2. Acids, Bases and Salts Science class 10 exercise Additional Questions With Solutions
2. Acids, Bases and Salts Science class 10 exercise Additional Questions With Solutions ncert book solution in english-medium
NCERT Books Subjects for class 10th Hindi Medium
Chapter Review
Chapter Review:
- There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators.
- Vanilla, onion and clove, can be used as olfactory indicators.
- The metal combines with the remaining part of the acid and forms a compound called a salt.
- Limestone, chalk and marble are different forms of calcium carbonate.
- The reaction between an acid and a base to give a salt and water is
known as a neutralisation reaction. - Metallic oxides react with acids to give salts and water, similar to the
reaction of a base with an acid, metallic oxides are said to be basic oxides. - All acids produce hydrogen ions, H+(aq), in solution.
- All bases produce OH–(aq), in solution.
- The pH of a neutral solution is 7.
- Values less than 7 on the pH scale represent an acidic solution.
- PH of rain water is less than 5.6, it is called acid rain.
- Tooth decay starts when the pH of the mouth is lower than 5.5.
- Salts of a strong acid and a strong base are neutral with pH value of 7.
- The salt formed by the combination of hydrochloric acid and
sodium hydroxide solution is called sodium chloride. - Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is
called rock salt - When electricity is passed through an aqueous solution of sodium
chloride (called brine). - The baking soda commonly used in the kitchen for making tasty crispy pakoras.
- On heating gypsum at 373 K, it loses water molecules and becomes
calcium sulphate hemihydrate. This is called Plaster of Paris.
Text-book Questions
In Text Questions
Page No: 18
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 colour of red litmus does not change then it is acid. If the colour of redlitmus changes to blue then it is base. If there is slight change in the colour of red litmus (such as purple) then it is distilled water.
Page No: 22
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, thereby spoiling the food.
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:
Hydrogen gas is usually liberated when an acid reacts with a metal.
Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2 ↑
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.
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:
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water.
Page No: 25
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 with water then they dissolve in water to form H+ or H3O+ ions which shows their acidic character. For example just see the following reactions
HCl (aq) → H+ + Cl-
H+ + H2O → H3O+
When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.
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 conducting electricity.
3. Why does dry HCl gas not change the colour of the dry litmus paper?
Solution:
Dry HCl gas not change the colour of the dry litmus paper because it has no Hydrogen ions (H+) in it.
4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Solution:
Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.
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. This means that the strength of the acid decreases.
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−) would increase when excess base is dissolved in a solution of sodium hydroxide.
Page No: 28
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:
A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.
2. What effect does the concentration of H+ (aq) ions have on the nature of the solution?
Solution:
If the concentration of H+ (aq) ions is increased (>10-7) then the solution become acidic and if the concentration of H+ (aq) ions is decreased (<10-7) then the solution become basic in nature.
3. Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?
Solution:
Yes, basic solution also has H+ ions. However, their concentration is less as compared to the concentration of OH- ions that makes the solution basic.
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 soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.
Page No: 33
1. What is the common name of the compound CaOCl2?
Solution: Bleaching Powder.
2. Name the substance which on treatment with chlorine yields bleaching powder?
Solution: Calcium hydroxide [Ca(OH)2]
3. Name the sodium compound which is used for softening hard water.
Solution: Washing soda (Na2CO3.10H2O)
4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Solution:When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.
Exercise
NCERT Solutions Exercise
Q1. A solution turns red litmus blue, its pH is likely to be
(a) 1
(b) 4
(c) 5
(d) 10
Ans. (d) 10
Q2. 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
Ans. (b) HCl
Q3. 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
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL
Ans. (d) 16 mL
Q4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Ans. (c) Antacid
Q5. 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.
Ans.
