Chapter 2 of class 10 NCERT science is Acid, Bases, and Salt. This chapter will help you understand the basic concepts of acids, bases, and salts. Learn different characteristics of acids, bases, and salts about the reaction with other chemical elements. You will get a brief explanation & study about the neutralization reaction and the measures of pH scale. There are fifteen questions in the exercise of this chapter. Swiflearn will provide its detailed solution that will help in tackling difficult questions easily.
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NCERT Solution for Class 10 Science Chapter 2 Acid, Bases, and Salt PDF
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?
Let us mark the three test tubes as A, B, and C put the given red litmus paper in each solution. If the colour of red litmus paper changes to blue (suppose in test tube A), then it is a base and if there is no colour change, then it is either acidic or neutral. Now, a drop of the solution from test tube A is put on the red litmus paper. Same process is repeated with solution B and C. If either of them changes colour to blue, then it is basic (let’s suppose B)
Therefore, out of three, one is eliminated.
Out of the remaining two (A and C), anyone can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining other two solutions separately and then check the nature of the drops of the obtained mixtures. If the colour of red litmus turns blue, then the second solution is neutral (C) and if there is no change in colour, then in that case, the second solution is acidic (A). This is because of the property that acidic and basic solutions neutralise each other. In this way we can identify the contents of each test tube.
Why should curd and sour substances not be kept in brass and copper
The acids are sour in taste. Thus, curd and other sour substances contain acids. When they are kept in brass and copper vessels, the metal of the vessel reacts with the acid present in sour substances and the curd to liberate hydrogen gas and harmful products which spoil the food.
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?
On reaction of an acid with a metal, hydrogen gas is usually liberated. Example to test the presence of hydrogen gas when acid reacts with metal is given below:
• In a test tube, take few pieces of zinc granules and add dilute H2SO4 to it.
• Shake it and pass the gas produced after reaction into a soap solution.
• Bubbles formed when gas is passed through the soap solution.
• These soap bubbles contain hydrogen gas.
The chemical equation of the reaction is:
3 2 2 2 CaCO HCl CaCl CO H O + → + + 2
H SO Zn ZnSO H 2 4 4 2 + → +
If we bring a burning candle near the soap bubbles, it will burn with a pop sound.
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.
The balanced chemical equation for the reaction:
Calcium carbonate hydrochloric acid Calcium chloride Carbon dioxide Water.
3 2 2 2 CaCO HCl CaCl CO H O + → + + 2
Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while
solutions of compounds like alcohol and glucose do not show acidic
On dissociation, HCl or HNO3 forms hydrogen ions which always occurs in the presence of water. Hydrogen ions (H+ ) combine with H2O to form hydronium ions (H3O+).
The reaction is as follows:
Due to the presence of hydronium ions (H3O+), HCl, HNO3, etc., show acidic characters.
Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate
in water to form hydrogen ions. Therefore, they do not show acidic character.
Why does an aqueous solution of acid conduct electricity?
In aqueous solution, acid dissociates into ions which are responsible for conduction of electricity.
Why does dry HCl gas not change the colour of the dry litmus paper?
Dry HCl gas does not contain H+ ions. Only in aqueous solution an acid dissociates to give ions. The litmus paper colour is changed by the hydrogen ions. In this case, neither HCl is in the aqueous form nor the litmus paper is wet, hence, the litmus paper colour does not change.
While diluting an acid, why is it recommended that the acid should be
added to water and not water to the acid?
It is always recommended that acid should be added to water, because the process of dissolving an acid in water is exothermic. If the reverse process is done, then due to generation of large amount of heat, the mixture splashes out and causes burns. This may cause accident.
How is the concentration of hydronium ions (H3O+ ) affected when a solution of an acid is diluted?
When acid is added to water or when acid is diluted, the hydronium ions (H3O
+ ) concentration per unit volume decreases and the strength of the acid decreases as well.
How is the concentration of hydroxide ions (OH− ) affected when excess base is dissolved in a solution of sodium hydroxide?
The hydroxide ions (OH− ) concentration per unit volume would increase when excess base is dissolved in sodium hydroxide solution.
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?
The pH < 7 indicates an acidic solution, while pH > 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and it has more hydrogen ion (H+
) concentration than the solution of pH = 8 which is a basic solution. The solution of pH = 8 has more hydroxide ion (OH– ) concentration.
What effect does the concentration of H+ (aq) ions have on the nature of the
With an increase in concentration of H + , the solution becomes more acidic, whereas with its decrease of concentration, the solution becomes less acidic and causes an increase in the basicity of the solution.
Do basic solutions also have H+
(aq) ions? If yes, then why are these basic?
Yes, basic solution also has H+
(aq) ions. However, their concentration is less as compared to
the concentration of OH− ions which makes the solution basic.
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)?
If the soil is acidic which is improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.
What is the common name of the compound CaOCl2?
Name the substance which on treatment with chlorine yields bleaching
The compound is calcium hydroxide [Ca(OH)2], which on treatment with chlorine, yields bleaching powder.
Name the sodium compound which is used for softening hard water.
Washing soda (Na2CO3.10H2O), the sodium compound is used for softening hard water.
What will happen if a solution of sodium hydro carbonate is heated? Give
the equation of the reaction involved.
