MOECDC Class 8 Materials Used in Daily Life
MOECDC Class 8 Science and Technology | Materials Used in Daily Life | Nepal Class 8 | Exercise | Question Answer
MOECDC Class 8 English Medium Science Chapter 10 Materials Used in Daily Life Exercise Question Answer Solution.
| Board | Government of Nepal. |
| Class | Eight (8). |
| Subject | Science and Technology. |
| Chapter | Materials Used in Daily Life |
| Topic | Exercise Solve / Question Answer / Notes. |
Exercise 1 :
(1) Choose the correct alternatives :
(a) Which of the following is a property of an acid?
(i) Bitter
(ii) Slippery
(iii) Sour
(iv) Colorless
Answer :
(iii) Sour – is a property of an acid.
(b) Which of the following turns red litmus blue?
(i) Curd
(ii) Tomato
(iii) Coca-Cola
(iv) Shampoo
Answer :
(iv) Shampoo – turns red litmus blue.
(c) Which of the following liquid will be in the test tube if bubbles come out as soon as zinc pieces are placed?
(i) Water
(ii) Acid
(iii) Base
(iv) Salt
Answer :
(iv) Salt – will be in the test tube if bubbles come out as soon as zinc pieces are placed.
(d) What is the reason for using ash to reduce soil acidity?
(i) Ash is cheap
(ii) Ash is available at home
(iii) Ash is alkaline
(iv) Ash is salt
Answer :
(iv) Ash is salt – is the reason for using ash to reduce soil acidity.
(e) Which salt is used in fire extinguishers?
(i) Sodium carbonate
(ii) Potassium carbonate
(iii) Sodium bicarbonate
(iv) Potassium sulphate
Answer :
(iii) Sodium bicarbonate – salt is used in fire extinguishers.
(2) Differentiate between :
(a) Organic acid and inorganic acid.
Answer :
Organic acid and inorganic acid: Acids that are found in plants and animals naturally are called organic acids, whereas those acids which are prepared in the laboratory by using minerals are called inorganic acids.
(b) Strong acid and weak acid.
Answer :
Strong acid and week acid: Those acids which give more hydrogen ions when dissolved in water are called strong acids, whereas those acids which give less hydrogen ions are called weak acid.
(c) Bases and alkalis
Answer :
Bases and alkalis: Metallic oxides and hydroxides are called bases, whereas bases that dissolve in water are called alkalis.
(3) Givea reason :
(a) Generally, rainwater is acidic.
Answer :
Generally, rainwater is acidic because carbonic acid is formed by the chemical reaction of carbon dioxide and water in the atmosphere.
(b) Ammonium chloride is an acidic salt.
Answer :
Ammonium chloride is an acidic salt because it formed after the chemical reaction between a strong acid and a weak base.
(c) Both lemon juice and sulfuric acid are acidic, sulfuric acid corrodes cloth but lemon does not.
Answer :
Both lemon juice and sulfuric acid are acidic, sulfuric acid corrodes cloth but lemon does not because the acid that makes lemon juice acidic, is a weak acid which is not usually corrosive.
(d) Gastritis patients are cured by consuming magnesium hydroxide.
Answer :
Gastritis patients are cured by consuming magnesium hydroxide because it is an antacid which neutralizes hyperacidity.
(4) Answer the following questions:
(a) What is an acid?
Answer :
The substances that give hydrogen ions when dissolved in water are called acids.
(b) Show in a table the reaction of an acid with indicators.
Answer :
(c) Define bases.
Answer :
Metallic oxides and hydroxides are called bases.
(d) Make a table to show the reaction of a base with indicators.
Answer :
(e) What is salt?
Answer :
A neutral compound formed after the chemical reaction between an acid and a base is called salt.
(f) Make a table to show the reactions of salts with indicators.
Answer :
(g) List out the reasons for acid rain.
Answer :
Acid rain is caused by two reasons.
(i) By natural events like decay of animals and plants, volcanic eruption.
(ii) By human activities like burning fossil fuels, use of unnecessary vehicles, harmful chemicals produced in factories and industries.
