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Pragya tested the solubility of three different substances at
different temperatures and collected the data as given below
(results are given in the following table, as grams of substance
dissolved in 100 grams of water to form a saturated solution).
(a) What mass of potassium nitrate would be needed to
produce a saturated solution of potassium nitrate in
50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride
in water at 353 K and leaves the solution to cool at room
temperature. What would she observe as the solution
cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has
the highest solubility at this temperature?
(d) What is the effect of change of temperature on the
solubility of a salt?
Answer
(a) At 313K,
Mass of potassium nitrate needed to produce a saturated solution of potassium nitrate in 100g water = 62g
Mass of potassium nitrate needed to produce a saturated solution of potassium nitrate in 1g water = 62g/100g
Mass of potassium nitrate needed to produce a saturated solution of potassium nitrate in 1g water = 62gx50g/100g
= 62g/2
=31 g
(b) Solubility of solids in liquid decreases with decrease in temperature.
Room temperature is 298K while the saturated solution was formed at 253K. Hence, she will find crystals of potassium chloride when the solution cools down.
(c) Solubility is the maximum amount of solute which can be dissolved in 100 gm of Solvent at a particular temperature.
Hence the solubility of the following at 293K is
- Potassium Nitrate - 32
- Sodium Chloride - 36
- Potassium Chloride - 35
- Ammonium Chloride - 37
(d) From the above table we can see that the solubility of a salt is directly proportional to the temperature.
As the temperature increases the solubility also increases.
