KSEEB Class 8 Science Important Questions Chapter 12 Chemicals in Our Daily Life

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

Question 1.
List some of the chemicals that we use in our daily life.
Answer:
The various chemicals that we use in our daily life include sodium chloride, sugar, kerosene, petrol, diesel, bleaching powder, washing soda, baking soda, polyvinyl chloride (PVC), butane gas, CNG, and glucose.

Question 2.
Name some of the chemicals that contain chlorine, that we use in our daily life.
Answer:
The compounds of chlorine that we use in our daily life include sodium chloride, bleaching powder and PVC.

Question 3.
What is chlorine? Write its symbol.
Answer:
Chlorine is a chemical element having atomic number 17. Its chemical symbol is Cl.

Question 4.
Name some common minerals containing chlorine.
Answer:
The commonly known minerals containing chlorine are halite, sylvite, carnallite and chlorapatite.

Question 5.
Who was the first to prepare chlorine gas in the laboratory? How did he do it?
Answer:
Chlorine was first prepared in 1774 by the Swedish chemist Carl Wilhelm Scheele. He prepared it by the action of hydrochloric acid on manganese dioxide.

Question 6.
Who gave chlorine its name?
Answer:
Sir Humphrey Davy gave chlorine its name.

Question 7.
How is chlorine prepared in the laboratory? Write a balanced chemical equation to represent the reaction.
Answer:
Chlorine is prepared in the laboratory by the action of concentrated hydrochloric acid on manganese dioxide.

Question 8.
Draw a neat labelled diagram showing the arrangement of apparatus in the laboratory preparation of chlorine from manganese dioxide.
Answer:

Question 9.
Describe the method of preparing chlorine in the laboratory by using manganese dioxide (or potassium permanganate) and cone, hydrochloric acid.
Answer:
Take about 20 g of manganese dioxide (or potassium permanganate) in a round bottomed flask fitted with a two-holed rubber cork. Fix a thistle funnel through one of the holes and a delivery tube through the other. Ensure that the bottom end of the thistle funnel touches the bottom of the flask.

Arrange the apparatus as shown in the figure, to pass the chlorine gas through water and then through cone, sulphuric acid. Finally connect the delivery tube taken from the flask containing cone, sulphuric acid to a gas jar. Pour cone, hydrochloric acid to the flask through the thistle funnel.

Heat the flask (No heating is necessary if potassium permanganate is used instead of manganese dioxide). Chlorine gas is liberated. Pass the liberated greenish yellow gas through a jar of water to remove the fumes of hydrogen chloride and next through another jar of concentrated sulphuric acid to remove the moisture from the gas. This gas is collected in the jar by the upward displacement of air.

Question 10.
Why should the lower end of the thistle funnel touch the bottom of the round bottomed flask while preparing chlorine in the laboratory?
Answer:
If the lower end of the thistle funnel does not touch the bottom of the round bottomed flask, there is a possibility that the gas produced in the flask will rush through the thistle funnel itself. This makes the acid contained in the thistle funnel to spew around which can cause injuries. To avoid this, the base of the thistle funnel should touch the bottom of the round bottomed flask.

Question 11.
Why is chlorine gas usually collected in a jar by the upward displacement of air?

OR

Pure and dry chlorine gas is collected by the upward displacement of air. Give reason.
Answer:
Chlorine is slightly heavier than air. Therefore, it is collected by the upward displacement of air.

Question 12.
Why should the chlorine gas prepared in the laboratory be passed through cone, sulphuric acid?
Answer:
Chlorine gas prepared in the laboratory is passed through cone, sulphuric acid to remove moisture that may be present in the gas.

Question 13.
List some of the physical properties of chlorine.
Answer:
Some of the physical properties of chlorine are:

1. Chlorine is greenish-yellow in colour with a pungent smell.
2. Chlorine is acidic.
3. Chlorine bleaches in the presence of water.
4. Chlorine is a supporter of combustion.

Question 14.
List some of the chemical properties of chlorine.
Answer:
Chlorine is acidic in nature. It supports combustion to some extent. In the presence of water, chlorine bleaches organic colours. Chlorine reacts with almost all other elements to form compounds in the form of chlorides.

Question 15.
There are two gas jars containing chlorine. A dry red rose petal is put into one jar and a wet red rose petal is introduced into another jar. What happens in the two jars? Why?
Answer:
The wet rose petal gets decolourized quickly while the dry rose petal takes much longer time for decolourization. This shows that the bleaching action of chlorine happens best in the presence of water.

