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).
| Substance Dissolved | Temperature in K | ||||
283 | 293 | 313 | 333 | 353 | |
Solubility | |||||
| Potassium nitrate | 21 | 32 | 62 | 106 | 167 |
| Sodium chloride | 36 | 36 | 36 | 37 | 37 |
| Potassium chloride | 35 | 35 | 40 | 46 | 54 |
| Ammonium chloride | 24 | 37 | 41 | 55 | 66 |
(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?
Pragya tested the solubility of three different substances at different temperatures and collected the data as shown below (solubility is in grams of substance dissolved in 100 grams of water to form a saturated solution):
| Substance Dissolved | Temperature in K | ||||
|---|---|---|---|---|---|
| 283 | 293 | 313 | 333 | 353 | |
| Potassium nitrate | 21 | 32 | 62 | 106 | 167 |
| Sodium chloride | 36 | 36 | 36 | 37 | 37 |
| Potassium chloride | 35 | 35 | 40 | 46 | 54 |
| Ammonium chloride | 24 | 37 | 41 | 55 | 66 |
At 313 K, the solubility of potassium nitrate is 62 grams per 100 grams of water. So, for 50 grams of water, the mass of potassium nitrate required is:
\[ \text{Mass of KNO}_3 = \frac{62}{100} \times 50 = 31 \, \text{grams} \]
So, 31 grams of potassium nitrate would be needed to produce a saturated solution in 50 grams of water at 313 K.
At 353 K, the solubility of potassium chloride is 54 grams per 100 grams of water. As the solution cools, the solubility decreases. When the temperature drops, the solubility of potassium chloride at a lower temperature (e.g., 293 K) is only 35 grams per 100 grams of water. Therefore, some of the dissolved potassium chloride would precipitate out of the solution as the temperature decreases, and the excess solute will no longer remain in the solution.
The solubility of each salt at 293 K is as follows:
The salt with the highest solubility at 293 K is **ammonium chloride**, with a solubility of 37 grams per 100 grams of water.
As the temperature increases, the solubility of most salts increases. This is because higher temperatures provide more energy to break the bonds between the solute particles, allowing them to dissolve more readily in the solvent. However, there are some salts whose solubility remains constant or decreases with increasing temperature, such as sodium chloride, which has nearly the same solubility across different temperatures in the given data.