Polylactic acid (PLA) is a biodegradable polyester derived from renewable resources. It is synthesised via the condensation polymerisation of lactic acid (CH3CH(OH)COOH\text{CH}_3\text{CH}(\text{OH})\text{COOH}CH3CH(OH)COOH), during which water is eliminated.
A chemical plant processes 1.00 tonne1.00\text{ tonne}1.00 tonne of lactic acid to produce PLA. Assuming 100% conversion and that PLA is a very high-molecular-weight polymer (allowing the loss of polymer end groups to be neglected), what is the theoretical mass of water produced as a byproduct, and what is the atom economy for the production of the PLA polymer?
(Relative formula masses: Lactic acid = 90.0, Water = 18.0, PLA repeating unit = 72.0)
0.20 tonnes0.20\text{ tonnes}0.20 tonnes of water, Atom economy = 80.0%80.0\%80.0%
0.20 tonnes0.20\text{ tonnes}0.20 tonnes of water, Atom economy = 20.0%20.0\%20.0%
0.25 tonnes0.25\text{ tonnes}0.25 tonnes of water, Atom economy = 75.0%75.0\%75.0%
0.80 tonnes0.80\text{ tonnes}0.80 tonnes of water, Atom economy = 80.0%80.0\%80.0%
83 exam-style questions on OCR GCSE Chemistry Organic chemistry. Each one has a worked solution and a mark scheme showing where the marks go.