Class 10 Science: Acids, Bases and Salts important questions

Acids, Bases and Salts is a chapter of Class 10 Science for the CBSE. These 12 questions are marked Very Important, Important or Practice, and each answer has been checked by our team. Use them to revise, not as a prediction of what will come in the exam.

1. Practice · 1 marks

   1. With the reference to four gases CO2,CO, Cl2 and O2, which one of the options in the table is correct? Option Acidic Used in Product of Product of oxide treatment of respiration incomplete water combustion (a) CO Cl2 O2 CO (b) CO2 Cl2 CO2 CO (c) CO2 O2 O2 CO2 (d) CO O2 CO2 CO2

   (b) CO2, Cl2, CO2, CO

2. Practice · 1 marks

   2. Mild non-corrosive basic salt is a) Ca (OH)2 b) NaCl c) NaOH d) NaHCO3

   d) NaHCO3

3. Practice · 1 marks

   3. An aqueous solution ‘A’ turns the phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, the pink colour disappears. Which of the following statement is true for the solutions ‘A’ and ‘B’. A. A is strongly basic and B is a weak base. B. A is strongly acidic and B is a weak acid. C. A has a pH greater than 7 and B has a pH less than 7. D. A has a pH less than 7 and B has a pH greater than 7.

   C. A has a pH greater than 7 and B has a pH less than 7

4. Important · 3 marks

   4. A. (i) In the given series of reactions, name the compounds X and Z. (ii) Which type of reaction is X to Z? (iii) You are given 3 unknown solutions A, B, and C with pH values of 6, 8 and 9.5 respectively. In which solution will the maximum number of hydronium ions be present? Arrange the given samples in the increasing order of H+ ion concentration. OR B. Comment on the following statements: (i) Bee sting is treated with baking soda paste whereas wasp sting is treated with dilute vinegar. (ii) Farmers treat soil with quicklime when tilling. (iii) Ancient sculptures and marble structures are conserved by treating them with certain chemicals.”

   A. (i) X = NaHCO3; Z = Na2CO3 (ii) Decomposition reaction (iii) Solution A (iv) Increasing order or H+ ions C<B<A OR B. (i) As bee sting is acidic and wasp sting is basic. (ii) To change the nature of soil to (neutral or basic). (iii) To protect sculptures from the effects of certain gases present in environment and acid rain.

5. Practice · 1 marks

   5. Four statements about the reactions of oxides with dilute hydrochloric acid and aqueous sodium hydroxide are listed. I. Aluminium oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. II. Calcium oxide reacts with dilute hydrochloric acid and aqueous sodium hydroxide. III. Zinc oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. IV. Sulphur dioxide does not react with either dilute hydrochloric acid or aqueous sodium hydroxide. Which statements are correct? A. I and II B. I and III C. II and IV D. III and IV

   B. (I) and (III)

6. Practice · 1 marks

   6. Methyl orange is added to dilute hydrochloric acid and to aqueous sodium hydroxide. What is the colour of the methyl orange in each solution? Sample colour in dilute colour in aqueous hydrochloric acid sodium hydroxide A Orange Red B Red Yellow C Red Orange D Yellow Red

   B. Red Yellow

7. Practice · 1 marks

   7. Which of the following substances when dissolved in equal volume of water, will have the highest pH value? A. Sulphuric acid B. Acetic acid C. Magnesium hydroxide D. Sodium hydroxide

   D. Sodium hydroxide

8. Very Important · 4 marks

   8. Sara took 2 mL of dilute NaOH solution in a test tube and added two drops of phenolphthalein solution to it. The solution turned pink. She added dilute H2SO4 drop by drop until the solution became colourless; 40 drops were needed. When she added a drop of NaOH, the colour changed back to pink. She repeated the activity with different volumes of NaOH: Volume of dil. NaOH taken (mL): 2, 3, 4 Drops of dil. H2SO4 used: 20, 30, 40 A. If Sara used concentrated H2SO4 instead of dilute H2SO4, how many drops would be needed for the colour change: (a) 40 (b) < 40 (c) > 40? Justify your answer. B. 20 drops of dil. H2SO4 measure 1 mL. If the colour of the NaOH solution changed after adding 3 mL of H2SO4, how many mL of NaOH did she take? OR Sara takes 10 drops of dilute H2SO4, adds two drops of phenolphthalein, and then adds NaOH dropwise. She sees a colour change after 20 drops of NaOH. What change does she see, and why? C. Write the balanced chemical equation for the reaction. Is it (a) neutralisation and double displacement (b) neutralisation and precipitation (c) precipitation and double displacement (d) all three? Why?

   A. (b) < 40, because concentrated H2SO4 gives more H+ ions than the dilute acid. B. 3 mL of H2SO4 = 60 drops. From the table, 10 drops neutralise 1 mL of NaOH, so 60 drops neutralise 6 mL of NaOH. OR The colour changes from colourless to pink: phenolphthalein is colourless in acid and pink in a basic solution, so the extra NaOH has made the solution basic. C. 2NaOH + H2SO4 → Na2SO4 + 2H2O. (a) neutralisation and double displacement: the base is neutralised to form salt and water, and the ions exchange partners (Na+ with SO4²⁻, H+ with OH−). It is not precipitation because Na2SO4 is soluble in water.

9. Practice · 1 marks

   9. Rishita summarizes the chlor-alkali process in the following table. Option Product Formed Use I Hydrogen At cathode Used as a fuel II Chlorine At anode Used to make margarines III Sodium Hydroxide Near cathode To make soap IV Sodium Hydroxide Near anode To make bleaching powder Identify the options that are correctly matched. A. I, II and III B. I and III C. II and IV D. I, II, III and IV

   B. I and III II & IV are incorrect as Chlorine is produced at the anode, but it is not used to make margarine. And sodium hydroxide is deposited near cathode.

10. Practice · 1 marks

    10. Which of the following salts contain water of crystallisation: (i) Plaster of Paris, (ii) Washing soda, (iii) Baking soda and (iv) Gypsum. A. (i), (ii) and (iii) B. (i), (iii) and (iv) C. (ii), (iii) and (iv) D. (i), (ii) and (iv)

    D. (i), (ii) and (iv) Plaster of Paris is CaSO4.1/2 H2O, Washing soda Na2CO3.10 H2O Baking soda NaHCO3 and Gypsum is CaSO4.2H2O

11. Practice · 1 marks

    11. Assertion (A): Onion extract loses its smell, when it is added to baking soda solution whereas it retains its smell when added to lemon juice. Reason (R): Onion acts as an olfactory indicator. A. Both A and R are true, and R is the correct explanation of A. B. Both A and R are true, and R is not the correct explanation of A. C. A is true but R is false. D. A is false but R is true.

    B. Both A and R are true, and R is not the correct explanation of A.

12. Important · 3 marks

    12. Give reason for the following : A. A solution of sports electrolyte drink conducts electricity, but coconut oil does not. B. Milkiness disappears when excess of carbon dioxide is passed through lime water. C. An iron bridge near the sea rusts much faster than an iron bridge located in a dry hilly region.

    A. A sports drink contains ions (electrolytes) which help conduct electricity. Coconut oil does not contain ions so it cannot conduct electricity. B. Limewater turns milky due to the formation of insoluble calcium carbonate (CaCO₃). When excess CO₂ is passed, calcium carbonate reacts further to form soluble calcium hydrogen carbonate, causing the milkiness to disappear. C. Air near the sea contains high moisture (humidity), which speeds up rusting. In a dry hilly region, moisture is low, so rusting occurs much slowly.