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

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

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts is the first stepping stone for a student in the competitive world. With the introduction of the CBSE Board Exam for class 10 a few years back, this has become an important gateway for a student as based on the results of class 10th a student selects his future stream of Science, Commerce, or Arts.

Takshila Learning provides you with detailed and well explained NCERT Solutions for Class 10 of each chapter of each subject for NCERT Class 10. These NCERT Solutions help you to easily understand every concept so that you can score high in your CBSE Class 10 Board Exams.

Below you can find the NCERT solution for Class 10 Science Chapter 2. You can get a Solution for the all-important question of “Class 10 Science Chapter 2 Acids, Bases and Salts”

Ques 1: You are given three test tubes. The three test tubes contain distilled water, acidic solution and the basic solution respectively. There is only red litmus paper available in order to identify what is there in each test tube. How will you find out what is in each of the test tubes?

Soln: 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 changes to red colour the solution is acidic solution.
• If you did not observe any colour change then the solution is distilled water.

 

 

Page Number – 22

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

Soln: Curd and sour food substances contain acids; these acidic substances combine with metal. This reaction turns food to poison which damage people’s health.

 

Ques 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?

Soln: When an acid reacts with any metal, salt and hydrogen gas are formed.

Metal + Acid → Salt + Hydrogen gas

Ques 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.

Soln: As metal compound released is Calcium Chloride the gas evolved here is CO2. Hence metal A should be Calcium Carbonate. Hence the reaction between Calcium Carbonate and HCL is

CaCO₃ (s)+2Hcl(Aq) → CaCl₂( Aq)+ Co₂ (g)+H₂O (l)

 

 

Page Number – 25

Ques 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?

Soln: Release of H+ ion in water will make a compound acidic or non- acidic. Acids are substances that dissociate with water resulting in the production of hydrogen ions. Some compounds show acidic character as they dissolve in aqueous solution resulting in the production of hydrogen ions (acids such as HCl, HNO3).

Compounds similar to glucose or alcohol contain hydrogen elements but do not show signs of acidic nature. The fact is that the hydrogen in them will not differ like hydrogen in acids. They will not dissociate to become hydrogen ions when dissolved in water.Therefore the separation of hydrogen gas will determine the acidic or non-acidic nature of a compound.

  Ques 2: Why does an aqueous solution of an acid conduct electricity? Soln: Charged particles are responsible for the conduction of electricity in an acid. These charged particles, termed as ions, are caused by the electric current in the acid.

 

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

Soln: HCL does not give out Hydrogen ions, therefore HCL does not show any acidic behaviour and colour of the litmus paper remain the same on reacting with HCl gas.

 

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

Soln: When diluting an acid, it is recommended that the acid should be added to the water and not to add water to the acid because if water is added to the concentrated acid, it releases a large amount of heat resulting in an explosion. And can withstand acid O, clothing and body parts. Therefore it is safe to add acid to water but not acid to water.

 

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

Soln: When acid is added to water a certain amount of hydronium present in a certain amount of solution will be present. If we reduce the amount of hydronium ion solution in the solution, the hydronium concentration in the solution decreases.

 

Ques 6: How is the concentration of hydroxide ions (OH– ) affected when excess base is dissolved in a solution of sodium hydroxide?

Soln: When the base dissolves in the sodium hydroxide solution, its hydroxide ions increase but it will reach saturation at some point. The saturation point hydroxide ion concentration is not further affected after adding the base.

 

 

Page Number – 33

Ques 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?

Soln: To find the hydrogen ion concentration, we can use the rule that states, “The pH of any solution is inversely proportional to the hydrogen ion concentration”. Therefore, this means that the solution that has a lower pH number will have a higher hydrogen ion concentration. Therefore, solution A will have higher hydrogen ion concentrations. Furthermore, solution B will be basic and A will be acidic.

 

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

Soln: The hydrogen ion concentration decides the nature of the solution. If the hydrogen ion concentration increases then the solution becomes acidic and similarly if the hydrogen ion concentration decreases then the solution becomes basic.

 

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

Soln: Basic solutions has H+ ions, but hydroxide ions present in basic solution are more in basic solution . Hence Hydroxide ions turn solution to basic.

 

Ques 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)?

Soln: 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).

 

 

Page Number – 34

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

Soln: Common name of CaOCl₂ is bleaching powder.

 

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

Soln: The substance which on treatment with chlorine yields bleaching powder is Calcium hydroxide.

 

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

Soln: Sodium carbonate is the compound which is used for softening hard water.

Ques 4: What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Soln: Heating sodium hydrocarbonate yields sodium carbonate and carbon dioxide gas is liberated in the process.

2NaHCO₃ → heat → Na₂CO₃ + H₂O + CO₂

 

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

Soln: The chemical equation for the reaction of Plaster of Pans and water is

CaSO₄.1/2H₂O+3/2H₂O → CaSO₄.2H₂O

 

 

EXERCISE

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

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

Soln: Answer is 10 because litmus paper turns blue when reacts with basic solution (PH more than 7). Hence 10 is the answer.

