OBJECTS AROUND US
There is such a vast variety of objects everywhere. We see around us, a chair, a bullock cart, a cycle, cooking utensils, books, clothes, toys, water, stones and many other objects. All these objects have different shapes, colours and uses.
All objects around us are made of one or more materials. These materials may be glass, metal, plastics, wood, cotton, paper, mud or soil.
Properties of Materials :
We choose a material to make an object depending on its properties, and the purpose for which the object is to be used.
Some properties of materials are
(i) Appearance : Materials usually look different from each other. Wood looks very different from iron. Iron appears different from copper or aluminium. At the same time, there may be some similarities between iron, copper and aluminium that are not there in wood.
Some materials have lustre. These are usually metals. Iron, copper, aluminium and gold are examples of metals. Some metals often lose their shine and appear dull, because of the action of air and moisture on them.
Activity : To show that certain materials have lustre Material required : • Small pieces of (i) paper (ii) cardboard • a thin piece of wood • a small strip of plastic • thin wires of copper, aluminium and iron. Heavy scissors or a metal cutter • sand paper. Method:
(a) Cut each of the materials with heavy scissors or metal cutter. Carefully observe the cut surface of each material. You will notice that in case of paper card board, wood plastic, etc., the cut surface is not shining. However, in case of thin wires of copper, aluminium and Iron, the cut surface is shining.
(b) Rub each of the material with sand paper. Carefully observe the sand papered surface of the material. You will notice that in case of paper cardboard, plastiC and wool, the sand papered surface is not shining. However, in case of thin wires of copper, aluminium and iron, the sand papered surface is shining.
(ii) Hardness : When we press different materials with our hands, some of them may be hard to compress while others can be easily compressed. We can easily scratch some materials, while some cannot be scratched so easily. Materials which can be compressed or scratched easily are called soft while some other materials which are difficult to compress are called hard. For example, cotton or sponge is soft while Iron is hard.
(iii) Solubility: Some substances like sugar, salt etc. completely disappear or dissolve in water. These substances are soluble In water. Other substances like sand, chalk powder etc. do not mix with water and do not disappear even after we stir for long time. These substances are insoluble in water. Water plays an important role in the functioning of our body because it can dissolve a large number of substances.
Activity : To prove that some solids are soluble in water.
Material required : · Small pieces of (i) paper (ii) Carboard · a thin piece of wood
· a small strip of plastic · thin wires of copper, aluminium and iron
· heavy scissors or a metal cutter · sand paper
Method : Add a pinch of chalk powder in the first test tube, a pinch of common salt in the third test tube, a pinch of sand in the fourth test tube and a pinch of washing soda in the fifth test tube. Pour water into each test tube such that half of each test tube is filled with water. Shake each test tube vigorously and replace in the rack. You will notice that sugar, common salt and washing soda disappear in water, and hence are soluble substances. Sand and chalk powder do not dissolve in water, and hence are insoluble substances.
Some liquids like vinegar, lemon juice etc. completely mix with water. These liquids are said to be miscible in water. Some others like oil do not mix with water and form a separate layer when kept aside for some time. These liquid are immiscible in water. Some gases are soluble in water whereas others are not. Water, usually, has small quantities of some gases dissolved in it. For example, oxygen gas dissolved in water is very important for the survival of animals and plants that live in water.
(iv) Transparency : Those substances or materials, through which things can be seen, are called transparent. Light passes completely through these materials Glass, water, air and some plastics are examples of transparent materials. On the other hand, there are some materials through which we are not able to see i.e. light does not pass through them. These materials are called opaque. Wood, cardboard and metals, are example of opaque materials.
The materials through which light passes partially and objects can be seen but not clearly, are known as translucent. We can therefore group materials as opaque, transparent and translucent.
Activity:
To find out substance which sink/float in water. Material required : • a small stone • a small piece of wood. a coin • a leaf • a brass screw • a small piece of ice • a glass bowl filled with water.
Method : Take a glass bowl filled with water. In the water drop the above mentioned substances one by one and observe what happens. You will notice that the stone, the key, the coin and the brass screw sink in water. Thus, they can be grouped as substances heavier than water.
