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Class- 5 th Science Study Booklet PHYSICAL and CHEMICAL CHANGES
Class- 5th Science Study Booklet
PHYSICAL and CHEMICAL CHANGES
PHYSICAL and CHEMICAL CHANGES
1. Introduction
When one or more properties of a thing become different, we say that it has changed or a change has taken place in it. When a change takes place, there may be a change in the state, position, shape, size, colour, temperature, composition or structure of the material of the object. When ice melts, it forms water. Now, we know that ice is a solid whereas water is a liquid. So, the melting of ice involves a change in state (from solid state to liquid state). Some of the important changes observed by us in our daily life are: Formation of curd from milk. Cooking of food. Burning of fuels.
Drying of clothes. Rusting of iron.
Some changes are beneficial to us whereas some are harmful to us. For example, the ripening of fruits is a beneficial change. So, we try to make the ripening of fruits faster by using artificial methods. On the other hand, the spoiling of cooked food is a harmful change, so we try to slow down this change by keeping the cooked food in a refrigerator. The change in a material (or object) does not occur on its own. There is always a ‘cause’ which brings about a change in a material. For example, ice does not melt to form water on its own. Ice must be given heat to melt and change into water. Thus, heat is the cause of the change of state of ice from solid to liquid. Some of the ways of bringing about changes in materials are by applying heat, light, electricity, or force.
2. Classification of Changes
A substance undergoes a change to form a ‘new substance’ only when certain agents like heat, light, electricity or force, etc., are applied to it. All the changes around us can be classified into two groups:
(a) Reversible changes, and (b) Irreversible changes.
2.1 REVERSIBLE CHANGES A change which can be reversed to form the ‘original substance’ is called a reversible change. The melting of ice (to form water) is a reversible change. This reversible change can be represented as follows:
( ) ( )
Heat
CoolSolid LiquidIce Water
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Some of the examples of reversible changes (or changes which can be reversed) are: Melting of ice; Boiling of water; Melting of wax; Stretching of a rubber band; Stretching of a spring; Inflating a balloon; Ironing of clothes. The boiling of water (or evaporation of water) is a reversible changes. Change of state is a reversible change. This can be shown as follows:
( ) ( )
Heat
CoolLiquid WaterVapour or gasWater Steam
Expansion (on Heating) is a Reversible Change When an object is heated, it increases in size. The increase in size on heating is called expansion. The expansion of an object on heating is a reversible change. This is because when the hot object is cooled, it decreases in size and come back to the original size. The decrease in size of an object on cooling is called contraction. Expansion occurs on heating whereas contraction occurs on cooling. The reversible change of expansion is used: (i) In fixing an iron rim on the wooden wheel of a cart, and (ii) In fixing the iron blade of a digging tool (like a spade) to a wooden handle.
2.2 IRREVERSIBLE CHANGES
A change which cannot be reversed to form the original substance (or substances) is called an irreversible change. The burning of paper is an irreversible change. Some of the examples of irreversible changes (or changes which cannot be reversed) are: Burning of paper; Burning of fuels (like Wood, Coal and LPG) ; Formation of curd from milk ; Cooking of food ; Rusting of iron and Grinding of wheat grains into flour.
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3. Reversible and Irreversible Changes
3.1 Folding of paper and Cutting of paper
Take a sheet of paper and fold it to form a toy aeroplane. Now, when we unfold this toy aeroplane, we will get exactly the same sheet of paper. So, the folding of paper is a reversible change. We again take a sheet of paper. This time we cut the sheet of paper into a number of small pieces with the help of scissors. Now, we cannot combine the various pieces of paper to get back exactly the original sheet of paper. So, the cutting of paper is an irreversible change.
3.2 Rolling a Roti and Baking a Roti
The rolling of roti out of dough is a reversible change. Baking of roti is an irreversible change.
