Question: What is the solubility curve of KNO3
Prediction: Draw a sketch to show the shape of the curve you expect for the solubility of a typical solid dissolving in water at different temperatures. Plot solubility on the y-axis and temperature on the x-axis.
Large test tube
Two-hole stopper to fit the test tube, with a thermometer inserted into one hole
graduated cylinder or pipette or burette
hot plate or Bunsen burner with ring clamps and wire gauze
retort stand and thermometer clamp
potassium nitrate, KNO3
1.Read through the steps in this procedure. Prepare a data table to record the mass of the solute, the initial volume of water, the total volume of water after step 9, and the temperatures at which the solutions began to crystallize.
2.Put the test tube inside a beaker for support. Place the beaker on a balance pan. Set the readings on the balance to zero. Then measure 14.0g of KNO3 into the test tube.
3.Add on of the following volumes of distilled water to the test tube, as assigned by your teacher: 10.0mL, 15.0mL, 20.0mL, 25.0mL, 30.0mL. (If you use a graduated cylinder, remember to read the volume from the bottom of the water meniscus. You can make more a more accurate volume measurement using either a pipette or a burette.)
4.Pour about 300mL of tap water into the beaker. Set up a hot-water bath using a hot plate, retort stand, and thermometer clamp. Alternatively, use a Bunsen burner, retort stand, ring clamp, thermometer clamp, and wire gauze.
5.Put the stirring wire through the second hole of the stopper. Insert the stopper, thermometer, and wire into the test tube. Make sure that the thermometer bulb is below the surface of the solution.
6.Place the test tube in the beaker. Secure the test tube and thermometer to the retort stand using clamps. Begin heating the water bath gently.
7.Using the stirring wire, stir the mixture until the solute completely dissolves. Turn the heat source off, and allow the solution to cool.
8.Continue stirring. Record the temperature at which crystals begin to appear in the solution.
9.Remove the stopper from the test tube. Carefully add 5.0mL of distilled water. The solution is now more dilute and therefore more soluble. Crystals will appear at a lower temperature.
10.Put the stopper, with the thermometer and stirring wire, back in the test tube. If crystals have already started to appear in the solution, begin warming the water bath again. Repeat steps 7 and 8.
11.If no crystals are present, stir the solution while the water bath cools. Record the temperature at which crystals first begin to appear.
12.Dispose of the aqueous solutions of potassium nitrate into the labelled waste container.