CHM 1311 Lecture Notes - Lecture 1: Eudiometer, Vapor Pressure, Graduated Cylinder
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Hello I need help with the calculations for my data on my Gas Laws Lab report.
| My data | Trial 1 | Trial 2 | Trial 3 | Trial 4 |
| Mass Mg (g) | .034 | .044 | .043 | |
| Volume H2 (mL) | 35.5 | 43.5 | 42.5 | |
| Temperature (°C) | 20 | 20 | 20 | |
| Atmospheric pressure (mmHg) | 29.8 | 29.8 | 29.8 | |
| Height difference (mmH2O) | 20 cm | 12.5 cm | 15cm |
Calculations:
Moles Mg used
Theoretical moles
H2 produced
Vapor pressure of water (mmHg)
Pressure from height diff (mm Hg)
Pressure of H2 (mm Hg)
Pressure of H2 (atm)
Actual moles H2 produced
Percent yield of H2
Experimental R value (L·atm/mol·K)
I think once I see how to do the calculations for trial 1 I can do the rest for the other 2 trials.
Below is the procedure for the lab and the calculations if needed.
PROCEDURE: Obtain a 50 ml gas buret, a â00â rubber stopper and a 600 ml beaker. Your instructor will demonstrate the set-up of the equipment. Place approximately 450 ml of distilled water in your 600 ml beaker. Obtain a 2 inch piece of magnesium metal. Record the mass of the magnesium metal. The mass should not exceed 0.050 g. Wrap the magnesium metal with string so that it will hang down in the gas buret. Place the gas buret in a buret holder on a ring stand. Add 8-10 ml of 6 M HCl to the gas buret. Using your wash bottle carefully add distilled water down the side of the buret, being careful not to disturb the hydrochloric acid you just placed in the buret. If done properly, the distilled water will remain âon top ofâ the hydrochloric acid and not mix with it. Continue adding water until the buret is completely filled. Carefully place the magnesium metal so that it hangs several cm down into the gas buret (holding onto the string). Gently insert the stopper into the buret so that the stopper holds the string in place. Check to be sure that an air bubble has not formed at the stopper. If an air bubble is present, remove the stopper, add more distilled water and re-insert the stopper. Using your distilled water bottle, fill the holes of the stopper with distilled water. Place your finger over the stopper holes and invert the gas buret into the beaker so that the top of the buret is below the water level in the beaker. Clamp the buret in place and allow the reaction to proceed. The more dense hydrochloric acid solution will diffuse downward and react with the magnesium metal to produce hydrogen gas. What do you observe suggesting that a reaction is occurring? Your instructor will write the atmospheric pressure on the board for the day. When the reaction is completed, record the distance between the water in the beaker and the solution in the buret (see figure 1, Pht diff). Without moving the buret, read the volume to the nearest ± 0.02 ml on the buret. This is the volume of the hydrogen gas. Take the temperature of the solution in the beaker. The temperature of the solution is equal to the temperature of the gas. Stir the solution in the beaker. Wait one minute and record the temperature again. If the temperature is not the same, repeat the process until it remains unchanged. Record the temperature to the nearest ± 0.1 °C. Rinse out your glassware and the buret and repeat the analysis two more times, recording the exact mass of magnesium for each trial. If the data appears suspect for any reason, a fourth trial must be done. Enter your raw data into the lab computer before you leave.
CALCULATIONS: We will look at the data in two different ways: 1. Use the ideal gas law to calculate the actual yield of hydrogen gas and compare it to the theoretical yield based on the moles of magnesium used. 2. Alternatively, using the reasonable assumption for this particular reaction that the yield of hydrogen gas is essentially 100%, the value of R can be determined experimentally from the ideal gas law. You cannot use the theoretical value of R to solve for the experimental R value. The stoichiometrically calculated value for moles of H2 must be used in this instance.
