NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases And Salts

The Class 10 NCERT Solutions for Science Chapter 2 Acids, Bases And Salts includes all the intext and exercise questions. Class 10 Science Chapter 2 Acids, Bases And Salts NCERT questions and answers help students to clear their doubts and to obtain good marks in Class 10 board exam. All the solutions provided in this article are strictly based on the CBSE syllabus and curriculum.

Class 10 Science Chapter 2 NCERT Questions and Answers

Class 10 Science Chapter 2 Acids, Bases And Salts NCERT Questions and Answers are prepared by experts with a detailed explanation that will help students complete their assignments & homework. Having a good grasp over CBSE NCERT Solutions for Class 10 Science will further help the students in their preparation for board exams and other competitive exams such as NTSE, Olympiad, etc.

NCERT Solutions for Class 10 Science Chapter 2 Intext Questions

Intext Questions (Page No. 18)

Question 1: You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer: We can identify the content in each of the test tubes using red litmus paper. This can be done by noticing the colour change of the red litmus paper.

  • If the red litmus paper changes to blue colour the solution is a basic solution.
  • If the red litmus paper experiences no change in acidic solution.
  • If the red litmus paper changes to purple colour the solution is distilled water.

Intext Questions (Page No. 22)

Question 1: Why should curd and sour substances not be kept in brass and copper vessels?

Answer: Curd and sour substances contain acids. These acids can react with brass and copper vessels to form toxic compounds. This makes the substances unfit for human consumption. Hence, they are not kept in brass and copper vessels.

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Question 2: 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 is usually liberated when an acid reacts with a metal.

 Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

The equation given above illustrates how zinc reacts with dilute hydrochloric acid resulting in the liberation of hydrogen gas and the formation of the salt zinc chloride.

A burning match stick, when brought near the mouth of the test tube where H2 gas is being released makes a pop sound. This confirms the presence of hydrogen gas.

Question 3: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Answer: Metal compound A is Calcium carbonate (CaCO3). When A reacts with dilute hydrochloric acid it produces effervescence. The chemical equation is given as:

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O (l)

The gas evolved is CO2. CO2 extinguishes a burning candle.

Intext Questions (Page No. 25)

Question 1: 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: When HCl or HNO3 are mixed with water, they dissolve in water to form hydrogen ions (H+) or Hydronium ions (H3O+) which show their acidic character.

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Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character.

Question 2: Why does an aqueous solution of acid conduct electricity?

Answer: An acid dissolves in water and dissociates to form H+ or H3O+ ions. Electricity is conducted through these moving ions.

Question 3: Why does dry HCl gas not change the colour of the dry litmus paper?

Answer: Colour of the litmus paper is changed by the hydrogen ions. Dry HCl gas does not contain H+ ions. It is only in the aqueous solution that an acid dissociates to give ions. Since in this case, neither HCl is in the aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change.

Question 4: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer: While diluting an acid, it is recommended that the acid should be added to water and not water to the acid because if water is added to concentrated acid, it release huge amount of heat which may result in explosion and can cause acid burns o face, clothes and body parts. Hence it is safe to add acid to water but not water to acid.

 Question 5: How is the concentration of hydronium ions H3O+ affected when a solution of an acid is diluted?

Answer: When the solution of acid is diluted then the concentration of hydronium ion H3O+ per unit volume decreases. On adding water, the H+ ions of the acid and hydroxyl ions of water react to form water molecules and the concentration of hydronium ions decreases. 

Question 6: How is the concentration of hydroxide ions OHaffected when excess base is dissolved in a solution of sodium hydroxide?

Answer: When the base is mixed with sodium hydroxide solution there is an increase in the number of hydroxide ions whereas the volume remains almost the same. This leads to an increase in the concentration of OH ions per unit volume.

Intext Questions (Page No. 33)

Question 1: 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: A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.

Question 2: What effect does the concentration of H+(aq)ions have on the nature of the solution?

Answer: Concentration of H+(aq) can have a varied effect on the nature of the solution. With an increase in H+ ion concentration, the solution becomes more acidic, while a decrease of H+ ion causes an increase in the basicity of the solution.

Question 3: Do basic solutions also have H+(aq) ions? If yes, then why are these basic?

Answer: Yes, basic solutions also have H+ ions, but they are basic in nature due to a greater number of OH ions than the H+ ions.

