ACIDS, BASES AND SALTS
Acids: The substance which has sour taste and acidic properties is known as acid.
Acidic Substances; The substances which have sour taste are called acidic substances.
Acidus/ Acere: The term acid has been derived from the Latin word Acidus or Acere.
Natural Acids: The acids which are found in plants and animals are commonly called natural acids or organic acids.
Mineral Acids: The acids which are prepared from non-living things like the minerals of the Earth by chemical means are called mineral acids.
Bases: The substances which have a bitter taste and soapy ( slippery) touch are known as bases. The nature of bases is basic.
Indicators: The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Neutral substances: The substances which are neither acid, nor basic and do not affect indicators are called neutral substances. Ex. Distilled water
Acid Rain: Rain containing traces of mineral acids, such as Hydrochloric Acid (HCl), Nitric Acid ( HNO3) is called acid rain.
Neutralisation: The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation. It is the reaction between an acid and a base producing salt and water with the evolution of heat.
Salt: A new substance obtained by neutralization of an acid with a base is called salt.Salt may be acidic, basic or neutral in nature.
Things to remember:
SOUR BITTER
Taste of curd is sour Taste of amla is bitter
Taste of lemon juice is sour Taste of baking soda solution is bitter
Taste of unripe mangoes is sour Taste of soap solution is bitter
Taste of tamarind is sour
Taste of vinegar is sour
Taste of plain soda water is sour
SOUR AND SWEET
Taste of grapes is sour and sweet
Taste of orange juice is sour and sweet
Natural Acids: The acids which are found in plants and animals are commonly called natural acids or organic acids.
1. Citric Acid found in citrus fruits such as oranges and lemons etc.
2. Oxalic acid found in tomatoes and spinach etc.
3. Lactic Acid found in sour milk or curd
4. Acetic Acid found in vinegar
5. Malic Acid found in apple
6. Amino Acids found in proteins
7. Formic Acid found in ant’s sting
8. Tartartic Acid found in grapes, tamarind, unripe mangoes, goose and berries etc.
9. Ascorbic Acid found in amla and citrus fruits
( Vitamin C)
A protein molecule is made up of a large number of smaller molecules called amino acids. Proteins in our body contain 20 different amino acids. Our body can make only 10 amino acids which are called non-essential amino acids. The other 10 Amino acids which our body can not make are called essential amino acids, must be present in our food.
Name of Mineral Acids
The acids which are prepared from non-living things like the minerals of the Earth by chemical means are called mineral acids.
Sulphuric Acid : H2 S O4
Nitric Acid : H N O3
Hydrochloric Acid : H C L
Phosphoric Acid : H3 P O4
Mineral Acids are highly corrosive in nature. They can cause sever burn on the skin.
Fatty Acids: The fats or oils which we consume contain complex compounds called Fatty Acids.
DNA: Deoxyribonucleic Acid: The DNA has specific genetic information and controls every feature of living body, such as look, colour of eyes etc.
If the yellow stain caused by turmeric is rubbed with soap solution, the colour of the stain changes to brownish red.
The soap solution always contains a small amount of chemical called sodium hydroxide. (NaOH)
If we rub a freshly cut lemon on the changed brownish red stain, it changes to yellow colour.
Lemon contains citric acid.
Acids turn blue litmus red.
Bases turn red litmus blue.
Antacid such as milk of magnesia contains magnesium hydroxide and aluminiumhydroxide.
Name of bases
The substances which have a bitter taste and soapy touch are known as bases. The nature of bases is basic.
Sodium hydroxide : NaOH found in soap
Potassium hydroxide : KOH found in liquid soap
Calcium hydroxide : Ca(OH)2 found in lime water
Magnesium hydroxide : Mg (OH)2 found in milk of magnesia
Ammonium Hydroxide : NH4OH found in window cleaner solution
indicators : The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Name of indicators Name of Neutral substance
Turmeric Distilled water
Litmus solution /litmus paper Alcohol
Phenolphthalein solution/paper Common Salt solution
China rose petals/paper
Turmeric as indicator
Turmeric as an indicator identifies basic solution only. Its colour changes to red when come in contact with basic solution. It colour does not change in acidic or neutral solution.
Litmus as indicator
Litmus is extracted from lichen plants. The solution of litmus in distilled water is mauver (purple) in colour. When added to acidic solution, it turns red and when added to basic solution, it turns blue.
The neutral litmus solution/ paper turns red, when added to some acidic solution.
The neutral litmus solution/paper turns blue, when added to some basic solution.
Litmus is available in the form of solution or in the form of strips of paper. Litmus paper is available in red and blue colours.