(a) Zn (s) + H2SO4 (aq) = ZnSO4 (aq) + H2 (g)
(b) Mg (s) + 2HCl (aq) = MgCl2 (aq) + H2 (g)
(c) 2Al (s) + 3H2SO4 (aq) = Al2(SO4)3 (aq) + H2 (g)
(d) Fe(s) + 2HCl (aq) = FeCl2 (aq) + H2 (g)
Q6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Ans. Take a solution of glucose, alcohol, hydrochloric acid, sulfuric acid etc. Put two nails on a cork and place the cork in a 100 mL beaker. Now connect the keys to both the terminals of a 6 volt battery through a bulb and switch. Now pour a little dilute HCl into the beaker and pass an electric current. Repeat the same process with dilute sulfuric acid. Compounds like alcohol and glucose also contain hydrogen but they are not classified as acids because they do not form H+ ions.
Q7. Why does distilled water not conduct electricity, whereas rain water does? Acids, Bases and Salts 35.
Ans. Distilled water is pure. Therefore, they do not conduct electricity because ions are required for the conduction of electricity. Whereas rain water conducts electricity because a small amount of acid is present in it. Which combine with the sulfur-dioxide and nitrogen dioxide present in the air to make it acidic. Being acidic, they produce H+ ions, due to which electricity conducts.
Q8. Why do acids not show acidic behaviour in the absence of water?
Ans. Acids are not acidic in the absence of water because H+ ions dissociate from acids only in the presence of water.
Q9. 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.
Ans.
solutions | pH values | tested with universal indicator |
A | 4 | weakly acidic |
B | 1 | strongly acidic |
C | 11 | strongly acidic |
D | 7 | neutral |
E | 9 | weakly acidic |
As the concentration of H+ ions increases, the value of pH decreases in the same way.
C < E< D< A < B
Q10. 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?
Ans. There will be more effervescence in test tube 'A' because hydrochloric acid is a stronger acid than acetic acid.
Q11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Ans. The pH value of fresh milk is 6. Lactic acid is formed in the process of curd formation. Hence the pH of curd will be less than 6.
Q12. 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?
Ans. (a) Changes the pH of fresh milk from 6 to slightly alkaline because Lactobacillus bacteria present in milk make the milk acidic. Baking soda is added to milk so that the milk remains alkaline for a long time so that it remains for a long time.
(b) It takes more time for this milk to become curd because the lactic acid formed in this process first neutralizes the base (baking soda) found in fresh milk and then converts it into acid due to which curd is formed.
Q13. Plaster of Paris should be stored in a moisture-proof container.
Explain why?
Ans. Plaster of Paris should be kept in a moisture proof container because it absorbs water in the presence of moisture to form the solid material gypsum. Due to which the property of freezing with water is destroyed in it.
Q14. What is a neutralisation reaction? Give two examples.
Ans. The reaction in which base and acid react to form water and salt, this reaction is called neutralization reaction. In this reaction, acid and base neutralize or neutralize each other's effect.
Q15. Give two important uses of washing soda and baking soda.
Ans.
Uses of washing soda:-
(1) Sodium carbonate is used in glass, soap and paper industries.
(2) It is used in the production of sodium compounds such as borax.
(3) Sodium carbonate is used for cleaning in homes.
(4) It is used to remove permanent hardness of water.
Uses of Baking Soda:-
(1) Baking soda is used to make food items soft, spongy and crispy.
(2) Baking soda being alkaline, it is used to bring relief by reducing or neutralizing the excess amount of acid in the stomach.
(3) Sometimes it is also used for quick cooking of food.
(4) It is also used in soda-acid fire extinguishers.
Additional Questions With Solutions
Extra Queations:-
Q1.Write three importance of pH in daily life.
Ans: Importance of pH in daily life.
(i)If pH of our mouth lowers than 5.5 then starts tooth decay.
(ii)Our body works within the range of pH 7.0 to 7.8.
(iii)To find out specific pH range of Soil, in which they grow well.
Q2.Why is Sodium Hydrogen Carbonate a main component of antacid?
