Final answer:
The viscosity of biodiesel tends to be higher than petrodiesel due to stronger intermolecular forces from its long fatty acid chains and functional groups. Temperature affects viscosity, with higher temperatures leading to lower viscosities. Viscosity measurements involve observing the flow of liquid or the fall of steel balls through the liquid.
Step-by-step explanation:
The viscosity difference between biodiesel and petrodiesel is primarily due to their molecular structure and intermolecular forces. Biodiesel, which can be made from soybeans, palm oil, or used vegetable oils, contains esters of long-chain fatty acids. These long molecules can interact with each other via Van der Waals forces, making them flow less readily, hence a higher viscosity compared to petrodiesel, which consists mostly of smaller hydrocarbon molecules with weaker intermolecular forces. Additionally, the presence of oxygen-containing functional groups in biodiesel molecules leads to stronger intermolecular interactions compared to the largely hydrocarbon makeup of petrodiesel.
As temperatures increase, viscosity decreases due to the increase in kinetic energy, which allows molecules to overcome attractive forces more easily. This is why motor oils and lubricants, such as those used in automobile engines, are carefully formulated to maintain an effective viscosity under a range of temperatures using additives that control intermolecular interactions. Viscosity measurements can be performed by observing the rate at which steel balls fall through the liquid, or the time it takes for the liquid to flow through a narrow tube; the higher the viscosity, the slower the movement.