Class 10 NCERT Solutions Science Chapter 2 Acids, Bases and Salts

This article contains the Class 10 NCERT Solutions Science Chapter 2: Acids, Bases and Salts. You must have a solid grasp of the theories, practise with the reactions, equations, and formulas, and respond to questions from the NCERT Chemistry books if you wish to do well in Science on the Class 10 board exams as well as the JEE and NEET. To get a high score, it is essential to read through each question's detailed answers.

NCERT Class 10 Solutions: Science Chapter 2 (Page 18)

Page Number: 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: First, let us understand the litmus paper. We have two colours of litmus paper one is red and the other is blue.

Red litmus changes to blue on coming in contact with a basic solution. If it is in acidic or other solution then it stays red.

Blue litmus changes to red on coming in contact with an acidic solution. If it is in basic or other solution then it stays blue.

I hope after reading the above explanation it will be easy to crack the answer to the above question.

We have red litmus and three test tubes. What we will do is, first we will dip the red litmus in each of the test tubes. Since one of them is base it will change its colour to blue while the other two will not change the litmus paper colour and it will stay red.

The test tube which turns the litmus blue has the basic solution and now we are left with blue litmus paper and two test tubes.

With the blue litmus, we will dip it in the remaining two test tubes. The test tube which will change the litmus paper colour to red will be an acidic solution and we will be left with only one test tube which will be the distilled water.

Page Number: 22

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

Answer: Sour substances and curd are acidic types of substances. Acid can react with the components in brass or copper and if a chemical reaction takes place it will definitely result in some new compound, which may be dangerous for the body and can result in food poisoning or other diseases.

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: Whenever an acid reacts with any metal then hydrogen gas is liberated during the chemical reaction.

If we take zinc granules and dilute sulfuric acid in a test tube then the zinc displaces the hydrogen from the acid to form a compound. Zn + H₂SO₄ → ZnSO₄ + H₂

There are various methods through which we can test the presence of hydrogen gas. Hydrogen gas is insoluble in water. If the above reaction is performed in a test tube and if it is passed through a soap solution then it will rise as a soap bubble which will contain hydrogen gas. If a burning candle is brought near the bubbles formed then the bubble bursts with a pop sound.

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: A is a metal compound and the gas evolved extinguishes a burning candle then the gas has to be carbon dioxide. If this is the case then the metal must be calcium carbonate because one of the compounds formed in the reaction is calcium chloride which is a salt. We know that if a metal carbonate reacts with acid it forms a salt, carbon dioxide and water. The chemical reaction is: CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

Page Number: 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: Hydrochloric and Nitric acid i.e. HCl, HNO₃ when dissolved in an aqueous solution form hydrogen ions i.e. H⁺ ions while this does not happen in the case of alcohol or glucose therefore hydrochloric acid and nitric acid shows acidic characteristics while alcohol and glucose doesn't.

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

Answer: We know that acid when dissolved in an aqueous solution generated hydrogen ions which are charged particles, in fact, they are cations as they are positively charged and we know that charged particles are always a good conductor of electricity.

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

Answer: HCl gas shows acid when dissolved in an aqueous solution because it forms hydrogen ions. Since dry HCl does not form hydrogen ions therefore it does not shows acidic characteristics as a result of which it doesn't change the colour of the litmus paper.

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: Dilute acids are acids in which water quantity is more while concentrated acid has acid in high quantity. While diluting acid we should always add acid to water because it won't create any harm or reaction. On the other hand, if water is added to acid then it evolves a large amount of heat at once and because of that heat, water changes to steam rapidly and it can splash the acid which may harm or cause acid burns.

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

Answer: There are a definite number of hydronium ions per volume of the solution when a certain amount of acid is introduced to water. The concentration and number of hydronium ions per volume decrease with dilution.

Question 6: How is the concentration of hydroxide ions (OH^-) affected when an excess base is dissolved in a solution of sodium hydroxide?

Answer: When an extra base is dissolved in a sodium hydroxide solution, the concentration of hydroxide ions will rise, but only to a certain point, beyond which it will become virtually constant.