3.3 Shaping of Wet Clay into Clay Pot and Baking a Clay Pot The shaping of lump of wet clay into a pot by a potter on his wheel is a reversible change. This is because the wet clay pot can be converted back into the original clay. The baking of clay pot in an oven is, however, an irreversible change.
3.4 Inflating a Balloon and Bursting a Balloon We take a balloon and blow air into it. The shape and size of balloon change. The balloon gets inflated. Now allow the air filled in the balloon to escape. We will find that when all the air escapes, the balloon comes back to its original shape and size. Inflating a balloon is a reversible change.
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Again, take a balloon and blow air into it so that it gets inflated to its full size. Tie the mouth of the balloon tightly with a thread. Now, press the balloon between the palms of your hands. The balloon bursts. This burst balloon cannot be changed back to its original shape and size. The bursting of balloon is an irreversible change.
3.5 Melting of Wax and Burning of Wax
Wax is a solid substance. On heating, solid wax melts to form a liquid which is called molten wax. On cooling, the molten wax becomes solid again. So, melting of wax is a reversible change, and the burning of wax is an irreversible change.
4. Physical and Chemical Changes When one or more properties of a substance become different, we say that a change has taken place in it. Changes can also be classified as follows:
(i) Physical changes, and (ii) Chemical changes
4.1 PHYSICAL CHANGES
Those changes, in which no new substances are formed, are called physical changes. The changes in state, size, shape and colour of a substance are physical changes. The physical changes are temporary changes which can be easily reversed to form the original substance. Very little energy (in the form of heat, etc.) is either absorbed or evolved in physical changes. Examples of physical changes are: Melting of ice (to form water); Freezing of water (to form ice); Boiling of water (to form steam); Condensation of steam (to form water); Evaporation of water (to form water vapour) and Condensation of water vapour (to form liquid water). Thus, the important characteristics of a physical change are as follows: (a) No new substance is formed in a physical change. (b) A physical change is a temporary change. A physical change can be easily
reversed. (c) Very little energy is either absorbed or evolved in physical change. (d) A temporary change in colour may take place in a physical change.
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4.2 CHEMICAL CHANGES
Those changes, in which new substances are formed, are called chemical changes. The properties of new substances formed in chemical changes are entirely different from those of the original substances. The chemical changes are permanent changes which can usually not be reversed to form the original substance. Some examples of chemical changes are: Souring of milk; Formation of curd from milk; Cooking of food (like rice and chapatis); Spoilage of food; Change in colour of cut apple (cut brinjal or cut potato) on keeping in air; photosynthesis; Digestion of food; Neutralisation reaction; Explosion of a firework (or cracker), etc. The various characteristics of a chemical change are as follows:
(a) One or more new substances are formed in a chemical change. (b) A chemical change is a permanent change. A chemical change usually
cannot be reversed. (c) A lot of energy (in the form of heat, light, etc.) is either absorbed or
given out in a chemical change. (d) Sound may be produced in a chemical change. (e) A change in smell may take place or a new smell may be given off in a
chemical change. (f) A permanent change in colour may take place in a chemical change. (g) A gas may be formed in a chemical change.
Following chemical reactions illustrates the chemical changes: (a) Burning of Magnesium Ribbon: Magnesium is a metal which burns easily on
heating. A long and thin strip of magnesium metal is called magnesium ribbon. When a magnesium ribbon is heated, it burns in air with a brilliant white light to form a powdery ash called magnesium oxide. This magnesium oxide is an entirely new substance. Thus, a new substance is formed during the burning of magnesium ribbon. So, the burning of magnesium ribbon is a chemical change.
(b) Reaction between Baking Soda and Vinegar: When baking soda and vinegar are mixed together, then bubbles of carbon dioxide gas are formed (along with some other substances). This carbon dioxide is an entirely new substance. The reaction between baking soda and vinegar is a chemical change because it forms carbon dioxide as one of the new substances.
