KSEEB Solutions for Class 8 Science Chapter 12 Chemicals in Our Daily Life

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Karnataka State Syllabus Class 8 Science Chapter 12 Chemicals in Our Daily Life

KSEEB Class 8 Science Chemicals in Our Daily Life Textbook Exercise Questions and Answers

I. Four alternatives are given to each of the following incomplete statements/questions. Choose the right answer.

Question 1.
Chlorine is prepared in the laboratory by the action of
(a) Zn and HCl
(b) MnO₂ + HCl
(c) CaCO₃ and HCl
(d) Pb (NO₃)₂ and HCl
Answer:
(b) MnO₂ + HCl

Question 2.
The chief sources oils used to make soap are
(a) petroleum products
(b) coal and coke
(c) animals and plants
(d) detergents
Answer:
(c) animals and plants

II. Fill in the blanks:

Question:
1. Mn O₂ + 4 HCl → Mn Cl₂ + ________ + ________.
2. Common name of sodium chloride is ________.
3. Chemical name of baking soda is ________.
Answer:
1. Cl₂ ↑ + 2 H₂O,
2. Common salt,
3. Sodium bicarbonate

III. Answer the following:

Question 1.
Pure and dry chlorine gas is collected by the upward displacement of air, give a reason.
Answer:
Chlorine gas is collected by the upward displacement of air since chlorine is heavier than air.

Question 2.
Name the compound of chlorine.

which is an anesthetic
which is used as a refrigerant
which is disinfectant
which is used to make pipes and tubes
which liberates chlorine on exposure to air.

Answer:

Chloroform,
Chlorofluoro Carbon (CFC),
Bleaching powder chloride,
Polyvinyl Chloride (PVC),
Calcium Oxychloride

Question 3.
Mention four uses of chlorine.
Answer:
Uses of chlorine are:

used in the manufacture of bleaching powder and H Cl
used in paper and pulp industry for whitening
used in the manufacture of P.V.C and C.F.C
used to prepare pesticides like D.D.T &B.H.C :

Question 4.
Name the metal and the acid to be selected to prepare sulphur dioxide oh the laboratory.
Answer:
To prepare sulphur dioxide in the laboratory copper turnings and sulphuric acid are used.

Question 5.
Name the acid formed when sulphur dioxide dissolves in water.
Answer:
When sulphur dioxide dissolves in water sulphurous acid is formed.

Question 6.
Give two uses of sulphur dioxide.
Answer:
Sulphur dioxide is used:

to manufacture sulphuric acid which is the raw material for detergents, fertilizers, etc.
in the sugar industry .to remove the colouring matter from sugar.
to prevent the decolourisation of dried fruits.
to increase the shelf life of food as it prevents the growth of bacteria and fungus.

Question 7.
Mention any two differences between soap and synthetic detergents.
Answer:
Soap:

Not good for washing when the water is hard.
Prepared from vegetable oil or animal fat.
does not cleanse well in acidic medium.
biodegradable.

Detergents:

Cleanse well even in hard water.
made from hydrocarbons obtained from petroleum.
Cleanse well even in acidic medium.
Non- biodegradable

Question 8.
How is detergent industrially manufactured?
Answer:
Long-chain hydrocarbons obtained from petroleum are treated with concentrated sulphuric acid. The organic acid produced during the process is neutralized with sodium hydroxide. The sodium salt thus obtained is detergent.

Question 9.
Why is detergent better than soap in cleaning action?
Answer:
Soaps do not give lather with hard water. The soaps react with’ the salts present in the hard water to form insoluble precipitates which hinder the cleansing action whereas detergent gives lather even with hard water and do not form an insoluble scum.

KSEEB Class 8 Science Chemicals in Our Daily Life Additional Questions and Answers

Question 1.
Name the chemical name of common salt.
Answer:
Sodium chloride

Question 2.
Which is the common element present in bleaching powder and common salt?
Answer:
Chlorine

Question 3.
Name the minerals of chlorine.
Answer:
Halite or rock salt, sylvite, carnallite, chlorapatilte are the common minerals of chlorine.

