Purpose: The purpose of this lab was to learn how to correct the measured volume of a gas collected over water to the STP volume of the dry gas. Also the purpose was to calculate the molar volume of a gas at STP from experimental data, and to calculate the percentage of a compound in a mixture.
Theory: When potassium chlorate is heated, it will decompose to give oxygen gas, which may be collected and its volume measured. Since the gas will be collected over water, Dalton's Law must be used to correct for the water vapor present. The STP volume occupied by the gas may be calculated. From a knowledge of the weight of gas produced and the STP volume of the gas produced, the STP molar volume may be determined. Also using the weight of gas produced together with the balanced equation, the weight of potassium chlorate in the mixture may be determined. The mixture will consist of KCL, and inert ingredient for bulk; MnO2, a catalyst to ensure that the decomposition is rapid and complete" and KCLO3, the compound which is being decomposed.
Procedure: Assemble and apparatus shown in the lab worksheet. Fill the flask completely full of tap water; also fill the beaker half full with water. Fill the connecting rubber tubing between the flask and beaker by removing the stopper from the test tube, opening the pinch clamp, and blowing air into the open end of the tube. When the water flows freely into the beaker, raise the beaker above the flask and allow water to siphon back into the flask until it is nearly full (the water level should be just below the tube coming from the test tube). Then close the clamp. Use one of the numbered unknowns on the center table and weigh out between one point two and one point five grams of the unknown. Weigh the empty test tube on an analytical balance, pour the mixture into the tube, and reweigh. Record the weighings in the data table. Connect the test tube to the system with the rubber stopper and clamp the test tube to the system with the rubber stopper and clamp the test tube securely to a ring stand.