1. What are acids? Give some examples.
Answer: A substance which reacts with a base to form a salt (and water) is called an
acid. Acids have sour taste. Acids turn blue litmus to red. Acetic acid, Citric acid,
Hydrochloric acid, Sulphuric acid and Nitric acid.
2. What are the types of acid?
Answer: Acids are of two types: (a) Organic acid (b) Mineral acid
3. What are organic acids? Give example.
Answer: Organic acids are the naturally occurring acids. They are found in various
types of plants and animals. Ex: Acetic acid, Formic acid, Citric acid.
4. Write the sources of some organic acids.
Answer:
Acetic acid is found in vinegar (or sirka). Vinegar is used as a preservative in
foods.
Formic acid is present in ant's sting. The sharp pain caused by the sting of an
ant is due to acid pushed into our skin during the sting.
Citric acid is present in citrus fruits such as lemons and oranges.
Lactic acid is present in curd and in sour milk.
Tartaric acid is present in tamarind (imli), unripe grapes and unripe mangoes.
Ascorbic acid is present in amla and citrus fruits (such as lemons and
oranges). Ascorbic acid commonly known as vitamin C.
Oxalic acid is present in spinach (palak).
5. Which acids are weak acids and why?
Answer: Organic Acids are weak acid, because they contain naturally occurring acids
in them and are not harmful for the body.
6. What are mineral acids? Write the common types of mineral acids.
Answers: The acids prepared from the mineral of the earth are called mineral acids.
They are also known as laboratory acids.
Most common types of mineral acids are:
Hydrochloric Acids
Sulphuric Acids
Nitric Acids
7. Write some uses of mineral acids in our daily life.
Answer: We also use mineral acids in our daily life. For example, hydrochloric acid is
used in cleaning kitchen sinks and bathroom sanitaryware (like wash basin and
toilet seat). Sulphuric acid is used in making storage batteries for cars, buses, trucks
and inverters. Nitric acid is used by goldsmiths for cleaning gold and silver
ornaments.
8. What are Concentrated and Dilute acids?
Answer: A concentrated acid is an acid which is in either pure form or has a high
concentration.
And dilute acid is that in which the concentration of water mixed in the acid is
higher than the concentration of acid itself.
9. Why concentrated mineral acids are very dangerous?
Answer: These acids can burn our hands and clothes. These acids should be handled
with great care.
10. What are the two groups of acids?
Answer: All acids can be divided into two groups:
Strong Acids: Mineral acids, such as Hydrochloric acid, Sulphuric acid, Nitric
Acid.
Weak Acids: Formic acids, Acetic acids, Citric acids.
11. What are strong acids? Give example. Write an exception of mineral acid which is
not strong acid.
Answer: Strong acids dissociate fully in water to produce maximum number of H+
Ions. Examples are: Hydrochloric acid, Sulphuric acid, Nitric Acid.
Only one mineral acid, carbonic acid, is a weak acid.
12. What are weak acids? Give examples.
Answer: Weak acids are those acids which partially or not fully get dissociate in
water. Examples: Ethanoic Acid (CH3COOH) and other organic acids.
13. Where is carbonic acid used?
Answer: Carbonic acid is used in fizzy soft drinks and soda water. It gives them a pleasant taste.
14. What is acid rain?
Answer: The rain which contains a higher level of acid than normal is called acid
rain.
15. Write the cause of acid rain?
Answer: Acid rain is caused by the acidic gases like suphur dioxide, nitrogen dioxide and
carbon dioxide which are released into the air as pollutants during the burning of
various types of fuels. Sulphur dioxide gas dissolves in falling rain drops to form
sulphuric acid; nitrogen dioxide gas dissolves in rain drops to form nitric acid, whereas
carbondioxide gas dissolves in ran drops to form carbonic acid. The presence of
sulphuric acid, nitric acid and carbonic acid in rain water makes the rain water acidic.
And when this acidic rain water falls on the earth, we call it acid rain.
16. What are the effects of acid rain?
Answer: Acid rain causes damage to aquatic animals (1ike fish), trees, crop plants, metal
structures and stone buildings and monuments.
This happens as follows :
Acid rain makes the water of lakes, ponds and rivers too acidic due to which fish
and other aquatic animals get killed.
Acid rain eats up the leaves of the trees gradually. By losing leaves, the trees die.
Acid rain also damages crop plants in the fields.
Acid rain damages the metal structures like steel bridges, etc., when it falls on
them.
Acid rain damages the surtaces of buildings and monuments made of stone.
17. What are bases? Give examples.
Answer: A substance which can neutralize an acid to form a salt (and water) is called a
base. Bases have bitter taste. Bases turn red litmus to blue.
Examples: Sodium Hydroxide, Potassium Hydroxide.
18. What is alkali? Give examples.
Answer: A base which is soluble in water is called an alkali.
Examples: Sodium Hydroxide, Potassium Hydroxide.
19. Write the sources of some common bases.
Sodium hydroxide and potassium hydroxide are found in soap.
Calcium hydroxide is found in lime water.
Magnesium hydroxide is found in milk of magnesia.
Ammonium hydroxide (also called ammonia solution) is found in window
cleaners.