( ) ( )Baking Soda VinegarSodium Hydrogen carbonate Acetic Acid Sodium Acetate Carbon dioxide Water
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When carbon dioxide gas is passed through lime water, then calcium hydroxide combines with carbon dioxide to form a white solid substance ‘calcium carbonate’ (which makes lime water appear milky.)
Calcium hydroxide + Carbon dioxide Calcium carbonate + Water Ca(OH)2 (CO2) (CaCO3) (H2O)
The reaction between lime water and carbon dioxide gas is a chemical change because a new substance ‘calcium carbonate’ is formed during this change.
(c) Reaction Between Copper Sulphate Solution and Iron: When an iron object
(like an iron nail, etc.) is kept immersed in the blue coloured solution of copper sulphate, then a chemical change takes place to form green coloured iron sulphate solution and a brown deposit of copper on the iron object.
Copper sulphate solution + Iron Iron sulphate solution + Copper (Blue) (Grey) (Green) (Brown)
5. Importance of Chemical Changes Chemical changes are very important in our lives. Some of the examples of the importance of chemical changes are given below:
(i) Metals are extracted from their naturally occurring compounds called ‘ores’ by a series of chemical changes. For examples, iron metal is extracted from the iron ore by chemical changes.
(ii) Medicines are prepared by carrying out a chain of chemical changes. (iii) The materials such as plastics, soaps, detergents, perfumes, acids, bases,
salts, etc., are all made by carrying out various types of chemical changes. (iv) Every new material is discovered by studying different types of chemical
changes.
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6. Differences between Physical and Chemical Changes
Physical change Chemical change No new substance is formed in a physical change.
A new substance is formed in a chemical change.
A physical change is a temporary change.
A chemical change is a permanent change.
A physical change is easily reversible. A chemical change is usually irreversible.
Very little energy is absorbed or given out in a physical change.
A lot of energy is absorbed or given out in a chemical change.
7. A Protective Shield of Ozone
Ozone is a gas. There is a layer of ozone gas high up in the atmosphere. The ozone layer in the upper atmosphere is very useful. The ozone layer protects us from the harmful ultraviolet radiations which come from the sun. This happens as follow: Ozone absorbs ultraviolet radiations coming from the sun and breaks down to form oxygen. In this way, ozone layer absorbs harmful ultraviolet radiations coming from the sun and prevents them from reaching the earth. The breaking down of ozone into oxygen is a chemical change. Ultraviolet radiations can cause skin cancer, damage our eyes and plants.
8. RUSTING OF IRON
When an iron object is left in damp air or water for a considerable time, it gets covered with a red-brown flaky substance called rust. This is called rusting of iron. During the rusting of iron, iron metal combines with the oxygen (of air) in the presence of water to form a compound ‘iron oxide’. This iron oxide is rust. The process of rusting can be represented by the following word equation.
Iron + Oxygen + Water Iron oxide (Fe) (O2) (H2O) (Fe2O3)
Rust is iron oxide (Fe2O3). Rusting of iron is a chemical change (because a new substance ‘iron oxide’ is a formed in this process).
8.1 Conditions Necessary for Rusting
I. Presence of oxygen (of air): Damp air alone provides both the things, oxygen and water, required for the rusting of iron to occur.
II. Presence of water or water vapour (called moisture): Ordinary water also supplies both the things, oxygen and water, needed for the rusting of iron.
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8.2 Rusting Damages Iron Objects
Rust is soft and porous, and it gradually falls off the surface of a rusted iron object, and then the iron below starts rusting. Thus, rusting of iron is a continuous process which slowly eats up the iron objects and makes them useless.
8.3 How Do We Prevent Rusting of Iron
Some of the methods of preventing rusting of iron are given below: (a) Rusting of iron can be prevented by painting. When a coat of paint is
applied to the surface of an iron object, then air and moisture cannot come in contact with the iron object and hence no rusting takes place. The window grills, railings, steel furniture, iron bridges, railway coaches, and bodies of cars, buses and trucks, etc., are all painted regularly to protect them from rusting.