Question 16.
What happens when a burning magnesium ribbon is introduced into a jar containing chlorine? What is the product formed during the process? Write a balanced chemical equation to represent this reaction.
Answer:
When a burning magnesium ribbon is introduced into a jar containing chlorine, the ribbon continues to burn more violently with a white flame and forms milky white magnesium chloride.

Question 17.
How does chlorine react with phosphorus? Explain. Write equations to represent the reactions.
Answer:
When dry chlorine is passed over heated phosphorus, phosphorus trichloride is formed. With excess of chlorine, we get phosphorus pentachloride.

Question 18.
What happens when a small piece of dry sodium is introduced into a jar containing chlorine? Write a balanced equation to represent this reaction.
Answer:
Introduce a small piece of freshly-cut metallic sodium into ajar containing chlorine gas. Sodium reacts with chlorine, producing a bright yellow light and fumes of sodium chloride. The sodium chloride fumes get deposited on the walls of the jar.

Question 19.
Describe the reaction that occurs when heated aluminium powder is sprinkled into a jar containing chlorine. Write a balanced equation to represent this reaction.
Answer:
When hot aluminium powder is sprinkled into a jar containing chlorine, the aluminium particles burn brightly in chlorine to form aluminium chloride.

Question 20.
What is the acid formed when chlorine gas dissolves in water?
Answer:
When chlorine gas dissolves in water, hypochlorous acid is formed. Hypochlorous acid releases nascent oxygen and forms hydrochloric acid.

Question 21.
Why is chlorine a good bleaching agent and a sterilizing agent?
Answer:
Chlorine releases nascent oxygen when dissolved in water. Nascent oxygen is a very good oxidising agent. This is why chlorine is a good bleaching and sterilizing agent.

Question 22.
Why is chlorine used to process potable water?
Answer:
Chlorine is a good disinfectant. It kills microorganisms present in water. It also controls the growth of slime and algae in water-conducting pipes and storage tanks. Chlorine also removes undesirable nitrogenous substances that may be present in water. This is why chlorine is used to process potable water.

Question 23.
Suggest a method of sterilization without using chemicals.
Answer:
Any process that removes or kills all forms of microbial life such as fungi, bacteria, and viruses present on a surface, foods or any other substance is known as sterilization. Applying chemicals is one way of removing them.

The other methods include heat treatment, radiation treatment, applying high pressure and filtration. Sometimes a combination of these methods is used to eliminate microbes.

Question 24.
List the uses of chlorine.
Answer:
Some of the uses of chlorine are listed below:

1. Chlorine is used to manufacture bleaching powder, polyvinyl chloride, chlorofluorocarbons, pesticides and herbicides.
2. It is used as a bleaching agent.
3. Chlorine is used in the processing of drinking water to remove microbes and other harmful substances.
4. Many compounds of chlorine are extremely useful to us. For instance, sodium chloride (common salt) is an integral part of our food. It is also used to make intravenous saline.
5. Chlorine is used in the manufacture of hydrochloric acid.
6. Chlorine is also used in paper and pulp industry.

Question 25.
Give two medical applications of chlorine.
Answer:

• Common salt is the basic component of intravenous saline solutions.
• It is used in the preparation of chloroform which is used as an anaesthetic.

Question 26.
What is bleaching powder? How is it prepared?
Answer:
Bleaching powder is a compound of chlorine called calcium hypochlorite. It is prepared by passing chlorine gas through calcium hydroxide (slaked lime) at 400 °C.

Question 27.
What is bleaching? Give an example for a bleaching agent.
Answer:
The process of removing the natural colours from textiles, fibres, yarns, wood pulp or any other organic substance either by using chemicals is called bleaching. Any substance that removes colours and makes things white or colourless is called a bleaching agent. E.g. sodium oxychlorate, calcium oxychlorate, etc.

Question 28.
Name the compound of chlorine which

1. is an anaesthetic
2. is a refrigerant
3. is a disinfectant
4. is a material to make pipes and tubes
5. liberates chlorine on exposure to air.

Answer:

1. Chloroform.
2. Chlorofluorocarbons.
3. Bleaching powder.
4. Polyvinyl chloride (PVC).
5. Chlorine dioxide.

Question 29.
Why should we avoid the use of DDT?
Answer:
DDT is a non-biodegradable chemical. It does not decompose through natural processes. Once let into the environment, DDT remains as it is and pollutes soil and water. It enters the food chain and goes on accumulating in the body of organisms at higher trophic levels. Therefore, we should avoid the use of DDT.

