Class-7 Science Chapter-5, Acids, Bases and Salts / Additional Exercises in line with NCERT book / CBSE Syllabus
Chapter
5
Acids, Bases
and Salts
Additional
Exercises
Choose the correct
answer:
(1)
Curd,
lemon juice, orange juice and vinegar taste sour. The chemical nature of these
substances is
a.
Acidic
(✓)
b.
Basic
c.
Salt
d.
None
of the above
(2)
Base
which is used as window cleaner is
a.
Calcium
hydroxide
b.
Ammonium
hydroxide (✓)
c.
Sodium
hydroxide
d.
Potassium
hydroxide
(3)
Sodium
hydroxide/potassium hydroxide is found in which of the following widely used
substance?
a.
Milk
of magnesia
b.
Lime
water
c.
Window
cleaner
d.
Soap
(✓)
(4)
Litmus
turns ______ in basic solution?
a.
Red
b.
Blue
(✓)
c.
Mauve
d.
Orange
(5)
Which
of these indicators is extracted from lichens?
a.
Litmus
(✓)
b.
Turmeric
c.
China
rose petal
d.
Phenolphthalein
(6)
China
rose indicator turns acidic solution to dark pink and basic solution to_______
a.
Magenta
b.
Orange
c.
Green
(✓)
d.
Blue
(7)
I
don't care should be taken while handling laboratory acids and bases because
these are_____
a.
corrosive in nature
b.
Irritating
c.
harmful to skin
d.
all the above (✓)
(8)
In
neutralization reaction a new substance is formed. this is called____
a.
Acid
b.
Bas
c.
Salt (✓)
d.
indicator
Match the column
(a)
|
A
|
B
|
|
Baking soda
|
Antacid
|
|
Vinegar
|
Bitter in taste
|
|
Milk of magnesia
|
Mauve in distilled water
|
|
Litmus
|
Synthetic Indicator
|
|
Methyl Orange
|
Sour
|
Ans-
|
A
|
B
|
|
Baking soda
|
Bitter in taste
|
|
Vinegar
|
Sour
|
|
Milk of magnesia
|
Antacid
|
|
Litmus
|
Mauve in distilled water
|
|
Methyl Orange
|
Synthetic Indicator
|
(a)
Match
these acids with the names of substances they are found in.
|
Name of acid
|
Found in
|
|
Acetic acid
|
Oranges, lemons
|
|
Formic acid
|
Amla
|
|
Citric acid
|
Spinach
|
|
Lactic acid
|
Vinegar
|
|
Oxalic acid
|
Ant’s sting
|
|
Ascorbic acid
|
Curd
|
|
Tartaric acid
|
Tamarind, Grapes, Unripe mangoes
|
Ans-
|
Name of acid
|
Found in
|
|
Acetic acid
|
Vinegar
|
|
Formic acid
|
Ant’s sting
|
|
Citric acid
|
Oranges, lemons
|
|
Lactic acid
|
curd
|
|
Oxalic acid
|
Spinach
|
|
Ascorbic acid
|
Amla
|
|
Tartaric acid
|
Tamarind, Grapes, Unripe mangoes
|
Give One Word:
(1)
Substances
which are bitter and feel soapy on touching.
Ans-
Bases
(2)
Substance
that tastes sour.
Ans-
Acid
(3)
Name
of base found in lime water
Ans-
Calcium Hydroxide
State whether the
following statements are true or false:
(1)
Litmus
solution turns red when added to an acidic solution and blue when added to a
basic solution. (True)
(2)
Acids
turn red Litmus blue and bases turns blue litmus red. (False)
(3)
Excessive
use of chemical fertilizers makes the soil acidic. (True)
(4)
A
salt may be acidic basic or neutral in nature. (True)
Select the odd one
(1)
Sulphuric acid,
Ammonium hydroxide, sodium hydroxide, calcium hydroxide (Bases)
(2)
Vinegar,
lemon juice, Baking soda, oxalic acid ,
tartaric acid (Acids)
(3)
China
rose solution, turmeric, tamarind,
phenolphthalein, Litmus (Indicators)
(4)
Lemon
juice, orange juice, milk of magnesia,
vinegar (Acids)
Fill in the blanks:
(1)
The
solutions, which do not change the colour of either red or blue litmus are
known as neutral solutions.
(2)
The
new substance formed in neutralization reaction is called salt.
(3)
Solutions,
which are neither acidic nor basic are called neutral.
(4)
Acids
are sour in taste.
(5)
Bases
are bitter in taste and soapy to touch.
(6)
Acids
turn blue litmus red.
Answer the following
questions:
Q. What are indicators?
Name some naturally occuring indicators.
Ans- Indicators are special
type of substances that are used to test whether a substance is acidic or basic.
Indicators change their
colour when added to a solution containing acidic or basic substance.
Some naturally occuring
indicators are as follows:
1- Turmeric
2- Litmus
3- China rose petals
(Gudhal)
Q. Given below are the
names of some bases. Write their chemical names.
