Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f ) Digestion of food
(a) Photosynthesis - Chemical change
Those changes in which new substances are formed, are called chemical changes. Photosynthesis is a chemical change because chemical reaction occur in it which is completed in the presence of sunlight.
(b) Dissolving sugar in water - Physical change
The physical changes are temporary changes which can be easily reversed to form the original substances. Physical changes are those changes which can be easily reversed by physical methods: evaporization and condensation.
(c) Burning of coal - Chemical change
(d) Melting of wax - Physical change
(e) Beating aluminium to make aluminium foil - Physical change
(f) Digestion of food - Chemical change
Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.
Down Across
(D) 1 : Thorough washing (A) 1 : Keeps warm
2 : Animal fibre 2 : Its leaves are eaten by silkworms
3 : Long thread like structure 3 : Hatches from egg of moth
Sketch the cross section of soil and label the various layers.
Take three test-tubes. Fill æth of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2?
Here is a crossword puzzle: Good luck!
Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body
Down
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water
Sketch the reproductive parts of a flower.
Solve the following crossword puzzle with the clues given:
Across
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.
Down
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Describe how crystals of copper sulphate are prepared.
Match the items in Column I with those in Column II:
Column I Column II
(i) A home for living organisms (a) Large particles
(ii) Upper layer of the soil (b) All kinds of soil
(iii) Sandy soil (c) Dark in colour
(iv) Middle layer of the soil (d) Small particles and packed tight (v) Clayey soil (e) Lesser amount of humus
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Write one similarity and one difference between the nutrition in amoeba and human beings.
Outline your role as an active citizen in relation to sanitation.
Sketch the cross section of soil and label the various layers.
Explain the function of bar screens in a wastewater treatment plant.
When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
The mountaineers carry oxygen with them because:
(a) At an altitude of more than 5 km there is no air.
(b) The amount of air available to a person is less than that available on the ground.
(c) The temperature of air is higher than that on the ground.
(d) The pressure of air is higher than that on the ground.
Name two chemicals used to disinfect water.
You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.
Why do we often sneeze when we inhale a lot of dust-laden air?
Match the following :
(i) Land breeze blows during (a) summer
(ii) Sea breeze blows during (b) winter
(iii) Dark coloured clothes are preferred during (c) day
(iv) Light coloured clothes are preferred during (d) night
Explain the relationship between sanitation and disease.