China Rose as indicator
The coloured solution extracted from the petals of China rose is light pink in colour. When it is used as an indicator, its colour changes to green in basic solution and dark pink colour (magenta) in acidic solutions. In neutral solution it colour does not change.
Phenolphthalein as indicator
Phenolphthalein solution is colourless When it comes in contact with basic solution, its colour changes to pink. But when the solution is acidic or neutral it remains colourless.
GENERAL PHYSICCAL PROPERTIES OF ACIDS
1. Acids have a sour taste.
2. Acids turn blue litmus solution red, but do not affect red litmus solution.
3. Most of the acids are soluble in water
4. All acid solutions in water are good conductors of electricity
5. Nature of acid substances are acidic
6. Acids do not affect turmeric solution.
7. Acids do not affect phenolphthalein solution.
8. Acids do not affect phenolphthalein solution.
9. Most of the acids are highly corrosive in nature.
10. All the acids contains Hydrogen ions.
11. Acids turn china rose solution to deep pink colour
GENERAL PHYSICCAL PROPERTIES OF BASES
1. Bases are basic in nature.
2. Bases have a bitter taste.
3. They conduct electric current.
4. Bases turn red litmus solution blue, but do not affect blue litmus solution.
5. Bases turn yellow turmeric solution reddish brown.
6. Bases turn phenolphthalein solution pink
7. Bases turn china rose solution green.
8. Bases like sodium hydroxide, potassium hydroxide and calcium hydroxide
cause blister on skin and are highly corrosive in nature.
9. Most of the bases are insoluble in water.
10. All bases have slippery touch like that of soap.
ACID RAIN
Rain containing traces of mineral acids, such as hydrochloric acid, nitric acid and sulphuric acid is called acid rain. Carbon dioxide, sulphur dioxide and nitrogen dioxide are released in to the atmosphere as pollutants and dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
The acid rain can cause extensive damage to the forests, crops , buildings, historical monuments, plants and animals .
What do you know about the formation of acid.
Ans. A non metal reacts with oxygen in the air produces nonmetallic oxide. This non metallic oxide dissolves in water and acid is produced.
C + O2 → CO2
CO2 + H2 O → H2 CO3
S + O2 →SO2
SO2 + H2 O →H2 SO3
What is the difference between concentrated and dilute acid?
Ans. If the solution contains large amount of acid, it is known as concentrated acid and if the solution contains small amount of acid, it is known as dilute acid.
What is Neutralisation
The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation. Or
the reaction between an acid and a base is known as Neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water + Heat Energy ↑
HCL + NaOH →NaCl + H2O + Heat Energy ↑
H2SO4 + 2 NOAH → N2 OSO4 + 2H2O + Heat Energy ↑
PRIVATE BOOK QUESTIONS (ACIDS, BASES AND SALT) CH-5
I. Fill in the blanks
a) The acid found in lemon is citric acid.
b) The bases have a bitter taste and soapy touch.
c) The sting of the ant contains formic acid.
d) Sulphuric acid is highly corrosive acid
e) Acidic soils are neutralized with slaked lime.
II. Statements given below are incorrect. Write the correct statement.
1. Sulphuric acid is an example of an organic acid. ( a mineral acid )
2. Blue litmus paper turns red in a basic solution. ( an acidic solution)
3. China rose solution turns green in citric acid solution.( basic solutions)
4. Formic Acid is found in the sting of a grasshopper ( an ant)
5. During neutralization, an acid reacts with a salt to form water and a base, as products. ( base, salt)
III. Write True or False
1. Tooth decay is caused by the presence of basic substances in mouth. FALSE
2. The substances which show different colours in acids and bases are called indicators. TRUE
3. Milk of magnesia and slaked lime are the examples of neutral substances. FALSE
4. Acid rain is caused by the excess of carbon dioxide in air.
5. Potassium hydroxide turns blue litmus red. FALSE
6. Most of the fruits contain organic acids. TRUE
IV. Match the statements in column A with those in column B.
1. A substance which turns tumeric solution reddish brown. Base
2. A reaction between an acid and a base Neutralisation
3. An acid present in vinegar Acetic acid
4. An indicator derived from the lichen Litmus
5. An insect whose sting contains formic acid Ant/bee
V. Answer the following questions.
1. Name three organic and three inorganic acids.
Ans. The acids which are found in plants and animals are commonly called natural acids or organic acids. Name of some organic or natural acids are:
1. Citric Acid 8. Formic Acid
1. Tartartic Acid 9. Ascorbic Acid
2. Oxalic acid
3. Lactic Acid
4. Acetic Acid (HC2H3O2)
5. Malic Acid
6. Amino Acids
The acids which are prepared from non-living things like the minerals of the earth by chemical means are called mineral acids or inorganic acids. Name of some inorganic or mineral acids are :
Sulphuric Acid : H2 S O4
Nitric Acid : H N O3
Hydrochloric Acid : H C L
Phosphoric Acid : H3 P O4
Q.2. What are indicators? Name any three indicators and state the colour change which takes place in (i) acids (ii) bases.
