Introduction:

In 1787 Charles repeated work done by Amontons in 1699 dealing with the change in the volume of air as the temperature of the air changed. Amontons results were not widely circulated. Charles did not publish his results. In 1802 Gay-Lussac repeated the same work and published the results. Some text books honor Gay-Lussac with the relationship between temperature and volume, some acknowledge Charles even though he did not publish his results, and some finally acknowledge Amonton who preceded both and did publish his data.

The relationship they found was that the volume of the gas was directly proportional to the temperature. What Charles observed was that the volume increased by 1/273 for every degree increase in Celsius degrees. William Thomson used this in 1848 to set up the absolute temperature scale still used today. It is called the Kelvin temperature scale (Thomson was knighted as Lord Kelvin).

The mathematical equation is: , when the quantity of gas is constant and the pressure is also constant. You can set up two relationships at constant quantity and pressure: , and . You can rearrange these equations to: and . Since both ratios equal k they are equal to one another: ; this is Charles' Law. You can rearrange this to be: . Both are Charles' Law.

Equipment:

125 mL filtration flask, 250 mL Florence flask, no hole rubber stopper for filtration flask, 2 hole rubber stopper for Florence flask, two tubes already present in 2 hole stopper, rubber tubing, tubing clamp, 250 mL beaker, 600 mL beaker, hot plate, Celsius thermometer, 100 mL graduated cylinder.

Procedure:

Set up the equipment as shown in the diagram.
 
 

 Half fill a 600 mL beaker with tap water. Place the beaker on the hot plate, but do not heat the beaker yet. Stopper the filtration flask. Attach a rubber tube to the side arm of the flask. Place the dry filtration flask into the 600 mL beaker but do not allow water to enter the flask. Fill the Florence flask with water. Place about 50 mL of water into the 250 mL beaker.

Place the tube from the 2-hole stopper that is attached to the glass tube that reaches to the bottom of the Florence flask into the 250 mL beaker. Stopper the Florence flask with the 2-hole stopper. Be sure there is a clamp attached to this tube that is going into the beaker. The clamp should be open.

Using the method illustrated by your instructor fill the siphon tube with water. Lift the beaker to siphon water back into the flask. When the water in the flask is just below to entrance of the other glass tube going into the 2-hole stopper, close the clamp.

After 10 minutes the air in the flask should be at the same temperature as the water in the beaker. Measure the temperature of the water with a thermometer. Attach the end of the tubing from the filtration flask to the short glass tube in the 2-hole stopper.

You now have to test your siphon tube to make sure there are no air leaks. Carefully open the clamp. A small amount of water should move from the Florence flask into the beaker. If water continues to drain into the beaker it means you have an air leak. Your instructor will help you check out the equipment. If there is no further movement, carefully lift the beaker until the level of water in the beaker and the level of water at the top of the Florence flask are even or level. Close the clamp to the beaker.

Carefully lift the tube out of the water in the beaker so as not to lose any water from the tube. Discard the water that is in the beaker. Put the tube back into the beaker. Again open the clamp. Turn on the hot plate and heat the water until it has been boiling for 5 minutes. Take the temperature of the boiling water with the same thermometer. Lift the beaker until the levels of water in the beaker and in the flask are the same. Close the clamp on the tube. Turn off the hot plate. Remove the tube from the water in the beaker and measure the amount of water in the beaker by transferring it to a dry 100 mL graduated cylinder.

The amount of water displaced from the Florence flask is almost equal to the increase in the volume of the trapped air in the filtration flask. What you need is the volume of the air in the filtration flask and tubing to the Florence flask. This you can get by removing the stopper, filling the filtration flask with water until it comes out the tubing attached to the side arm. Place your finger over the end of the tube and slowly continue to add water to the flask until it is completely full. Carefully place the stopper in the flask opening and push it in at the same time letting water drain from the tube. This way you have kept the flask completely full but have not built up a pressure that would squirt water all over the place. Now measure the water in the flask and tube. You may have to fill the graduated cylinder several times.

Your calculation for this experiment is to find the constant added to the temperature in degrees Celsius so as to give a simple relation between the temperature and volume.

V₁ = Starting volume (the volume of the flask and tubing)

V₂ = V₁ + the volume of water displaced from the Florence flask.

t₁ = Starting temperature of the water bath in degrees Celsius.

t₂ = Temperature of the boiling water bath in degrees Celsius.

Rearrange the equation: V₁ t₂ + V₁ k = V₂ t₁ + V₂ k , rearrange again:

V₁ t₂ - V₂ t₁ = V₂ k - V₁ k ; or: V₁ t₂ - V₂ t₁ = k ( V₂ - V₁ )

or: , the value of k should be around the value of ( t₁ + 273 ).