Ans: Sodium Hydrogen carbonate is a main component of antacid because it is a basic substance which reacts with stomach’s acid HCl and neutralizes it.
Q3. Why is distilled water not conductor of electric while rain water is a good conductor?
Ans: distilled water is not conductor of electric because there is no H+ ions in it, distilled water is neutral, while rain water’s property is weak acidic. There is no H+ ions which is responsible for carrying the electric current.
Q4. What is the common name of CaOCl2 compound?
Ans: Bleaching Powder.
Q5. Name the substance which reacts with chlorine to form bleaching powder.
Ans. calcium hydroxaide
Q6. Which sodium compound is used to soften hard water?
Ans. Na2CO3.10H2O (washing soda)
Q7. What will happen when sodium hydrogencarbonate solution is heated? Write the equation for this reaction.
Ans. When sodium hydrogen carbonate solution is heated, sodium carbonate, water and carbon dioxide gas are emitted.
Additional Questions With Solutions
Additional Questions With Solutions
Question 1: Name two natural detectors.
answer :
(i) litmus paper
(ii) Turmeric
Question 2: Name two synthetic detectors.
answer :
(i) Methyl Orange
(ii) phenolphthalein
Question 3: Some substances whose smell changes in acidic or basic medium. What are they called?
Answer: Aromatic indicator.
Question 4: The metal reacts with acid residues to form a compound and release hydrogen gas. What is this compound called?
Answer: Salt.
Question 5: Name the different forms of calcium carbonate.
Answer: Chosen stone, quarry, marble.
Question 6: On passing carbon dioxide gas through lime water, a white precipitate of calcium carbonate and water is obtained.
(i) Write the overall equation of this reaction.
(ii) What is this white precipitate called?
(iii) What is obtained when a large amount of carbon dioxide gas is passed through?
answer:
(i) Overall equation of this reaction :
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O (l)
(ii) Calcium Carbonate (CaCO3)
(iii) Ca(HCO3)2 (aq) soluble in water is obtained.
Question 7: The reaction between an acid and a base, in which salt and water are obtained, what is this reaction called?
Answer: Neutralization reaction.
Question 8: What is a neutralization reaction called?
Answer: The reaction between an acid and a base in which salt and water are obtained and they neutralize each other's effect, this reaction is called neutralization reaction.
base + acid → salt + water
Question 9: What is the nature of metallic oxides?
Answer: Metallic oxides are basic in nature.
Question 10: What is the nature of non-metallic oxides?
Answer: Metallic oxides are acidic in nature.
Question 11: Why curd and sour substances should not be kept in brass and copper utensils?
Answer: Curd and sour substances are acidic in nature, the acid present in it reacts immediately with brass and copper and destroys the vessel. And the substances kept in it also get spoiled.
Question 12: Which gas is usually released when an acid reacts with a metal? Explain with an example. How will you check the presence of this gas?
Answer – Normally hydrogen gas is evolved when an acid reacts with a metal. like-
2HCl + Mg → MgCl2 + H2 (g)
To check the presence of this gas, when we take a burning candle near this gas, the combustion of hydrogen gas occurs with the sound of burst.
Question 13: What is a base soluble in water called?
Answer: alkali.
Question 14: Tooth enamel is one of the hardest substances in our body. How does this decay happen by eating chocolates and sweets? What should be done to prevent it? What is enamel made of? What is the pH value of the mouth?
Answer – Bacteria present in the mouth after the meal degrade the waste sugar and food items in the mouth to produce acid. This acid becomes less than the pH value of the mouth, due to which tooth decay starts. To prevent this, the mouth should be cleaned after meals. Enamel is made up of calcium phosphate. The pH value of the mouth is 5.5.
Question 15: Why do muscles have cramps?
Ans- Cramps occur due to excess of lactic acid in the muscles.
Question 16: A substance A is obtained by the action of washing soda with vinegar. What is substance A?