Ans. The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Name of indicators colour changes in acid colour change in base
1) Turmeric no change in colour brown or reddish brown
2) litmus solution changes to red changes to blue
3) Phenolphthalein solution no change (colourless) changes to deep pink
4) china rose petals changes to dark pink changes to green
( magenta)
Q.3. What are neutral substances? Give examples of two neutral substances.
Ans. The substances which are neither acidic nor basic and do not affect indicators are called neutral substances. Examples of two neutral substances are distilled water, alcohol and common salt solution.
Q.4. You are given three unlabelled bottles A, B, and C containing colourless solutions, such that one of them is acid, the other being basic and neutral. How will you distinguish between them by using china rose as an indicator.
Ans. When china rose is used as an indicator, its colour change to green in basic solution and dark pink (magenta) in acidic solutions. In neutral solutions, its colour does not change. Hence, the solution in the unlabelled bottle which changes the colour of the china rose to green contains basic solution. The solution in the unlabelled bottle which changes the colour of the china rose to dark pink (magenta) contains acidic solution. The solution in the unlabelled bottle which does not change the colour of the china rose contains neutral solution.
Q.5. What do you understand by the term neutralization? Describe an activity in which neutralization of hydrochloric acid takes place with sodium hydroxide, using phenolphthalein as an indicator.
Ans. The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation.
Description of the activity in which neutralization of Hydrochloric acid with sodium hydroxide takes place using phenolphthalein as an indicator is narrated below.
Materials required: 1. Dilute sodium hydroxide solution ( NaOH)
2. Dilute hydrochloric acid ( HCl)
3. Phenolphthalein solution ( indicator)
4. Beaker
5. a dropper
Method: Pour about 20 cc of sodium hydroxide (NaOH) solution in the beaker. Add phenolphthalein solution to the sodium hydroxide solution in the beaker. It is observed that the solution turns deep pink. Add hydrochloric acid to the deep pink solution in the beaker with the help of a dropper drop by drop and go on stirring the solution.
It is observed that at some stage, by the addition of one drop of acid the solution suddenly becomes colourless.
It is because at this stage the sodium hydroxide solution has completely reacted with hydrochloric acid to form salt and water. Thus the last drop of HCl makes the acid in excess, and hence, the colour of the phenolphthalein changes from pink to colourless. Immediately the warmth of the beaker can be felt because of the evolution of the heat.
HCl + NaOH ----------→ NaCl + H2O + Heat ↑
Hence, it is observed that when an acid completely reacts with a base salt and water is produced with the evolution of heat.
Q.6. Explain why:
a) Farmers add slaked lime to acidic soils.
Ans. Plants grow well in neutral soil. Due to excessive use of artificial fertilizers, a natural soil becomes acidic and reduces the fertility of the soil. So to convert the acidic soils into neutral soils, farmers add calcium oxide (quick lime) or calcium hydroxide (slaked lime) to acidic soil. These chemicals neutralize soil acids and make the soil neutral and fertile.
b) Soap solution or baking soda paste is applied on the part of body stung by a bee.
Ans. The strings of a bee contain formic acid which is acidic in nature. When a bee stings, it injects formic acid into the skin which causes painful irritation and swelling. To neutralize the effect of formic acid, the area around the sting is rubbed with soap or baking soda solution which contains zinc carbonate (base). It helps in relieving pain.
c) Factory wastes and city sewerage is neutralized before discharging in rivers.
Ans. Factory wastes and city sewerage contains acids. Unless these are neutralize before discharging in rivers, the fish and other aquatic organisms will die. So, to prevent such a situation, the wastes are treated with lime which neutralizes acids.
d) Antacids are used for relieving stomach acidity.
Ans. The gastric juice secreted in the stomach contains hydrochloric acid. The acidity of stomach or indigestion is caused by f excessive secretion of this hydrochloric acid. To relieve indigestion or stomach acidity, antacid is used. Antacid contains magnesium hydroxide and aluminium hydroxide. These hydroxides neutralize the effect of excessive hydrochloric acid and help in controlling acidity of stomach.
Q.7. Give four differences between the acids and the alkalis.
Q.8. Write an equation when hydrochloric acid neutralizes sodium hydroxide.