When a solution of sodium hydro carbonate or sodium hydrogen carbonate is heated, sodium carbonate and water are formed with the evolution of carbon dioxide gas. Sodium Hydrogen carbonate Sodium carbonate Water Carbon dioxide
2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)
Write an equation to show the reaction between Plaster of Paris and water.
The chemical equation can be represented as:
4 2 2 4 2
1 3 . .2
CaSO H O H O CaSO H O + →
3( ) ( ) 2( ) 2( ) 2 ( ) 2 CaCO HCl CaCl CO H O s aq aq g l + → + +
A solution turns red litmus blue, its pH is likely to be
(d) Bases turn red litmus blue. Basic solution has a pH > 7. Since, the solution turns red litmus blue, its pH would likely to be 10.
A solution reacts with crushed egg-shells to give a gas that turns lime-water
milky. The solution contains
(b) The solution contains HCl which reacts with crushed egg-shells to give a gas that turns lime-water milky.
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
(a) 4 ml
(c) 12 ml
(d) 16 ml
(d) 10 ml of a solution of NaOH neutralises 8 ml of a solution of HCl
Thus, 20 ml of a solution of NaOH neutralises (20*8/10)ml =16 ml of HCl solution.
Which one of the following types of medicines is used for treating
(c) Antacid is commonly used for treating indigestion.
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.
(a) Word equation: Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
Balanced equation : Zn + H2SO4 —> ZnSO4 + H2
(b) Word equation: Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen.
Balanced equation: 2HCl (aq) + Mg (s) →MgCl2 (aq) + H2(g)
(c) Word equation: Sulphuric acid + Aluminium → Aluminium sulphate +Hydrogen
Balanced equation: 2Al+dil.3H2SO4——Al2(SO4)3+3H2
(d) Word equation: Hydrochloric acid + Iron → Ferric chloride + Hydrogen
Balanced equation: 2HCl + Fe —->FeCl2 + H2
Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.
• Two nails are fitted on a cork kept it in a 100 mL beaker.
• The nails are then connected to the terminals of a 6-volt battery through a bulb and a switch.
• Some dilute HCl is poured in the beaker and the current is switched on.
• The same experiment is then performed with glucose solution and alcohol solution.
The bulb glows in the HCl solution and does not glow in the glucose or alcohol solution.
In aqueous solution, 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, the glucose solution does not dissociate into ions. Therefore, the bulb does not glow.
All acids contain hydrogen but not all compounds containing hydrogen are acids. So, alcohols and glucose contain hydrogen, but they are not categorised as acids.
Why does distilled water not conduct electricity, whereas rain water does?
Distilled water is a pure form of water which contains no ionic species. Therefore, it does not conduct electricity. Rain water is an impure form of water, contains many ionic species acids and thus, it conducts electricity.
Why do acids not show acidic behaviour in the absence of water?
Acids can only dissociate in aqueous solution to from hydrogen ions which are responsible for the acidic behaviour. Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only.
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
(b) Strongly alkaline?
(c) Strongly acidic?
(d) Weakly acidic?
(e) Weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
(a) Neutral: Solution D with pH=7
(b) Strongly alkaline: Solution C with pH=11
(c) Strongly acidic: Solution B with pH=1
(d) Weakly acidic: Solution A with pH=4
(e) 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.
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?
The fizzing occurs strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and generates more H+ ions. Therefore, HCl produces hydrogen gas at a faster rate due to which fizzing occurs.
Fresh milk has a pH of 6. How do you think the pH will change as it turns
into curd? Explain your answer.
The pH of fresh milk is 6. As it changes into curd, the pH will decrease because curd contains lactic acid which reduces the pH.
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?
(a) In alkaline condition, milk does not set as curd easily due to the formation of lactic acid.
(b) Since, this milk is slightly basic than normal milk, acids produced to set the curd are neutralised by the base added to the milk. Thus, it takes a longer time for the curd to set.
Plaster of Paris should be stored in a moisture-proof container. Explain
Plaster of Paris (POP) should be stored in a moisture-proof container because it is a powdery mass, absorbs water or moisture to form a hard solid mass known as gypsum.
Gypsum (Hard solid)
Plaster of Paris Water
4 2 2 4 2
1 3 . .2
CaSO H O H O CaSO H O + →
What is a neutralisation reaction? Give two examples.
Neutralisation reaction: A reaction in which an acid and base react with each other to give a salt and water.
(i)NaOH + HCl———->NaCl + H2O.
(Base) (Acid) (Salt) (Water)
(ii) During indigestion (caused due to the production of excess acid in the stomach), we tak ean antacid (milk of magnesia, Mg(OH)2 which is basic in nature). The antacid neutralises the excess of acids and thus gives relief from indigestion.
Mg(OH)2 + 2HCl = MgCl2 + 2H2O
Give two important uses of washing soda and baking soda.
Uses of washing soda:
(a) It is used to remove permanent hardness of water.
(b) It is used in glass, soap, and paper industries.
Uses of baking soda:
(a) It is used baking powder. Baking powder is a mixture of baking soda and tartaric acid. Baking powder makes bread or cake fluffy.
(b) It is used in soda-acid fire extinguishers.