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Karnataka State Syllabus Class 8 Science Chapter 12 Chemicals in Our Daily Life
KSEEB Class 8 Science Chapter 12 Textual Questions & Answers
I. Four alternatives are given to each of the following incomplete statement/ question. Choose the right answer.
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
b) MnO2 + HCl
The chief sources oils used to make soap are
a) petroleum products
c) animals and plants
d) soap and detergents
c) animals and plants
II. Fill in the blanks :
MnO2 + 4HCl → MnCl2 +…………..
Common name of sodium chloride is ……………….
Chemical name of baking soda is …………….
III. Answer the following.
Pure and dry chlorine gas is collected by the upward displacement of air give reason.
Chlorine gas collected by the upward displacement of air because chlorine is heavier than air.
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.
- chlorofluorocarbon (CFC)
- Sodium chloride
- polyvinyl chloride (PVC)
- Calcium oxychloride
Mention four uses of chlorine.
Chlorine is used in the manufacture of bleaching powder.
- Chlorine is used in the manufacture of hydrochloric acid
- It is used in the paper and pulp industry.
- It is used as a bleaching agent and in the purification of water
- It is used in the manufacture of polyvinyl chloride and Chlorofluorocarbons. (C.F.C)
- Chlorine is used in the preparation of pesticides like benzene hexachloride commonly called BHC. dichloro diphenyl trichloroethane (DDT)
- It is used in the preparation of chloroform which is used as an anesthetic.
Name the metal and the acid to be selected to prepare sulfur dioxide on the laboratory,
To prepare sulfur dioxide in the laboratory copper turnings and sulfuric acid are used.
Name the acid formed when sulfur dioxide dissolves in water.
When sulfur dioxide dissolves in water sulfurous acid is formed.
Give two uses of sulfur dioxide.
Sulfur dioxide is used in the manufacture of sulfuric acid
- It is used to increase the shelf life of foods.
- In the sugar industry, sulfur dioxide is used to remove coloring matter from sugar.
- It is used to prevent the decolonization of dried fruits.
Mention any two differences between soap and synthetic detergents.
- prepared from vegetable oil or animal fat
- Not good for washing, when the water is hard
- does not cleanse well in acidic medium
- made from hydrocarbons obtained from petroleum
- cleanse well even in hard water
- cleanse well even in acidic medium.
How is detergent industrially manufactured?
A method of manufacturing detergents: A long chain hydrocarbons obtained from petroleum are treated with concentrated sulfuric acid. Then it is neutralized with sodium hydroxide the sodium salt thus obtained is detergent.
Why are detergents better than soap in cleaning action?
Soap does not give lather with hard water. The soap reacts with the salts present in the hard water to form insoluble precipitates which hinder the cleaning action whereas detergents give lather with hard water and do not form an insoluble scum.
KSEEB Class 8 Science Chapter 12 Additional Questions & Answers
Mention the chemical name of common salt.
The chemical name of common salt is sodium chloride. (NaCl)
Name the common element present in bleaching powder and common salt?
Chlorine is the common element present in bleaching powder and common salt.
Name the minerals of chlorine.
The most common minerals of chlorine are Halite, (rock salt), sylvite carnallite, chlorapatite.
How is chlorine manufactured industrially?
In industry, chlorine is produced by passing an electric current through an aqueous solution of sodium chloride or through molten sodium chloride. The products produced along with chlorine are sodium hydroxide and hydrogen.
What is aqueous solution?
Solutions made using water are called aqueous solution.
Explain the preparation of chlorine in the laboratory.
Take nearly 20 g of manganese dioxide in the flask add concentrated hydrochloric acid to it through thistle funnel so that tip of the thistle funnel is dipped in the acid. Heat the flask. The gas liberated. The liberated gas is collected in the jar by the upward displacement of air.
MnO2 + 4HCl → MnCl2 + Cl2 ↑+ 2H2O
Explain the preparation of chlorine gas from potassium permanganate and con. HCl.
Take potassium permanganate in the flask, Add concentrated Hydrochloric acid through the droping Funnel chlorine gas is bi berated. The liberated gas is collected in separated bottles by the upward displacement of air.
Write the physical properties of chlorine are.
The physical properties of chlorine are.
- Chlorine is pale greenish-yellow in colour.
- It is a supporter of combustion.
- It is heavier than air.
- It turns blue litmus red therefore acidic.
Mention the chemical properties of chlorine.
The chemical properties of chlorine.
- Burning magnesium ribbon react with chlorine to form magnesium chloride.
Mg + Cl2 → MgCl2
- Chlorine reacts with hot red phosphorous giving phosphorus pentaxide
2p + 3Cl2 → 2PCl3 (Limited supply of chlorine)
2p + 5Cl2 —» 2PCl5 (Excess supply of chlorine)
- Sodium burns vigorously on chlorine with golden yellow flame to form sodium chloride.