Answer: Substance A is sodium acetate, the reaction of this reaction is as follows.
Question 17: To stabilize a broken bone, doctors use a paste made of white powder in water.
1. Name this substance.
2. Write its chemical formula.
3. State one special property of this substance.
4. Why should this substance be kept in a damp proof container?
answer :
1. The name of this substance is plaster of paris.
2. Its chemical formula is CaSO4. 1/2 H2O.
3. A special property of this substance is that as soon as water is mixed, it becomes hard immediately. Therefore it is used in making toys.
4. This material is kept in a moisture proof vessel because it reacts with moist air to form gypsum.
Question 18: What is dilution?
Answer: On adding acid or base to water, the concentration of ion (H3O/OH) per unit volume decreases, this process is called dilution.
Question 19: Write the importance of pH in daily life.
answer :
1. Our body works in the pH range of 7.0 to 7.8.
2. If the pH of the soil is acidic in nature then it is not favorable for the crop.
3. Our stomach contains hydrochloric acid which helps in digestion without harming the stomach.
4. If the face value of the mouth is less than 5.5, then the teeth are destroyed.
Question 20: Write three uses of how bleaching powder is prepared.
Answer: Bleaching powder is formed by the action of chlorine on dry slaked lime [Ca(OH)2].
Answer : Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses of bleaching powder:
(i) For bleaching cotton and linen in the textile industry, wood marrow in the paper factory and for bleaching clean clothes in the laundry.
(ii) As an auxiliaries in chemical industries.
(iii) As a disinfectant to make drinking water free from bacteria.
Question 21: Where do we get litmus paper?
Answer: It is obtained from lichen plant of Thallophyta group.
Question 22: Name three natural substances which indicate the presence of acids and bases.
answer:
1. Turmeric
2. litmus paper
3. Red Cabbage
Question 23: Write two chemical properties of acid and base.
Answer: Chemical properties of acids:-
(i) It provides H+ ions with water.
(ii) Acid reacts with metal to give salt and hydrogen gas.
Chemical properties of bases:-
(i) It provides (OH)- ion with water.
(ii) Base reacts with acid to give salt and hydrogen gas.
Question 24: Why is distilled water not a conductor of electricity while rain water is?
Answer: Distilled water is not a conductor of electricity because it does not contain H+ ions, distilled water is neutral. Whereas rain water is weakly acidic in nature. It contains H+ ions which conduct electricity.
Question 25: Why curd and sour substances are not kept in brass and copper utensils?
Answer: Do not keep curd and sour substances in brass and copper utensils because the acid present in curd and sour substances reacts with brass and copper and destroys the vessel and the taste of the substance changes.
Question 26: Effervescence is produced when a metal compound 'A' reacts with dilute hydrochloric acid. The gas produced by this extinguishes the burning candle. If one of the compounds produced is calcium chloride, then write the balanced chemical equation for this reaction.
Answer: Ca + 2HCl → CaCl2 + H2
Question 27: Tooth enamel is one of the hardest substances in our body. How does this decay happen by eating chocolates and sweets? What should be done to prevent it? What is enamel made of? What is the pH value of the mouth?
Answer: (i) This can be prevented by rinsing the mouth after meals. Using an alkaline toothpaste to clean the mouth can neutralize the excess acid that results in tooth decay.
(ii) Tooth enamel is made up of calcium phosphate.
(iii) The pH value of the mouth is 5.5.
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Science Chapter List
1. Chemical Reactions and Equations
2. Acids, Bases and Salts
3. Metals and Non-metals
4. Carbon and its Compounds
5. Periodic Classification of Elements
6. Life Processes
7. Control and Coordination
8. How do Organisms Reproduce
9. Heredity and Evolution
10. Light-Reflection and Refraction
11. Human Eye and Colourful World
12. Electricity
13. Magnetic Effects of Electric Current
14. Sources of Energy
15. Our Environment
16. Management of Natural Resources
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