Question

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 100grams 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 50grams of water at 313K?
B.Pragya makes a saturated solution of potassium chloride in water at 353K 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 293K. Which salt has the highest solubility at this temperature?
D.What is the effect of change of temperature on the solubility of a salt?

Substance Dissolved	Temperature in K
283	293
Solubility
Potassium nitrate	21
Sodium chloride	36
Potassium chloride	35
Ammonium chloride	24

Answer 1

It becomes easy to find the answers of such questions by looking at the information provided in the given table. At lower temperatures, solubility generally decreases for a saturated solution and at higher temperatures, solubility of the salt increases but it depends on the type of salt we are looking at.

Complete step-by-step answer:
(a)Mass of potassium nitrate present in 100g of water in a saturated solution at 313K is 62 grams. Therefore, mass of potassium nitrate in 50 grams of water in the saturated solution at 313K will be
$= \dfrac{{62g}}{{100g}} \times 50g = 31g$
(b)When a saturated solution of potassium chloride is cooled at 353K, the solubility of potassium chloride in water basically decreases. Due to this, the amount of potassium chloride which exceeds its solubility at lower temperature separates out as crystals.
(c)As per the given data, that is
Solubility of potassium nitrate at 293K = $\dfrac{{32g}}{{100g}}$ of water
Solubility of sodium chloride at 293K = $\dfrac{{36g}}{{100g}}$ of water
Solubility of potassium chloride at 293K = $\dfrac{{35g}}{{100g}}$ of water
Solubility of ammonium chloride at 293K = $\dfrac{{37g}}{{100g}}$ of water
From this data, we can easily see that ammonium chloride has the highest solubility at 293K.
(d) We know that the solubility of a salt increases with temperature in general. This increase is different for different salts. For example, there is an appreciable increase in the solubility of potassium nitrate but that of ammonium chloride increases slightly and that of potassium chloride increases marginally while that of sodium chloride almost remains constant.

Note: A solution which contains the maximum amount of solute dissolved in a given amount of solvent at a particular temperature and which cannot dissolve any more amount of solute at that temperature is known as a saturated solution. Solubility is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium point.