You will notice that the wax, the plastic ball, the wood, the leaf and ice float on the surface of water. Thus, they can be grouped as substances lighter than water. You can repeat the activity by dropping the above substances in kerosene oil or any other liquid and find out which float or sink in it.
(b) Need to group materials: In everyday life, we often group materials for our convenience. At home we usually store things in such a manner that similar objects are placed together. Such an arrangement helps us to locate them easily. Similarly, a grocer usually keeps all type of biscuits at one corner of his shop all soaps at another while grains and pulses are stored at some other place.
There is another reason why we find such grouping useful. Dividing materials in groups makes it convenient to study their properties and also observe any patterns In these properties.
OBJECTIVE QUESTIONS
1. Sorting of materials is useful as
(A) it makes their study convenient
(B) any pattern in their properties can be observed
(C) properties of a substance can be predicted
(D) All of these
2. Which of the following is lustrous?
(A) Iron (B) Diamond
(C) Wood (D) Glass
3. Which of the following allow/s light to pass through it ?
(A) Transparent (B) Translucent
(C) A & B both (D) Opaque
4. Objects which sink in water are -
(A) insoluble and heavier than water
(B) insoluble and lighter than water
(C) soluble and lighter than water
(D) soluble and heavier than water
5. Which of the following is insoluble in water?
(A) Sugar (B) Salt
(C) Kerosene (D) Oxygen
6. A substance is called hard when
(A) it is easy to scratch and compress
(B) it is difficult to scratch and compress
(C) it is shiny and opaque
(D) it is insoluble in water
7. Metals can be identified as
(A) hard (B) lustrous
(C) sonorous (D) All of above
8. sinks in the water, while __ floats on the water.
(A) Oil, mercury (B) Oil, petroleum
(C) Mercury, oil (D) Mercury, alcohol
9. When sand is mixed in water, its particles settle down at the bottom of the vessel. This process is known as
(A) dissolution (B) sedimentation
(C) condensation (D) precipitation
10. Wood is different from iron in
(A) transparency & lustre
(B) hardness & solubility
(C) smoothness & solubility
(D) hardness and lustre
11. Metals lose their shine due to action of
(A) other metal (B) water
(C) air (D) both(B) and (C)
12. Most part of our body is made up of water because
(A) water has large difference between freezing point and boiling point
(B) water dissolves a large number of substances
(C) water is transparent
(D) water is neutral
13. When vinegar is mixed with water, it will
(A) float (B) sink
(C) explode D) dissolve
14. We can see objects through transparent substances because -
(A) transparent substances are hollow
(B) transparent Substances are lustrous
(C) transparent substances allow light to pass
(D) transparent substances are colourless
15. Aquatic organisms are able to survive in water because
(A) their body is resistant to water
(B) water is transparent
(C) water contains dissolved gases
(D) all of the above
SUBJECTIVE QUESTIONS
1. Why is gold used in making omaments ?
2. If a material of scratches material ‘B’, which is more hard?
3. Why do we need to group materials?
4. Give an example each of an opaque and a transparent material?
5. Why does oil float on water?
ANSWER KEY
1. D 2. A 3. C 4. A 5. C 6. B 7. D 8. C
9. B 10. D 11. D 12. B 13. D 14. C 15. D
MULTIPLE CHOICE QUESTIONS
1. An iron nail is kept in each of the following liquids. In which case would it lose its shine and appear dull?
(a) Mustard oil (b) Soft drink (c) Coconut oil (d) Kerosene
2. Pick one material from the following which is completely soluble in water.
(a) Chalk powder (b) Tea leaves (c) Glucose (d) Saw dust
3. You are provided with the following materials
(i) Magnifying glass (ii) Mirror (iii) Stainless steel plate (iv) Glass tumbler
Which of the above materials will you identify as transparent?
(a) (i) and (ii) (b) (i) and (iii) (c) (i) and (iv) (d) (iii) and (iv)
4. Boojho found a bag containing the following materials
(i) Mirror
(ii) Paper stained with oil
(iii) Magnet
(iv) Glass spectacles
Help Boojho in finding out the material(s) which is/are opaque.