Page Number: 28

Question 1: You have two solutions A and B. The pH of solution A is 6 and the pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which one is basic?

Answer: A pH value helps to indicate whether a solution is acidic, basic or neutral depending on the reading. If the pH has a value less than 7 it means that the solution is acidic while pH value greater than 7 means that the solution is basic and if it is 7 it means that the solution is neutral.

Now it can be easily identified that A has a value of 6 which is less than 7, therefore, A is acidic while B has a value of 8 which is greater than 7 which means B is a basic solution.

In some above answers, we have seen that acids when added to an aqueous solution then hydrogen ions get produced so the acidic solution will be having a high hydrogen ion concentration. Here A is acidic therefore A has a higher hydrogen ion concentration.

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

Answer: Dry HCl does not change the colour of the litmus paper while an aqueous solution of HCl does because an aqueous solution produces hydrogen ions. Therefore we can say that the concentration of hydrogen ions defines whether any solution is acidic or basic. The acidic solution has a greater amount of hydrogen ions.

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

Answer: Yes, the basic solution has the hydrogen ions i.e. H⁺ (aq) ions in them. However, the amount of OH^- ions present is very greater as compared to hydrogen ions therefore they are regarded as the base.

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 condition is not favourable for the growth of the crop then farmers use quick lime or slaked lime or chalk. Basically, it means that soil is acidic and has a high pH value.

Page Number: 33

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

Answer: The common name of the compound CaOCl₂ is Bleaching powder.

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

Answer: When Slaked lime Ca(OH)₂ is treated with chlorine then it yields bleaching powder.

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

Answer: Sodium Carbonate is the compound which is 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 a solution of sodium hydrogen carbonate is heated then it produces products; sodium carbonate, water, and carbon dioxide gas, which is released in this reaction.

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

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

Answer:

NCERT Solutions for Class 10 Science Chapter 2 Textbook Chapter Questions

Question 1: A solution turns red litmus blue, its pH is likely to be

1. 1
2. 4
3. 5
4. 10

Answer: d (10), because a red litmus will turn blue only if the solution is basic. Also, a pH value greater than 7 indicates that the solution is a basic solution.

Question 2: A solution reacts with crushed-egg shells to give a gas that turns lime water milky. The solution contains

1. NaCl
2. HCl
3. LiCl
4. KCl

Answer: b.) HCl, because egg shells are completely made up of calcium carbonate (CaCO₃) and when hydrochloric acid reacts with calcium carbonate it forms calcium chloride, water and carbon dioxide and carbon dioxide is the gas which turns lime water milky.

Question 3: 10 mL of a solution of NaOH is found to be completely neutralised 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 neutralise it will be

1. 4 mL
2. 8 mL
3. 12 mL
4. 16 mL

Answer: d.) 16 mL

Question 4: Which one of the following types of medicines is used for treating indigestion?

1. Antibiotic
2. Analgesic
3. Antacid
4. Antiseptic

Answer: c.) Antacid

Question 5: Write word equations and then balanced equations for the reaction taking place when

1. dilute sulphuric acid reacts with zinc granules
2. dilute hydrochloric acid reacts with magnesium ribbon
3. dilute sulphuric acid reacts with aluminium powder
4. dilute hydrochloric acid reacts with iron filing

Answer: a.) Zinc + dilute sulphuric acid → Zinc sulphate + Hydrogen

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

b.) Magnesium ribbon + dil. Hydrochloric acid → Magnesium chloride + Hydrogen

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

c.) Aluminium powder + dil. Sulphuric acid > Aluminium sulphate + Hydrogen

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

d.) Iron filings + Dilute hydrochloric acid > Ferric chloride + Hydrogen

2Fe (s) + 6HCl (aq) → 2FeCl₃ (aq) + 3H₂ (g)

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

Answer: Alcohol and glucose both of them contain hydrogen. However, in order to act as an acid, they need to produce hydrogen ions when current is passed through them. And this doesn't happen i.e. hydrogen and glucose didn't produce any kind of hydrogen ions on the passing of electric current.

