NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts provides detailed step-by-step answers to help students build a solid foundation in chemical concepts, indicators, pH scale calculations, and practical salt preparations for board examinations.
Overview of Topics & Subtopics
Intext Questions - Page Number: 18
Q1: You have been provided with three test tubes containing distilled water, acidic solution, and basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer:
1. Dip the red litmus paper into each test tube one by one. The tube that turns the red litmus paper blue contains the basic solution.
2. Take the newly turned blue litmus paper and dip it into the remaining two test tubes. The tube that turns the blue litmus paper back to red contains the acidic solution.
3. The remaining test tube, which causes no color change on either red or blue litmus paper, contains distilled water.
Q2: Why should curd and sour substances not be kept in brass and copper vessels?
Answer: Curd and sour substances naturally contain acids (such as lactic acid). Acids react with metals like copper and brass to form toxic, harmful metal compounds that make the food unfit for consumption.
Q3: 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?
Answer: Hydrogen gas (H2) is liberated.
Example: When zinc granules react with dilute sulphuric acid:
Equation: Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)↑
Test: Bring a burning candle near the gas bubbles. Hydrogen burns rapidly with a characteristic 'pop' sound.
Intext Questions - Page Number: 22
Q1: Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer: Acids like HCl and HNO3 dissociate in water to produce hydrogen ions [H+(aq) or H3O+], which are responsible for acidic behavior. Compounds like glucose and alcohol contain hydrogen but do not dissociate into free H+ ions in water; hence, they do not show acidic properties.
Q2: Why does an aqueous solution of an acid conduct electricity?
Answer: An aqueous solution of an acid dissociates into free ions (hydronium ions and anions) in water. These mobile ions allow the flow of electric current through the solution.
Q3: Why does dry HCl gas not change the colour of dry litmus paper?
Answer: Dry HCl gas lacks water, meaning it does not produce free hydrogen ions [H+(aq)]. Since acidity depends on the presence of H+ ions, dry HCl gas does not exhibit acidic behavior and cannot alter the color of dry litmus paper.
Intext Questions - Page Number: 28
Q1: 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 ion concentration? Which of this is acidic and which one is basic?
Answer:
• Solution A (pH = 6) is acidic and has a higher hydrogen ion concentration.
• Solution B (pH = 8) is basic and has a lower hydrogen ion concentration.
Note: Lower pH values represent higher H+ ion concentrations.
Q2: What effect does the concentration of H+(aq) ions have on the nature of the solution?
Answer: An increase in H+(aq) ion concentration makes the solution more acidic (lowering the pH value). Conversely, a decrease in H+ ion concentration makes the solution less acidic or more basic.
Intext Questions - Page Number: 33
Q1: What is the common name of the compound CaOCl2?
Answer: Bleaching Powder.
Q2: Name the substance which on treatment with chlorine yields bleaching powder.
Answer: Dry slaked lime [Calcium Hydroxide, Ca(OH)2].
Q3: Name the sodium compound which is used for softening hard water.
Answer: Washing Soda (Sodium Carbonate Decahydrate, Na2CO3·10H2O).
Q4: Write an equation to show the reaction between Plaster of Paris and water.
Equation: CaSO4·½H2O + 1½H2O → CaSO4·2H2O
(Plaster of Paris + Water → Gypsum)
Textbook Chapter End Exercise Questions
Q1: A solution turns red litmus blue, its pH is likely to be:
(a) 1
(b) 4
(c) 5
(d) 10
Correct Answer: (d) 10 (Solutions that turn red litmus blue are basic, with pH > 7).
Q2: 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
Correct Answer: (b) HCl (Egg shells contain calcium carbonate, which reacts with acid to produce carbon dioxide gas that turns lime water milky).
Q3: Why does distilled water not conduct electricity, whereas rain water does?
Answer: Distilled water is a pure form of water containing no dissolved ionic compounds or mineral salts. Rainwater dissolves atmospheric gases like CO2 and SO2, forming weak acids that dissociate into free ions to conduct electricity.
Q4: Why do acids not show acidic behaviour in the absence of water?
Answer: Acids only dissociate to release hydrogen ions [H+(aq)] in the presence of water. Without water, ion separation cannot occur, so the acid cannot display acidic behavior.
Q5: Plaster of Paris should be stored in a moisture-proof container. Explain why.
Answer: Plaster of Paris rapidly absorbs moisture from the atmosphere and undergoes hydration to transform into a hard solid mass known as Gypsum (CaSO4·2H2O), destroying its setting properties.
