I. Tick ( ) the most appropriate answer. 1. Physical or chemical changes are a result of absorption of :

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1 4 CHANGES AROUND US I. Tick ( ) the most appropriate answer. 1. Physical or chemical changes are a result of absorption of : (a) heat energy only (b) light energy only (c) sound energy only (d) some kind of energy 2. A chemical change involves : (a) change of state only (b) change of colour only (c) change of state as well as composition (d) none of these 3. A physical change is a/an (a) temporary change (b) permanent change (c) irreversible change (d) none of these 4. An example of a physical change is (a) magnetisation of iron (b) burning of wood (c) photosynthesis by plants (d) digestion of food 5. An example of a chemical change is (a) exposure of a photographic plate (b) tearing of paper (c) melting of sulphur (d) formation of dew 6. An example of an undesirable change is : (a) melting of snow on mountains (b) evaporation of water (c) earthquake (d) flowering of plants 7. An example of a periodic change is : (a) swinging of a clock pendulum (b) landslides during rains (c) rusting of iron (d) sneezing 8. During physical and chemical changes : (a) energy is always absorbed (b) energy is always released (c) no energy is absorbed or released (d) energy is either absorbed or released 9. A change is an alteration in the physical and chemical properties of matter due to the effect of : (a) light (b) heat (c) some kind of energy (d) pressure 10. Physical changes are : (a) permanent (b) irreversible (c) temporary and irreversible (d) temporary and can be reversed 1

2 11. Chemical changes involve : (a) change in shape (b) change in colour (c) change in molecular composition (d) none of these 12. An example of a physical change is : (a) boiling of water (b) frying an egg (c) burning of wood (d) making curd 13. An example of a chemical change is : (a) photosynthesis (b) tearing of cloth (c) crushing an ice cube (d) magnetising an iron needle 14. When marble is heated strongly and then cooled : (a) calcium oxide is formed (b) calcium oxide and water are formed (c) calcium oxide and carbon dioxide are formed (d) none of these 15. Electrochemistry deals with the effect of... on chemical reactions. (a) heat (b) pressure (c) electricity (d) light 16. Iron articles are coated with paint to prevent them from : (a) rusting (b) evaporating (c) dissolving (d) conducting electric current 17. A substance which favours a chemical reaction but does not undergo any change itself is called : (a) reactant (b) solution (c) catalyst (d) none of these 18. When a change occurs : (a) energy changes do not occur (b) energy is always given out (c) energy is always absorbed (d) energy is either absorbed or given out 19. Which of the following is not a reversible change? (a) The change of water into water vapour (b) The melting of iron (c) The condensation of water vapour (d) The burning of kerosene 20. Which of the following is a periodic change? (a) The change of seasons (b) The melting of wax (c) The curdling of milk (d) The clotting of blood 2 2

3 21. Which of the following factors helps water to evaporate faster? (a) A low temperature (b) Humid weather (c) A large surface area (d) A high atmospheric pressure 22. During which of the following changes are new substances formed? (a) Melting (b) Sublimation (c) Dissolving (d) Burning 23. In which of the following processes is light absorbed? (a) Sublimation (b) Burning (c) Photosynthesis (d) Rusting Ans. 1. (d) 2. (c) 3. (a) 4. (a) 5. (a) 6. (c) 7. (a) 8. (d) 9. (c) 10. (d) 11. (c) 12. (a) 13. (a) 14. (c) 15. (c) 16. (a) 17. (c) 18. (d) 19. (d) 20. (a) 21. (c) 22. (d) 23. (c). II. [A] Fill in the blank spaces by choosing the correct words from the following list : List: chemical, state, composition, reversed, physical, current, evaporation, photosynthesis, magnetisation, heat. 1. Heating of zinc oxide is a... change. 2. Burning of coal is a... change. 3. There is a change in... and... during a chemical change. 4. Glowing of the filament of an electric bulb is a physical change, because the change can be... by stopping the flow of Plants make their food by the process of of water is a physical change is given out during chemical reactions of iron is a physical change. Ans. 1. physical 2. chemical 3. state, composition 4. reversed, current 5. photosynthesis 6. evaporation 7. heat 8. magnetisation. [B] 1. When a solid dissolves in a liquid, the volume of the liquid... (changes/does not change). 2. The higher the temperature, the... is the evaporation of a liquid (faster/slower). 3. Evaporation of water is... in dry air than in humid conditions (faster/slower). 4. A current of air... in the evaporation of a liquid (hinders/helps). 5. Iron combines with oxygen and... of the air to form rust (nitrogen/moisture). Ans. 1. does not change 2. faster 3. faster 4. helps 5. moisture 3

