CHARLES' LAW LABORATORY EXERCISE

            This law states that as the temperature of a gas changes its volume will vary proportionally. The pressure acting on the system must remain constant as well as the amount of gas (air in this lab) must remain the same.

 V₁ / T₁  =  V₂ / T₂         V₂  =  (V₁T₂ ) /  T₁      V₂ = unknown, can be found by formula and experimentally

 OBJECTIVES:
1. to observe the change in volume of a gas when its temp. is changed
2. to practice laboratory techniques involving gases
3. to perform a lab with a % error less than 2%

SAFETY PRECAUTIONS:

1. Handling extremely hot glassware and working with boiling water requires attention given to equipment and instructions.
2. Use of the Bunsen burner requires careful lighting and one lab group member assigned to watch the burner at all times.
3. Clean dry equipment will always provide better results and perform in a safe manner.

PROCEDURE:

1. Place stopper (with glass tubing already inserted) into the 250 mL Erlenmeyer flask firmly and as level as possible. Using tape mark the flask where the stopper extends.. This should be even around the neck of the flask.

2. Attach the universal clamp to the neck of the flask and also to the ring stand. The flask should extend down as far as possible in an 400/600 mL beaker sitting on wire gauze ring attached to the ring stand. Add water to the beaker so that it fills the beaker to approximately 1 inch below the lip of the flask. NO water should boil or splash out of the beaker.  Use boiling chips.

3. Heat the empty flask using this water bath arrangement till the water has been boiling for 8-10 minutes. Record the temperature of the water. This should now also be the temperature of the air inside the flask.

4. Disconnect the clamp from the ring stand. Place your finger over the end of the glass tubing in the stopper and transfer the entire flask and clamp to the standing water in the sink. This must be done so that no air enters or escapes from the flask. Only remove your finger when the entire flask is submerged.

5. Keep the flask completely submerged for approximately 8-10 minutes. Record the temp of the water in the sink. This should be the temperature of the water and air inside the flask.

6. The most critical step in attempting to reduce the % error comes at this point. Continue to submerge the end of the flask with the stopper but raise the base of the flask. Look inside the flask and attempt to have the water level inside the flask correspond to the water level of the water in the sink. This sounds more difficult that it really is. By keeping the water levels inside and out of the flask exactly the same the atmospheric pressure inside and outside the flask will be the same (held constant) and we can eliminate it from our calculations.                                                                                              

 7. Place your finger over the end of the glass tubing (maintaining the same level of water inside and out) and then lift out the entire flask and clamp. Remove and dry the clamp with paper towels. Carefully pour the water inside the flask into a dry graduated cylinder and record the amount.

8. Fill the flask with water up to the mark made earlier (the neck where the stopper had extended). Again pour this water into a dry graduated cylinder (this may take several full cylinders, just accumulate the volume). The final volume (V₂) can be found by using the formula or by simply subtracting the amount left in the flask after cooling from the original total amount (V).

SAMPLE DATA TABLE

Temp. of water bath  =  T₁       ___________º C
Temp. of water in sink  =  T₂   ___________º C
Volume of water in flask after cooling    __________ mL
Total volume of water in flask (V₁)          ___________mL
Final  volume of air in flask (by subtraction:  =  V₂)  _______________mL

 CALCULATIONS: 

1. Find V₂ using Charles' Law:

2. Perform graphing example as shown in class:  value of absolute value found: ___________º C

3. Perform the following percentage calculations:

 PERCENTAGE ERROR:
% error = |experimental – theoretical result|/ theoretical result   x 100 =

 

 PERCENTAGE DIFFERENCE: (for V₂)
% difference =  |difference of two values| / larger of two values  x  100  =

 

 QUESTIONS: 

1.  Explain what your lab group could have done to reduce your error.
2.  Why/how did we eliminate the need to measure the atmospheric pressure inside the flask after cooling.
3.  Find examples of Charles' Law in our daily lives.

Answer Space: