NCERT Solutions Class 10 for Science Chapter 2 Acids, Bases and Salts : In this post, we will share with you all the detailed NCERT Solutions of Class 10 Science Chapter 2 Acids, Bases and Salts. This will contain both in-text and back-exercise questions for Science and Social Science, and all exercise questions for Mathematics. For all school and board level examinations, doing all the NCERT Questions is a must.

Why are NCERT Questions Important?

NCERT Questions and Answers not only help you get hold of concepts firmly and enhance your understanding, but also form the base of all types of questions asked in exams. Questions asked in exam are more or less the same type as mentioned in NCERT. Moreover, sometimes the questions in NCERT are directly asked in exams, as it is, without any changes.

Hence, it’s very important to understand NCERT Questions and Answers.

In-Text Questions (Page 18)

Question 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?

Answer 1:
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.

  • On litmus paper, the three solutions in the test tubes are poured separately.
  • The solution which turns red litmus to blue contains a basic solution.
  • Divide the formed blue litmus paper into two parts.
  • The solution from the test tube which turns blue litmus paper to red will be the acidic solution.
  • Solution of the test tube which do not change either red or blue litmus paper contain water.

NOTE: After immediate distillation, distilled water has a pH of 7. However, just within a few hours after distillation, it absorbs carbon dioxide from the atmosphere and turns slightly acidic with a pH of 5.8.

In-Text Questions (Page 22)

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

Answer 1:
Curd and sour food substances contain acids; these acidic substances combine with metal. This reaction turns food to poison which damage people’s health.

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 2:
When an acid reacts with any metal, salt and hydrogen gas are formed.
Metal + Acid → Salt + 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 3:
As the end product is calcium chloride and the gas formed is carbon dioxide, the metal compound A must be calcium carbonate. Therefore, the reaction between calcium carbonate and hydrochloric acid is

In-Text Questions (Page 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 1:
H+ ions in aqueous solution are responsible for acidic character. HCl, HNO3, etc. give H+ ions in water while alcohol and glucose do not give H+ ion in water. Therefore, alcohol and glucose do not show acidic character.

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

Answer 2:
Charged particles are responsible for the conductance of electricity in an acid. These charged particles called as ions are the reason behind conductance of electricity in acid.

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

Answer 3:
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.

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 4:
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 to dilute it, then a large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on one’s face or clothes and cause acid burns.

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

Answer 5:
When acid is added to water there will be a fixed amount of hydronium present in the fixed volume of solution. If we dilute the solution hydronium ion per volume of solution decrease, this in-turn decreases Hydronium concentration in the solution.


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

Answer 6:
When base is dissolved in sodium hydroxide solution its hydroxide ions increase but it will reach saturation at some point. After saturation point hydroxide ion concentration is not affected even after adding base further.

In-Text Questions (Page 28)

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 1:
A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Since solution A has more hydrogen ion concentration, solution A is acidic and solution B is basic.

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

Answer 2:
More the concentration of H+ ions, higher the acidic nature of the solution.

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

Answer 3:
Basic solutions have H+ (aq) ions. But these are far less in number than OH– ions that is responsible for their basic nature.

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 4:
If the soil is too acidic (having low pH) then it is treated with materials like quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).

In-Text Questions (Page 33)

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

Answer 1:
Bleaching powder.

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

Answer 2:
Slaked lime Ca (OH)2.

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

Answer 3:
Sodium carbonate.

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

Answer 4:
Solution of sodium hydrogen carbonate on heating gives sodium carbonate and carbon dioxide gas is evolved.

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

Answer 5:

Exercise Questions (Page 34-35)

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

Answer 1:
Answer is 10 because litmus paper turns blue when reacts with basic solution (PH more than 7). Hence 10 is the 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 2:
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

Question 3:
0 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HC1. If we take 20 mL of the same solution of NaOH, the amount of HC1 solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL

Answer 3:
Since 10 ml of NaOH requires 8 mL of HCL, 20 ml of NaOH require 8 x 2 = 16mL of HCl. Hence the answer is option d 16mL.

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

Answer 4:
Indigestion is due to excess production of acid in the stomach. Medicines used to treat indigestion is called as Antacid.

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 filing

Answer 5:
(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) + 2 HCl (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 6:
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.

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

Answer 7:
Distilled water does not conduct electricity because it does not contain any ionic compound (like acids, bases or salts) dissolved in it.
Rainwater, while falling to the earth through the atmosphere, dissolves an acidic gas carbon dioxide from the air and forms carbonic acid (H2CO3). Carbonic acid provides hydrogen ions, H+ (aq) and carbonate ions, CO(aq)32to rainwater. Hence, due to the presence of carbonic acid which provides ions to rainwater, the rainwater conducts electricity.

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

Answer 8:
The acidic behaviour of acids is due to the presence of hydrogen ions, [H+ (aq) ions], in them. The acid produces hydrogen ions only in the presence of water. So in the absence of water, an acid will not form hydrogen ions and hence will not show its 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 9:
In increasing order of hydrogen ion concentration:

pH 11(C) < pH 9(E) < pH 7(A) <  pH 4(D) < pH 1 (B)
PH11 – Strongly alkaline
pH9 – weakly alkaline
PH7 – Neutral
pH4 – Weakly acidic
pH1 – Strongly acidic

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 10:
HCl is a strong acid whereas acetic is a weaker acid. Fizzing occurs because of the production of the hydrogen gas obtained due to reaction of the acid on the magnesium ribbon. Since HCl is a very strong acid there is a lot of liberation of hydrogen gas from test tube A. therefore, more fizzing take place in test tube A.

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 11:
Fresh milk is turned to curd due to production of lactic acid. Lactic acid reduces the pH of the milk.

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 12:
(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 13:
Plaster of Paris should be stored in a moisture proof container because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration. This will make the plaster of Paris useless after sometime.

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

Answer 14:
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

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

Answer 15:
Uses of washing soda :
(i) Washing soda is used in glass, soap and paper industries.
(ii) It is used for removing permanent hardness of water.

Uses of baking soda :
(i) Baking soda is used as an antacid in medicines to remove acidity of the stomach.
(ii) Baking soda is used for making baking powder (used in making cakes, bread, etc.).