2Na + Cl2 → 2NaCl
- When heated aluminium powder is sprinkled into jar of chlorine it burns brightly with flashes of light.
2Al + 3Cl2 → 2AlCl3
- Chlorine reacts with water to form hypochlorous acid.
Write a short note on the Historical use of chlorine.
Chlorine was first used in the sterilization of drinking water to control the spread of water-borne diseases such as typhoid. Cholera, dysentery, and gastro-enteritis which killed people more than the people who were killed in all wars in history.
Write the chemical name of bleaching powder? How it is prepared?
The chemical name of bleaching powder is calcium oxychloride. Molecular formula of bleaching powder (Calcium oxychloride) is CaOCl2. It is prepared by passing chlorine gas into slakes lime at 4Q0°C.
Ca(OH)2 +4Cl2 → CaOCl2 + H2O
Mention the food items which contain sulfur.
Garlic, onion, reddish, cauliflower, Egg, yolk.
Name parts of the Human body which contain sulfur.
Hair, nails, and skin contain sulfur.
Write a short note on the Discovery of sulfur dioxide.
Priestley prepared sulfur dioxide in the year 1774 by heating concentrated sulfuric acid with mercury and called it “vitriolic acid air.
Write the methods by which sulfur dioxide can be manufactured on a large-scale.
Sulfur is present in many minerals one of the minerals is mercurous sulfide. It is commonly called cinnabar. The ”
sulfide burns in the presence of air and sulfur dioxide are obtained as a by-product.
HgS+O2 → Hg + SO2 ↑
During the extraction of zinc from zinc blend. Sulfur dioxide is obtained as a byproduct.
2ZnS+ 3O2 → 2ZnO+ 2SO2↑
Write the laboratory preparation of sulfur dioxide.
Set up the apparatus as in the figure. Take copper turning in the flask. Add concentrated sulfuric acid to it through thistle Funnel. Heat the flask Sulfur dioxide gas can be collected in the jar.
Cu + 2H2SO4 → CuSO4+ SO2 + 2H2O
Mention the physical properties of sulfur dioxide.
The physical properties of sulfur dioxide are
- It is Colorless
- It is has a pungent smell
- It is – Not a supporter of combustion
- It is – Turns blue litmus red therefore acidic
What is Acid rain? Mention, its effects.
Water molecules in the atmosphere react with sulfur dioxide to form acid rain.
SO2+ H2O → H2SO3 The effects are :
- Acid rain corrodes monuments, statues and buildings.
- It affects the soil fertility and effects plants growth.
What happens when a burning magnesium ribbon is kept inside a jar containing sulfur dioxide gas?
Magnesium containing to burn displacing sulfur particles which stick to the jar
2Mg + SO2 → 2MgO+ S
How is baking soda manufactured?
Baking soda is manufactured by passing carbon dioxide through saturated sodium carbonate solution in water.
Na2CO3 + CO2 + H2O→ 2NaHCO3
Write the uses of baking soda.
Uses of baking soda
- It is used in bakery to make the bakery items.
- It is used in medicine which acts ‘ as antacid, to treat excess of acid formed in the stomach.
- It is used as a mild cleaning agent
- It is used to prepare aerated water (soda water)
What is soap? Mention the raw materials used to make soap.
A cleaning substance made from animal fats or vegetable oil is called soap. The raw materials are, oil or fat, sodium hydroxide or potassium hydroxide, and common salt.
Explain the method of preparation of soap.
The mixture of fats and sodium hydroxide is allowed to boil in the kettle using the steam within the kettle. After boiling, the mass thickness as the fat reacts with sodium hydroxide producing soap and glycerin. Salt is added to separate soap from glycerin.
The soap forms its layer at the top and the glycerin settles at the bottom the glycerin is taken out from the bottom of the kettle. Soap is taken off from the top the soap is then cooled.
Oil/Fat + Sodium hydroxide → Soap + glycerol.
What is glycerol? Mention the uses.
Glycerol or glycerin is a sweet viscous liquid soluble in water. Uses of Glycerol are :
- It is used in the manufacture of explosives, elastics, and pharmaceuticals.
- It is also used to prevent freezing.
Overuse of synthetic detergents cause water pollution why? Give reason.
Overuse of synthetic detergents cause water pollution because detergents are non-biodegradable.
What are detergents?
A cleaning substance which is made using petroleum is called detergents.
How is liquid soap prepared?
A method of manufacturing liquid soap. Heat the mixture of oil and potassium hydroxide solution. Stir well. As the soap cooks it will be converted to the gel phase. Add distilled water and stir well and add little scent, liquid soap is ready.
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