Question

calculate the mass of potassium nitrate that will be precipitated if the
saturated solution was cooled from 65 °C to 25 °C.

Answer 1

Answer:

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

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

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 disso