4 III. Fill in the blanks with suitable words. 1. During a... change the identity of the substance does not change. 2. New substances are formed during a... change are always accompanied by some external indications such as production of heat or light, precipitation, change in colour and appearance. 4. Magnetising an iron needle is a... change. 5. The study of chemical reactions that take place in the presence of light energy is called Photosynthesis in plants is a... change. 7. Heat is given out during... reactions. 8. Melting of ice is a... change. 9. When candles burn, wax melts. Melting of wax is a... change. 10. Burning of a fuel is a... change. 11. Sublimation is a... change. 12. Revolution of the earth around the sun is a... change. 13. Growing of a seedling into a plant is... change. Ans. 1. physical 2. chemical 3. Changes 4. physical 5. photochemistry 6. chemical 7. exothermic 8. physical 9. physical 10. chemical 11. physical 12. periodic 13. slow IV. Statements given below are incorrect. Write the correct statements: 1. A physical change cannot be reversed. Ans. A physical change can generally be reversed. 2. During a chemical change, there is no change in weight of the various reactants. Ans. During a chemical change, there is usually a change in weight of the various reactants. 3. During a physical change, new products are formed. Ans. During a physical change, no new substances are formed. 4. During a physical change, the state and molecular composition change. Ans. During a physical change, the state and molecular composition do not change. 4 4

5 5. Glowing of the filament of a bulb is an example of a chemical change. Ans. Glowing of the filament of a bulb is an example of a physical change. 6. Formation of frost during winter is a chemical change. Ans. Formation of frost during winter is a physical change. 7. Change of phases of the moon is a non-periodic change. Ans. Change of phases of the moon is a periodic change. 8. Formation of day and night is a fast change. Ans. Formation of day and night is a slow change. V. State whether the following statements are true or false : 1. Digestion of food is a chemical change. 2. Formation of steam from water is a physical change. 3. During chemical change, the molecular composition remains the same. 4. During physical change, the state as well as the composition of a substance changes. 5. Distillation of water is a chemical change. 6. When copper sulphate dissolves in water, a chemical change takes place. 7. Eruption of a volcano is a periodic change. 8. Switching on an electric bulb is an irreversible change. 9. Chopping onions is a chemical change. 10. Souring of milk is a chemical change. 11. Glowing of an electric bulb is a physical change. 12. Making butter from cream is a physical change. 13. Melting of sulphur is a physical change. 14. Sublimation of a solid is a physical change. 15. Cutting of paper into pieces is a chemical change. 16. Rusting of iron is a chemical change. 17. Earthquake is a desirable change. 18. Burning of sugar is a temporary change. Ans. 1. T 2. T 3. F 4. F 5. F 6. F 7. F 8. F 9. F 10. T 11. T 12. F 13. T 14. T 15. F 16. T 17. F 18. F 5

6 VI. (a) Match the statements in Column A with those in Column B: Column A Column B 1. Crushing of an ice cube a. Chemical change 2. Making of curd b. Periodic change 3. Growth of child into an adult c. Non-periodic change 4. Falling of leaves from a tree d. Photosynthesis 5. Plants making their food in sunshine e. Physical change 6. Formation of day and night f. Slow change Ans. 1. (e) 2. (a) 3. (f) 4. (c) 5. (d) 6. (b). (b) Column A Column B 1. Sodium reacts with water a. on passing electric current. 2. Photosynthesis in plants b. on contact. takes place 3. Iron and sulphur react c. because it starts burning as soon as it comes in contact with moist air. 4. Potassium chlorate and sulphur d. in the presence of sunlight. 5. Sodium is preserved in kerosene e. when the mixture is heated. 6. Water decomposes into f. explode when struck with oxygen and hydrogen a hammer. Ans. 1. (b) 2. (d) 3. (e) 4. (f) 5. (c) 6. (a). (c) Column A Column B 1. Evaporation of water a. Desirable change 2. Milk turning sour b. Non-periodic change 3. Earthquake c. Chemical change 4. Change of seasons d. Periodic change 5. Glowing of a bulb e. Physical change Ans. 1. (e) 2. (c) 3. (b) 4. (d) 5. (a). VII. Give reasons for the following: 1. In a physical change the identity of the substance does not change. Ans. In a physical change, the identity of the substance does not change 6 6