Question 4: Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

Answer: If the soil is acidic in nature (PH below 7) then such field should be treated with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).

Intext Questions (Page No. 34-35)

Question 1: What is the common name of the compound CaOCl2?

Answer: CaOCl2 (chemical name-calcium oxychloride) is commonly called bleaching powder.

Question 2: Name the substance which on treatment with chlorine yields bleaching powder.

Answer: Bleaching powder is prepared by treating Calcium hydroxide CaOH2 with chlorine. The chemical equation for the reaction is:

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Question 3: Name the sodium compound which is used for softening hard water.

Answer: Sodium carbonate is commonly used for softening hard water.

Question 4: What will happen if a solution of sodium hydrogen carbonate is heated? Give the equation of the reaction involved.

Answer: When sodium hydrogen carbonate (NaHCO3) is heated, sodium carbonate, water and carbon dioxide gas are obtained. The chemical equation for the reaction is

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Question 5: Write an equation to show the reaction between Plaster of Paris and water.

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NCERT Solutions for Class 10 Science Chapter 2 Exercise Questions

Question 1: A solution turns red litmus blue; its pH is likely to be:
(a) 1
(b) 4
(c) 5
(d) 10

Answer: (d) 10

A solution which turns the colour of red litmus to blue must be basic in nature. A basic solution has a pH value of greater than 7. The only option with pH greater than 7 is 10 which will be the correct answer.

Question 2: 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

Egg shells are made up of calcium carbonate, which on reaction with HCl liberates CO2 gas. When CO2 reacts with lime water (Ca (OH)2), it forms calcium carbonate which gives the  solution a milky appearance.

CaCO3 + 2HCl → CaCl2 + H2O + CO2

Ca(OH)2 + CO2 → CaCO3 + H2O

Question 3: 10 ml of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralize it will be:
(a) 4 ml
(b) 8 ml
(c) 12 ml
(d) 16 ml

Answer: (d) 16 ml

The amount of Hydroxide ions and hydrogen ions are directly proportional to the volume of their respective solutions. Hence, the problem can be solved by a unitary method.

Since 10 ml NaOH reacts with = 8 ml HCl

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  16 ml of HCl solution will be required to completely neutralize 20 ml of NaOH solution.

Question 4: Which of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic

Answer: (c) Antacid

An antacid is used for the treatment of indigestion which is caused due to excessive acidity in the stomach. The antacid chemical is basic in nature and thus, it neutralizes the acidity in the stomach. 

Question 5: Write word equations and then balanced equations for the reaction taking place when
(a) Dilute sulphuric acid reacts with zinc granules.
(b) Dilute hydrochloric acid reacts with magnesium ribbon.
(c) Dilute sulphuric acid reacts with aluminium powder.
(d) Dilute hydrochloric acid reacts with iron filings.

Answer: (a) Sulphuric acid + Zinc → Zinc sulphate + Hydrogen

H2SO4(aq) + ZnS(s) → ZnSO4(aq) + H2(g)

(b) Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen

2HCl (aq) + MgS(s) → MgCl2(aq) + H2(g)

(c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen

3H2SO4(aq) + 2Al(s) → Al2(SO4)3(aq) + 3H2(g)

(d) Hydrochloric acid + Iron Ferrous chloride + Hydrogen

6HCl (aq) + 2Fe(s) → 2FeCl2(aq) + 3H2(g)

Question 6: Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Answer: Two nails are fitted on a cork and are kept in a 100 ml beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured into the beaker and the current is switched on. The same experiment is then performed with a glucose solution and an alcohol solution.

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Observations:  It will be observed that the bulb glows in the HCl solution and does not glow in the glucose or alcohol solution.

Result:  HCl dissociates into H+ and Cl ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, neither the glucose solution nor the alcohol solution dissociates into ions. Therefore, these two solutions do not conduct electricity.

Conclusion: From this activity, it can be concluded that all acids generate hydrogen ions but not all compounds containing hydrogen are acids. That is why, though alcohols and glucose contain hydrogen, they are not categorized as acids.

Question 7: Why does distilled water not conduct electricity, whereas rainwater does?

Answer: Distilled water is a pure form of water and its pH is 7 and is devoid of any ionic species. Therefore, it does not conduct electricity. Rainwater, being an impure form of water, contains CO2, SO2, NO. These oxide gases react with water and get chemically converted into acids which are responsible for the release of ions that conduct electricity-contains many ionic species(acids) whose pH is less than 7 and therefore it conducts electricity

Question 8: Why do acids not show acidic behaviour in the absence of water?