Ans. HCl + NaOH ----------→ NaCl + H2O + Heat ↑
NCERT BOOKS
1. State differences between acids and bases.
Acids bases
Acids are sour in test Bases are bitter in taste
Acids are acidic in nature Bases are basic in nature
Acids turn blue litmus red Bases turn red litmus blue
pH value of an Acid is lower than 7 The pH value of a base is always
more than 7
2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Ans. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. When red litmus comes in contact with basic solution, it turns blue. Hence, ammonia found in window cleaner is basic in nature.
3. Name the source from which litmus solution is obtained. What is the use of this solution?
Ans. Litmus is a natural dye. It is extracted from lichen plants found in Tundra region.
Litmus solution is prepared from this litmus. It is used as a natural indicator to
Identify basic, acidic and neutral substances. The solution of litmus in distilled
water is mauver (purple) in colour and is called neutral litmus solution. When added to acidic solution, it turns red and when added to basic solution, it turns blue Litmus is available in the form of solution or in the form of strips of paper. Litmus paper is available in red and blue colours.
4. Is the distilled water acidic/basic/neutral? How would you verify it ?
Ans. Distilled water is neither acidic nor basic. It is neutral. This can be verified by using any of the indicators. The colour of the indicator does not undergo any change when comes in contact with either an acidic substance or a basic substance. Hence, the neutrality of the distilled water is verified.
5. Describe the process of neutralization with the help of an example.
Ans The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water is called Neutralisation. It is the reaction between an acid and a base producing salt and water with the evolution of heat. When an acidic solution is mixed with a basics solution, both the solution neutralize the effects of each other.
For example, when hydrochloric acid ( an acid ) is mixed with sodium hydroxide ( a base ), sodium chloride ( a salt ) and water are produced with evolution of heat.
HCl + NaOH ----------→ NaCl + H2O + Heat ↑
6. Mark True or False
i) Nitric Acid turns red litmus blue. FALSE
ii) Sodium hydroxide turns blue litmus red. FALSE
iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. TRUE
ii) Indicator is a substance which shows different colours in acidic and basic solutions. TRUE
iii) Tooth decay is cause by the presence of a base. TRUE
7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labeled. He has to serve the drinks on the demand of customers. One customer wants acidic drink; another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Ans. When neutral litmus solution is used as an indicator, its colour change to blue in basic solution and red in acidic solutions and its colour does not change in neutral substances. Hence, the solution in the unlabelled bottle which changes the colour of the litmus solution to blue contains basic solution. The solution in the unlabelled bottle which changes the colour of the litmus solution to red contains acidic solution. The solution in the unlabelled bottle which does not change the colour of the litmus solution contains neutral solution. By this way, the drinks can be identified and served accordingly.
8. Explain why:
a) An antacid tablet is taken when you suffer from acidity.
The gastric juice secreted in the stomach contains hydrochloric acid. The acidity of stomach or indigestion is caused by excessive secretion of this hydrochloric acid. To relieve indigestion or stomach acidity, antacid is used. Antacid contains magnesium hydroxide and aluminium hydroxide. These hydroxides neutralize the effect of excessive hydrochloric acid and help in controlling acidity of stomach
b) Calamine solution is applied on the skin when an ant bites
Ans. The strings of an ant contain formic acid which is acidic in nature. When an ant stings, it injects formic acid into the skin which causes painful irritation and swelling. To neutralize the effect of formic acid, the area around the sting is rubbed with Calamine solution as it contains zinc carbonate (base). Zinc carbonate neutralizes the effect of formic acid and helps in relieving pain.
c) Factory waste is neutralized before disposing it into the water bodies.
Ans. Factory wastes and city sewerage contains acids. Unless these are neutralize before discharging in rivers, the fish and other aquatic organisms will die. So, to prevent such a situation, the wastes are treated with lime which neutralizes the effect of acids.
9. Three liquids are given to you. One is hydrochloric acid; another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Ans. When turmeric is used as an indicator, it identifies basic solutions only. Its colour does not change in acidic or neutral solution
10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
11. Consider the following statements:
a) Both acids and bases change colour of all indicators.
b) If an indicator gives a colour change with an acid, it does not give a change with a base.
c) If an indicator changes colour with a base, it does not change colour with an
acid.
a) Change of colour in an acid and a base depends on the type of the indicator.
b)
Which of these statements are correct?
i) All four ii) a and b iii) b and c iv) only d
Acids: The substance which has sour taste and acidic properties is known as acid.
Acidic Substances; The substances which have sour taste are called acidic substances.
Acidus/ Acere: The term acid has been derived from the Latin word Acidus or Acere.
Natural Acids: The acids which are found in plants and animals are commonly called natural acids or organic acids.