i.) Take solutions of glucose and alcohol for the experiment

(ii.) Insert two nails in a cork and place the cork in a beaker. Fill the beaker with water up to 100mL.

iii.) Take a 6-volt battery and connect the two nails with the two terminals of the battery. Also, impose a switch and a bulb in the connection.

iv.) Now pour the alcohol into the beaker and turn on the switch and let the current pass.

v.) The bulb will not glow in this case.

vi.) Similarly if the same procedure is followed with glucose, the bulb will not glow in that case also.

vii.) So it basically gives us a conclusion that there were no hydrogen ions obtained in the solution because of which the bulb did not glow. Thus, it proves that alcohols and glucose are not acids.

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

Answer: Distilled water is clean water and in order to conduct electricity there should be some kind of particles which forms ions. Because distilled water doesn't have any kind of impurity therefore it does not conduct any kind of electricity.

Lots of gases are present in the atmosphere and one of them is carbon dioxide. So when the rain starts and falls towards the earth's surface it gets mixed with carbon dioxide gas, creating carbonic acid (H₂CO₃). Rainwater is enriched with carbonate ions CO₃^2-(aq) and hydrogen ions H⁺(aq) from carbonic acid. Rainwater conducts electricity due to the presence of these ionic compounds.

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

Answer: Acids' acidic behaviour is caused by the hydrogen ions, or H+ (aq) ions, that are present in them. Only in the presence of water, the acid generates hydrogen ions. Therefore, in the absence of water, an acid won't produce hydrogen ions and won't behave like an acid.

Question 9: Five solutions A, B, C, D and E when tested with a universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is

1. Neutral
2. Strongly alkaline
3. Strongly acidic
4. Weakly acidic
5. Weakly alkaline

Arrange the pH in increasing order of hydrogen ion concentration.

Answer:

a.) D is neutral because it has a pH value of 7.

b.) C is strongly alkaline because it has the greatest value which is greater than 7.

c.) B is strongly acidic because it has the least value which is less than 7.

d.) A is a weak acid compared to B because its value is closer to 7 if compared to B.

e.) E is weakly alkaline because its value is less than C and greater than 7.

Bases contain the least hydrogen ions while acids contain the most so the arrangement will be from the base towards the acid. Therefore the pH in increasing order of hydrogen ion concentration is

C < E < D < A < B

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. In which test tube will the fizzing occur more vigorously and why?

Answer: Magnesium reacts with acid. So the strong acid will create more fizzing in the test tube. Here HCl is a strong acid compared to acetic acid therefore test tube A will show more fizzing than test tube B. A strong acid is defined by a strong concentration of hydrogen ions thus we can say that here hydrochloric acid has a strong concentration of hydrogen ions than acetic acid.

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: Here the fresh milk has a pH value of 6. If the formation of curd starts the lactobacillus bacteria will produce lactic acid and we know that as the substance gets acidic its pH value falls. So the pH value of the milk will get reduced when curd formation is in process.

Question 12: A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Answer:

a.) In order to prevent milk from easily turning sour due to the production of lactic acid in it, milk is made slightly alkaline.

b.) Because the lactic acid that is created has to neutralise the alkali first in the milk before it can set into curd, so alkaline milk takes longer to become curd.

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

Answer: Plaster of Paris should be kept in a moisture-proof container since moisture might cause it to hydrate, which can slow down the setting process. The plaster of Paris will eventually become unusable as a result of this.

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

Answer: The reaction between an acid and a base to form salt and water is called a neutralisation reaction.

Examples:

NaOH + HCl → NaCl + H₂O

CH₃COOH + NaOH → CH₃COONa + H₂O

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

Answer: Washing Soda is used for:

i.) Washing soda is used in the paper, soap, and glass industries.

ii.) It is employed to eliminate the water's enduring hardness.

Uses of Baking Soda:

i.) Baking soda is utilised as an antacid in medications to reduce stomach acidity.

ii.) Baking powder is used in the bakery industry for making cakes, bread, etc.