Chemistry, asked by saswatpradhan9b4245, 6 months ago

What mass of KNO3 is required to prepare 70g of KNO3 from its saturated solution

at 80C? Its solubility at 80C is 150g and at 20C is 90g.​

Answers

Answered by Zenix
0

Explanation:

So, you know that potassium nitrate,

KNO

3

, has a solubility of

155 g

per

100 g

of water at

75

C

and of

38.0 g

at

25

C

.

What that means is that at

75

C

, you can dissolve as much as

155 g

of solid potassium nitrate in water without the solution becoming saturated.

Once you hit that

155 g

mark, the solution becomes saturated, which means that the solution can't dissolve any more solid.

Now, the same thing can be said for the solution at

25

C

. At this temperature, dissolving less than

38.0 g

of potassium nitrate per

100 g

of water will result in an unsaturated solution.

At the

38.0 g

mark, the solution will become saturated.

Now, take a look at how the solubility graph for potassium nitrate looks like

So, you are starting with

100 g

of saturated solution at

75

C

. Mind you, you have

100 g

of solution that contains as much dissolved potassium nitrate as possible.

This solution will contain

100.0

g solution

155 g KNO

3

(

155

+

100

)

g solution

=

60.78 g KNO

3

Now, potassium nitrate's solubility is given per

100 g

of water. Calculate how much water you have in this initial solution

m

water

=

100.0 g

60.78 g

=

39.22 g

Next, determine how much potassium nitrate can be dissolved in

39.22 g

of water at

26

C

in order to make a saturated solution, i.e. have the maximum amount of dissolved potassium nitrate possible

39.22

g water

38.0 g KNO

3

100

g water

=

14.9 g KNO

3

This means that when the initial solution is cooled from

75

C

to

25

C

, the amount of water that it contained will only hold

14.9 g

of dissolved potassium nitrate.

The rest will crystallize out of solution

m

crystallize

=

60.78 g

14.9 g

=

45.9 g

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