Calculating the Ideal Gas Constant

(Partner: Caitlin M.)


Observations:

Data:

Length of Mg strip = 2.7 cm
Mass of Mg = 0.19 g
T=Temperature of Water (same as temp of H2 gas) = 23 oC = add 273 to give 296 K
Ptotal=Atmospheric Pressure = 0.99 atm

V=Volume of gas = 36 mL = 0.036 L 

Calculations:

1)

2)

3)

4) 

5)

Post Lab Questions:


1) Why was it important for the stopper to have a hole in it? (What would happen if the stopper did not have a hole in it?)
- That way, we could make sure all of the air was out of the tube by putting the pipette through the hole and adding more water into the tube.


2) Why was it important to make sure that the eudiometer was filled completely with water before you inverted it? If it weren’t completely filled, how would this have affected the volume of H2 gas (too high or too low)? How would your value for R be affected? (Too high or too low?) Explain your reasoning.
- Because if it was not completely filled the volume of the gas in the tube would be a combination of H2 gas and air. It would make the volume of H2 too high and therefore the R too high.


3) How would the calculated number of moles of H2 gas (from calculation #2) be compared to your actual moles of H2 gas produced be affected if some of your magnesium did not react (Too high or too low)? How would your value for R be affected? (Too high or too low)? Explain your reasoning.
- If some of the magnesium didn't react, the moles of H2 gas would be too low because the H2 gas was formed from the chemical reaction of the magnesium and the liquid in the tube. To get the right amount of H2 gas, all of the magnesium would have to react. Since the volume of H2 was too low, the R would be too low as well.


4) When measuring the pressure of H2 gas in the tube. You rightly assumed that there was some water vapor in the tube along with the H2. Thus, you corrected our P value by subtracting out the pressure due to the water vapor. If you had not made this correction, would your pressure value be too high or too low? How would this have affected your R value? (Too high or too low)? Explain your reasoning.
- If we hadn't corrected the value of P, our pressure would have been too high because it would have included the pressure from the water vapor not just of the H2 gas. This also would have made the R value too high.


5) Was your value for R too high or too low? Give 2 reasons that could account for your specific results.
- Our R value was too low most likely because we lost some the contents in the tube as we transfered it over, which would lower the R value.