Answer: The acidic behaviour from acids is because of the presence of hydrogen ions. Hydrogen ions can only be produced in the presence of water and therefore water is definitely needed if acids are to show their acidic behaviour.

Question 9: Five solutions A, B, C, D , and E , when tested with universal indicator, showed pH as 4, 1,11,7 and 9, respectively. Which solution is
(a) neutral?
(b) Strongly alkaline?
(c) Strongly acidic?
(d) Weakly acidic?
(e) Weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.

Answer: At 25oC pH of neutral solutions = 7

As the pH falls below 7, it denotes acidic character with a pH of 1 being highly acidic. When the pH goes above 7, it implies that the solution is basic with 14 being highly basic.

Neutral → Solution D with pH 7

Strongly→ alkaline Solution C with pH 11

Strongly acidic → Solution B with pH 1

Weakly acidic → Solution A with pH 4

Weakly alkaline→ Solution E with pH 9

The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1

Question 10: Equal lengths of magnesium ribbons 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. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Answer: The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a quicker rate due to which fizzing occurs more vigorously in test tube A.

Mg + 2HCl → MgCl2 + H2 ↑ (faster)

Mg + 2CH3COOH → Mg(CH3COO)2 + H2 (slower)

Question 11: Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Answer: The pH of milk is 6. As it gets converted to curd (pH between 4.5 to 5.5) the pH will reduce because curd has lactic acid which is more acidic in nature. Thus, the pH drops below 6 when milk gets converted to curd.

 Question 12: A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?

Answer: (a) He shifted the pH of the fresh milk from 6 to slightly alkaline to prevent milk from getting sour due to production of lactic acid.

(b) This milk takes long time to set into curd because the lactic acid produced here first neutralises the pH then the pH is reduced to turn milk to curd.

Question 13: Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer: Plaster of Paris (POP) should be stored in a moisture-proof container because Plaster of Paris, a powdery mass, absorbs water (moisture) to form a hard solid known as gypsum.

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Question 14: What is a neutralization reaction? Give two examples.

Answer: A reaction in which an acid and a base react with each other to give a salt and water is termed as a neutralization reaction. In this reaction, energy is evolved in the form of heat and thus, such reactions are usually exothermic by nature.

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(ii) During indigestion (caused due to the production of excess of hydrochloric acid in the stomach), we administer an antacid (generally milk of magnesia, MgOH2 which is basic in nature). The antacid neutralizes the excess acid and thus gives relief from indigestion.

Mg(OH)2 + 2HCl → MgCl2 + 2H2O

Question 15: Give two important uses of washing soda and baking soda.

Answer: Two important uses of washing soda are as follows:
(i) It is used in glass, soap, and paper industries.
(ii) It is used to remove the permanent hardness of the water.

Two important uses of baking soda are as follows:

(i) It is used in baking industries. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed with water, it releases CO2 that makes bread or cake fluffy.

(ii) It is used in soda-acid fire extinguishers.

Topics covered under Class 10 Science Chapter 2 Acids, Bases And Salts

Below we have listed the topics discussed in NCERT Solutions for Class 10 Science Chapter 2. The list gives you a quick look at the different topics and subtopics of this chapter.

Section in NCERT BookTopics Discussed
2.1Understanding the chemical properties of Acids and Bases
2.1.1Acids and Bases in the Laboratory
2.2What Do All Acids and All Bases Have in Common?
2.2.1What happens to an Acid or a Base in a Water Solution?
2.3How Strong Are Acids Or Base Solutions?
2.3.1Importance of pH in Everyday Life
2.4More About Salts

NCERT Solutions for Class 10 Science Chapter 2 – A Brief Discussion

Chapter Overview: In this chapter, you will learn about the chemical properties Acids, Bases and Salts. This chapter mainly describes the chemical nature of acids, bases and salts, their reaction with metals, non-metals and with each other. The chapter covers topics like the importance of pH in everyday life, the pH range of acidic, basic and neutral solution and the wide applications of pH scale. Further, you will learn the chemical formulae, chemical reactions of various important salts and their preparation which are used in day to day life such as washing and baking soda, bleaching powder, and plaster of Paris. This chapter has many practical experiments that help students to grasp the concepts more easily.

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