Project Work de Stir the contents of the beaker with a spoon. What do you observe? Where do the parti Take a beaker. Fill it half with water. Add two spoons of table salt in the water o gentle flame till the entire water of the beaker vapourizes. See the contents of the be Taste few drops of the salt solution. You will find it salty. Now, heat the beaker salt go ? What is left in the beaker ? Taste it. Does it still taste salty ? How is this residue left ? Hint : 1. The particles of salt occupy space between the inter-molecular spacing of water. 2. On heating when the water vaporizes, the inter-molecular spacing of water increases only the particles of salt are left behind.
Answers
Answer:
amount of sand. She then tried the
method suggested in Activity 7, to
recover the salt. She found, however,
that she could recover only a small part
of the salt that she had taken. What
could have gone wrong?
Can water dissolve any
amount of a substance?
In chapter 4, we found that many Fig 5.14 Dissolving salt in water
substances dissolve in water and form would have remained mixed with the
a solution. We say that these substances sand and could not be recovered. She
are soluble in water. What will happen could solve her problem by using a
if we go on adding more and more of larger quantity of water.
these substances to a fixed quantity of Suppose, she did not have sufficient
water? quantity of water to dissolve all the salt
Activity 8 in the mixture. Is there some way that
water could be made to dissolve more
You will need a beaker or a small pan, a salt before the solution gets saturated?
spoon, salt and water. Pour half a cup Let us try and help Paheli out.
of water in the beaker. Add one
Activity 9
teaspoonful of salt and stir it well, until
the salt dissolves completely (Fig 5.14). Take some water in a beaker and mix
Again add a teaspoonful of salt and stir salt in it until it cannot dissolve any
well. Go on adding salt, one teaspoonful more salt. This will give you a saturated
at a time, and stir. solution of salt in water.
After adding a few spoons of salt, do Now, add a small quantity of salt to
you find that some salt remains this saturated solution and heat it. What
undissolved and settles at the bottom do you find? What happens to the
of the beaker? If yes, this means that undissolved salt in the bottom of the
no more salt can be dissolved in the beaker? Does it dissolve, now? If yes,
amount of water we have taken. The can some more salt be dissolved in this
solution is now said to be saturated. solution by heating it?
Here is a hint as to what might have Let this hot solution cool. Does the
gone wrong when Paheli tried to recover salt appear to settle at the bottom of the
large quantity of salt mixed with sand. beaker again?
Perhaps the quantity of salt was much The activity suggests that larger
more than that required to form a quantity of salt can be dissolved in water
saturated solution. The undissolved salt on heating.