Sodium carbonate is found in washing soda.
Sodium hydrogencarbonate is found in baking soda.
20. Write some examples of strong and weak bases.
Answer: Sodium hydroxide is commonly known as 'caustic soda' and potassium
hydroxide is commonly known as 'caustic potash’ (caustic means 'corrosive' or
burning'). Sodium hydroxide and potassium hydroxide are dangerous bases which
can burn our skin. They must be handled very carefully. Calcium hydroxide,
ammonium hydroxide and sodium carbonate are weak bases but their solutions are
unsafe to drink. Magnesium hydroxide is, however, a very weak base which is safe
to drink.
21. How toothpaste prevents tooth decay?
Answer: some of the sugary food eaten by us is converted into acid by the bacteria
present in our mouth. And this acid causes tooth decay. The toothpaste which we
use for brushing and cleaning our teeth is basic in nature. Since toothpaste is basic,
it neutralizes the acid in our mouth and hence prevents tooth decay.
22. Write the differences between acids and bases.
Acids have sour taste. Bases have bitter taste.
Acids are not soapy to touch. Bases feel soapy to touch.
Acids turn blue litmus to red. Bases turn red litmus to blue.
23. What is an indicator?
Answer: Indicators are special type of chemicals which are used to test whether a given
substance is an acid or base. Indicators change their colour when added to a solution
containing an acid or a base.
An indicator is a 'dye' that changes colour when it is put into an acid or a base. An indicator
gives different colours in acid and base. Thus, an indicator tells us whether the substance
we are testing is an acid or a base by change in its colour.
24. What are the types of Acid-Base indicators? Write examples.
Answer: Acid-base indicators are of two types : Natural indicators and Synthetic
indicators.
(i) Litmus, China rose and Turmeric are naturally occurring indicators.
(ii) Phenolphthalein is a synthetic indicator.
25. What is litmus?
Answer: Litmus is a natural indicator. Litmus solution is purple (mauve) coloured
dye in distilled water, extracted from a type of plant called lichen. When acid is
added to the litmus solution its colour changes to red and when base is added to the
litmus solution its colour changes to blue.
Litmus can be used in the form of solution or in the form of strips of paper-Blue
litmus paper and Red litmus paper.
26. How litmus paper is used to identify whether the solution is acidic or basic?
Answer: Litmus is the most common indicator for testing acids and bases in the
laboratory.
Acids turn blue litmus to red.
Bases turn red litmus to blue.
27. What is the convenient way to find out whether a solution is acidic or basic?
Answer: A convenient way to find out whether a solution is acidic or basic is to test
it with blue litmus paper and red litmus paper, turn by turn, and observe the change
in colour which takes place.
If a drop of the given solution turns blue litmus paper to red, then the given
solution will be acidic in nature (or it will be an acid).
For example, a drop of lemon juice turns blue litmus paper to red, so lemon juice is
acidic in nature. That is, lemon juice contains an acid.
If a drop of the given solution turns red litmus to blue, then the given
solution will be basic in nature (or it will be a base).
For example, a drop of baking soda solution turns red litmus paper to blue, so
baking soda is basic in nature. That is, baking soda is a base.
28. What is China rose indicator? How it shows colour change with acids and bases?
Answer: China rose is also a natural indicator. China rose indicator is a light pink
coloured solution which is extracted from the red flowers of China rose plant with
water.
When acid and base are tested with china rose indicator, the following colour
changes to indicate the type of nature of the substance:
Acid turns the colour of China rose indicator to magenta (deep pink)
Bases turns the colour of China rose indicator to green.
29. How can you prepare China rose indicator?
Answer: We can make the China rose indicator ourselves as follows: Collect some
petals of China rose flower and place them in a beaker. Add some warm water.
Keep the China rose petals immersed in water for some time till water in the beaker
acquires a light pink colour. Remove the petals by filtration. The light pink solution
thus obtained is the China rose indicator. This China rose indicator can now be used
for testing acids and bases.
30. How can you prepare turmeric paper?
Answer: Turmeric paper can be prepared as follows Take a tablespoonful of
turmeric powder, add a little water and make a paste. Deposit the turmeric paste on
a blotting paper (or filter paper) and dry it. The yellow paper thus obtained is the
turmeric paper. Cut thin strips of turmeric paper. Use these strips of turmeric paper
as indicator.
31. How turmeric paper is used as indicator?
Answer: Turmeric paper is used as indicator. Turmeric paper is yellow in colour.
(i) Turmeric paper is yellow in acid solution.
(ii) Bases turn the yellow turmeric paper to red.
32. Why yellow stain of curry on white shirt changes to red when soap is scrubbed on
it?
Answer: This is due to the fact that soap solution is basic in nature which changes
the colour of turmeric in the curry stain to red.
33. How phenolphthalein is used as an indicator?
Answer: Phenolphthalein is a synthetic or man-made acid-base indicator.
Phenolphthalein indicator is colourless in acid solution.
Phenolphthalein indicator gives pink colour in basic solution.
34. How can we test the presence of an acid in a substance by performing the litmus
test?
