Nancy Delicana

Charles' Law

Objectives:  Students must be able to:

•    State Charles’ Law.
•   Gather data from a laboratory experiment illustrating Charles' law.
•   Describe the relationship between the volume and temperature of gases in the Kelvin   scale  when pressure remains constant.
•   Analyze  and graph the data derived from the laboratory experiment.
•   Present the laboratory results to class.
•   Answer essential questions related to Charles Law.

CA Content Standards: 4a, 4c, 4d, 4f, I&E a, c d

4.c. Students know how to apply the gas laws to relations between the pressure, temperature, and volume of any amount of an ideal gas or any mixture of ideal gases.

4.e.  Students know how to convert between the Celsius and Kelvin temperature   scales.

I&Ea.  Select and use appropriate tools (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, and collect data, analyze relationships, and display data.

I&Ec.  Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.

Prior Knowledge: properties of gases, unit conversions, graphing and graphical analysis, Boyle’s Law

Background

In the mid-1700s, Jacques Charles, a French scientist, was investigating hot air balloons. He discovered that the volume of a gas increases as the temperature rises. Charles' Law states that the volume of a sample of gas (V) at constant pressure (P) is directly proportional to its temperature (T) measured in kelvins (K).

The Kelvin temperature scale is defined as relative to the coldest temperature possible, sometimes called "absolute zero." Absolute zero is defined as 0 K, which is equal to -273.16 C. Although 0 K is not the same temperature as 0C, a temperature change of 1 K is the same as a temperature change of 1C. To convert a temperature in C to a temperature in kelvins, simply add 273.16 to a temperature in C.

Mathematical equations related to Charles’ Law :

V  =  constant (or)    V  =  V       (at constant P)

T                               T     T

Where:   V = initial volume of the gas

T = initial temperature of the gas in kelvins

V = final volume of the gas

T = final temperature in kelvins

Materials: For each group of 4-5 students

1 pipet                                        15-cm plastic ruler

1 thermometer                            calculator

1 250-mL beaker                         supply of room temperature and 50C water

1 50-mL beaker                           data sheets

safety goggles                              hot plate

Experimental Procedure

1.    Put approximately 10 mL of water and 1 drop of food coloring into your 50-mL beaker.

2.    Hold your pipet vertically over the 50-mL beaker containing colored water. Squeeze the pipet bulb very slightly and lower the open end into the colored water.

3.    Reduce the squeezing pressure just enough so that 1-2 cm of colored water is drawn into the stem of the pipet and comes to rest no more than 2 cm from the bulb. If you don’t get your pipet set up properly the first time, try again until you are satisfied with the result.

4.    Remove the pipet from the beaker and turn the pipet upside down so that its open end points up. You should now have a small column of colored water in the lower portion of the pipet stem and no water in the bulb. Your teacher will demonstrate this set up.

5.    If your pipet does not look similar to the one demonstrated by your teacher, don’t get discouraged. Gently squirt the colored water back into the beaker and repeat steps 2-4. It may take a couple of tries before you achieve your desired result.

Important note: For the remainder of the lab do not tilt the pipet away from the vertical position.

6.    Place approximately 200 mL of tap water in the 250-mL beaker. Take the temperature of the water and record it in Table 1 on your student datasheet as the temperature in Trial 1.

Trial 1:

7.    Lower the pipet, bulb down, into the 250-mL beaker. If you have trouble holding the pipet at the correct level, tape it carefully to the ruler. The water in the beaker should cover the bulb and come as close to the bottom level of your colored water. If the water does not cover the bulb, add more water and take the temperature again to make sure it did not change.

8.    Insert your ruler into the water and measure the length, in millimeters, from the top of the pipet bulb to the bottom of the colored water column. Record this measurement for Trial 1 in Table1on you datasheet.

Trial 2:

9.    Carefully remove the pipet and the ruler from the 250-mL beaker, making sure to keep the pipet in vertical position.

10. Pour approximately half of the room temperature water out of the 250-mL beaker and add about 100 mL of warm water from the warm water station set up by your teacher. Stir slightly then record the temperature of the water on your datasheet for Trial 2 in Table 1 of your datasheet.

11. Re-submerge the pipet and the ruler in the 250-mL beaker of warm water and measure the distance from the bulb base to the bottom of your water column. Record this measurement for Trial 2.

Trial 3:

12. Repeat steps 9-11, recording your results as Trial 3 in the datasheet.

Organizing Data

1.    In every trial there was air in both the bulb and in the stem of the pipet. The volume of the pipet bulb is 5.5 mL and each mm of the pipet stem has a volume of 0.012 mL. The sum of these two amounts is the total volume of air in the pipet.

a.    On your datasheet, transfer the temperature and distance measurements you recorded in Table1 to the appropriate spaces in Table 2 below it.

b.    Use the distance measurements to complete the calculations for each row in Table 2.

Analyzing Data:

1.    On a graphing paper, label the x-axis as temperature ( K) and the y-axis as volume (mL). The volume range should be 0 to 8 mL and the temperature range should be 275-375 K.

2.    Plot your data for trials 1, 2 and 3 and draw a “line of best-fit”.

3.     Prepare a group output in a large post it graphing paper and be prepared to orally present your result to the whole class.

Name:__________________________________            Block_____ Date__________

Charles’ Law

Student Data Sheet

Table 1

 Trial Water Temperature (⁰ C) Distance From Top Of Pipet Bulb To Bottom Of Water Column (mm) 1 2 3

Table 2

 Water Temp. (⁰ C) Distance from top of pipet bulb to bottom of water column (mm) x Volume of each mm of pipet stem (mL) = Volume of air in pipet stem (mL) + Volume of air in pipet bulb (mL) = Total Volume of Air in Pipet (mL) x 0.012 = + 5.5 = x 0.012 = + 5.5 = x 0.012 = + 5.5 =

Questions:

1.  From your experimental data, describe the relationship between volume and temperature of the gas at constant pressure.

2. What is the assumption you should have in mind when you're working on Charles' Law?

3.  Would your data look different if you used the degrees Celsius instead of kelvin?

4.  What are the possible sources of errors in your experiment?

1.  How does a tire  on a car look on a cold day?

After driving for a while, what do you notice with the tire?

What made the difference in the tire?

2.  Why do breads and muffins rise when baked?

Reference: Ten Core Chemistry Labs

A project of the High School Science Instructional Guide, LAUSD