7 because it does not involve any alteration in the atoms or molecules of the substance. There is always a drastic change in the molecular arrangement of the substance which leads to the change of state of matter. 2. Sodium is preserved in kerosene. Ans. Sodium is preserved in kerosene because it is a very reactive metal and catches fire as soon as it comes in contact with air. 3. Photosynthesis cannot take place at night. Ans. Photosynthesis always takes place in the presence of sunlight. So, it cannot take place at night. 4. Iron articles are coated with paint. Ans. Iron articles are coated with paint because it cuts off the contact of air and moisture with iron and prevent the articles from rusting. 5. Decomposition of water is a chemical change. Ans. Decomposition of water is a chemical change because when current is passed through water it decomposes into hydrogen and oxygen. 6. Presence of manganese dioxide enhances the rate of decomposition of potassium chlorate. Ans. Manganese dioxide enhances the rate of decomposition of potassium chlorate because it acts as a catalyst and oxygen is given off rapidly from potassium chlorate. 7. Boiling, evaporation and condensation are physical changes. Ans. Boiling, evaporation and condensation are physical changes because they are temporary changes and can be easily reversed. VIII. Answer the following questions. 1. Classify the following changes as fast or slow changes : (i) Germination of seed (ii) Milk changing to curd (iii) Burning of cooking gas in a gas stove Ans. (i) Germination of seed is a slow change. (ii) Milk changing to curd is a slow change. (iii) Burning of cooking gas in a gas stove is a fast change. 2. Classify the following changes as reversible or irreversible changes: (i) Stretching of a rubber band (ii) Breaking of a glass tumbler (iii) Cooking of food 7

8 Ans. (i) Stretching of a rubber band Reversible change. (ii) Breaking of a glass tumbler Irreversible change. (iii) Cooking of food Irreversible change. 3. Classify the following changes as desirable or undesirable changes: (i) Formation of manure from dung (ii) Melting of snow (iii) Breaking of glassware (iv) Waste produced from plastic bags Ans. (i) Formation of manure from dung Desirable change. (ii) Melting of snow Desirable change. (iii) Breaking of glassware Undesirable change. (iv) Waste produced from plastic bags Undesirable change. 4. Classify the following changes as periodic or non-periodic changes: (i) A child on a swing (ii) Rusting of an iron nail (iii) Sneezing (iv) Beating of heart (v) Earthquake Ans. (i) A child on a swing Periodic (ii) Rusting of an iron nail Non-periodic (iii) Sneezing Non-periodic (iv) Beating of heart Periodic (v) Earthquake Non-periodic 5. (i) Define a physical change. (ii) Give four examples of physical changes. Ans. (i) A change in which no new substance is formed, as the molecules of the substance undergoing change are not affected, is known as a physical change. A physical change involves a change in the physical properties such as size, shape, colour, volume, mass, etc. (ii) Four examples of physical changes (a) Melting of ice (b) Evaporation of water (c) Magnetisation of iron (d) Colour change due to heat as in case of zinc oxide 6. (i) Define a chemical change. (ii) Give four examples of chemical changes. Ans. (i) A change which alters the specific properties of a substance by bringing about a change in its molecular composition, followed by a change in its state is called a chemical change. (ii) Four examples of chemical changes. (a) Rusting of iron (b) Ripening of fruit (c) Curdling of milk (d) Cooking of food 8 8

9 7. Classify the following changes as physical change or chemical change: (i) Burning of wood (ii) Glowing of an electric bulb (iii) A magnet attracting iron nails (iv) Burning of magnesium ribbon in air (v) Photosynthesis in plants (vi) Moulding of glass (vii) Formation of fog (viii) Digestion of food Ans. Physical Changes. Glowing of an electric bulb, a magnet attracting iron nails, moulding of glass, formation of fog. Chemical Changes. Burning of wood, burning of magnesium ribbon in air, photosynthesis in plants, digestion of food. 8. Give four differences between a physical change and a chemical change. Ans. Physical Changes Chemical Changes (1) Physical changes involve (1) Chemical changes involve changes in colour, state, changes in colour, state, texture, etc. However, the texture, etc. along with the composition remains the same. change in composition. (2) Physical changes can be (2) Chemical changes cannot be be reversed easily. reversed easily. (3) No new substances are (3) New substances with new formed in a physical change. chemical properties are. produced in a chemical change. (4) In physical changes, no (4) In chemical changes, there is net absorption or release always a net absorption or of energy occurs. release of energy. 9. What is a change? Explain giving examples. Ans. A change can be defined as an alternation in the physical and chemical properties of matter due to the effect of some kind of energy. For example, changes in weather, growth of living organisms, cooking of food, etc. 10. State an experiment to show that a physical change is temporary and reversible. Ans. Take 2 gm white powder of zinc oxide in a dry test tube and heat it strongly. After two minutes of heating, we observe that the colour of zinc oxide changes to yellow colour. 9

