Question

Part 1: Catalyst solution and units	Value with correct significant figures and units
Volume of absolute methanol	20 mL
Mass of NaOH pellets	0.535 g
Mass of ground NaOH	0.402 g

Part 2: Synthesis of biodiesel	Value with correct significant figures and units
Volume of vegetable oil	10 mL
Volume of catalyst solution	2 mL
Time stirred	20 min.
Time sitting for separation	45 min

Part 3: Analysis of biodiesel	Value with correct significant figures and units
Height of biodiesel in capillary	55 mm
Height of vegetable oil in capillary	25 mm
Mass of glycerol	1.046 g

1. Based on the values you recorded during the lab session for volume of methanol and mass of NaOH, calculate the correct concentration of the resulting solution in units of molarity.

2. If the NaOH solid absorbed water from the atmosphere during this process (as described above), is the concentration you calculated in #1 too high or too low? Explain.

3. Based on the definition of “catalyst” you provided in your prelab, is the exact concentration of the NaOH/methanol solution critical to the stoichiometry of the transesterification reaction? Explain.

4. If you worked slowly in the preparation of the NaOH/methanol solution and the solid NaOH absorbed water from the atmosphere, how would the stoichiometry of the biodiesel synthesis be affected, if at all? Explain.

5. Any absorbed water discussed in question #4 would be present in the reaction mixture. Using your knowledge of intermolecular forces, in which product layer would the water most likely be found (biodiesel or glycerol)? Explain.

6. Based on your observations, compare the intermolecular forces of the food dye with the vegetable oil. Were they similar or different? How do you know?

7. Why was it unnecessary to clean the graduated cylinder between measuring the vegetable oil and then the NaOH/methanol solution in steps 7-8 of Part 2 in the procedure? Explain.

8. Referring to the respective intermolecular forces of the molecules, explain why glycerol forms a homogeneous mixture with water, but not biodiesel.

9. Using the final measured weight of glycerol, calculate the actual yield and percent yield for glycerol based on the theoretical yield you calculated as part of the pre-lab questions.

10. Identify a minimum of THREE potential sources of error for this experimental procedure and comment on how they could help explain (or not) you’re the percent yield of glycerol you calculated in question #8. Your comments should be thoughtful and you should explain how the error would impact your results.

Answer 1

The method described here is synthesis of biodiesel. The reaction is called transesterification, and in the first step methanol is mixed with the catalyst, i.e. a strong base NaOH. In the second step methanol/NaOH is then reacted with the vegetable oil (fatty acid) for the transesterification reaction.

1. Given Parameters:

MeOH volume= 20 mL;

NaOH weight = 0.402g

Molarity of the solution (NaOH) = (weight of NaOH/Molar mass of NaOH)*(1000/Volume of MeOH)= (0.402/40)*(1000/20)

= 0.502 mmol

2. If the NaOH solid absorbed water from the atmosphere during this process, the concentration changes are mild but the water can react with the fatty ester and form acids.

3.From stoichiometry view point, the esterification is needed 3:1 molar ratio of methanol to vegetable oil. 3 moles of alcohol is needed to form 3 moles of alkyl ester. But, due to high volatile nature of methanol excess methanol is needed to shift the reaction/equillibrium towards right and rise the product of bio diesel

4. The water absorbed by NaOH can react with triglyceride and forms free fatty acids and a diglyceride. It dissociates NaOH into Na+ and OH^-, where Na+ react with the free fatty acid to form soap. The sodium bound with the fatty acid and unusable and complicates separation and recovery.