Solubility of KNO3 in Water

About 20g of water was weighed as accurately as possible into a test-tube whose length was eight inches. 9g of potassium nitrate was added to the water, and the test tube was shaken until all the salt was submerged in the water. A coated wire stirrer was then placed in the tube after which a thermometer was inserted in such manner that the bulb of the thermometer did not get in contact with the sides or the bottom of the test tube. It was ensured that the wire stirrer could move upwards and downwards (in the test tube) without upsetting the thermometer. The solution was stirred and heated lightly. The heating stopped when all the crystals liquefied. The flame was removed, after which a beaker containing cold water was placed under the test tube.

The beaker was raised so that the test tube was partially immersed in the water. Thereafter, the solution was stirred vigorously until it became cloudy. The cloudiness was an indication that crystals were starting to develop. The precise temperature at which crystals began to form was noted and recorded as the solubility temperature. The more accurate estimation of the same temperature was determined by reheating the tube and stirring the contents vigorously until the temperature was between 2 and 3 ^oC higher than the previously recorded temperature. The test tube was removed from the heat, after which the salt was stirred vigorously without cooling in a water bath. The temperature at which the first cloudiness appeared was noted and recorded as the true solubility temperature.

The above procedures were repeated until consistent temperatures were obtained. The purpose of repetition was to check the accuracy of the results. 3g of KNO₃ was added to the previously used mixture to make a concentration of 12g. The solubility of the new concentration was determined as previously described. The procedure was repeated to obtain solubility temperatures for concentrations of 15g and 18g. The obtained values were recorded in a table alongside corresponding molal solubility in terms of moles of KNO₃ per kilogram of solvent mass (Grossie and Underwood 259).