Temperature Dependence of Carbon Dioxide in Water
Purpose:
The purpose of this lab is to investigate how the temperature of water affects the amount of carbon dioxide found in the water and relate this to changes in global carbon dioxide levels and climate.
Background : We are using Alka Seltzer tablets to provide the carbon dioxide for the lab and putting the tablets in different water temperatures. In order to determine the amount of carbon dioxide, we are measuring the pH of the solution. This can help determine the amount of carbon dioxide because the carbon dioxide will react with the water to produce carbonic acid. The more carbon dioxide in the water, the lower the pH should be.
Materials : pH strips, tap water, hot plate, beaker tongs, thermometer, 250 mL beakers, ice, Alka
Seltzer tablets, balance, weighing tray
Procedures :
1.
Measure out 200 mL of tap water in your 250 mL beaker.
2.
Record the temperature ( o C) of the water in your data table.
3.
Add a 1.00 gram Alka Seltzer tablet to the beaker of water and let it dissolve.
4.
When the tablet has completely dissolved, dip the pH strip into the water and record the pH using the color chart on the pH dispenser.
5.
Repeat this procedure a minimum of 5 times using different temperatures by heating the beaker on the hot plate to raise the temperature or adding ice to the beaker to lower the temperature. Each time record them temperature and corresponding pH value in your table.
Pre-Lab Analysis: Answer the following questions based on prior information given in class, from notes, or by using the textbook. These should be completed prior to beginning the lab.
1.
What is the purpose of adding the Alka Seltzer to the water?
2.
Why is it important to use the same amount of water each time and the same amount of Alka
Seltzer?
3.
What are you measuring when you record the pH?
4.
The title of the lab is called temperature dependence of carbon dioxide in water, but you are not measuring the carbon dioxide levels of the water, you are measuring the pH. What will the pH level tell you about the amount of carbon dioxide in the water? (Think about what happens to carbon dioxide when it is dissolved in water).
5.
How do carbon dioxide levels in the atmosphere contribute to the acidification of the ocean?

2
5
9
15
18
Lab Write-Up:
1.
Title
2.
Pupose
3.
Pre-Lab Questions
4.
Hypothesis -
Formulate a hypothesis that examines the relationship between the temperature of the water and the relative carbon dioxide levels of the water. (Remember we will be using pH to help us determine the relative concentration of carbon dioxide in the water and will not be measuring the carbon dioxide levels directly.)
5.
Independent variable
6.
Dependent variable
7.
Control
8.
Materials
9.
Procedures
10.
Data Table
11.
Graph (the temperature vs. the pH should be graphed to examine the relationship – make a line graph with temperature on the x and pH on the y)
12.
Post-Lab Analysis a.
What was the relationship between pH and temperature in the lab? b.
Discuss the relationship between the pH and carbon dioxide levels. c.
From this, what can you conclude about the connection between the temperature of water and the solubility of carbon dioxide? d.
In class we discussed that as the levels of carbon dioxide in the oceans is increasing, the pH at the poles is changing faster than it is at the equator. Thinking in terms of temperature, why do you think this is happening? e.
On the basis of what you learned, if the earth’s climate warms because of additional carbon dioxide in the atmosphere, what will happen to the oceans ability to absorb carbon dioxide?
Will it stay the same, increase, or decrease? Why? f.
If the amount of carbon dioxide in the atmosphere determines the amount of heating of the earth due to the Greenhouse effect, how do you think the warming of the ocean water will affect the global climate?
Lab Data
:
Temperature ( o C) pH Temperature ( o C) pH
24
5
5
5
5.5
5.5
6
35
46
58
75
80
91
6
6
6
6.5
6.5
7