Quicklime,
slaked lime, baking soda, milk of magnesia
Ans-
quicklime
|
calcium oxide
|
|
calcium hydroxide
|
slaked lime
|
|
baking soda
|
sodium hydrogen carbonate
|
|
milk of magnesia
|
magnesium hydroxide
|
Q. What do you understand
by neutralization? Explain with an example.
Ans- The reaction between
an acid and a base is known as neutralization. Salt and water are produced in
this process with the evolution of heat.
Acid
+ Base → Salt + Water( heat is evolved)
The following reaction is
an example:
Hydrochloric acid ( HCl) + Sodium hydroxide (NaOH)
→Sodium Chloride (NaCl) + Water(H2O)
Give reason. Why?
(1)
Milk
of magnesia is used as an antacid.
Ans- Our stomach contains hydrochloric acid. It
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. It neutralizes the
effect of excessive acid.
(2)
Calamine
solution or most baking soda is rubbed at the spot of an ant bite.
Ans- When an ant bites, it injects an acidic
liquid (formic acid) into the skin. The effect of an acid can be neutralized by
rubbing moist baking soda or calamine solution which contains zinc carbonate
(3)
Soil
is treated with bases like quicklime or slaked lime.
Ans- Excessive use of chemical fertilizers
makes the soil acidic. Plants do not grow well when the soil is too acidic. Therefore
it is treated with bases like quicklime ( calcium oxide) or slaked lime(
calcium hydroxide).
(4)
Organic
matter is added to the soil.
Ans- Plants
do not grow well when the soil is too basic.Iif the soil is basic, organic
matter is added to it. Organic matter releases acids which neutralize the basic
nature of the soil.
(5)
Factory
wastes are neutralized by adding basic substances.
Ans- The wastes from factories contain acid.If
they are allowed to flow into the water bodies, the acids will kill fish and
other organisms. The factory wastes are, therefore, neutralized by adding basic
substances.
Exercises
from Textbook
Q. State differences
between acids and bases.
Ans-
Acids
|
Bases
|
Acids are sour in taste.
|
Bases are bitter in taste.
|
Acids turn the blue litmus red.
|
Bases turn the red litmus blue.
|
Acids are not soapy to touch.
|
Basses are soapy to touch.
|
Acids contain hydrogen (H+)
ion.
|
Bases contain hydroxyl (OH-)
ion.
|
Vinegar, lemon juice and Sulphuric
acid are examples of acids.
|
Baking soda, lime water and Ammonium
hydroxide are examples of bases.
|
Q. Ammonia is found in
many household products, such as window cleaners. It turns red litmus blue. What
is its nature?
Ans- Ammonia is a base
because it turns red litmus blue. Because of its soapy nature (being a base),
it is used in many household products like window cleaners.
Q. Name the source from
which Litmus solution is obtained. What is the use of this solution.
Ans- Litmus solution is obtained from
Lichens. It is a natural indicator which has a mauve (purple) colour in
distilled water.
When litmus is added to an acidic
solution, it turns red and when it is added to a basic solution, it turns blue.
Q. Is the distilled water
acidic/ basic/ neutral? How would you verify it?
Ans- Distilled water is neutral in
nature. This can be verified by using litmus. Distilled water doesn’t change
the colour of either blue or red litmus paper.
Q. Describe the process
of neutralisation with the help of an example.
Ans- 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 is evolved)
The following reaction is an example:
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH)
→ Sodium chloride (NaCl) + Water (H2O)
Q. Mark T if the
statement is true and F if it is false:
1.
Nitric
acid turns red litmus blue. F
2.
Sodium
Hydroxide turns blue Litmus red. F
3.
Sodium
Hydroxide and Hydrochloric acid neutralize each other and form salt and water. T
4.
Indicator
is a substance, which shows different colours in acidic and basic solution. T
5.
Tooth
decay is caused by the presence of a base. F
Q. Dorji has a few
bottles of soft drink in his restaurant. But, unfortunately these are not
labelled. He has to serve the drinks on the demand of customer. One customer
wants acidic drink, another wants basic and third one wants neutral drink. How
will do you decide which drink is to be served to whom?
Ans- Dorji can serve drinks after
testing their nature with litmus paper.
(1)
The drink,
which converts blue litmus paper into red is an acidic drink.
(2)
The drink,
which converts red litmus paper into blue, is a basic drink.
(3)
The drink,
which does not change the colour of either red or blue litmus paper, is the neutral
drink.
Q. Explain why
(1)
An
antacid tablet is taken when you suffer from acidity.
Ans- Our stomach contains hydrochloric
acid. It 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 tablet.
It neutralizes the effect of excessive acid.
(2)
Calamine
solution is applied on the skin when an ant bites.
Ans- When an ant bites, it
inject an acidic liquid (formic acid) into the skin. The effect of an acid can
be neutralized by rubbing or Calamine solution which contains zinc carbonate.
(3)
Factory
waste is neutralized before disposing it into water bodies.