 

Ques 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

Soln: Answer is HCl.

Egg shells contains calcium carbonate, which on reaction with HCl liberates CO₂ gas which turn lime water to milky.

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

 

Ques 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 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

Soln: Since 10 ml of NaOH requires 8 mL of HCL, 20 ml of NaOH require 8 x 2 = 16mL of HcL Hence the answer id option d 16mL.

 

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

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

Soln: Indigestion is due to excess production of acid in the stomach. The medicines used to treat indigestion are called as Antacids.

 

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

• Dilute sulphuric acid reacts with zinc granules.
• Dilute hydrochloric acid reacts with magnesium ribbon.
• Dilute sulphuric acid reacts with aluminium powder.
• Dilute hydrochloric acid reacts with iron filings.

Soln: (a) Dilute sulphuric acid reacts with zinc granules :

⇒  dilute sulphuric acid + zinc → Zink Sulphate + Hydrogen Gas

⇒  H₂SO₄(aq) + Zn → ZnSO₄(aq) + H₂(g)

 

(b) Dilute hydrochloric acid reacts with magnesium ribbon.

⇒  dilute Hydrochloric + Magnesium → Magnesium Chloride + Hydrogen Gas

⇒  2HCl(aq) + Mg → MgCl₂(aq) + H₂(g)

 

(c) Dilute sulphuric acid reacts with aluminium powder.

⇒  dilute Sulphuric Acid + Aluminium → Aluminium Sulphate + Hydrogen Gas

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

 

(d) Dilute hydrochloric acid reacts with iron filings.

⇒  dilute Hydrochloric Acid + Iron → Ferrous Chloride + Hydrogen Gas

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

 

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

Soln: Insert two nails on the wooden or rubber cork and place them on a beaker as shown in figure. Connect iron nail to a bulb, 6 volt battery and a wire connected to switch. Pour some alcohol or glucose so as to dip the nails in glucose or alcohol. Turn the switch on and you the see the bulb not glowing despite of connection to switch. Now empty the beaker and add HCL solution. This time bulb glows. This proves acid can conduct electricity but alcohol and glucose does not conduct electricity.

Ques 7: Why does distilled water not conduct electricity, whereas rain water does?

Soln: Distilled water does not conduct electricity but rail water does because-

1.     Distilled water does not contain any ionic compounds.2.     While rainwater contains much, much more compounds.3.     Rainwater has dissolved acidic gases such as carbon dioxide from the air and this produces carbonic acid. This means that it has hydrogen ions and carbonate ions. Therefore, with the presence of acid, rainwater can conduct electricity.

 

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

Soln: Acidic behavior from acids is due to 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 behavior.

 

Ques 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

• Neutral?
• Strongly alkaline?
• Strongly acidic?
• Weakly acidic?
• Weakly alkaline?

Soln: In increasing order of hydrogen ion concentration:

pH 11(B) → pH 9(E) → pH 7(A) → pH 4(D) → pH 1 (B)

pH 11-Strongly alkaline

pH 9- weakly alkaline

pH 7-Neutral

pH 4- Weakly acidic

pH 1- Strongly acidic

 

Ques 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?

Soln: HCl is a strong acid while acetic is a weak acid. Fizzing occurs due to the production of hydrogen gas obtained due to the reaction of the acid on the magnesium ribbon. Since HCl is a very strong acid, there is a lot of release of hydrogen gas from test tube A, so test tube A has more fizzing.

 

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

Fresh milk is turned to curd due to production of lactic acid. Lactic acid reduces the pH of the milk.

 

Ques 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?

Soln:

(a) They shifted the pH of fresh milk slightly from 6 to alkaline to prevent the milk from turning sour due to the production of lactic acid.

(b) It takes a long time for this milk to set in the curd because the lactic acid produced here first neutralizes the pH and then the pH is reduced to convert the milk into curd.

 

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

Soln: Plaster of Paris should be stored in a moisture-proof container because moisture can affect the plaster of Paris by slowing down the setting of the plaster due to hydration. This will make the plaster useless.

 

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

Soln: The reaction of the acid + base gives a product of salt + water, which is considered as neutralization reaction. Examples:

NaOH + HCl → NaCl + H₂O

Mg(OH)₂ + H₂CO₃ → MgCO₃ + 2H₂O

 

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

Soln:

Washing soda	Baking soda
1. It can be used to test garden soil for acidity. If bubbles develop, the soil is very acidic.	1. It is used as an electrolyte. 1. It can be used to test garden soil for acidity. If bubbles develop, the soil is very acidic.
2. It can be used domestically as a water softener for washing clothes. 2. If used on a car wash it will remove dead bug bodies without damaging the paint or paint on the car.	2. It can be used domestically as a water softener for washing clothes. 2. If used on a car wash it will remove dead bug bodies without damaging the paint or paint on the car.

 

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