Aspirin (acetylsalicylic acid, MW: 180g/mol) is a relatively stable compound. However, exposure of aspirin to heat or moisture hastens its decomposition to acetic acid and salicylic acid, as depicted below:
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Reaction 1
.A student investigates the decomposition rate of aspirin at different temperatures. The amount of decomposition can be measured by adding iron(III), which binds in a bright violet complex with salicylic acid.

In the first trial, the student weighs 90 mg of aspirin and dissolves it in water to make a 10 mL solution. After 5 minutes of incubation at 90 °C, the reaction was stopped upon insertion in an ice bath with Fe(NO₃)₃. It was later found that 0.05 mmol of salicylic acid was produced.

In a second trial, the student repeats the experiment, but with 60 mg of aspirin and finds that 0.033 mmol of salicylic acid is produced.
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