Chapter 5 – Substances in the Surroundings – Their States and Properties
1. In the paragraph below, write ‘solid’, ‘liquid’ or ‘gas’ in each of the brackets depending on the substance referred to just before.
On a bright sunny day, Riya and Gargi are playing with a ball ( ) in the park. Gargi feels thirsty. So, Riya brings tender coconut water ( ) for her. At the same time, a strong breeze ( ) starts blowing and it also begins to rain ( ). They run back into the house ( ), change their clothes ( ) and then their mother gives them a cup ( ) of hot milk ( ) to drink.
Ans: On a bright sunny day, Riya and Gargi are playing with a ball (solid) in the park. Gargi feels thirsty. So, Riya brings tender coconut water (liquid) for her. At the same time, a strong breeze (air) starts blowing and it also begins to rain (liquid). They run back into the house (solid), change their clothes (solid) and then their mother gives them a cup (solid) of hot milk (liquid) to drink.
2. Discuss.
(a) Riya pours some water from her bottle into another bottle. Does it change the shape of the water?
Ans: Yes, the shape of water changes and takes the shape of the new bottle, as water is in liquid state. Liquids do not have a shape of its own. They take the shape of the container.
(b) Halima picks up a small stone from the ground and puts it in the water in a dish. Does the shape of the stone change?
Ans: No, the shape of the stone does not change. As the stone is in a solid state, it retains its shape.
3. Write the properties of these substances.
Water, glass, chalk, iron ball, sugar, salt, flour, coal, soil, pen, ink, soap.
Ans:
| Substance | State | Properties |
|---|---|---|
1. Water | Liquid | Fluidity, density, solubility, transparency, thermal conductivity. |
2. Glass | Solid | Brittleness, hardness, density, transparency. |
3. Chalk | Solid | Brittleness, density. |
4. Iron ball | Solid | Hardness, density, malleability, ductility, electrical ductility, conductivity, thermal conductivity, luster, sonority. |
5. Sugar | Solid | Brittleness, density, solubility. |
6. Salt | Solid | Brittleness, density, solubility. |
7. Flour | Solid | Density, solubility. |
8. Coal | Solid | Brittleness, density, thermal conductivity. |
9. Soil | Solid | Brittleness, density. |
10. Pen | Solid | Hardness, density. |
11. Ink | Liquid | Fluidity, density, solubility. |
12. Soap | Solid | Brittleness, hardness, density, solubility |
4. What is sublimation? Write the names of everyday substances that sublimate.
Ans: The change of a solid substance directly into a gas or vapour without first changing into a liquid is called sublimation. Substances that sublimate are iodine, naphthalene balls, camphor, etc.
5. What is it made from? Why?
(a) A sickle to cut sugarcane.
Ans: The sickles used for cutting sugarcane are made from iron or other strong metals. Hardness, malleability, and ductility are the characteristics of iron. Therefore, it is ideal to use it in the making of a sickle. For cutting the sugarcane, we need strong equipment.
(b) The sheets used for roofing.
Ans: The sheets used for roofing houses are made from aluminuim. Aluminuim is a metal that is light in weight, durable, and rust-free. It can protect the house well from rain and sun.
(c) A screwdriver
Ans: The screwdriver is made from good-quality steel. Steel is a mixture of different metals. It is strong and is thus helpful in joining nuts and bolts. The work done by a screwdriver thus becomes efficient.
(d) A pair of tongs.
Ans: In olden times, a pair of tongs were made from iron, but now they are made from stainless steel, which is durable, strong, and rust-free. Usually in a kitchen, this equipment is used, and hence it is made from high-quality metals.
(e) Electric cables.
Ans: Electric cables are either copper or aluminium. Copper is a good conductor of electricity. Therefore, most of the electric cables are made of copper.
(f) Ornaments.
Ans: Ornaments are made of metal. Metals are malleable and ductile, i.e., they can be drawn into sheets or wires.
(g) Pots and pans.
Ans: Pots and pans are made of mud, clay, or metal. Pots and pans are used for cooking, and as mud, clay, and metals are good conductors of heat, they are used to make pots and pans.
6. What will happen if….? And why?
(a) Nails are made of plastic.
Ans: Nails should be made from metals that have characteristics of hardness. Plastic is a brittle substance. It cannot withstand hammering, nor can it enter the material through which we may try to pierce it. Therefore, nails made of plastic cannot be used.
(b) A bell is made of wood.
Ans: Sonority is a characteristic of metals. The sound produced by a metal bell would be melodious. A similar sound cannot be produced by a wooden bell, as wood does not have the characteristic of sonority.
(c) Rubber is not fitted on a pair of tongs.
Ans: A pair of tongs are made of metal. They will get heated due to thermal conductivity during use of the kitchen. If they are not fitted with rubber, they may cause burns. This can hurt us.
(d) A knife is made of wood.
Ans: The wood is not metal and is thus not hard. The work of a knife cannot be performed by a wooden knife. It cannot cut the objects due to a lack of hardness.
(e) An axe is made of rubber.
Ans: Rubber is a substance with elasticity. The rubber axe will rebound when hit by an object. The metal axe can perform a function as the metals are hard substances. The rubber axe will not be able to perform this function.
7. Who am I?
(a) I’m found in a thermometer, I measure your temperature.
Ans: Mercury
(b) I make things hot or cold.
Ans: Heat
(c) I have no shape whatsoever!
Ans: Liquid and gas
(d) I dissolve in water, but not in kerosene.
Ans: Salt
8. Why does this happen?
(a) Coconut oil thickens in winter.
Ans: In winter, the temperature of the air is lower. At this temperature, the freezing point of coconut oil is reached. Therefore, it freezes and appears to be thickened.
(b) Kerosene left open in a dish disappears.
Ans: The kerosene left in an open dish evaporates. The temperature of the surrounding air hastens this process of evaporation, and thus the kerosene completely evaporates and disappears.
(c) The fragrance of incense sticks lighted in one corner of a room spreads to the other corner.
Ans: When fragrance sticks are lit, they emit fragrant smoke. This smoke is in the form of gas and thus can spread anywhere. With the smoke, the fragrance also reaches the entire room, and thus the fragrance of incense sticks lit in one corner of a room spreads to the other corner.
(d) What you see in the picture.
Ans: We see that the air-filled balloon put in the trough of water is floating, but the apple sinks to the bottom. Apple is a solid substance, and hence its density is higher. A balloon floats as it is filled with air, i.e., a gaseous substance.