Mineral Acids: The acids which are prepared from non-living things like the minerals of the Earth by chemical means are called mineral acids.
Bases: The substances which have a bitter taste and soapy ( slippery) touch are known as bases. The nature of bases is basic.
Indicators: The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Neutral substances: The substances which are neither acid, nor basic and do not affect indicators are called neutral substances. Ex. Distilled water
Acid Rain: Rain containing traces of mineral acids, such as Hydrochloric Acid (HCl), Nitric Acid ( HNO3) is called acid rain.
Neutralisation: The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation. It is the reaction between an acid and a base producing salt and water with the evolution of heat.
Salt: A new substance obtained by neutralization of an acid with a base is called salt.Salt may be acidic, basic or neutral in nature.
Things to remember:
SOUR BITTER
Taste of curd is sour Taste of amla is bitter
Taste of lemon juice is sour Taste of baking soda solution is bitter
Taste of unripe mangoes is sour Taste of soap solution is bitter
Taste of tamarind is sour
Taste of vinegar is sour
Taste of plain soda water is sour
SOUR AND SWEET
Taste of grapes is sour and sweet
Taste of orange juice is sour and sweet
Natural Acids: The acids which are found in plants and animals are commonly called natural acids or organic acids.
1. Citric Acid found in citrus fruits such as oranges and lemons etc.
2. Oxalic acid found in tomatoes and spinach etc.
3. Lactic Acid found in sour milk or curd
4. Acetic Acid found in vinegar
5. Malic Acid found in apple
6. Amino Acids found in proteins
7. Formic Acid found in ant’s sting
8. Tartartic Acid found in grapes, tamarind, unripe mangoes, goose and berries etc.
9. Ascorbic Acid found in amla and citrus fruits
( Vitamin C)
- The Sour taste of lemon is due to : Citric Acid
- The sour taste of grapes and tamarind is due to : Tartartic Acid
- The sour taste of vinegar is due to : Acetic Acid
- The sour taste of curd is due to : Lactic Acid
- The stings of brown ants, bees and nettles contain: Formic Acid
- Vitamin C is ascorbic acid.
- Apples contain Malic Acid
- Tomato and spinach contain: Oxalic acid
- Proteins contain amino acids.
A protein molecule is made up of a large number of smaller molecules called amino acids. Proteins in our body contain 20 different amino acids. Our body can make only 10 amino acids which are called non-essential amino acids. The other 10 Amino acids which our body can not make are called essential amino acids, must be present in our food.
Name of Mineral Acids
The acids which are prepared from non-living things like the minerals of the Earth by chemical means are called mineral acids.
Sulphuric Acid : H2 S O4
Nitric Acid : H N O3
Hydrochloric Acid : H C L
Phosphoric Acid : H3 P O4
Mineral Acids are highly corrosive in nature. They can cause sever burn on the skin.
Fatty Acids: The fats or oils which we consume contain complex compounds called Fatty Acids.
DNA: Deoxyribonucleic Acid: The DNA has specific genetic information and controls every feature of living body, such as look, colour of eyes etc.
If the yellow stain caused by turmeric is rubbed with soap solution, the colour of the stain changes to brownish red.
The soap solution always contains a small amount of chemical called sodium hydroxide. (NaOH)
If we rub a freshly cut lemon on the changed brownish red stain, it changes to yellow colour.
Lemon contains citric acid.
Acids turn blue litmus red.
Bases turn red litmus blue.
Antacid such as milk of magnesia contains magnesium hydroxide and aluminiumhydroxide.
Name of bases
The substances which have a bitter taste and soapy touch are known as bases. The nature of bases is basic.
Sodium hydroxide : NaOH found in soap
Potassium hydroxide : KOH found in liquid soap
Calcium hydroxide : Ca(OH)2 found in lime water
Magnesium hydroxide : Mg (OH)2 found in milk of magnesia
Ammonium Hydroxide : NH4OH found in window cleaner solution
indicators : The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Name of indicators Name of Neutral substance
Turmeric Distilled water
Litmus solution /litmus paper Alcohol
Phenolphthalein solution/paper Common Salt solution
China rose petals/paper
Turmeric as indicator
Turmeric as an indicator identifies basic solution only. Its colour changes to red when come in contact with basic solution. It colour does not change in acidic or neutral solution.
Litmus as indicator
Litmus is extracted from lichen plants. The solution of litmus in distilled water is mauver (purple) in colour. When added to acidic solution, it turns red and when added to basic solution, it turns blue.
The neutral litmus solution/ paper turns red, when added to some acidic solution.
The neutral litmus solution/paper turns blue, when added to some basic solution.
