CBSE Class 10 Science Chapter-2 Acids, Bases and Salts Important Questions – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 2 – Acids, Bases and Salts prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Acids, Bases and Salts Chapter-2 Important Questions
CBSE Class 10 science Important Questions Chapter 2 – Acids, Bases and Salts
2 Mark Questions
1. What happens to the crystals of washing soda when exposed to air?
Ans. 
Washing soda(White Crystals) 
Washing Power(White power)
Washing soda undergoes efflorescence.
2. What is the chemical name of washing soda? Name three raw materials used in making washing soda by Solvay process?
Ans. Chemical name – Sodium carbonate decahydrate 
Raw materials – Brine, Lime stone, Ammonia
3. What is efflorescence? Give an example?
Ans. It in the process of the loss of molecules of water of crystallization from a substance when exposed to air for example
Washing soda(White Crystals) Washing Power(White power)
4. Why is sodium hydrogen carbonate an essential ingredient is antacids?
Ans. Sodium hydrogen carbonate is an essential ingredient in antacids because it neutralizes the effect 
which is released in the stomach. So it is called as an antacid 
5. Give the name and formula of two
(i) strong monobasic acids
(ii) two weak dibasic acids
Ans. (i) Hydrochloric acid (HCl), Nitric acid (HNO3).
(ii) Carbonic acid (H2CO3), oxalic acid (C2H4O4).
6. Why alkalis like sodium hydroxide and potassium hydroxide should not be left exposed to air?
Ans. Alkalis should not be left exposed to air because they are hygroscopic in nature and absorb moisture from atmosphere in which they get dissolved.
7. Dry ammonia has no action on litmus paper but a solution of ammonia in water turns red litmus paper blue. Why is it so?
Ans. In dry state Ammonia contains no hydroxyl ions. On dissolving in water, it forms NH4OH which dissociates to give NH4+ and OH–ions. Thus solution becomes basic and turns red litmus paper blue.
NH3 (g) + H2O (l) 
NH4OH (aq)
NH4OH (aq) NH4+ (aq) + OH– (aq)
8. Bleaching powder forms a milky solution in water. Explain.
Ans. When bleaching powder gets dissolved in water, the solution turns milky due to the formation of Ca (OH)2
CaOCl2 + H2O Ca (OH)2 + 2HCl (Bleaching powder)
9. Why does not an acid show any acidic behavior is the absence of water?
Ans. An acid gets ionized only in aqueous solution which means in the presence of water. Also it releases H+ ions and show acidic behavior in the presence of water
10. Fresh milk has a pH of 6. What will be the PH value if milk changes into a curd Justify.
Ans. When milk changes into a curd, its PH value decreases i.e. lactose gets converted into lactic acid. As more of acid is formed, its PH value decreases.
11. What is the reaction between hydrogen in concentration ion concentration of an aqueous solution and pH?
Ans. 
Where 
is hydrogen in concentration
12. How will you show that acetic acid is monobasic acid
Ans. When acetic acid reacts with 
solution only one it atom of the acid gets replaced which shows acetic acid is a monobasic acid.
13. Why should curd and sour substance not be kept in brass and copper vessels.
Ans. Brass and copper vessels contain copper and zinc metal that reacts with acids present in curd and sour substance forming soluble salts. These salts are poisonous in nature and make curd unfit for consumption.
14. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Ans. Usually hydrogen gas is liberated when an acid reacts with a metal. For example
Zn + Cl2 ZnCl2 +H2
When a burning candle or matchstick is bought near hydrogen gas it burns with pop sound.
15. Why does an aqueous solution of an acid conduct electricity?
Ans. Electricity is conducted in a solution by ions. Acid release H+ ions in a solution so, it conducts electricity.
16. Why does dry HCl gas not change the colour of the dry litmus paper?
Ans. Colour of litmus paper changes only when it come in contact of H+ ions and H+ ions is produced only when HCl gas comes in contact with water. Therefore, dry HCl do not change the colour of dry litmus paper.
17. While diluting an acid, why it is recommended that the acid should be added to water and not water to the acid?
Ans. Addition of water to acid is an exothermic reaction. If we add water to acid lot of heat is produced that may breaks the glass container or sprout to burns the person adding it. But when acid is added to water with constant stirring, the heat produced is absorbed by water and no harm occurs.
