Lab 18: Gas Law Lab

Summary 

In this lab students were tasked with finding the volume of a balloon filled with carbon dioxide. The balloon was inflated by a reaction between alka seltzer powder and water; students then measured the circumference of the balloon using a piece of string and use this measurement in finding the volume. After finding all of the required values, students had to find the volume of the balloon using three alternative methods: by utilizing gas laws or finding the volume of a sphere. 

Data Table (page 58)

Calculations (page 59) 

Setup 

Balloon filling up from reaction between alka seltzer and water. 

Analysis Question 

1. Discuss an area in this lab where experimental error may have occurred. 

Experimental error may have occurred when we were transferring water from the balloon to the graduated cylinder in order to find its volume; we found that a lot of water splashed everywhere and that the transfer was a difficult process. Error may also have occurred when we began measuring the circumference of the balloon with the string, which was also difficult because the string kept slipping off of the surface of the balloon, and we had to estimate where the circumference of the balloon actually was. Several other errors may have occurred during the measurement process, especially when using the graduated cylinder; we did not measure fro the meniscus, which could skew our results. In addition, while we were filling the balloon with water bwe believe thst we may have overfilled the balloon somewhat, which would have made the calculations larger than they actually were. 

2. Choose one error from above and discuss if it would make "n" the number of moles of CO2    
too big or too small. 

   The loss of water during the transfer from balloon to graduated cylinders would have a great impact on the "n" number of CO2    moles of  too small. Loss of water would cause the recorded volume to be less than what it would have been without the loss, which would mean that the final carbon dioxide molar count would be less than what it would have been. However, it is also to be noted that while we were filling the balloon, we may have filled it past the circumference because we noted that the string fitted much more snugly than it had on the carbon dioxide balloon; this may prove my prediction incorrect. 

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 in cm, calculate the volume of the balloon mathematically. Remember that the circumference of a sphere is 2πr and volume is 4/3πr2. 

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? Remember that 1cm3 =1 mL. 

This answer is somewhat close to the collected value, for while the hundredth value remained the same the data was a whole 64.6 mL off. However, I feel that the calculated value found above is more accurate because while we were filling the balloon with water we could only guess at how tightly the string should fit and where the circumference was actually located; with the mathematical calculations, the chances of error were smaller because there was less chance for error.  In addition, there was no guesswork involved in the calculations of the balloon's volume.

5. The ideal gas law technically applies to ideal gases. Give two differences between a real gas and an ideal gas. You may not use your computer or book to do research. 

In gases, an ideal gas has no mass due to the exceedingly small size of its particles and the gas has no intermolecular forces within. However, a real gas does indeed have mass and does experience intermolecular forces; despite their speed and distance, gas particles still do experience intermolecular bonds. 

6. Would the CO2 you collected in this lab be considered ideal? Why or why not? 

  The carbon dioxide we collected in this lab would not be considered ideal because it did indeed have both mass and volume (eliminating one aspect of the definition of an ideal gas) and there is a major discrepancy between expected values and actual values of the gas, which would indicate that it is not ideal. 

Advanced Questions 

3. CO2 is water soluble. The solubility around room temperature is around 90 mL/100 mL of water. What effects does this have on your calculated "n" value?

This would affect our data by making the calculated volume of carbon dioxide lower than it actually was. If carbon dioxide dissolved in the water beneath the balloon it would not be found in the balloon and therefore unable to be recorded. This means that our calculated "n" value should be more accurate than a measurement taken in the lab because it is not affected by this solubility.