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

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 $\boldsymbol{{\text{O}}_{2}}$ you used.

For instance, I had to estimate how many $\text{PSI}$ I used and simply wrote, "a bit less than $\text{450 PSI}$" 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)