Molar Volume of Oxygen


Introduction

                        Today you will determine experimentally the volume of one mole of oxygen gas at standard conditions of temperature and pressure (STP). One mole of any ideal gas under these conditions (0° C, 1atm) occupies 22.4 liters.

You will be heating a mixture of potassium chlorate and manganese dioxide (a catalyst).  The only reaction that will occur under the conditions of the reaction is the following:

       2  KClO3 (s)           2 KCl (s)  +   3 O2 (g)

            The oxygen formed will be collected as a gas.  The manganese dioxide and potassium chloride formed during the reaction will remain in the test tube.  Therefore, the loss in mass of the mixture in the test tube during the reaction should equal the mass of oxygen collected.

 

Equipment

2 ring stands

ring

2 test tube clamps

500 mL Florence flask

600 mL beaker

side-arm test tube

analytical balance

burner

tubing clamps

250 mL graduated cylinder

 

 

 

Chemicals

Student – potassium chlorate (KClO3)- Warning Strong Oxidizer, manganese (IV) oxide (MnO2) Material Safety Data Sheets are in the appendix of this lab book.  Please refer to these before using any chemicals.

 

Disposal

Spill/Disposal: A, -for spent reactants and very small spills of KClO3 or MnO2.

           

 

 

 

 

 

 

figure (1)

Procedure

 

1.  Set up the apparatus as shown in the figure (1) except for the test tube with its rubber stopper.  The long glass tubing in the 500 mL Florence flask should extend almost to the bottom of the flask.  Fill the flask with water and add approximately 200mL of water to the beaker.  Displace the air in the rubber tubing that leads to the beaker by steadily blowing into the rubber tubing, which will be connected to the test tube.  Cut straws are supplied so that you need not put your mouth directly to the tubing.  Do not inhale, as KClO3 is a toxic substance.  Remove any remaining air bubbles in the rubber tubing that leads to the beaker by raising or lowering the beaker.  Finish with the Florence flask nearly filled with water (one inch below the rubber stopper) and then place a clamp on the rubber hose that leads to the beaker.

 

2.  Weigh out approximately 1.0 grams of KClO3.  Be sure that there are no lumps in it.  (DO NOT GRIND KClO3 , IT COULD EXPLODE. JUST REMOVE THE LUMPS AND REPLACE WITH NEW KClO3) Next, weigh out approximately 0.1 grams of MnO2.  Mix the KClO3 and the MnO2 together gently. Place the mixture in a clean, dry side-arm test tube.  Insert the solid stopper tightly in the test tube and weigh them both on an analytical balance to 0.001 grams. Record the weight on your data sheet.


3.  Connect the test tube with its stopper to the rubber tubing that leads to the Florence flask.  The mixture of KClO3 and MnO2 should be spread out along the test tube.  Open the clamp on the rubber tubing leading to the beaker.  A little water may flow into the beaker from the flask but it should cease quickly.  If the water doesn't stop flowing, your system is not airtight and you will have to check your connections.

 

4. Raise the beaker until the water level inside the beaker is the same as in the flask.  Clamp the rubber tubing while the water levels are equal. The pressure inside the flask is now equal to atmospheric pressure.  Empty all the water from the beaker.  Handle the rubber tubing carefully as not to shake any of the water out of it.  Replace the tube back into the beaker and open the clamp.  Have your lab instructor check your setup before proceeding.

           

5. Heat the mixture in the test tube gently at first by moving the flame back and forth along the tube and then more strongly as needed to maintain a steady evolution of oxygen gas as shown by its displacement of the water into the beaker.  When the decomposition of KClO3 is complete, allow the entire system to cool to room temperature without disconnecting anything.  The cooling should take about ten minutes.  (If the water in the flask has dropped below the glass tubing see your instructor)  When the system is at room temperature, adjust the pressure in the flask once again by equalizing the water levels.  While the levels are equal, clamp the rubber tubing coming from the flask.

 

6. Measure the volume of water in the beaker using a 250 mL graduated cylinder.  Record the volume.  This is equal to the volume of gas evolved, measured under the conditions of the experiment.

 

7. Disconnect the test tube and weigh it with its stopper.  Record the weight.  The loss in weight of the reactants is equal to the mass of oxygen evolved.

 

8. Record the barometric pressure.

 

9. Measure the temperature of the gas in the flask by partially removing the stopper and inserting a thermometer into the vapor.  Then measure the temperature of the remaining water.  Record the temperatures.

 

10. The vapor pressure of water at the temperature of the water in the flask is found in the CRC Handbook of Chemistry and Physics available in the lab.

 

Disposal

            The contents of the test tube may be washed into the sink.

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