(h) How do you know that acid rain is harmful?
Answer :
Acid rain is harmful for living organisms as well as other environmental elements. Acid rain makes water sources acidic which is harmful to aquatic life. It damages the leaves of plants and reduces the quality of the soil. Acid rain also destroys temples, monuments and idols of archaeological importance.
(i) What can be done to prevent acid rain?
Answer :
Measures to prevent acid rain:
(a) Reducing the use of fossil fuels.
(b) Reducing air pollution by using renewable sources of energy like hydroelectricity, solar energy etc.
(c) Establishing industries and factories away from residential areas.
(l) What suggestion do you give to improve the declining agricultural production due to acid rain?
Answer :
To improve the declining agricultural production due to acid rain, industries and factories should be establish away from agricultural areas, air and water pollution should be reduce.
(k) Results obtained by reacting two samples with a different indicator are shown in the table below:
(i) Which colour do X and Y represent?
(ii) An1ong A and B, which will produce carbon dioxide gas when reacts with calcium. carbonate?
Answer :
(i) X represents colorless and Y represents yellow.
(ii) Among A and B, A will produce carbon dioxide gas when reacts with calcium carbonate.
Exercise 2 :
(1) Choose the correct alternatives :
(a) Hard water contains which of the following salts?
(i) Magnesium sulphate
(ii) Magnesium oxida
(iii) Magnesium nitrate
(iv) Magnesium sulphide
Answer :
Hard water contains – (i) Magnesium sulfate salts.
(b) Which method should be used to remove the permanent hardness of water?
(i) By boiling
(ii) Clark’s method
(iii) Permutit method
(iv) Using calcium hydroxide
Answer :
(iii) Permutit method – should be used to remove the permanent hardness of water.
(c) Which of the following water has the lowest hardness?
(i) Rain water
(ii) Well water
(iii) Tube bell water
(iv) River water
Answer :
(i) Rain water – has the lowest hardness.
(d) What is the reason for the increment in the use of alloys instead of pure metals?
(i) Alloys are cheaper.
(ii) The properties of metals are improved in the alloy.
(iii) Alloys are easily available in the market
(iv) The use of alloy is good for health.
Answer :
(ii) The properties of metals are improved in the alloys – is the reason for the increment in the use of alloys instead of pure metals.
(e) Which metals are mixed to make brass?
(i) Copper and zinc
(ii) Copper and tin
(iii) Copper and carbon
(iv) Copper and nickel
Answer :
(i) Copper and zinc – are mixed to make brass.
(f) Which property of iron is lost when carbon is mixed with iron?
(i) Becomes black after ageing
(ii) Becoming heavy
(iii) Rusting properties
(iv) Copper and nickel
Answer :
(iii) Rusting properties – property of iron is lost when carbon is mixed with iron.
(g) Which alloy is formed when copper is mixed with tin?
(i) Steel
(ii) Stainless steel
(iii) Brass
(iv) Bronze
Answer :
(iv) Bronze – is formed when copper is mixed with tin.
(h) Which of the following sentences is true?
(i) An alloy is harder than the metal it is made of.
(ii) An alloy is more flexible than its constituents metal.
(iii) An alloy is dull than the n1etal it is made up of.
(iv) The alloy is more ductile than the metal it is 1nade of.
Answer :
(i) An alloy is harder than the metal it is made of – is true.
(2) Differentiate :
(a) Soft water and hard water
Answer :
Soft water and hard water:
(i) Water which does not contain soluble salts of calcium and magnesium is called soft water, whereas Water which contains soluble salts of calcium and magnesium is called hard water.
(ii) Soap gives more lather in soft water, whereas it gives less lather in hard water.
(b) Temporary hardness of water and permanent hardness of the water.
Answer :
Temporary hardness of water and permanent hardness of the water:
(i) The water contains dissolved bicarbonate salts of calcium and magnesium is called temporary hardness of water. Whereas the water contains sulfate and chloride salts of calcium and magnesium is called permanent hardness of water.
