Final answer:
Potassium carbonate is added in biodiesel synthesis to shift the equilibrium towards the product side, favor the forward reaction, and neutralize free acids in the vegetable oil, thereby increasing the biodiesel yield and improving reaction efficiency.
Step-by-step explanation:
In the synthesis of biodiesel, a small amount of potassium carbonate is added to the reaction mixture. This compound acts as a catalyst that favorably shifts the equilibrium toward the product side. In other words, the presence of potassium carbonate ensures that the forward reaction is favored, facilitating the conversion of reactants into biodiesel. By doing so, potassium carbonate helps to shift the equilibrium to the right, increasing the yield of the biodiesel product.
During the reaction, the potassium carbonate may also neutralize any free fatty acids present in the vegetable oil, which would otherwise consume the catalyst (usually a strong base such as lye) and decrease the efficiency of the biodiesel conversion process. As an added benefit, the use of potassium carbonate can help reduce the amount of lye required for the reaction, by neutralizing these acids beforehand, as indicated by the titration experiment described to determine free acid content. Therefore, by optimizing the reaction conditions, potassium carbonate makes the process more efficient and cost-effective.