(a) (i) only (b) (iv) only (c) (i) and (iii) (d) (ii) and (iv)
5. While doing an activity in class, the teacher asked Paheli to handover a transluscent material. Which among the following materials will Paheli pick and give her teacher?
(a) Glass tumbler (b) Mirror (c) Muslin cloth (d) Aluminium foil
6. Which pair of substances among the following would float in a tumbler half filled with water?
(a) Cotton thread, thermocol (b) Feather, plastic ball
(c) Pin, oil drops (d) Rubber band, coin
7. Which among the following are commonly used for making a safety pin?
(a) Wood and glass (b) Plastic and glass
(c) Leather and plastic (d) Steel and plastic
8. Which of the following materials is not lustrous?
(a) Gold (b) Silver (c) Wood (d) Diamond
9. Which of the following statements is not true?
(a) Materials are grouped for convenience.
(b) Materials are grouped to study their properties.
(c) Materials are grouped for fun.
(d) Materials are grouped according to their uses.
10. Find the odd one out from the following
(a) Tawa (b) Spade (c) Pressure cooker (d) Eraser
11. Which type of the following materials is used for making the front glass (wind screen) of a car?
(a) Transparent (b) Translucent (c) Opaque (d) All the above
VERY SHORT ANSWER QUESTIONS
12. It was Paheli’s birthday. Her grandmother gave her two gifts made of metals, one old dull silver spoon and a pair of lustrous gold earrings. She was surprised to see the difference in the appearance of the two metals. Can you explain the reason for this difference?
13. Mixtures of red chilli powder in water, butter in water, petrol in water, and honey in water were given to Radha, Sudha, Sofia and Raveena, respectively. Whose mixture is in solution form?
14. On a bright sunny day, Shikha was playing hide and seek with her brother. She hid herself behind a glass door. Do you think her brother will be able to locate her. If yes, why? If no, why not?
15. Take a small cotton ball and place it in a tumbler/bowl filled with water. Observe it for atleast 10 minutes. Will it float or sink in water and why?
SHORT ANSWER QUESTIONS
16. Which among the following materials would you identify as soft materials and why?
Ice, rubber band, leaf, eraser, pencil, pearl, a piece of wooden board, cooked rice, pulses and fresh chapati.
17. You are provided with the following materials— turmeric, honey, mustard oil, water, glucose, rice flour, groundnut oil. Make any three pairs of substances where one substance is soluble in the other and any three pairs of substances where one substance remains insoluble in the other substances.
18. During summer holidays, a group of children collected a lump of salt, green grass, broken glass piece, a small thermocol box, pen, iron nail, glass marbles, hair, naphthalene ball, a piece of sugar candy (mishri) and tried to group them on the basis of properties given in Table 4.1 below. Help them in filling the Table.
19. Arrange the jumbled words to arrive at the appropriate names of materials and also write two uses of each.
(a) milaunuim (b) tcaslpi (c) soekrnee (d) gavnier
20. Match the objects given in Column I with the materials given in Column II.
21. Pick five objects from the word box given as Fig. 4.2 which are opaque and would sink in water.
LONG ANSWER QUESTIONS
22. Chalk, iron nail, wood, aluminium, candle, cotton usually look different from each other. Give some properties by which we can prove that these materials are different.
23. Why do you think oxygen dissolved in water is important for the survival of aquatic animals and plants?
24. Differentiate among opaque, translucent and transparent materials, giving one example of each.
25. Sugar, salt, mustard oil, sand, sawdust, honey, chalk powder, petals of flower, soil, copper sulphate crystals, glucose, wheat flour are some substances given to Paheli. She wants to know whether these substances are soluble in water or not. Help her in identifying soluble and insoluble substances in water.
ANSWER KEY
1. b 2. c 3. c 4. c 5. c 6. b 7. d
8. c 9. c 10. d 11. a
12. The silver spoon an long exposure to moist air has lost its shine and appears dull where as gold does not farnish
