Something to Know
A. Fill in the blanks.
1. A substance which dissolves completely in a liquid is said to be soluble in it.
2. The substance that dissolves in a medium to form a solution is known as the solute.
3. Mustard oil is insoluble in water.
4. Aquatic animals breathe the oxygen gas dissolved in water.
5. Change of a liquid into its vapour form is called evaporation.
6. Condensation is the process of change of vapours into liquid.
B. Write True or False for the following statements.
1. Sugar and salt are soluble in water. True
2. Hair oil is insoluble in water. True
3. Pebbles float on water. False
4. Sand sinks in water. True
5. Water vapours can be changed into liquid water by heating. False
C. Tick (✔) the correct option.
1. In a solution of sugar and water-
(a) water is the solute.
(b) sugar is the solvent.
(c) both water and sugar are solutes.
(d) water is the solvent. (✔)
Answer – (d) water is the solvent. (✔)
2. When sand is mixed with water, it-
(a) dissolves and floats on water.
(b) does not dissolve but floats on water.
(c) does not dissolve but sinks in water. (✔)
(d) dissolves and sinks in water.
Answer – (c) does not dissolve but sinks in water. (✔)
3. Wet clothes get dried due to-
(a) water cycle
(c) respiration
(b) evaporation (✔)
(d) condensation
Answer – (b) evaporation (✔)
4. Mixture of sugar, salt and lemon juice in water is a-
(a) solution (✔)
(b) solvent
(c) solute
(d) floating mixture
Answer – (a) solution (✔)
D. Answer the following questions in brief.
1. Define a solution.
Answer – Solution is a mixture formed when a substance dissolves completely in any medium.
2. What is a solvent?
Answer – Solvent is the medium in which a substance is dissolved to form a solution.
3. Name two substances that are soluble in water.
Answer – Salt and sugar
4. Name two substances that are insoluble in water.
Answer – Sand and pebbles
5. Write the names of four substances that float on water.
Answer – Cork, butter paper, thermocole, saw dust.
6. Name the three forms of water.
Answer – Three forms of water are liquid water, ice (solid), water vapour (gas).
E. Answer the following questions.
1. Give two examples each of:
(a) liquids which dissolve in water.
Answer – Ink, alcohol.
(b) liquids which are insoluble in water.
Answer – Mustard oil, carbon tetrachloride.
(c) solids which float on water.
Answer – Cork, thermacole
(d) solids which sink in water.
Answer – Sand, pebbles
2. What do we understand by the terms ‘evaporation’ and ‘condensation’?
Answer – Evaporation is the change of a liquid into its vapour form but condensation is the change of vapour form of a substance into liquid form on cooling.
3. How are clouds formed?
Answer – Water from water bodies, changes into vapour as it evaporates due to the heat of the sun. These water vapours rise up and get cooled and condensed to form tiny droplets of water vapour. In this way, clouds are formed.
4. How does rain water get impure?
Answer – By the time raindrops reach the surface of the earth, they become impure because they dissolve many harmful gases present in air and also get dust and smoke mixed up with them.
5. Draw a diagram showing the water cycle.
Answer – Diagram given in page number 81.
Value Based Question
One day, when Anant came back after playing football with his friends, he was thirsty. He requested his mother to prepare lemonade for him. After washing his hands, he went to help his mother to prepare it.
He took water in a tumbler, added two spoons of sugar to it and stirred it. Sugar got dissolved in water.
His mother then added a pinch of salt and some lemon juice to the sugar solution. Anant stirred the mixture and added some ice to it. A cool lemonade drink was now ready.
1. In the solution prepared by Anant, name the solutes and the solvent.
Answer – The solutes are sugar, salt and lemon juice and the solvent is water.
2. If the glass tumbler, containing the cold lemonade, is kept on the table for sometimes, what change will be observed?
Answer – If the glass tumbler containing the cool lemonade is kept on the table for sometimes, tiny water droplets will be formed on the surface of the tumbler because of the condensation of atmospheric water vapour.
3. State the values displayed by Anant.
Answer – Values displayed by Anant are helpfulness, self-dependent and health conscious.
4. Share your experiences, of having helped someone, with your friends.
Answer – I, along with my friends helped some slum children in getting them food, old clothes and books.
Something to Do
1. The window panes of a closed car, with people sitting inside, often get foggy in winter. Find out the reason for this observation.
Answer – People inside the car exhale air which may contain water vapour also. Water vapour gets condensed in window panes when comes in contact with cold temperature outside. This makes the window panes foggy in winter.
2. Perform the following experiments and discuss the observations in the class with your teacher. Also, draw your own conclusion about the properties of water.
Experiment 1:
To learn about the effect of heating on the amount of a substance that gets dissolved in water.
Take a glass tumbler and fill it half with water. Add two teaspoons of sugar to it and stir. Sugar will dissolve. Add some more sugar and stir. A stage soon comes when sugar does not dissolve in water but starts ‘settling down’. Take another tumbler with moderately hot water in it and repeat the experiment.
Which of the two dissolves a greater amount of sugar?
Answer – The hot water dissolves more amounts of sugar than the cold water because heat increases the solubility of the solvent.
Experiment II:
Check the solubility of the following materials in water and find out whether they float on the surface of water or sink in it.
Rubber eraser, chalk piece, marble, wood shaving, ice cube, a five rupee coin, cooking oil, cork.
Answer – Things which float on the surface of water: Rubber eraser, chalk piece, marble, a five rupee coin.
Things which sink in water: Wood shavings, ice cubes, cooking oil, cork.
3. Fill the boxes with suitable words on the basis of the clues given below:
Down
(1) These sink in water. Coins
(3) A grey substance that does not dissolve in water and sinks in it. Sand
Across-
(2) A sweet substance that is soluble in water. Sugar
(4) A liquid that is soluble in water. Ink
Inside Questions
1. Give examples of solids which are soluble in water.
Ans- Salt, sugar, baking soda, coffee powder.
2. Give examples of solids which are insoluble in water.
Ans- Sand, pebbles, coins.
3. Give examples of liquids which are soluble in water.
Ans- Lemon juice, ink, alcohol, acids.
4. Give examples of liquids which are insoluble in water.
Ans- Carbon tetrachloride, oil, pure honey.
5. Give examples of gases which are soluble in water.
Ans- Oxygen, carbon dioxide.
6. Give an example of a gas which is insoluble in water.
Ans- Nitrogen
7. List some solids which sink in water.
Ans- Sand, coins, pebbles, iron nails, marbles.
8. List some solids which float on the surface of water.
Ans- Cork, butter paper, thermocole, saw dust.
9. What is transpiration?
Ans- Transpiration is the loss of water from parts of plants specially leaves.
By Sunaina Karmakar