Does any one know what the random errors are in enthalpy of combustion of alcohols experiment? like methanol, ethanol, etc.

1 Answer
May 28, 2017

Some common errors or issues I had when doing my combustion of soybean oil lab:

  • The combustion was not quite complete, i.e. didn't wait long enough (formed soot on the reaction pan).

Thus, the actual yield might be a bit lower than expected.

  • No water was put inside the bomb calorimeter to saturate its atmosphere, so the force from the combustion may not have condensed all the water vapor back into a liquid (since the calorimeter was sealed, at a constant volume).

To account for this, I found the vapor pressure of water at my lab's temperature and pressure, and used water to measure the bomb's volume. The temperature I used was the temperature of the room.

Then, I used the ideal gas law to calculate the mols of water that was still gaseous, subtracting those mols from the total mols of water (liquid + vapor) formed.

  • The measurement of what pressure #bb("O"_2)# you used.

For instance, I had to estimate how many #"PSI"# I used and simply wrote, "a bit less than #"450 PSI"#" in my report.

  • Technical error, such as the calorimeter failing to run (usually not an issue you need to report, since it doesn't affect the results you'd have when you redo it)