The solubility of potassium nitrate in water increases with temperature.
A saturated solution of potassium nitrate at 80 °C is cooled to 25 °C in a closed container.
Which of the following statements is/are correct?
A. 2 and 3 only
B. 1 and 3 only
C. 1 only
D. 2 only
E. 1, 2 and 3
1. The mass of undissolved potassium nitrate will increase.
The mass of undissolved KNO_3 WILL increase. Solubility increases with temperature but with cooling it decreases, hence more sediment will form.
2. The concentration of the potassium nitrate solution remains the same.
The concentration of KNO_3 in solution will NOT remain the same.
Less solute in the solvent. This builds on the first statement if we know that less will be dissolved and more solid KNO_3 will be formed (which does not contribute to the concentration of the solution).
3. The total mass of solvent present remains the same.
The total mass of the solvent present will remain the same. Why? Water temperature is decreasing, so density is increasing. This change in density may mean that the same mass occupies a greater or less volume, but the mass itself remains the same. Volume may change slightly because solid form of KNO_3 is more dense than in solution (more gaps and space when there are interactions between the water molecules and the ions K^+ and NO_3^- but same mass.