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Acids, Bases and Salts class 10 questions and answers
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts of Intext questions
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 18
Ques 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?
Solution: If the red litmus paper does not change its color then it is acid. On the other hand, if the color of red litmus changes to blue then it is base. Also, if there is a slight change in the color of red litmus then it is distilled water.
Identifying the contents of test tube:
Out of the remaining two, any one can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked.
If the color of red litmus turns blue, then the second solution is neutral and if there is no change in color , then the second solution is definitely acidic. This is due to the fact that acidic and basic solutions neutralize each other. Therefore, in this way we can distinguish between the three types of solutions.
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 22
Ques 1: Why should curd and sour substances not be kept in brass and copper vessels?
Solution: Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, and hence spoiling the food substances.
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?
Solution: When an acid reacts with a metal then Hydrogen gas is usually liberated.
example:
Take a few pieces of zinc granules and add 5 ml of dilute H2SO4 in it. Now shake it and pass the gas that is produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles has the hydrogen gas.
Reaction involved: H2SO4 + Zn → ZnSO4 + H2 ↑
Test to check the presence of hydrogen gas:
We can test the evolved hydrogen gas by its burning with a pop sound when a burning candle is brought near to the soap bubbles formed.
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.
Solution: Balanced chemical equation for the reaction:
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l) ,OR,
Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 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?
Solution: When HCl or HNO3 are mixed in water then they dissolve in water to form H+ or H3O ions which exhibits their Acidic character. For example:
HCl (aq) → H + Cl-
H + H2O → H3O
On the other hand, when alcohols and glucose are mixed in water then they do not dissolve to form ions. Therefore, they do not exhibit acidic character when mixed in the water.
Ques 2: Why does an aqueous solution of an acid conduct electricity?
Solution: The presence of hydrogen (H ) or hydronium (H3O ) ions in the aqueous solution of an acid are responsible for conduction of electricity in that aqueous solution.
Ques 3: Why does dry HCl gas not change the color of the dry litmus paper?
Solution: Dry HCl gas not change the color of the dry litmus paper due to the fact that it has no Hydrogen ions (H ) in it.
Ques 4: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Solution: The process of dissolving an acid in water is exothermic reaction ,i.e. heat is evolved, so it is always recommended that acid should be added to water. If it is done in the alternative way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.
Ques 5: How is the concentration of hydronium ions (H3O ) affected when a solution of an acid is diluted?
Solution: When an acid is diluted, the concentration of hydronium ions (H3O ) per unit volume decreases. As a result of which the strength of the acid decreases.
Ques 6: How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide
Solution: The concentration of hydroxide ions (OH−) will increase when excess base is dissolved in a solution of sodium hydroxide.
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 28
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?
Solution: On a pH scale, a pH value of less than 7 shows an acidic solution, while greater than 7 shows a basic solution. Therefore, the solution with pH = 6 is acidic in nature and has more hydrogen ion concentration than the solution of pH = 8 which is basic in nature.
Ques 2: What effect does the concentration of H +(aq) ions have on the nature of the solution?
Solution: Concentration of H+(aq) can have a different effect depending on the nature of a particular solution. With an increase in H+ ion concentration, the solution becomes more acidic in nature, while a decrease of H+ ion causes an increase in the basic character of the given solution.
Ques 3: Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
Solution: Yes, basic solutions do have H+(aq) ions. However, their concentration is very low in comparison to the concentration of OH- ions. This makes the solution basic despite having H+ ions.
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)?
Solution: If the farmer has the type of soil which is acidic and improper for cultivation of crops, then to increase the basic nature of the soil, the farmer would treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 33
Ques 1: What is the common name of the compound CaOCl2?
Solution: Its common name is Bleaching Powder.
Ques 2: Name the substance which on treatment with chlorine yields bleaching powder?
Solution: Calcium hydroxide [Ca(OH)2] on treatment with chlorine yields bleaching powder.
Ques 3: Name the sodium compound which is used for softening hard water.
Solution: Washing soda (Na2CO3.10H2O) 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.
Solution: When the sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.
The reaction involved is:
2NaHCO3→Na2CO3 + H2O + CO2
Ques 5: Write an equation to show the reaction between Plaster of Paris and water.
Solution: The reaction between Plaster of Paris and water:
CaSO4.1/2H2O + 3/2H2O→CaSO4.2H2O
NCERT Solutions for Class 10 Science Chapter 2 on Page No: 34
NCERT Solutions for Class 10 Science Chapter 2 of Exercise questions
Ques 1: A solution turns red litmus blue, its pH is likely to be(a) 1
(b) 4
(c) 5
(d) 10
Solution: (d) as the Bases turn red litmus blue and the acids turn blue litmus red. Basic solution has a pH value more than 7. Since the solution turns red litmus blue, its pH is likely to be 10.
Ques 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
Solution: (b) HCl
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 of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8mL
(c) 12 mL
(d) 16 mL
Solution: (d) 16 mL
Ques 4: Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Solution: (c) Antacid is used for treating the problem of indigestion.
Ques 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.
Solution: (a) H2SO4 (aq) Zn (s) → ZnSO4 (aq) H2 (g)
(b) 2HCl (aq) Mg (s) → MgCl (aq) H2 (g)
(c) 3H2SO4 (aq) 2Al (s) → Al2SO4 (aq) 3H2 (g)
(d) 6HCl (aq) 2Fe (s) → 2FeCl3 (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.
Solution: Activity:
Two nails are fitted on a cork and are kept it 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 in the beaker and the current is switched on. A similar experiment is then performed with glucose solution and alcohol solution.
Observations: It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.
Result:
HCl breaks into H+ and Cl−ions. These ions are responsible for the conduction of electricity in the solution resulting in the glowing of the bulb. But, the glucose solution does not break into ions. Hence, it does not conduct electricity.
Conclusion:
From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorized as acids.
Ques 7: Why does distilled water not conduct electricity, whereas rain water does?
Solution: Distilled water is a pure form of water and it does not have any ions. Hence, it does not conduct electricity. Rain water, being an impure form of water, contains many ions like acids and hence it successfully conducts electricity.
Ques 8: Why do acids not show acidic behavior in the absence of water?
Solution: Acids do not show acidic behavior in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is to be noted that it is the hydrogen ions that are responsible for the 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
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
Solution:
(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.
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. In which test tube will the fizzing occur more vigorously and why?
Solution: The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added or present. This is because HCl is a stronger acid in comparison to the CH3COOH and hence it produces hydrogen gas at a greater speed due to which the fizzing occurs.
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.
Solution: The pH of milk is 6. As it changes to curd, the pH value will decrease as the curd is acidic in nature. The acids present are responsible for the decrease in the pH value.
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?
Solution: (a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily.
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.
Ques 13: Plaster of Paris should be stored in a moisture-proof container. Explain why?
Solution: The Plaster of Paris should be stored in a moisture-proof container because it absorbs the water from the moisture present and turn into a hard substance (known as Gypsum).
Ques 14: What is a neutralization reaction? Give two examples.
Solution: A reaction in which an acid and base react with each other to give a salt and water is termed as neutralization reaction.
Example of neutralization reaction:
(i) NaOH HCl → NaCl H2O
(ii) HNO3 KOH → KNO3 H2O
Ques 15: Give two important uses of washing soda and baking soda.
Solution:
Two important uses of washing soda are:
1. It is used in glass, soap, and paper industries.
2. It is used to remove permanent hardness of water.
Two important uses of baking soda are:
1. It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases CO2 that makes bread or cake fluffy.
2. It is used in soda-acid fire extinguishers.
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