(b) Rusting of iron can be prevented by applying grease or oil. When some grease or oil is applied to the surface of an iron object; then air and moisture cannot come in contact with it and hence rusting is prevented.
(c) Rusting of iron can be prevented by galvanisation. The process of depositing a thin layer of zinc metal on iron objects is called galvanisation. Galvanisation is done by dipping an iron object in molten zinc metal. A thin layer of zinc metal formed on the surface of an iron object protects it from rusting (because zinc metal remains unaffected by air and moisture).
(d) Iron is coated with chromium to prevent rusting. This is called chrome-plating. Chromium metal is resistant to the action of air and moisture. So when a layer of chromium is deposited on an iron object, then the iron object is protected from rusting.
(e) Rusting of iron can be prevented by alloying it to make stainless steel. When iron is mixed (or alloyed) with carbon, chromium and nickel, then stainless steel is obtained. Stainless steel is an alloy of iron. Stainless steel does not rust at all. Cooking utensils, knives, scissors and surgical instruments are made of stainless steel and do not rust at all.
The Case of Ships Ships are made of iron and a part of the ship always remains under sea-water. Even on the part of ships which remain above sea-water, water drops keep clinging to their outer surface. Moreover, the sea-water contains many salts. The presence of salts in sea-water makes the process of rust formation on ships faster. So, inspite of being painted regularly, the ships suffer a lot of damage from rusting.
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The Iron Pillar at Delhi There is an iron pillar near the Qutub Minar in Delhi which is more than 7 metres high and weighs more than 6000 kg. It was built more than 1600 years ago. Even after such a long period, the iron pillar has not rusted at all. This shows that Indian scientists had made great advances in metal making technology as back as 1600 years which enabled them to make this iron pillar having the quality of great rust resistance.
9. Crystallisation
The solid particles having flat surfaces, straight edges and regular shapes are called crystals. Many substances form crystals. The process of cooling a hot, concentrated solution to obtain crystals is called crystallisation. The process of crystallisation is used to obtain large crystals of a pure solid substance from the impure solid substance. An impure solid substance usually contains two types of impurities: insoluble impurities and soluble impurities. The insoluble impurities are removed by filtering its solution whereas soluble impurities get removed during crystallisation.
10. Chemical Reactions
Chemical reactions are the processes in which new substances with new properties are formed. Chemical reactions involve chemical changes. During chemical reactions, a rearrangement of atoms takes place between the reacting substances to form new substances having entirely different properties. Chemical reactions involve breaking of old chemical bonds which exist between the atoms of reacting substances, and then making of new chemical bonds between the rearranges atoms of new substances. During a chemical reaction, atoms of one element do not change into those of another element. Only a rearrangement of atoms takes place in a chemical reaction.
The substances which take part in a chemical reaction are called reactants.
The new substances produced as a result of chemical reaction are called products.
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In a chemical reaction, reactants are transformed into products. When a magnesium ribbon is heated, it burns in air with a dazzling white flame to form a white powder called magnesium oxide. Actually, on heating, magnesium combines with oxygen present in air to form magnesium oxide:
Magnesium + Oxygen Heat Magnesium oxide (As ribbon) (From air) (White powder)
The burning of magnesium in air to form magnesium oxide is an example of a chemical reaction. In this chemical reaction there are two reactants ‘magnesium and oxygen’ but only one product ‘magnesium oxide’. Before burning in air, the magnesium ribbon is cleaned by rubbing with a sand paper. This is done to remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon so that it may readily combine with the oxygen of air (on heating).
