between 1 to 3
(B) Between 6 to 8
(C) Between 8 to 10
(D) Between 11 to 13
Sol. (A) Between 1 to 3
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