18. How is concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Ans. Excess base dissolved in a solution of sodium hydroxide will release more hydroxide (OH–) ions. Therefore, concentration of hydroxide ions (OH–) will increase.
19. Do basic solutions also have H+ ions? If yes, then why are these basic?
Ans. Acidic and basic solutions both have H+ ions. The difference is that in acids H+ ions concentration is more than OH– ions concentration while in basic solution OH– ions concentration is more than H+ ions concentration.
20. Do basic solutions also have H+ ions? If yes, then why are these basic?
Ans. Acidic and basic solutions both have H+ ions. The difference is that in acids H+ ions concentration is more than OH– ions concentration while in basic solution OH– ions concentration is more than H+ ions concentration.
21. You have two solutions ‘A’ and ‘B’. The pH of solution ‘A’ is 6 and pH of solution ‘B’ is 8. Which solution has more hydrogen ions concentration? Which is acidic and which one is basic?
Ans. A solution having pH less than 7 is acidic and that having pH more than 7 is basic. So, solution ‘A’ is acid and ‘B’ is basic. Naturally ‘A ‘which is acidic has greater concentration of hydrogen ions concentrations.
22. What will happen if a solution of sodium hydrogen carbonate is heated? Give the equation of reaction involved.
Ans. Sodium hydrogen carbonate solution on heating gives sodium carbonate, carbon dioxide and water.
2NaHCO3 + heat Na2CO3 + CO2 +H2O
23. Write an equation to show the reaction between plaster of Paris and water.
Ans. The reaction between plaster of Paris and water is as follows:
CaSO4.1/2H2O + 3/2 H2O CaSO4.2H2O
24. Why does distilled water not conduct electricity, whereas rain water does?
Ans. Rain water contains small amount of acid because of which it conducts electricity. Distilled water is pure water. It does not contain ions. Therefore, it does not conduct electricity.
25. Why do acids not show acidic behavior in the absence of water?
Ans. Acids produce hydrogen ions or hydronium ions only in presence of water. Therefore, it shows acidic behavior only presence of water.
26. Equal lengths of magnesium ribbons are taken in test tubes A and B. hydrochloric acid is added to test tube A, while acetic acid is added to test B. In which test tube will the fizzing occur more vigorously and why?
Ans. HCl is stronger acid than CH3COOH. Therefore, H+ ions concentration in test tube A will be more than that in test tube B. hence, reaction will take place faster in test tube A than in test tube B. so, fizzing will occur more vigorously in test tube B.
27. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Ans. Bacteria change the fresh milk into curd by producing lactic acid. Because of the presence of lactic acid in curd, the pH will come down from 6 to lower value.
28. Plaster of Paris should be stored in moisture-proof container. Explain why?
Ans. Plaster of Paris reacts with moisture to form gypsum and sets to a hard mass. Therefore, it should be stored in moisture-proof container.
29. Kazi and priyam want to prepare dil 
.Kazi added conc. to water slowly with Constant stirring & cooling whereas Priyam added water to conc, .Name the Student Who was correct and why?
Ans. Kazi was correct. If water is added to a concentrated acid, the eat generated may cause the Mixture to splash our and cause burns. The glass container may also break due to excessive local heating.
30. A first aid manual suggests that vinegar should be used to treat wasp sting and baking soda for bee stings.
(i) What does this information tell you about the chemical nature of the wasp stings
(ii) If there were no baking soda in the ouse, what other household substance could you use to treat bee stings?
Ans. (i) Since vinegar (acetic acid) is used to heal or neutralize the effect of wasp stings This means that the chemical present in the stings must be some base.
(ii) 
31. A compound ‘X’ on electrolysis in aqueous solution produces a strong base. ‘Y’ along with two gases ‘A’ and ‘B’. ‘B’ is used in manufacture of bleaching powder. Identify X, Y, A and B. Write chemical equations.
Ans.
32. A yellow powder X gives a pungent smell if left open in air. It is prepared by the Reaction of dry compound Y with chlorine gas. It is used for disinfecting drinking Water. Identify X and Y. and write the reaction involved.
Ans.
33. A few drops of phenolphthalein indicator were added to an unknown solution A. It Acquired pink colour. Now another unknown solution B was added to it drop by Drop and the solution becomes colorless. Predict the nature of A & B.
Ans. Sol ‘A’ is basic in nature as phenolphthalein has imparted pink colour to it. Sol ‘B’ is an acid it has made solution A colourless by neutralizing by its basic effect.