Question 30.
What is sulphur dioxide? Mention its molecular formula.
Answer:
Sulphur dioxide is a gaseous compound of sulphur with oxygen containing only two atoms of oxygen in its molecule. The molecular formula of sulphur dioxide is SO₂.

Question 31.
Who discovered sulphur dioxide?
Answer:
Sulphur dioxide was discovered by Joseph Priestley in 1774.

Question 32.
Mention some natural substances that contain sulphur.
Answer:
Sulphur is present in small quantities in egg yolk, cauliflower, radish, onion and garlic. It is also present in hair, nails and skin.

Question 33.
What is ‘vitriolic acid air’?
Answer:
Priestley prepared sulphur dioxide by heating concentrated sulphuric acid with mercury. He called the gas produced ‘vitriolic acid air’.

Question 34.
How is sulphur dioxide manufactured on a large scale? Give the chemical equation for the reaction.
Answer:
1. Many minerals of metals are found in the form of their sulphides. Cinnabar is a mineral of mercury called mercurous sulphide. It burns in the presence of air to produce mercury and sulphur dioxide. Sulphur dioxide is obtained as by-product during the extraction of mercury from cinnabar.

2. Zinc blende is a sulphide ore of zinc. Sulphur dioxide can also be obtained during the extraction of zinc from zinc blende.

Question 35.
How is sulphur dioxide prepared in the laboratory? Give a balanced equation to represent this reaction.
Answer:
Sulphur dioxide is prepared in the laboratory by the action of concentrated sulphuric acid on copper turnings. During this reaction copper sulphate, sulphur dioxide and water are formed as products.

Question 36.
Name the metal and the acid required to prepare sulphur dioxide in the laboratory.
Answer:

• Metal – Copper turnings.
• Acid – Cone, sulphuric acid.

Question 37.
Draw a neat diagram showing the arrangement of apparatus for the preparation of sulphur dioxide in the laboratory.
Answer:

Question 38.
How is sulphur dioxide gas prepared starting from sodium sulphite? Give the balanced equation to represent the reaction.
Answer:
Sulphur dioxide is prepared by the action of dilute hydrochloric acid on sodium sulphite crystals.
Na₂SO₃ + 2 HCl → 2 NaCl + H₂O + SO₂↑
Sodium sulphite + dil. Hydrochloric acid → Sodium chloride + Water + Sulphur dioxide.

Question 39.
How is sulphur dioxide gas collected in a gas jar? Why?
Answer:
Sulphur dioxide is collected by the upward displacement of air. This is because sulphur dioxide is heavier than air.

Question 40.
What happens when a burning candle is introduced into a jar containing sulphur dioxide? Why?
Answer:
When a burning candle is introduced into ajar containing sulphur dioxide, the candle is put out. This is because, sulphur dioxide is neither a supporter of combustion nor a combustible gas.

Question 41.
What happens when a moist blue litmus paper is introduced into a jar containing sulphur dioxide gas? Why?
Answer:
When a moist blue litmus paper is introduced into a jar containing sulphur dioxide, the litmus paper turns red. This is because sulphur dioxide is acidic in nature.

Question 42.
What happens when a rose petal is introduced into a jar containing sulphur dioxide? Explain the changes that occur.
Answer:
When a wet rose petal soaked in water is introduced into a jar containing sulphur dioxide, the petal gets bleached. However, when a rose petal not soaked in water is introduced, the decolourization does not occur. This shows that sulphur dioxide acts as a bleaching agent under moist conditions. Dry sulphur dioxide does not bleach.

Question 43.
How does sulphur dioxide bleach? Is it temporary or permanent?
Answer:
Sulphur dioxide bleaches by reduction process. The bleaching action of sulphur dioxide is temporary.

Question 44.
How do you say that the bleaching action of sulphur dioxide is temporary?
Answer:
When a wet rose petal is introduced into ajar containing sulphur dioxide, the petal loses its colour and become white. When the bleached petal is taken out of the jar and kept exposed to air, the petal regains its original colour. This shows that the bleaching action of sulphur dioxide is temporary.

