When 36.0g of sodium chloride is added to 100 g of H2O (water) at 25°C all the salt particles dissolve.Yet if you add one more g of salt and stir,no matter how vigorously or how long only 0.2g of the last portion dissolve in the soln.why?
The solubility of a substance refers to the maximum amount of solute that can dissolve in a given amount of solvent under specific conditions, such as temperature. In this case, the solubility of sodium chloride in water at 25°C is exceeded when 36.0g of sodium chloride is added to 100g of water, causing all the salt particles to dissolve.
However, when one more gram of salt is added and stirred vigorously, only 0.2g of the last portion is able to dissolve, no matter how long you stir. This situation can be explained by the concept of saturation and equilibrium.
When a solution is saturated, it means that the maximum amount of solute has already been dissolved in the solvent. Adding more solute beyond this point will not result in more dissolution. This is because the solvent can no longer accommodate any extra solute particles due to the solubility limit at that specific temperature.
When you add the additional gram of salt, it surpasses the solubility limit of sodium chloride in water at 25°C. As a result, only a small portion (0.2g) of the last gram is able to dissolve while the remaining portion remains undissolved. This occurs because the solution is already saturated, and the excess salt particles do not have enough energy to break the forces holding them together and become solvated by the water molecules.
Even if you stir the solution vigorously, the stirring action does not provide enough energy to overcome the forces of attraction between the excess salt particles. Therefore, only a small portion dissolves and the rest remains undissolved.
To summarize, when 36.0g of sodium chloride is added to 100g of water at 25°C, it completely dissolves because it is within the solubility limit. However, when one more gram is added, the solution becomes saturated, and only a small portion of the last gram dissolves due to the solubility limit being exceeded.