Class 10 Science Chapter 2: Acids, Bases and Salts Download Free PDF of Ncert Solutions
We will covered following topics in this chapter;
Acids
Bases
Acid-Base Indicators
Olfactory indicators
pH scale
Reaction of acid with a metal
Reaction of base with a metal
How do metal carbonates and Metal Hydrogencarbonates React with metals?
Reaction of acids and bases together
Neutralisation reaction
Reaction of metallic oxide with acid
Why Acidic and basic solutions conduct electricity? Water of crystallisation
Some very important salts with their chemical name and formula
Acids: Those substances which when dissolved in water then produce H+ (aq) or Hydronium (H3O+) ions. They are sour in taste and change the colour of blue litmus to red. For example HCl, H2SO4, HNO3 etc.
Bases: Bases are generally metallic oxide or metallic hydroxide. When they are dissolved in water they produce OH-(aq) ions. They are bitter in taste and change the colour of red litmus to blue. For example CuO, NaOH, KOH etc.
Acid-Base Indicators: Indicators are basically dyes or mixtures which are used to detect whether the substance is acidic or basic with the help of their colour changing property. They are of two type, natural indicators and synthetic indicators. The examples of natural indicators are Litmus and turmeric. The examples of synthetic indicators are methyl orange and phenolphthalein.
Olfactory indicators: Those substances whose odour changes in acidic or basic medium are known as olfactory indicators. Some of the examples of olfactory indicators are vanilla, onion and clove.
pH scale: It is the measure of acidic or basic strength of an aqueous solution. The pH value of an acidic solution lies between 0 to 7. The pH value of a basic solution lies between 7 to 14. The pH value of a neutral substance is always 7.
Reaction of acid with a metal: When an acid reacts with a metal then Hydrogen gas is evolved along with corresponding salt.
Reaction of base with a metal: When a base reacts with a metal then Hydrogen gas is evolved along with corresponding salt. Salt is composed of metal and oxygen and has negative ion.
How do metal carbonates and Metal Hydrogencarbonates React with Acids?
When Metal carbonates and Metal Hydrogencarbonates react with acid they form corresponding salt with carbon dioxide and water as shown in following chemical equation
Reaction of acids and bases together: Whenever acids and bases react with each other they produce salt with water. For example
Neutralisation reaction: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example
Reaction of metallic oxide with acid: When metallic oxide reacts with acid they produce salt along with water. For example
Why Acidic and basic solutions conduct electricity?: Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
Water of crystallisation: It is the definite number of molecules of water that is chemically attached to each formula unit of a salt in its crystalline form. For example washing soda (Na2CO3.10H2O) or Gypsum (CaSO4.2H2O).
Some very important salts with their chemical name and formula.
Common Name Chemical Name Chemical Formula
Baking Soda
Sodium Bicarbonate
NaHCO3
Washing Soda
Hydrated Sodium Carbonate
Na2CO3.10H2O
Plaster of paris
Calcium Sulphate hemihydrates
CaSO4.½H2O
Bleaching Powder
Calcium Oxychloride
CaOCl2
Gypsum
Calcium Sulphate dihydrate
CaSO4.2H2O
Text Book Exercise
Question 1. A solution turns red litmus blue; its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
Answer: (d)
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: (b)
Question 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
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
Answer: (d)
Question 4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Answer: (c)
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 filings.
Answer:
Question 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Answer: As shown in figure insert two nails on the wooden or rubber cork and place it in a beaker. Now connect these iron nails with a bulb, a 6 volt battery and a switch using a wire. Now pour some alcohol or glucose such that the nails will dip into it. Now turn the switch on, you will see that the bulb will not glow. Now empty the beaker and add some HCl aqueous solution at this time the bulb will glow. This proves that an acid can conduct electricity while alcohols and glucose cannot, even when they are containing hydrogen.
Above diagram shows that an acid solution can conduct electricity.
Question 7. Why does distilled water not conduct electricity, whereas rain water does?
Answer: Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.
Question 8. Why do acids not show acidic behaviour in the absence of water?
Answer: The acidic behaviour of a substance is due to the presence of H+(aq) ions. As acids do not dissociate to produce H+(aq) ions in the absence of water so they do not show 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:(a) neutral -> D
(b) strongly alkaline -> C
(c) strongly acidic -> B
(d) weakly acidic -> A
(e) weakly alkaline -> E
The arrangement of pH in increasing order of hydrogen-ion concentration is 11<9<7<4<1
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: In both the test tubes hydrogen gas is formed. The HCl is strong acid then acetic acid so more hydrogen gas is formed in test tube A which results in vigorous fizzing.
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:When milk is turned into curd then its pH value will decrease due to the production of lactic acid in curd which is acidic in nature.
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:
He shifts the pH of the fresh milk from 6 to alkaline so that in basic form it will not spoil easily.
This milk takes a long time to set as curd because the lactic acid produced reacts with the baking soda.
Question 13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum) as shown in following chemical equation.
Question 14. What is a neutralisation reaction? Give two examples.
Answer: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example
Question 15. Give two important uses of washing soda and baking soda.
Answer:
(a) Two important uses of washing soda
(i) It is used in the manufacture of soap and glass.
(ii) It is used to remove the permanent hardness of water.
(b) Two important uses of baking soda
(i) It is used for making baking powder.