Question 45.
What happens when a burning magnesium ribbon is introduced into a jar containing sulphur dioxide? Explain the changes. Write a balanced chemical equation to represent the reaction.
Answer:
A burning magnesium ribbon continues to burn in sulphur dioxide. The heat will decompose sulphur dioxide into sulphur and oxygen. Magnesium combines with oxygen to form magnesium oxide. The sulphur which is displaced from sulphur dioxide sticks to the inner wall of the gas jar.

Question 46.
Name the acid formed when sulphur dioxide dissolves in water. Write a balanced equation for the reaction.
Answer:
When sulphur dioxide dissolves in water, a compound called sulphurous acid is formed.

Question 47.
List the properties of sulphur dioxide.
Answer:

1. Sulphur dioxide is colourless and has a pungent smell.
2. It does not support combustion.
3. It is acidic in nature.

Question 48.
List the uses of sulphur dioxide.
Answer:
The following are some of the uses of sulphur dioxide:

1. Sulphur dioxide is used to manufacture sulphuric acid, which is the raw material for the manufacture of detergents, fertilizers and many medicines.
2. It prevents the growth of bacteria and fungi; hence, it is used to increase the shelf life of foods.
3. In sugar industry, sulphur dioxide is used to remove colouring matter from sugar.
4. It is used to prevent decolourisation of dried fruits.

Question 49.
What is sodium bicarbonate commonly known as? Write its molecular formula.
Answer:
Sodium bicarbonate is commonly known as baking soda. Its molecular formula is Na₂CO₃.

Question 50.
How is sodium bicarbonate manufactured?
Answer:
Sodium bicarbonate is manufactured by passing carbon dioxide through a saturated solution of sodium carbonate in water.

Question 51.
List the properties of sodium bicarbonate (baking soda).
Answer:
The following are some of the properties of baking soda

1. Sodium bicarbonate is a white crystalline powder.
2. It is alkaline in nature. A solution of sodium bicarbonate turns red litmus to blue.
3. Sodium bicarbonate decomposes slowly on heating to give sodium carbonate and carbon dioxide and water.
   2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂
4. Dilute acetic acid reacts with sodium bicarbonate to yield carbon dioxide. Similarly, lemon juice produces carbon dioxide with sodium bicarbonate.

Question 52.
List the uses of sodium bicarbonate!baking soda.
Answer:

1. Sodium bicarbonate is used in baking industry to make cake and bread soft.
2. It is used to make medicines to neutralise excess of acidity in the stomach.
3. It is used as a cleaning agent for cleaning and scrubbing surfaces.
4. It is used in the manufacture of drinking soda.

Question 53.
What are soaps?
Answer:
A soap is a cleaning agent. It is essentially a sodium or potassium salt of fatty acids.

Question 54.
What are the raw materials required for making soap? What is the by-product of soap industry?
Answer:
The raw materials for soap making are animal fat or vegetable oil, sodium hydroxide (or potassium hydroxide) and common salt. Glycerol is the by-product of soap industry.

Question 55.
How is soap manufactured by kettle method?
Answer:
A mixture of animal fat or vegetable oil and a strong solution of sodium hydroxide is taken in a kettle. It is allowed to boil in the kettle using a heating coil within the kettle. The vegetable oil and sodium hydroxide react to form soap and glycerol. Soap is separated from the mixture by adding sodium chloride. The soap floats on the solution like a cream which is separated for making it into cakes.
Vegetable oil + Sodium hydroxide → Soap + Glycerine

Question 56.
Why is common salt added during the preparation of soap?
Answer:
Common salt is added during the preparation of soap to help separate soap from glycerine.

Question 57.
What is glycerol? Mention its uses.
Answer:
A colourless, water soluble, sweetish, viscous liquid formed as a by-product in soap manufacture is called glycerol. It is also known by the name glycerine. Glycerol is used in the manufacture of plastics, explosives, cosmetics and pharmaceuticals.

Question 58.
Give two examples for soaps.
Answer:
Examples of soap arc sodium stearate and potassium stearate.

Question 59.
What are liquid soaps? How are they prepared?
Answer:
Soaps in liquid form are known as liquid soaps. They are potassium salts of long chain fatty acids. Liquid soaps are prepared by heating a mixture of vegetable oil (or fat) with potassium hydroxide. The resulting soap will be in the form of a gel. This is diluted by adding distilled water. Sometimes a scent is added to the liquid soap.

Question 60.
What are detergents?
Answer:
A cleaning substance which is made using petroleum products is called detergent.

