In this lab, we found the mass of carbon dioxide that filled up a balloon. When Alka Seltzer tablets react with water, carbon dioxide gas is produced. We filled up a test tube with water and put crushed Alka Seltzer tablets (powder form) into a balloon. Next, we stretched the opening of the balloon around the rim of the test tube and let the powder mix with the water, which caused the solution in the tube to fizz. Once the fizzing stopped (when the maximum amount of carbon dioxide was given off), we measured the circumference. Then, we found the volume of the space inside the balloon by filling it up to the same circumference with water, and measuring that amount. Using all these measurements, we were able to calculate the mass of the carbon dioxide.
Data:
Calculations:
Before powder and water mixed:
While powder and water mixed:
Jason lookin' $weg in the background:
Analysis Questions:
1) Discuss an area in this lab where experimental error may have occurred.
There were several areas for errors to have occurred in this experiment. For example, some of the crushed tablet powder fell outside of the balloon when we poured it in. Also, we may have measured the circumference of the inflated balloon inaccurately, as it was not a perfect sphere but rather a three dimensional oval shape. In addition, some of the water from the balloon fell out as we poured it into the graduated cylinder.
2) Choose one error from above and discuss if it would make "n" the number of moles of CO2 too big or too small.
If the balloon circumference that we measured is too low, the volume used in the ideal gas law equation is too low. As volume is directly related to the number of moles, this would cause the number of moles to also be too low.
3) Filling the balloon with water may be one place where error could have occurred. Using the value for the circumference of the balloon in cm, calculate the volume of the balloon mathematically.
r = 4.97 cm
V = 514.23 cm^3 = 514 mL
4) Compare your answer to #3 to the volume obtained by filling the balloon with water. Is it close? Which do you feel is more accurate and why?
No, the measured volume and the calculated volume are not close. The volume obtained by filling the balloon with water is 192 mL greater, and is more accurate. This is due to the fact that the balloon was not filled to a perfect sphere by the carbon dioxide gas (as seen above) nor the water. In both instances it was a three dimensional oval shape.
5) The ideal gas law technically applies to ideal gases. Give two differences between a real gas and an ideal gas. You may use your computer or book to research.
An ideal gas doesn't have attractions or repulsions among its particles whereas a real gas could have these interactive forces. An ideal gas also doesn't have a net loss of energy caused by its particles colliding, but a real gas could.
6) Would the CO2 you collected in this lab be considered ideal? Why or why not?
No, the carbon dioxide gas would not be considered ideal. This is because real gases aren't ideal, and ideal gases don't exist.
Advanced Questions:
1) Using the information provided on the label, and stoichiometry, calculate the mass of CO2 that should be collected.
(We used two tablets instead of three)
2g citric acid ==> 1.374g CO2
3.832g sodium bicarbonate ==> 2.007g CO2
In this case, citric acid is limiting, so the theoretical yield of carbon dioxide is 1.37g CO2.
2) What percent is the percent yield for the CO2 collected in your sample?
1.26g/1.37g x 100 = 92.0%
3) CO2 is water soluble. The solubility around room temperature is around 90mL/100mL of water. What effect does that have on your calculated "n" value?
As carbon dioxide is water soluble, some of the gas could have dissolved in the water when we shook the test tube-and-balloon system. This would cause less carbon dioxide to fill the balloon, and the circumference and volume of the balloon would be too low. Therefore, our n value would also be lower.
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