Lesson 4 – Water Safe for Drinking
(A) Use your brain power !
Some rava has got mixed with sago pearls or sabudana. What sieve should we use to separate the two – the one that allows rava to pass through or the one that allows sago?
Ans: To separate rava and sabudana, we shall use the sieve that allows rava to pass through. So sabudana will remain in the sieve. Thus, the two can be separated.
(B) Answer the following questions.
1. Name the substances used to make the solution called lemon sherbet.
Ans: The substances used to make the solution called lemon sherbet are lemon, sugar, salt, and water.
2. Why is the water that looks clean and transparent may not be fit for drinking?
Ans: Water that looks clean and transparent may not be fit for drinking because harmful micro-organisms, that cannot be seen with naked eyes may be present in water. These micro-organisms if entered our body can cause us diseases and can be harmful for our health.
3. When making a sherbet, what do we do to make sugar dissolve quickly?
Ans: When making a sherbet, we stir with a spoon so that the sugar dissolves quickly in the water.
4. Does oil float on water or sink in it?
Ans: Oil floats on water because oil is lighter than water.
(C) Complete the table.
1. Write the information you obtained from the floating-sinking experiment, in the table below.
Repeat the experiment with other things besides those mentioned in the lesson. Write their names, too, in the proper places in the table.
Ans: Students must do this on their own.
2. Repeat the experiment in the lesson related to dissolving using some other substances. Make a table like the one above and fill in your findings in it.
Ans: Students must do this on their own.
(D) Fill in the blanks.
1. Substances like salt and sugar ________ after some time when added to water.
Ans: dissolves
2. The mixture obtained on dissolving a substance in water is called a ________.
Ans: solution
3. ORS is an example of ________ solutions.
Ans: useful
4. All micro-organisms are not useful. Some can cause ________ if they enter our body.
Ans: diseases
5. Things that float in water are ________ than it and things that sink are ________ than it.
Ans: lighter, heavier
6. A substance called ________ is swirled in muddy water to help clean the water.
Ans: alum
(E) True or false?
1. Alum powder does not dissolve in water.
Ans: Fals
2. Micro-organisms cannot live in water.
Ans: False
3. If muddy water remains still, a sediment is formed at its bottom.
Ans: True
4. An eraser floats in water.
Ans: False
5. Tea leaves can be separated from tea by filtration.
Ans: True
(F) How can we tell that water has become transparent?
Ans: When the suspended particles in the water settle down at the bottom, it looks transparent. When a piece of alum is swirled in muddy water, it dissolves in the water and takes mud particles along with it to the bottom. Since the mud particles are heavier than water, they form sediment at the bottom. Thus, such water is said to become transparent.