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CLASS- 5th (Science) Topic: Physical and Chemical Changes
Worksheet-1
1. How can you say that change has taken place ? 2. Write few of the examples of changes around us. 3. Write any three useful and harmful changes which take place around us. 4. What causes changes? Give an example to explain it. 5. What are the different types of changes? 6. How is physical change different from chemical change? 7. What is Reversible change? 8. Quote out few examples of Reversible changes. 9. What is the increase in size of an object, on heating called as? 10. What is contraction? 11. What is Irreversible change? Write examples. 12. Write any two examples where expansion mechanism is used. 13. Can Reversible or Irreversible changes take place involving same material? If yes, give example or if no, explain the reason. 14. “Inflating a balloon and bursting a balloon involve both the changes in same material”. Comment on the statement. 15. “Ice melts to form water”. What is the cause of this change? 16. “Milk can be changed into curd but curd cannot be changed back into milk”. What is the general name of such change ? 17. When is a change said to have taken place in a material? Explain with example. 18. Does change in a material occur on its own ? Explain with help of an example. 19. Name the cause of change which takes place during the:-
(a) Conversion of ice into water (b) Conversion of water into hydrogen and oxygen. (c) Formation of image of a person on photographic film. (d) Bending of iron-rods to make an iron-grille.
20. When a liquid X is added to a grey, powdery substance Y, the substance Y slowly sets into hard mass. A thick paste of substance Y and sand made in liquid X is used for plastering the walls of houses.
(a) What could the liquid X be ? (b) Name the substance Y. (c) What type of change occur on adding X to Y ?
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21. State the ways of bringing about changes in materials around us. 22. “Ice melts to form water”. What is the cause of this change? 23. State whether burning of paper is a reversible change or an irreversible change. 24. A child dropped his toy and broke it. Can this change be reversed? 25. A bag of cement lying in the open gets wet due to rain can the change which takes place in cement on getting wet be reversed by drying? 26. Give any two uses of expansion of an object on heating. 27. State five changes which are observed in our everyday life 28. Classify the following as reversible or irreversible changes.
(a) Growth of plant (f) Rusting of iron (b) Cooking of food (g) Inflating a balloon (c) Melting of wax (h) Ripening of fruits (d) Formation of curd (i) Boiling of water to form steam (e) Pulling of rubber string (j) Ironing of cloth
29. State the difference between Melting of wax and burning of wax. Give atleast two more such examples. 30. When is a change said to have taken place in a material? Explain with the help of an example. 31. What is meant by ‘reversible changes’ and ‘irreversible changes’? Explain with example. 32. Explain how, a metal rim is fixed around the wooden wheel of cart. What type of change takes place during this process? 33. Is it possible that the same material undergo reversible and irreversible changes? Give two examples to support your statement. 34. Explain why, the burning of paper is said to be an irreversible change whereas the boiling of water as reversible change. 35. What does the following symbol represent in a chemical reaction?
(a) s (d) aq (b) l (e) ∆ (c) g (f)
36. Define the following: (a) Exothermic Reaction (b) Endothermic Reaction (c) Combination Reaction
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CLASS- 5th (Science) Topic: Physical and Chemical Changes
Worksheet- 2
1. How can changes be classified on the basis of its properties. 2. Enlist the basic changes which we see around us in our daily life. 3. What are the different types of changes on the basis of its properties ? 4. What are the characteristics properties of physical change? 5. What type of change takes place in melting of Ice and freezing of water? 6. What are chemical changes? 7. Quote out characteristics of chemical change. 8. What is the importance of chemical change ? 9. What is the difference between Physical and chemical change ? 10. What do you understand by Corrosion? What type of change is this? 11. What is rusting of Iron? 12. How is rusting harmful ? How it can be prevented ? 13. Name the substances which are mixed with iron to make stainless steel. 14. Name the process which can be used to obtain pure copper sulphate from an impure sample. 15. Name a substance which can be purified by crystallization. 16. Classify the changes involved as physical or chemical changes-
(a) Photosynthesis (f) Formation of clouds (b) Melting of wax (g) Drying of clothes (c) Burning of coal (h) Burning of paper (d) Digestion of food (i) Formation of rust (e) Baking cake (j) Tearing of paper
17. Explain why, iron pipes for carrying water are coated with zinc. 18. What is meant by galvanization? Why is it done? 19. State three difference between physical change and chemical change with the help of an example. 20. What is stainless steel? How is stainless steel made? State an important property of stainless steel. 21. Explain why explosion of firework is chemical change? 22. Describe how, crystals of copper sulphate are prepared? 23. What is meant by rusting of iron? State two conditions necessary for the rusting of iron to occur. Explain how rusting damages iron objects.