10 Now cool the test tube. After a few minutes we observe that the colour of zinc oxide changes to white colour. This experiment proves that a physical change is temporary and reversible. 11. Write the various conditions that favour a chemical change. Ans. There are various conditions that favour a chemical change. These are as follows: (i) Contact. A chemical reaction occurs when two substances are in close contact with each other. For example, when sodium comes in contact with water, it burns and produces hydrogen and sodium hydroxide. (ii) Solution. Most of the chemical reactions occur when the solutions of the reactants are mixed together. (iii) Heat. Heat is necessary for most of the reactions. (iv) Light. A number of chemical reactions occur in the presence of light, e.g., photosynthesis. (v) Electricity. Passage of electric current through molten or aqueous solutions of compounds causes a chemical change. For example, water can be decomposed into hydrogen and oxygen by passing an electric current through it. (vi) Catalyst. A catalyst without undergoing any change can change the rate of a reaction. 12. Give an experiment to show that a new substance is formed during a chemical change. Ans. In a chemical reaction, the composition of a substance changes and a new substance with new properties is formed. We can show it by an experiment. Take a piece of marble and heat it strongly over a flame for 15 minutes. When this piece of marble is heated and then cooled, carbon dioxide is released and a new substance calcium oxide is left behind. This substance (calcium oxide) has different properties from marble (calcium carbonate). 13. What are exothermic and endothermic reactions? Ans. Exothermic reaction. A reaction in which heat is given out is called an exothermic reaction. For example, burning of magnesium is an exothermic reaction. Endothermic reaction. A reaction in which heat is absorbed is called an endothermic reaction. For example, reaction between iron and sulphur occurs when they are heated

11 14. What is photochemistry? Give two examples of photochemical reactions. Ans. Photochemistry. It is the branch of science in which effects of light on a chemical reaction is studied. Photosynthesis and blackening of a photographic plate are examples of photo-chemical reactions. 15. What is a reversible change? Ans. Reversible change. A change in which a substance can be brought back to its original form is called a reversible change. For example, ice melts on heating into water but on cooling it again changes into ice. 16. What is an irreversible change? Ans. A change in which a substance cannot be brought back to its original form is called an irreversible change. For example, rusting of iron is an irreversible change. 17. Define and explain periodic changes. Ans. Periodic changes. The changes which are repeated at regular intervals of time are called periodic changes. The swinging of a pendulum, beating of heart, change of seasons are some examples of periodic changes. 18. Define and explain non-periodic changes. Ans. Non-periodic changes. The changes which do not repeat themselves after regular intervals of time are called non-periodic changes. Earthquakes, floods, cyclones are some examples of non-periodic changes. IX. Find the odd one out. Give reasons. 1. Contact, heat, light, electricity, pressure, catalyst, particles Ans. Contact, heat, light, electricity, pressure and catalyst are some factors which favour chemical changes while particles are made up of atoms that take part in a chemical reaction. 2. Crushing, pulling, burning, tearing Ans. After burning a new substance is formed, while on crushing, pulling and tearing no new substance is formed. 3. Digestion, respiration, photosynthesis, freezing Ans. Freezing is a physical process while digestion, respiration and photosynthesis are chemical processes. 4. Endothermic, photochemical, thermochemical, exothermic Ans. A photochemical change is brought about by light energy while heat energy is involved during endothermic, exothermic and thermochemical reactions. **** 11

SETH ANANDRAM JAIPURIA SCHOOL VASUNDHARA,GHAZIABAD OLYMPIAD WORKSHEET CLASS VI SCIENCE TOPIC: Changes Around Us

SETH ANANDRAM JAIPURIA SCHOOL VASUNDHARA,GHAZIABAD OLYMPIAD WORKSHEET CLASS VI SCIENCE TOPIC: Changes Around Us 1. What is the common among the following phenomena? 1. Blinking of eyes. 2. Rotation of