(ii) It is used in soda- fire extinguishers.
Acids
Bases
Acid-Base Indicators
Olfactory indicators
pH scale
Reaction of acid with a metal
Reaction of base with a metal
How do metal carbonates and Metal Hydrogencarbonates React with metals?
Reaction of acids and bases together
Neutralisation reaction
Reaction of metallic oxide with acid
Why Acidic and basic solutions conduct electricity? Water of crystallisation
Some very important salts with their chemical name and formula
Acids: Those substances which when dissolved in water then produce H+ (aq) or Hydronium (H3O+) ions. They are sour in taste and change the colour of blue litmus to red. For example HCl, H2SO4, HNO3 etc.
Bases: Bases are generally metallic oxide or metallic hydroxide. When they are dissolved in water they produce OH-(aq) ions. They are bitter in taste and change the colour of red litmus to blue. For example CuO, NaOH, KOH etc.
Acid-Base Indicators: Indicators are basically dyes or mixtures which are used to detect whether the substance is acidic or basic with the help of their colour changing property. They are of two type, natural indicators and synthetic indicators. The examples of natural indicators are Litmus and turmeric. The examples of synthetic indicators are methyl orange and phenolphthalein.
Olfactory indicators: Those substances whose odour changes in acidic or basic medium are known as olfactory indicators. Some of the examples of olfactory indicators are vanilla, onion and clove.
pH scale: It is the measure of acidic or basic strength of an aqueous solution. The pH value of an acidic solution lies between 0 to 7. The pH value of a basic solution lies between 7 to 14. The pH value of a neutral substance is always 7.
Reaction of acid with a metal: When an acid reacts with a metal then Hydrogen gas is evolved along with corresponding salt.
Reaction of base with a metal: When a base reacts with a metal then Hydrogen gas is evolved along with corresponding salt. Salt is composed of metal and oxygen and has negative ion.
How do metal carbonates and Metal Hydrogencarbonates React with Acids?
When Metal carbonates and Metal Hydrogencarbonates react with acid they form corresponding salt with carbon dioxide and water as shown in following chemical equation
Reaction of acids and bases together: Whenever acids and bases react with each other they produce salt with water. For example
Neutralisation reaction: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example
Reaction of metallic oxide with acid: When metallic oxide reacts with acid they produce salt along with water. For example
Why Acidic and basic solutions conduct electricity?: Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
Water of crystallisation: It is the definite number of molecules of water that is chemically attached to each formula unit of a salt in its crystalline form. For example washing soda (Na2CO3.10H2O) or Gypsum (CaSO4.2H2O).
Some very important salts with their chemical name and formula.
| Common Name | Chemical Name | Chemical Formula |
Baking Soda
|
Sodium Bicarbonate
|
NaHCO3
|
Washing Soda
|
Hydrated Sodium Carbonate
|
Na2CO3.10H2O
|
Plaster of paris
|
Calcium Sulphate hemihydrates
|
CaSO4.½H2O
|
Bleaching Powder
|
Calcium Oxychloride
|
CaOCl2
|
Gypsum
|
Calcium Sulphate dihydrate
|
CaSO4.2H2O
|
Text Book Exercise
Question 1. A solution turns red litmus blue; its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
Answer: (d)
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: (b)
Question 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
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
Answer: (d)
Question 4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Answer: (c)
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 filings.
Answer:
Question 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Answer: As shown in figure insert two nails on the wooden or rubber cork and place it in a beaker. Now connect these iron nails with a bulb, a 6 volt battery and a switch using a wire. Now pour some alcohol or glucose such that the nails will dip into it. Now turn the switch on, you will see that the bulb will not glow. Now empty the beaker and add some HCl aqueous solution at this time the bulb will glow. This proves that an acid can conduct electricity while alcohols and glucose cannot, even when they are containing hydrogen.
Above diagram shows that an acid solution can conduct electricity.
Question 7. Why does distilled water not conduct electricity, whereas rain water does?
Answer: Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.
Question 8. Why do acids not show acidic behaviour in the absence of water?
Answer: The acidic behaviour of a substance is due to the presence of H+(aq) ions. As acids do not dissociate to produce H+(aq) ions in the absence of water so they do not show 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:(a) neutral -> D
(b) strongly alkaline -> C
(c) strongly acidic -> B
(d) weakly acidic -> A
(e) weakly alkaline -> E
The arrangement of pH in increasing order of hydrogen-ion concentration is 11<9<7<4<1
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: In both the test tubes hydrogen gas is formed. The HCl is strong acid then acetic acid so more hydrogen gas is formed in test tube A which results in vigorous fizzing.
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:When milk is turned into curd then its pH value will decrease due to the production of lactic acid in curd which is acidic in nature.
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:
He shifts the pH of the fresh milk from 6 to alkaline so that in basic form it will not spoil easily.
This milk takes a long time to set as curd because the lactic acid produced reacts with the baking soda.
Question 13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum) as shown in following chemical equation.
Question 14. What is a neutralisation reaction? Give two examples.
Answer: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example
Question 15. Give two important uses of washing soda and baking soda.
Answer:
(a) Two important uses of washing soda
(i) It is used in the manufacture of soap and glass.
(ii) It is used to remove the permanent hardness of water.
(b) Two important uses of baking soda
(i) It is used for making baking powder.
(ii) It is used in soda- fire extinguishers.
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