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24. What happens when magnesium ribbon is burnt in air? Write word equation for this process. Name the type of change which takes place. 25. What happens when carbon dioxide gas is passed through lime water? Write word equation for this process. Name the type of change which takes place. 26. What happens when an iron nail is kept immersed in copper sulphate solution? Write word equation for this process. Identify the type of change. 27. What is meant by crystallization? State its one use. 28. Write symbols for following elements.
(i) Hydrogen (v) Nitrogen (ii) Calcium (vi) Potassium (iii) Oxygen (vii) Copper (iv) Sodium (viii) Magnesium
29. Write chemical formula for following compounds. (i) Water (iv) Copper sulphate (ii) Iron oxide (v) Carbon dioxide (iii) Magnesium oxide (vi) Calcium carbonate
30. Define the following: (i) Chemical Reaction (ii) Reactant (iii) Product
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Olympiad Corner Topic: Physical and Chemical Changes
1. In a pressure-kerosene stove, (i) We pump kerosene and convert it into vapours. (ii) The vapours are then ignited. Which of the following is true about the above statements?
(a) (i) is a chemical change; (ii) is a physical change (b) (i) is a physical change; (ii) is a chemical change (c) Both (i) and (ii) are physical changes (d) Both (i) and (ii) are chemical changes.
2. Which of the figure represent a chemical change?
(a) (i) add (ii) (b) (ii) and (iii) (c) (i) and (iii) (d) All of these
3. Observe the figure carefully and identify substances marked as (p), (q) and (r).
(p) (q) (r) (a) Zinc Water Carbon dioxide (b) Magnesium Hydrochloric acid Oxygen (c) Magnesium Water Carbon dioxide (d) Zinc Hydrochloric acid Hydrogen 4. Match the column I with column II and select the correct option from the codes given below.
Column I Column II (p) Expansion of metals on heating (i) Neither physical nor chemical change (q) A stone kept in the sunlight (ii) Chemical change (r) Burning of a candle (iii) Combination of physical and chemical changes (s) Curding of milk (iv) Physical change
(a) (p) – (iv), (q) – (i), (r) – (iii), (s) – (ii) (b) (p) – (iv), (q) – (iii), (r) – (ii), (s) – (i)
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(c) (p) – (i), (q) – (ii), (r) – (iii), (s) – (iv) (d) (p) – (i), (q) – (iv), (r) – (ii), (s) – (iii)
5. Select the correct statement among the following. (a) Crystallization is a chemical change (b) Digestion of food is a chemical change (c) Burning of paper is a temporary change (d) A reversible change is always chemical. 6. Vishakha took few wire pieces made up of different metals and placed them in blue solution of copper sulphate. What will be the changes in the colour of the solutions present in beakers I, II and III? I II III (a) Green Blue Green (b) Blue Green Green (c) Green Blue Blue (d) Blue Blue Blue 7. Read the given statements and select the correct option. Statement 1: Breaking of a bone China plate is a physical change. Statement 2: When a bone China plate breaks, the pieces can be joined to get back the original plate.
(a) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1.
(b) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1
(c) Statement 1 is true and statement 2 is false (d) Both statements 1 and 2 are false
8. Kanav took two test tubes marked as I and II. In test tube I, he put calcium carbonate and hydrochloric acid while in test tube II, he put zinc granules and hydrochloric acid. He passed the gas coming out from both the test tubes in lime water. What would be his observations?