Litmus is available in the form of solution or in the form of strips of paper. Litmus paper is available in red and blue colours.
China Rose as indicator
The coloured solution extracted from the petals of China rose is light pink in colour. When it is used as an indicator, its colour changes to green in basic solution and dark pink colour (magenta) in acidic solutions. In neutral solution it colour does not change.
Phenolphthalein as indicator
Phenolphthalein solution is colourless When it comes in contact with basic solution, its colour changes to pink. But when the solution is acidic or neutral it remains colourless.
GENERAL PHYSICCAL PROPERTIES OF ACIDS
1. Acids have a sour taste.
2. Acids turn blue litmus solution red, but do not affect red litmus solution.
3. Most of the acids are soluble in water
4. All acid solutions in water are good conductors of electricity
5. Nature of acid substances are acidic
6. Acids do not affect turmeric solution.
7. Acids do not affect phenolphthalein solution.
8. Acids do not affect phenolphthalein solution.
9. Most of the acids are highly corrosive in nature.
10. All the acids contains Hydrogen ions.
11. Acids turn china rose solution to deep pink colour
GENERAL PHYSICCAL PROPERTIES OF BASES
1. Bases are basic in nature.
2. Bases have a bitter taste.
3. They conduct electric current.
4. Bases turn red litmus solution blue, but do not affect blue litmus solution.
5. Bases turn yellow turmeric solution reddish brown.
6. Bases turn phenolphthalein solution pink
7. Bases turn china rose solution green.
8. Bases like sodium hydroxide, potassium hydroxide and calcium hydroxide
cause blister on skin and are highly corrosive in nature.
9. Most of the bases are insoluble in water.
10. All bases have slippery touch like that of soap.
ACID RAIN
Rain containing traces of mineral acids, such as hydrochloric acid, nitric acid and sulphuric acid is called acid rain. Carbon dioxide, sulphur dioxide and nitrogen dioxide are released in to the atmosphere as pollutants and dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
The acid rain can cause extensive damage to the forests, crops , buildings, historical monuments, plants and animals .
What do you know about the formation of acid.
Ans. A non metal reacts with oxygen in the air produces nonmetallic oxide. This non metallic oxide dissolves in water and acid is produced.
C + O2 → CO2
CO2 + H2 O → H2 CO3
S + O2 →SO2
SO2 + H2 O →H2 SO3
What is the difference between concentrated and dilute acid?
Ans. If the solution contains large amount of acid, it is known as concentrated acid and if the solution contains small amount of acid, it is known as dilute acid.
What is Neutralisation
The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation. Or
the reaction between an acid and a base is known as Neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water + Heat Energy ↑
HCL + NaOH →NaCl + H2O + Heat Energy ↑
H2SO4 + 2 NOAH → N2 OSO4 + 2H2O + Heat Energy ↑
PRIVATE BOOK QUESTIONS (ACIDS, BASES AND SALT) CH-5
I. Fill in the blanks
a) The acid found in lemon is citric acid.
b) The bases have a bitter taste and soapy touch.
c) The sting of the ant contains formic acid.
d) Sulphuric acid is highly corrosive acid
e) Acidic soils are neutralized with slaked lime.
II. Statements given below are incorrect. Write the correct statement.
1. Sulphuric acid is an example of an organic acid. ( a mineral acid )
2. Blue litmus paper turns red in a basic solution. ( an acidic solution)
3. China rose solution turns green in citric acid solution.( basic solutions)
4. Formic Acid is found in the sting of a grasshopper ( an ant)
5. During neutralization, an acid reacts with a salt to form water and a base, as products. ( base, salt)
III. Write True or False
1. Tooth decay is caused by the presence of basic substances in mouth. FALSE
2. The substances which show different colours in acids and bases are called indicators. TRUE
3. Milk of magnesia and slaked lime are the examples of neutral substances. FALSE
4. Acid rain is caused by the excess of carbon dioxide in air.
5. Potassium hydroxide turns blue litmus red. FALSE
6. Most of the fruits contain organic acids. TRUE
IV. Match the statements in column A with those in column B.
1. A substance which turns tumeric solution reddish brown. Base
2. A reaction between an acid and a base Neutralisation
3. An acid present in vinegar Acetic acid
4. An indicator derived from the lichen Litmus
5. An insect whose sting contains formic acid Ant/bee
V. Answer the following questions.
1. Name three organic and three inorganic acids.
Ans. The acids which are found in plants and animals are commonly called natural acids or organic acids. Name of some organic or natural acids are:
1. Citric Acid 8. Formic Acid
1. Tartartic Acid 9. Ascorbic Acid
2. Oxalic acid
3. Lactic Acid
4. Acetic Acid (HC2H3O2)
5. Malic Acid
6. Amino Acids
The acids which are prepared from non-living things like the minerals of the earth by chemical means are called mineral acids or inorganic acids. Name of some inorganic or mineral acids are :
Sulphuric Acid : H2 S O4
Nitric Acid : H N O3
Hydrochloric Acid : H C L
Phosphoric Acid : H3 P O4
Q.2. What are indicators? Name any three indicators and state the colour change which takes place in (i) acids (ii) bases.