Ans- The waste from factories
contain acid. If they are allowed to flow into the water bodies, the acids will
kill fish and other organisms. The factory wastes are therefore, neutralized by
adding basic substances.
Q. Three liquids are
given to you. One is Hydrochloric acid, another is Sodium Hydroxide and third
is Sugar solution. How will you identify them? You have only turmeric
indicator.
Ans- Turmeric is an indictor which turns
bright red with bases.
Step-1 The solution with which turmesic gives a bright red
colour is Sodium Hydroxide (a base)
Step-2 Mix sodium hydroxide with remaining two solutions in
different test tubes. If the the testtube becomes warm, the added solution is
Hydrochloric acid (an acid)
Step-3 The third solution can be identified as Sugar solution.
Q. Blue litmus paper is
dipped in a solution. It remains blue. What is the nature of the solution?
Explain.
Ans- Blue litmus paper
turns red in an acidic solution.
If in a given solution,
blue litmus paper remains blue, there can be two possibilities:
(1)
The solution is
a base. or
(2)
The solution is
neutral.
Q. 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.
d.
Change
of colour in an acid and a base depends on the type of the indicator.
Which
of these statements are correct?
1-
All
four
2-
a
and d (✓)
3-
b
and c
4-
Only
Tables from Textbook
Table 5.1
Substance
|
Taste ( sour / bitter /any other)
|
Lemon juice
|
sour
|
Orange jiuce
|
sour
|
Vinegar
|
sour
|
Curd
|
sour
|
Tamarind (imli)
|
sour
|
Sugar
|
Sweet
|
Common salt
|
Salty
|
Amla
|
Pungent / sour
|
Baking soda
|
bitter
|
Grapes
|
Sour / sweet
|
Unripe mango
|
sour
|
Table 5.3
S.No.
|
Test solution
|
Effect on turmeric solution
|
remark
|
1
|
Lemon juice
|
No change
|
|
2
|
Orange juice
|
No change
|
|
3
|
Vinegar
|
No change
|
|
4
|
Milk of magnesia
|
Deep red
|
|
5
|
Baking soda
|
Deep red
|
|
6
|
Lime water
|
Deep red
|
|
7
|
Sugar
|
No change
|
|
8
|
Common salt
|
No change
|
Collect some China rose petals and place them in a beaker. Add some warm water. Keep the mixture for some time until water becomes coloured. Use the coloured water as an indicator. Add 5 drops of the indicator to each of the solutions given in table 5.4.
Table
5.4
Serial number
|
test solution
|
initial colour
|
final colour
|
1
|
Shampoo( dilute solution)
|
Light Pink
|
Green
|
2
|
lemon juice
|
Light Pink
|
Magenta
|
3
|
soda water
|
Light Pink
|
Green
|
4
|
sodium hydrogen carbonate solution
|
Light Pink
|
Green
|
5
|
vinegar
|
Light Pink
|
Magenta
|
6
|
sugar solution
|
Light Pink
|
No change
|
7
|
common salt solution
|
Light Pink
|
No change
|
Get some hydrochloric acid
sulphuric acid nitric acid Acetic Acid, Sodium Hydroxide, Ammonium hydroxide,
calcium hydroxide( lime water) water and observe the effect of these
solutions on Litmus Paper, turmeric paper and China rose solution.
S.No
|
Name of acid
|
Effect on litmus paper
|
Effect on turmeric paper
|
Effect on China rose solution
|
1
|
Dilute hydrochloric acid
|
Blue litmus paper turns red
|
No effect
|
Magenta
|
2
|
Dilute sulphuric acid
|
Blue litmus paper turns red
|
Red colour
|
Magenta
|
3
|
Dilute Nitric acid
|
Blue litmus paper turns red
|
No effect
|
Magenta
|
4
|
Sodium hydroxide
|
Red litmus paper turns blue
|
Red colour
|
Green
|
5
|
Ammonium hydroxide
|
Red litmus paper turns blue
|
Red colour
|
Green
|
6
|
Calcium hydroxide
|
Red litmus paper turns blue
|
Red colour
|
Green
|
Extended learning-
Activities and Projects
1- Using the knowledge of
acids and bases, write a secret message with the help of baking soda and
beetroot. explain how it works.
(Hint: Prepare baking soda solution in water.
Use this solution to write the message on a sheet of white paper with a cotton
bud. Rub a slice of fresh beetroot over the message.)
2- Prepare red cabbage
juice by boiling a piece of red cabbage in water. Use it as an indicator and
test the acidic and basic solution with it. Present your observations in the
form of a table.
3- Bring the soil sample of
your area. Find out if it is acidic, basic or neutral. Discuss with farmers if
the treat the soil in any manner.
4- Visit a doctor. Find out
the medicines, he prescribes to treat acidity. Ask him how acidity can be
prevented.
Did you know?
|
Each cell in our body
contains an acid, the deoxyribonucleic acid or DNA. it controls every
feature of the bodies such as our looks, colour, our height etc. Proteins
that build part of our cells are also made of amino acids. The fats in
our body contain fatty acids.
|
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