A Level Sciences Exam Questions by Topic

A triglyceride forms from one glycerol molecule (relative molecular mass, Mr = 92) and three identical fatty acid molecules (Mr = 284 each). Calculate the Mr of the triglyceride formed, and state the total mass lost as water during the reaction.

1. Add the Mr of the starting molecules: 92 + (3 x 284) = 92 + 852 = 944.
2. Three ester bonds form (one between glycerol and each fatty acid), each by a condensation reaction that releases one water molecule, so 3 water molecules are lost in total.
3. Calculate the mass lost as water: 3 x 18 = 54.
4. Subtract the mass of water lost from the total starting mass: 944 - 54 = 890.
5. Final answer: the triglyceride has an Mr of 890; a total mass of 54 is lost as three water molecules.