Lab 8-Density Measurement of Chemicals and Fuels

This video is the eighth in a series of eight chemistry labs on the fundamentals of biodiesel, specifically focusing on "Laboratory 8: Density Measurement of Chemicals and Fuels." Written procedures and background information are available on the biodiesel education website.

Density is defined as the mass of an object divided by its volume, quantifying how heavy or light a substance is for a given volume. For example, 1 liter of vegetable oil weighing 930 grams has a density of 930 g/L. Density can change with temperature; heating a substance increases molecular vibration, causing molecules to spread out, thus increasing volume and decreasing density for the same mass.

When two substances mix, several scenarios can occur. If substance B fits into the intermolecular voids of substance A, the mixture's density increases (e.g., salt dissolving in water). If voids are not large enough, the mixture's volume is the sum of individual volumes (e.g., atmospheric gases). Lastly, chemical reactions between substances can alter density depending on the structure of the new molecules formed.

The density of gases can be calculated mathematically from their molecular formula, as one mole of gas occupies 22.4 liters at standard temperature and pressure. However, liquid and solid densities are more complex. For the lab, calculations are made for the methanol needed and biodiesel/glycerol produced from 100 mL of soybean oil, using the transesterification reaction and known densities.

Ensure soybean oil, biodiesel, and petroleum diesel are at room temperature. Measure 100 grams of vegetable oil into a cylinder. Then, measure the calculated mass of biodiesel and 50 grams of petroleum diesel into separate cylinders. Observe and record the volumes. Finally, gradually add biodiesel to petroleum diesel until the mixture weighs 100 grams and measure its volume. Calculate the densities of soybean oil, biodiesel, and petroleum diesel.