Lab 3: Alka-Seltzer and Gas Solubility Lab
Purpose: In this lab you will determine the effect of temperature on the
solubility of a gas in a liquid.
Procedure:
1. Add 100 mL of water to each of three 250-mL beakers.
Place one beaker in an ice bath (use the larger beaker for the ice bath). Heat
one beaker on a hot plate. Let the third beaker equilibrate at room
temperature.
2. While the water is heating and cooling use a mortar and pestle to crush the
Alka-Seltzer tablets and then weigh out two 0.50 gram samples of Alka-Seltzer.
(Weigh out on paper)
3. When the hot water has reached a temperature between 74oC -80oC carefully
remove (using tongs) the beaker form the hot plate.
4. Add 1.0 mL of Bromothymol blue indicator to each of the three beakers.
5. Simultaneously add one Alka-Seltzer sample to the hot water beaker and the
other Alka-Seltzer sample to the cold water beaker. The room temperature
beaker is the control. Observe and record signs of physical and chemical
reactions.
6. When the Alka-Seltzer has fully dissolved in each beaker, record the color of
each solution.
7. Measure the temperature of each solution and label three test tubes with
the corresponding temperature.
8. Using a graduated cylinder, remove 25 mL from each beaker and pour into
the appropriately labeled test tube. Place the test tube with the cold solution
back into the ice bath.
9. Using a pipet or eye dropper add (one drop at a time) 1M NaOH solution to
the cold water test tube until it is the same color as the control. Gently Swirl
between drops to ensure mixing. Count and record the number of drops
required.
10. Using a pipet add (one drop at a time) 1M NaOH solution to the hot water
test tube until it is the same color as the control. Gently Swirl between
drops to ensure mixing. Count and record the number of drops required.
Analysis: The bubbles that you observed were carbon dioxide bubbles. When
carbon dioxide is dissolved in water an acid solution is produced. The more CO2
that is dissolved, the more acidic the solution is. When NaOH is added to an acid
solution, it neutralizes it. A more acidic solution will require more NaOH to
neutralize it. (Room temperature water was neutral).
Questions:
1. Which temperature solution required more NaOH to neutralize
it?_________
2. Which temperature solution was more acidic? ____________
3. Which temperature solution contained more dissolved CO2?__________
4. Explain your results
Need for 7 groups:
21
250 mL beakers
7
600 mL beakers
7 dropper bottles of bromthymol blue ( each group need 5 mL)
7 thermometers
21 large TT and 7 large test tube racks
7 dropper bottles of 1 M NaOH
7 pipets
50 tablets for al chem. classes
ice
hot plates
Buy and grind Alka-Seltzer
Make 1 M NaOH solution