Ans. The special types of substances, which change their colour when come in contact with acidic or basic substances are called indicators. These are used to test whether a substance is acidic or basic.
Name of indicators colour changes in acid colour change in base
1) Turmeric no change in colour brown or reddish brown
2) litmus solution changes to red changes to blue
3) Phenolphthalein solution no change (colourless) changes to deep pink
4) china rose petals changes to dark pink changes to green
( magenta)
Q.3. What are neutral substances? Give examples of two neutral substances.
Ans. The substances which are neither acidic nor basic and do not affect indicators are called neutral substances. Examples of two neutral substances are distilled water, alcohol and common salt solution.
Q.4. You are given three unlabelled bottles A, B, and C containing colourless solutions, such that one of them is acid, the other being basic and neutral. How will you distinguish between them by using china rose as an indicator.
Ans. When china rose is used as an indicator, its colour change to green in basic solution and dark pink (magenta) in acidic solutions. In neutral solutions, its colour does not change. Hence, the solution in the unlabelled bottle which changes the colour of the china rose to green contains basic solution. The solution in the unlabelled bottle which changes the colour of the china rose to dark pink (magenta) contains acidic solution. The solution in the unlabelled bottle which does not change the colour of the china rose contains neutral solution.
Q.5. What do you understand by the term neutralization? Describe an activity in which neutralization of hydrochloric acid takes place with sodium hydroxide, using phenolphthalein as an indicator.
Ans. The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water as the products is called Neutralisation.
Description of the activity in which neutralization of Hydrochloric acid with sodium hydroxide takes place using phenolphthalein as an indicator is narrated below.
Materials required: 1. Dilute sodium hydroxide solution ( NaOH)
2. Dilute hydrochloric acid ( HCl)
3. Phenolphthalein solution ( indicator)
4. Beaker
5. a dropper
Method: Pour about 20 cc of sodium hydroxide (NaOH) solution in the beaker. Add phenolphthalein solution to the sodium hydroxide solution in the beaker. It is observed that the solution turns deep pink. Add hydrochloric acid to the deep pink solution in the beaker with the help of a dropper drop by drop and go on stirring the solution.
It is observed that at some stage, by the addition of one drop of acid the solution suddenly becomes colourless.
It is because at this stage the sodium hydroxide solution has completely reacted with hydrochloric acid to form salt and water. Thus the last drop of HCl makes the acid in excess, and hence, the colour of the phenolphthalein changes from pink to colourless. Immediately the warmth of the beaker can be felt because of the evolution of the heat.
HCl + NaOH ----------→ NaCl + H2O + Heat ↑
Hence, it is observed that when an acid completely reacts with a base salt and water is produced with the evolution of heat.
Q.6. Explain why:
a) Farmers add slaked lime to acidic soils.
Ans. Plants grow well in neutral soil. Due to excessive use of artificial fertilizers, a natural soil becomes acidic and reduces the fertility of the soil. So to convert the acidic soils into neutral soils, farmers add calcium oxide (quick lime) or calcium hydroxide (slaked lime) to acidic soil. These chemicals neutralize soil acids and make the soil neutral and fertile.
b) Soap solution or baking soda paste is applied on the part of body stung by a bee.
Ans. The strings of a bee contain formic acid which is acidic in nature. When a bee stings, it injects formic acid into the skin which causes painful irritation and swelling. To neutralize the effect of formic acid, the area around the sting is rubbed with soap or baking soda solution which contains zinc carbonate (base). It helps in relieving pain.
c) Factory wastes and city sewerage is neutralized before discharging in rivers.
Ans. Factory wastes and city sewerage contains acids. Unless these are neutralize before discharging in rivers, the fish and other aquatic organisms will die. So, to prevent such a situation, the wastes are treated with lime which neutralizes acids.
d) Antacids are used for relieving stomach acidity.
Ans. The gastric juice secreted in the stomach contains hydrochloric acid. The acidity of stomach or indigestion is caused by f excessive secretion of this hydrochloric acid. To relieve indigestion or stomach acidity, antacid is used. Antacid contains magnesium hydroxide and aluminium hydroxide. These hydroxides neutralize the effect of excessive hydrochloric acid and help in controlling acidity of stomach.