(ii) Temporary hardness of water can be removed by boiling, whereas permanent hardness of water cannot be removed by boiling.
(c) Clark’s method and Permutit method
Answer :
Clark’s method and Permutit method: The method of removing the temporary hardness of water using calcium hydroxide is called the Clark’s method. Whereas the method of removing the permanent hardness of water using zeolite is called the Permutit method.
(d) Pure metals and alloys
Answer :
Pure metals and alloys:
(i) Pure metals usually rust easily, but alloys do not rust easily.
(ii) Alloys are harder than pure metals from which it is made up.
(e) Steel and stainless steel
Answer :
Steel and stainless steel:
(i) An alloy made of carbon and iron is called steel, whereas the alloy made of iron, chromium and nickel is called stainless steel.
(ii) Steel is used to make buildings, bridges, railings, etc. Whereas stainless steel is used to make kitchen utensils and surgical instruments in hospitals.
(3) Give reasons :
(a) Steel is used more than iron in making household kitchen utensils.
Answer :
Steel is used more than iron in making household kitchen utensils because pure iron is very soft when heated and is difficult to work with.
(b) rainwater produces more lather with soap while washing clothes.
Answer :
Rainwater produces more lather with soap while washing clothes because rainwater is soft water.
(c) Well water is hard.
Answer :
Well water is hard because ground water is hard water.
(d) The use of alloys is increasing day by day than pure metals.
Answer :
The use of alloys is increasing day by day than pure metals because making alloys from pure metals further improves the properties of the metal and increases its utility.
(4) Answer the following questions :
(a) Define the hardness of the water.
Answer :
Water which contains soluble salts of calcium and magnesium is called hard water.
(b) What are the causes of the hardness of water?
Answer :
When water contains dissolved bicarbonate, sulfate and chloride salts of calcium and magnesium which produces less lather, causes hardness of water.
(c) Roshan took out water from the well to wash his school uniform on Saturday. Sufficient lather is not produced while applying soap to it. What would you suggest to produce sufficient lather even in well water?
Answer :
To produce sufficient lather even in well water, we have to remove the hardness of water by boiling the required amount of water to wash Roshan’s school uniform.
(d) Riya always washes her clothes in tubewell water. White clothes became dull instead of shiny. What is the reason for this dullness of white clothes? What do you suggest to her to solve this problem?
Answer :
White clothes become dull instead of shiny after washed in tube well water because the water of tube well is hard and clothes washed in hard water will gradually get dull and whitish matter accumulates in the pipes and boilers.
To solve this problem Riya has to remove the hardness of water by boiling the required amount of water to wash her clothes.
(e) How can the hardness of water be removed by the permutit method? Describe with the necessary diagram.
Answer :
The method of removing the permanent hardness of water using zeolite is called the Permutit method. In this method, layers of small stones, sand and sodium zeolite are placed together. When hard water is passed, the sodium in sodium zeolite is replaced by calcium or magnesium ions. Hence the hardness of the water is removed and soft water is obtained.
(f) What is an alloy?
Answer :
A homogenous substance formed by the combination of metals with metals or with non-metals is called an alloy.
(g) Which metals are mixed in the following alloys?
(i) Steel
(ii) Stainless steel
(iii) Brass
(iv) Bronze
Answer :
(a) Steel – Carbon and iron
(b) Stainless steel – Iron, chromium and nickel
(c) Brass – Copper and zinc
(d) Bronze – Copper and tin
(h) What are the causes for the increasing popularity of alloys? Prepare a list.
Answer :
The causes of the increasing popularity of alloys are,
(i) Alloys do not rust easily.
(ii) The properties of alloys are improved than the properties of the constituent metals.
(iii) Alloys are stronger than metals from which it is made of.
(i) Rama won a bronze medal in a competition. Which metals are mixed to make the medal she has received?
Answer :
(i) Rama won a bronze medal in a competition. Copper and tin are mixed to make the medal she has received.
More Solutions :
👉 (2) Information and Communication Technology
👉 (3) Living Beings and Their Structure
👉 (4) Biodiversity and Environment
