Questions on Solar energy

1. A triglyceride can be prepared from the esterification reaction between propane-1,2,3-triol (glycerol) and palmitic acid.
The structure of palmitic acid is given in Section 34 of the data booklet.

(a) State the equation for the formation of this triglyceride.

(b) Explain why vegetable oils, such as the triglyceride above, cannot be used as diesel fuel.

(c) Vegetable oils can be converted into biodiesel by transesterification.
Deduce the equation for the transesterification of the triglyceride above with excess methanol in the presence of sodium hydroxide.

(d) Explain the function of the sodium hydroxide.

(e) Suggest why excess methanol is used in the transesterification reaction.

2. Ethanol can be prepared by fermenting a solution of glucose, C₆H₁₂O₆ with yeast.

(a) State the equation for this reaction.

(b) Explain why this method of producing ethanol will only give a solution of ethanol with a concentration of about 15% and describe how pure ethanol can be obtained from this solution.

3. (a) Compare the specific energy (in kJ kg^-1) of octane with the specific energy of ethanol.
(The relevant enthalpies of combustion and atomic masses can be found in the data booklet)

(b) Suggest two advantages that ethanol has over gasoline (petrol) as a fuel for cars.

4. The structure of chlorophyll is given in Section 35 of the data booklet.

(a) Identify the structural feature of the chlorophyll molecule that explains why it is able to absorb visible light.

(b) The UV-Vis absorption spectrum of chlorophyll is shown below.

Explain why leaves of plants are green.

Download the Solar energy questions to give to your students.

To see the worked answers go to Solar energy answers.