Question 61.
What are soapless soaps? Why are they called so?
Answer:
Synthetic detergents are called soapless soaps. This is because, detergents have the cleaning property of soap but do not contain soap molecules.

Question 62.
How are detergents manufactured in industries?
Answer:
Detergents are manufactured by the action of concentrated sulphuric acid on long chain hydrocarbons obtained from petroleum. The reaction produces organic acids. The organic acids obtained from the reaction above are neutralized with sodium hydroxide to obtain a detergent.

Question 63.
Mention any two differences between soaps and detergents.
Answer:
Soaps:

1. Soaps are prepared from oils and fats.
2. Soaps are biodegradable.
3. Soaps do not clean well in hard water.

Detergents:

1. Detergents are prepared from hydrocarbons obtained from petroleum.
2. Detergents are not biodegradable.
3. Detergents clean well even in hard water.

Question 64.
Why is detergent better than soap in cleaning action?
Answer:
Detergents give lather readily even with hard water and clean well even in hard water. Soaps do not clean well in hard water. This is why detergent is better than soap in cleaning action.

Question 65.
Mention one disadvantage of detergents over soaps.
Answer:
Unlike soaps, detergents contain non-biodegradable chemicals. They pollute water bodies and soil. Hence, they are not eco-friendly.

Multiple Choice Questions

Question 1.
Chlorine is prepared in the laboratory by the action of hydrochloric acid on
(a) zinc
(b) manganese dioxide
(c) calcium carbonate
(d) lead nitrate
Answer:
(b) manganese dioxide

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

Question 3.
Which of the following two gases each change the colour of damp blue litmus paper?
(a) ammonia and chlorine
(b) ammonia and hydrogen chloride
(c) carbon monoxide and chlorine
(d) chlorine and sulphur dioxide
Answer:
(d) chlorine and sulphur dioxide

Question 4.
During the preparation of sulphur dioxide, the gas is passed through concentrated sulphuric acid in order to
(a) remove its pungent smell
(b) to decolourize sulphur dioxide
(c) to remove moisture that may be present in the gas
(d) to eliminate toxicity of the gas
Answer:
(c) to remove moisture that may be present in the gas

Question 5.
Which one of the following compounds does not contain chlorine?
(a) Bleaching powder
(b) Ammonium sulphate
(c) Common salt
(d) DDT
Answer:
(b) Ammonium sulphate

Question 6.
The molecular formula of bleaching powder is
(a) CaCl₂
(b) Ca(HCO₃)₂
(c) CaOCl₂
(d) Ca(OH)₂
Answer:
(c) CaOCl₂

Question 7.
Soap is
(a) sodium salt of long chain fatty acids
(b) calcium salt of long chain fatty acids
(c) magnesium salt of long chain fatty acids
(d) potassium salt of short chain fatty acids
Answer:
(a) sodium salt of long chain fatty acids

Question 8.
The by-product of soap manufacturing is
(a) long chain fatty acids
(b) glycerol
(c) detergents
(d) vegetable oil
Answer:
(b) glycerol

Question 9.
Sodium chloride is used during the manufacture of soap. Sodium chloride actually
(a) dissolves soap in water
(b) reduces the solubility of soap
(c) increases the quality of soap
(d) gives soap a pleasant smell
Answer:
(b) reduces the solubility of soap

Question 10.
Which of the following is false about synthetic detergents?
(a) detergents are soapless soaps
(b) detergents clean well even in hard water
(c) detergents are non-biodegradable
(d) detergents are friendlier to environment than soap.
Answer:
(d) detergents are friendlier to environment than soap.

Question 11.
Sulphur dioxide is prepared in the laboratory by the action of concentrated sulphuric acid on
(a) copper
(b) sulphur
(c) oxygen
(d) sodium
Answer:
(a) copper

Question 12.
A gas that causes acid rain is
(a) carbon dioxide
(b) sulphur dioxide
(c) chlorine
(d) CFCs
Answer:
(b) sulphur dioxide

Fill In The Blanks

• The common name of sodium chloride is common salt
• The chemical name of baking soda is sodium bicarbonate
• MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂
• A chemical used to prepare soda water is sodium bicarbonate
• The acid formed when sulphur dioxide reacts with water is sulphurous acid
• The alkali commonly used to make toilet soap is potassium hydroxide
• Sulphur dioxide is neither combustible nor a supporter of combustion
• Chlorine gas was first prepared by Wilhelm Scheele