Question

A china dish weighs 25 g when empty. When a saturated solution of potassium chloride is poured into it at $40^\circ C$, the weight of the dish is 63 g. When the solution is totally evaporated, the chine dish along with the crystals weighs 40 g. Find the solubility of potassium chloride at $40^\circ C$ .
A. 35
B. 65.2
C. 39.5
D. 7.5

Answer 1

Hint: For solving the above question, we need to have better understanding of solubility. The ability of a substance or a solute to mix into a liquid or solvent is called solubility. The solute and a solvent when mixed together form a saturated solution.

Complete answer:
As we know that, when equal amounts of a substance mixed into a liquid solvent then solubility of a solution is derived. So, based on this concept we will solve the above question.
First we will write down all the given quantities:
Weight of china dish before the solution was poured = 25 g
Weight of the china dish when solution is poured= 63 g
So, the weight of the saturated solution becomes = (63 – 25) g = 38 g
As it’s mentioned in the question that the solution is totally evaporated, along with that the china dish with the crystals weighs 40 g.
So, the total weight of solid potassium chloride or $KCl$ crystal solution will be equal to = (40 - 25) = 15 g
Thus, the weight of water present in that saturated solution = (38 – 15) = 23 g
So, the formula for deriving the solubility of potassium chloride at ${40^ \circ }$ C is equal to $ = \dfrac{{{\text{weight of KCl crystals}}}}{{{\text{weight of water}}}} \times 100$
Now, we will substitute the values in the formula.
= $\dfrac{{15}}{{38}} \times 100 = 39.5$
Therefore, the solubility of potassium chloride is 39.5 (option C).

Note:
We must remember that when the temperature of water increases, then the particles of solid potassium chloride, $KCl$ get the opportunity to move easily between the solution and its solid state. This is how temperature affects the solubility of potassium chloride.