(a) The gas coming out from test tube I turned lime water milky (b) The gas coming out from test tube II turned lime water milky
(c) The gases coming out from both the test tubes turned lime water milky (d) None of these.
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9. Acetic acid + Sodium hydrogen carbonate (i) (i) + Ca(OH)2 (ii) + water What could (i) and (ii) be?
(a) (i) CaCO3; (ii) CO2 (b) (i) H2O; (ii) CaCO3 (c) (i) CO2; (ii) CaCO3 (d) (i) H2O; (ii) CO2
10. Read the statements given below and mark the correct option. Statement 1: A chemical change may be accompanied by evolution of a gas and change in colour, smell or sound. Statement 2: Photosynthesis and digestion are physical changes.
(a) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1
(b) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1.
(c) Statement 1 is true and statement 2 is false. (d) Both statements 1 and 2 are false
11. The ash which is collected after burning of magnesium ribbon is dissolved in water to give a solution X. What is the nature of the solution X when it is tested with indicators? (a) It turns blue litmus red and phenolphthalein pink, hence it is an acidic solution. (b) It turns red litmus blue and phenolphthalein pink, hence it is a basic solution. (c) It turns blue litmus red and gives no colour with phenolphthalein, hence it is an
acidic solution. (d) It does not change colour of red or blue litmus and phenolphthalein, hence it is
a neutral solution. 12. Match the column I with column II and mark the correct option from the codes given below.
Column I Column II (p) Limestone (i) NaHCO3 (q) Blue vitriol (ii) CuSO4 (r) Vinegar (iii) CaCO3 (s) Baking soda (iv) CH3COOH
(a) (p) – (iii), (q) – (ii), (r) – (iv), (s) – (i) (b) (p) – (i), (q) – (ii), (r) – (iv), (s) – (iii) (c) (p) – (ii), (q) – (iii), (r) – (i), (s) – (iv) (d) (p) – (iv), (q) – (i), (r) – (ii), (s) – (iii)
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13. Rusting causes a lot of harm to the bridges, ships, vehicles and other articles made of iron. Which of the following is not a suitable method for prevention of rusting? (a) Coating the iron articles with paint and grease. (b) Depositing a layer of zinc on iron. (c) Alloying of iron to make stainless steel (d) Coating the iron articles with a layer of salt. 14. Study the given figure carefully. Which of the following reactions explains the above change most appropriately? ZnSO4 + Cu CuSO4 + Zn
(a) CuSO4 + Fe FeSO4 + Cu (b) FeSO4 + Cu CuSO4 + Fe (c) CuSO4 + Zn ZnSO4 + Cu
15. Kirti kept a metal spoon in a glass jar filled with pickle for a few days. She observed that there were holes in the spoon. What could be the possible reason for this ?
(a) Oil present in pickle dissolves the metal. (b) Oil present in pickle liberates a gas in which metal gets dissolved. (c) Metal reacts with acid present in pickle to form salt hence metal is dissolved. (d) The glass reacts with metal to give acid which dissolves the metal.
16. Fill in the blanks by choosing the option with correct words. The process of rusting is a _____change. For rusting, both ___and _____ are required. The salt present in sea water makes the process of rusting _____.
(a) Chemical, Air, Water, Faster (b) Physical, Air, Water, Slower (c) Chemical, Air, Water, Slower (d) Physical, Air, Water, Faster
Directions: Observe the given flowchart and answer the questions 17, 18. 2 Re
2 ( )( )H OHeat d Litmus
SolutionWhite AshMg O X Y Z Change in colour
17. What is X ? (a) MgO (b) MgO2 (c) Mg2O (d) MgO3 18. What is Y ? (a) MgOH (b) Mg2OH (c) Mg(OH)2 (d) None of these
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