Lab 6: Charles’ Law

Introduction:

Investigation into gas behavior has yielded information in reference to how various factors influence gases. Four basic variables control the behavior of a gas: the number of molecules present (n), pressure, temperature, and volume. Of interest in this investigation are volume and temperature. Focus will be placed on how these two variables influence one another. In the last two hundred years much research has been done to describe this behavior. Ultimately these variables show a direct relationship with one another, meaning that as the value for either variable is increase a similar effect is seen with the second variable. In a system this relationship is constant, such that

Where V is the volume of a gas and T is the measured temperature of a gas in Kelvin.

The data on this subject can be summarized in a single equation known as Charles’ Law, named after one of the scientists who studied this phenomenon. Below is the equation for Charles’ Law.

Before performing this experiment answer these questions:

  1. Problem: What is the relationship between temperature and volume if number of moles and pressure are kept constant?
  2. Hypothesis: What will happen to the volume of air inside the flask as the temperature is decreased? Why? Explain with respect to space, speed, and collisions!!

Materials:

1000mL beaker

Hot plate

Dry Erlenmeyer flask

Stopper

Ring stand

Clamp

Thermometer

Large plastic tub

50mL graduated cylinder

100mL graduated cylinder

Procedure:

  1. Set up the hot plate on dial number 5. Fill a 1000mL beaker with 625mL of water and place it on the hot plate. This will be the hot water bath.
  2. Place a rubber stopper into a 250mL Erlenmeyer flask. Make sure the stopper is in tightly to prevent anything from getting into it, and that the stopper is even. It is really important that the inside of the flask be dry.Using a sticky label mark the flask where the black stopper extends into the flask. (The label should be even!)
  3. Set up the ring stand and clamp. Clamp the neck of the Erlenmeyer flask to the ring stand and submerge it fully into the hot water bath. If you need to, add more water so that it is almost fully submerged (About 1 inch of the flask should stick out of the water).
  4. Fill the large plastic tub with cool water.
  5. Boil the water for 10 minutes. This will allow the water and the air inside the flask to come to equilibrium. Measure the temperature of the water at the end of this period to record the T1.
  6. Carefully disconnect the clamp from the ring stand and cover the hole in the rubber stopper with your finger. Quickly transfer the clamp and flask into the large plastic tub with cool water.
  7. During the transfer work carefully and quickly to submerge the flask so that NO air gets into the hole. Once the flask, stopper, hole in the stopper, and your arm is submerged you can remove your finger.
  8. Allow the flask to stay submerged for 10 minutes. Record the temperature of the water at this time (this is T2).
  9. Continue to submerge the end of the flask with the stopper, but raise just the bottom base of the flask (like making it closer to upside down). When doing so, be sure that you don’t allow the top of the beaker and hole to come out of the water! Look inside the flask and attempt to have the water level inside the flask correspond to the water level of the water in the bucket. By keeping the water levels inside and out of the flask exactly the same, the atmospheric pressure inside and outside the flask will be thesame (held constant) and it can be eliminated/ignored from the calculations.
  10. Place your finger over the end of the hole in the stopper (maintaining the same level of water inside and out) and then lift out the entire flask and clamp. Remove and dry the clamp and the outside of the flask with paper towels. Carefully pour the water from inside the flask into a dry graduated cylinder and record the precise amount.
  11. 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). This total volume of the beaker corresponds to the initial volume of gas in the flask, V1. The final experimental volume (V2) can be found by subtracting the volume of water in the cooled flask from the total volume. Using the other data, an expected V2 can be calculated using Charles’ Law.

Data and Calculations:

Initial Temp of gas (°C) T1 / Final Temp of gas (°C) T2 / Volume of water in flask after cooling (mL) / Total Volume of water in flask V1(mL)
Experimental volume of gas V2 (mL) / Calculated expected V2 (mL)

Calculate the Percent error in the V2. If Percent error is greater than 10% perform the experiment again!

Mini Experiment using a soda can:

Procedure:

  1. Add 5-10 drops of water to an empty soda can.
  2. Place the can on a hot plate. Dial the hot plate to setting 10.
  3. The can will begin to steam.
  4. While the can is steaming, fill a 1000mL beaker with 600mL of water.
  5. After the can steams for 1-2 minutes, using tongs, flip the can upside down into the water-filled beaker.

Questions for Discussion:

  1. Describe your observations. ______.
  1. Explain what caused this event to happen using as much scientific terminology as possible. ______.
  1. From the perspective of a chemist, what gas law does this mini experiment show? How does this event relate to the law? ______.