Question 4.
How is chlorine manufactured industrially?
Answer:
In the industry, chlorine is produced by passing an electric current through an aqueous solution of sodium chloride or through molten sodium chloride.

Question 5.
What do you mean by aqueous solutions?
Answer:
The solutions made using water are called aqueous solutions.

Question 6.
Write the preparation of chlorine in the laboratory. Thistle funnel

Answer:
Take 20 g of manganese dioxide in the flask. Add concentrated HCl to it through thistle funnel, such that the tip of the thistle funnel is dipped in the acid. Heat the flask. The gas liberated is collected in the jar by the upward displacement of air.
Mn O₂ + 4 HCl → Mn Cl₂ + Cl₂ + 2 H₂O

Question 7.
Write the preparation of chlorine gas from potassium permanganate and con. HCI,

Answer:
Take potassium permanganate in the flask. Add concentrated HCI through the dropping funnel, drop by drop. The chlorine gas liberated is collected by the upward displacement of air.

Question 8.
Mention the chemical properties of chlorine.
Answer:
1. Burning magnesium ribbon reacts with chlorine to form Magnesium chloride.
Mg + Cl₂ → Mg Cl₂

2. Hot red phosphorus reacts in the limited supply of chlorine to form phosphorus trichloride and in an excess supply of chlorine form phosphorus pentachloride.
2P + 3 Cl₂ → 2 P Cl₃ [ Limited supply of Cl₂]
2P + 5 Cl₂ → 2 P Cl₅ [ Excess supply of Cl₂]

3. Sodium burns vigorously in chlorine with is the golden yellow flame to form sodium chloride.
2 Na + Cl₂ → 2 Na Cl

4. When the heated aluminium powder is sprinkled into a jar of chlorine it burns brightly with flashes of light.
2 Al + 3 Cl₂ → 2 Al Cl₃

5. Chlorine reacts with water to form t hypochlorous acid.

Question 9.
How does chloride act as a bleaching and sterilizing agent?
Answer:
When chlorine gas is dissolved in water, hypochlorous acid is formed which releases nascent oxygen. Nascent oxygen is a powerful oxidizing agent. Which is responsible for the bleaching and sterilizing property of chlorine.

Question 10.
What is the chemical name of bleaching powder? How it is prepared?
Answer:
The chemical name of bleaching powder is calcium oxychloride. It is prepared by passing chlorine gas into slaked lime at 400° C.
Ca (OH)₂ + Cl₂ → Ca O Cl₂ + H₂O

Question 11.
Name the food items which contain sulphur.
Answer:
Egg yolk, cauliflower, radish, onion and garlic contain sulphur.

Question 12.
Name parts of Human body which contain sulphur.
Answer:
Hair, nails, and skin contain sulphur.

Question 13.
Write the methods by which sulphur dioxide can be manufactured on a large scale.
a) By burning cinnabar (mercurous sulphide) in oxygen
Answer:
Hg S + O₂ → Hg + SO₂

b) by burning Zinc sulphide (Zinc blende) in oxygen –
Answer:
2 Zn S + 3 O₂ → 2 Zn O + 2 S O₂ ↑

Question 14.
What is Acid rain? Mention its effects.
Answer:
Water molecules in the atmosphere react with sulphur dioxide to form acid rain.

The effects are:

corrodes monuments, statues, and buildings.
effects soil fertility and PH value of the soil. This affects the plant’s growth.

Question 15.
Write an experiment to show that the bleaching property of sulphur dioxide is temporary.
Answer:
Introduce a few petals of rose flowers soaked in water, in a jar of sulphur dioxide. Decolourisation takes place. Now take out the petals from the jar and expose it to the air. Colour is regained this shows that the bleaching action of sulphur dioxide is temporary.