Q.7. Give four differences between the acids and the alkalis.
Q.8. Write an equation when hydrochloric acid neutralizes sodium hydroxide.
Ans. HCl + NaOH ----------→ NaCl + H2O + Heat ↑
NCERT BOOKS
1. State differences between acids and bases.
Acids bases
Acids are sour in test Bases are bitter in taste
Acids are acidic in nature Bases are basic in nature
Acids turn blue litmus red Bases turn red litmus blue
pH value of an Acid is lower than 7 The pH value of a base is always
more than 7
2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Ans. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. When red litmus comes in contact with basic solution, it turns blue. Hence, ammonia found in window cleaner is basic in nature.
3. Name the source from which litmus solution is obtained. What is the use of this solution?
Ans. Litmus is a natural dye. It is extracted from lichen plants found in Tundra region.
Litmus solution is prepared from this litmus. It is used as a natural indicator to
Identify basic, acidic and neutral substances. The solution of litmus in distilled
water is mauver (purple) in colour and is called neutral litmus solution. When added to acidic solution, it turns red and when added to basic solution, it turns blue Litmus is available in the form of solution or in the form of strips of paper. Litmus paper is available in red and blue colours.
4. Is the distilled water acidic/basic/neutral? How would you verify it ?
Ans. Distilled water is neither acidic nor basic. It is neutral. This can be verified by using any of the indicators. The colour of the indicator does not undergo any change when comes in contact with either an acidic substance or a basic substance. Hence, the neutrality of the distilled water is verified.
5. Describe the process of neutralization with the help of an example.
Ans The process due to which an acid completely reacts with a base with the evolution of heat to form salt and water is called Neutralisation. It is the reaction between an acid and a base producing salt and water with the evolution of heat. When an acidic solution is mixed with a basics solution, both the solution neutralize the effects of each other.
For example, when hydrochloric acid ( an acid ) is mixed with sodium hydroxide ( a base ), sodium chloride ( a salt ) and water are produced with evolution of heat.
HCl + NaOH ----------→ NaCl + H2O + Heat ↑
6. Mark True or False
i) Nitric Acid turns red litmus blue. FALSE
ii) Sodium hydroxide turns blue litmus red. FALSE
iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. TRUE
ii) Indicator is a substance which shows different colours in acidic and basic solutions. TRUE
iii) Tooth decay is cause by the presence of a base. TRUE
7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labeled. He has to serve the drinks on the demand of customers. One customer wants acidic drink; another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Ans. When neutral litmus solution is used as an indicator, its colour change to blue in basic solution and red in acidic solutions and its colour does not change in neutral substances. Hence, the solution in the unlabelled bottle which changes the colour of the litmus solution to blue contains basic solution. The solution in the unlabelled bottle which changes the colour of the litmus solution to red contains acidic solution. The solution in the unlabelled bottle which does not change the colour of the litmus solution contains neutral solution. By this way, the drinks can be identified and served accordingly.
8. Explain why:
a) An antacid tablet is taken when you suffer from acidity.
The gastric juice secreted in the stomach contains hydrochloric acid. The acidity of stomach or indigestion is caused by excessive secretion of this hydrochloric acid. To relieve indigestion or stomach acidity, antacid is used. Antacid contains magnesium hydroxide and aluminium hydroxide. These hydroxides neutralize the effect of excessive hydrochloric acid and help in controlling acidity of stomach
b) Calamine solution is applied on the skin when an ant bites
Ans. The strings of an ant contain formic acid which is acidic in nature. When an ant stings, it injects formic acid into the skin which causes painful irritation and swelling. To neutralize the effect of formic acid, the area around the sting is rubbed with Calamine solution as it contains zinc carbonate (base). Zinc carbonate neutralizes the effect of formic acid and helps in relieving pain.
c) Factory waste is neutralized before disposing it into the water bodies.
Ans. Factory wastes and city sewerage contains acids. Unless these are neutralize before discharging in rivers, the fish and other aquatic organisms will die. So, to prevent such a situation, the wastes are treated with lime which neutralizes the effect of acids.
9. Three liquids are given to you. One is hydrochloric acid; another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Ans. When turmeric is used as an indicator, it identifies basic solutions only. Its colour does not change in acidic or neutral solution
10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
11. Consider the following statements:
a) Both acids and bases change colour of all indicators.
b) If an indicator gives a colour change with an acid, it does not give a change with a base.
c) If an indicator changes colour with a base, it does not change colour with an
acid.
a) Change of colour in an acid and a base depends on the type of the indicator.
b)
Which of these statements are correct?
i) All four ii) a and b iii) b and c iv) only d