Answer: We can test the presence of an acid in a substance by performing the
litmus test For example: we can perform the litmus test to show the presence of
acid in lemon juice (or orange juice) we took some lemon juice in a test-tube and
add a little water to it.
Now we Put a drop of the lemon juice solution on a strip of red litmus paper
with the help of a dropper. We find that there is no change in the colour of red litmus paper. This means that lemon juice is not base in nature (because
only basic substances or bases turn red litmus to blue).
Now we put a drop of lemon juice solution on a strip of blue litmus paper.
The blue litmus paper turns red. This shows that lemon juice is acidic in
nature (or lemon juice contains an acid). This is because only acidic
substances or acids turn blue litmus to red.
35. What are neutral substances?
Answer: Those substances which are neither acidic nor basic in nature are called
neutral substances. Being neither acidic nor basic neutral substances do not change
the colour of any indicator.
Examples: Distilled water, Glucose, Common salt.
36. Define “Neutralization Reaction”.
Answer: The chemical reaction between acid and base is called neutralization
reaction. In this reaction salt and water is produced with the evolution of heat. The
generated heat raises the temperature of the reaction mixture.
Acid + Base= salt+ Water (Evolution of heat)
37. Give an example of neutralization reaction.
Answer: Sodium hydroxide is a base and hydrochloric acid is an acid. So, when
sodium hydroxide is treated with hydrochloric acid, then a neutralization reaction
takes place to form sodium chloride (salt) and water. This can be written as
Sodium hydroxide + Hydrochloric acid = Sodium chloride + Water + Heat
38. How we get relieve from indigestion?
Answer: Our stomach contains hydrochloric acid, which helps us to digest food. But
too much of acid in the stomach causes indigestion. Sometimes indigestion is
painful. To relieve indigestion, we take an antacid such as milk of magnesia, which
contains magnesium hydroxide. Being antacid, they are basic in nature, and react
with excess of acid in the stomach and neutralize it. Thus, magnesium hydroxide
neutralizes the effect of excessive acid.
39. How ant bite can be neutralized?
Answer: The sting of an ant contains an acid called formic acid. So, when an ant
stings (or bites) a person, it injects an acidic liquid into the skin of the person which causes burning pain. If an ant stings a person, then rubbing a mild base like baking
soda solution (or calamine solution) on the stung area of the skin gives relief. This is
because, being a base, baking soda solution (or calamine solution) neutralizes the
acidic liquid injected by the ant and cancels its effect. Please note that calamine
solution contains a base called zinc carbonate.
40. How soil treatment is done?
Answer: The soil may be acidic or basic naturally. The plants do not grow well if the
soil at a place is too acidic or too basic. The excessive use of chemical fertilizers in
the fields also makes the soil too acidic. When the soil is too acidic, it is treated with
bases such as quicklime (calcium oxide) or slaked lime (calcium hydroxide). The
bases such as quicklime (or slaked lime) neutralize the excess acid present in the soil
and reduce its acidic nature. Thus, a farmer should add quicklime (or slaked lime) in
the fields if the soil is too acidic. Sometimes, however, the soil is too basic. If the soil
is too basic, then decaying organic matter called manure or compost) is added to it.
The decaying organic matter releases acids which neutralize the excess bases
present in the soil and reduce its basic nature. Thus, a farmer should add decaying
organic matter (manure or compost) in his fields if the soil is too basic.
41. How factory wastes are made neutral?
Answer: The wastes of many factories contain acids. If they are allowed to flow into
the water bodies, the acids will kill the fish and other organisms. The factory wastes
are, therefore, neutralized by adding basic substances.
42. What is a salt?
Answer: A salt is a substance formed by the reaction of an acid with a base.
A salt has two parents-acid and base.
43. Name the salts obtained from various acids.
Answer:
The salts of hudrochloric acid are called chlorides.
The salts of sulphuric acid are called sulphates.
The salts of nitric acid are called nitrates.
The salts of carboic acid are called carbonates.
The salts of acetic acid are called acetates.
44. What are the types of salt? Define them with examples.
Answer: Salts can be of three types (i) Neutral salts (i) Acidic salts, and (ii) Basic
salts.
Neutral Salts: Those salts which form a neutral solution on dissolving in water are
called neutral salts. The salts formed by the neutralization of a strong acid by a
Strong base are neutral salts.
The two examples of neutral salts are sodium chloride (NaCl) and sodium sulphate
(Na2SO4). The solution of a neutral salt has no effect on any litmus.
Acidic Salts: Those salts which form an acidic solution on dissolving in water are
called acidic salts; the salts formed by the neutralization of a strong acid with a
weak base are acidic salts. The two examples of acidic salts are: ammonium chloride
(NH4Cl) and ammonium sulphate [(NH4)2SO4]. The solution of an acidic salt in
water turns blue litmus red.
Basic Salts: Those salts which form basic solutions on dissolving in water are called
basic salts. The salts formed by the neutralization of a weak acid with a strong base
are basic salts. The two examples of basic salts are: Sodium Carbonate (Na2CO3)
and Sodium hydrogencarbonate (NaHCO3). The solution of an basic salt in water turns red litmus blue.
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