Question 16.
What happens when a burning magnesium ribbon is kept inside a jar containing sulphur dioxide gas?
Answer:
Magnesium continues to burn to displace sulphur particles which stick to the jar.
2 Mg + SO₂ 2 Mg O + S

Question 17.
How is baking soda manufactured?
Answer:
Baking soda is manufactured by passing carbon dioxide through saturated sodium carbonate solution in water,
Na₂ CO₃ + CO₂ + H₂O 2 Na HCO₃

Question 18.
Mention the uses of baking soda.
Answer:
Baking soda is used:

to prepare baking powder.
as an antacid to treat the excess of acid formed in the stomach.
as a mild cleaning agent.
to prepare aerated water (soda water)

Question 19.
Why are detergents called soap-less soaps?
Answer:
Detergent acts like soap in the cleansing properties, but they do not contain the usual soap like sodium stearate.

Question 20.
What is glycerol? Mention the uses.
Answer:
Glycerol or glycerine is a sweet viscous liquid soluble in water. It is used in the manufacture of explosives, plastics and pharmaceuticals. It is also used to prevent freezing.

Question 21.
Overuse of detergents causes water pollution why?
Answer:
The overuse of detergents causes water pollution because detergents are non-biodegradable.

Question 22.
How is liquid soap prepared?
Answer:
Heat the mixture of oil and potassium hydroxide solution. Stir well. As soap cooks, it will be converted to the gel phase. Add distilled water and stir well and add a little scent!

II. Fill in the blanks:

The gas released during the purification of petroleum is ______.
The gas released during a volcanic eruption is ______.
______ prepared sulphur dioxide gas.
Priestly heated concentrated sulphuric acid with mercury and called the gas produced as ______.
Mercurous sulphide is commonly called as ______.
Zinc sulphide is commonly called as ______.
Sodium sulphate + ______ Sodium chloride + Water + Sulphur dioxide
Sulphur dioxide reacts with water to give ______ acid.
Sulphur trioxide reacts with water to give ______ acid.
Ammonium sulphate is obtained by the action of sulphuric acid on ______ gas.
The process of preparing soap is called ______.
Sodium stearate is an example of ______.

Answer:

Sulphur dioxide,
Sulphur dioxide,
Priestly,
Vitriolic acid air,
cinnabar,
Zinc blends,
dil. HCl,
sulphurous acid,
sulphuric acid,
ammonia,
saponification,
soap

III. Choose the correct answer:

Question 1.
The scientist who first prepared chlorine gas was
(a) Sir. Humphrey Dave,
(b) Carl Wilhelm
(c) Priestly
(d) Lavoisier
Answer:
(b) Carl Wilhelm

Question 2.
The colour of chlorine gas is
(a) yellow
(b) green
(c) red
(d) purple
Answer:
(b) green

Question 3.
The scientist who first prepared sulphur dioxide gas was ‘
(a) Sir Humphrey Dave
(b) Car! Wilhelm
(c) Priestley
(d) Lavoisier
Answer:
(c) Priestley

Question 4.
The peculiar smell when the skin is burnt is due to
(a) SO₂
(b) Protein
(C) C₆H₁₂O₆
(d) oil
Answer:
(a) SO2

Question 5.
The molecular formula of baking soda is
(a) Na CO₃
(b) NaCl
(c) CaCO₃
(d) NaHCO₃
Answer:
(d) NaHCO₃

Question 6.
The molecular formula of bleaching powder is
(a) Ca O Cl₂
(b) Ca Cl₂
(р) Ca O
(d) Ca₂ O Cl
Answer:
(a) Ca O Cl₂

Question 7.
The chemical which is used as an antacid
(a) Na O H
(b) Na CO₃
(с) Na₂ SO₄
(d) Na H CO₃
Answer:
(d) Na H CO₃

Question 8.
The chemical used to reduce the solubility of soap is
(a) NaCI
(b) Na OH
(c) KOH
(d) oil
Answer:
(a) NaCI

Question 9.
The common chemical used for the preparation of both soap and detergent
(a) oil/fat
(b) KOH
(c) Na O H
(d) H₂ SO₄
Answer:
(c) Na O H