The document describes a study on the hydrolysis of aspirin into salicylic acid (SA) and acetic acid, utilizing a standard calibration plot to measure SA concentration using a colorimeter. The experiment was conducted over 5 days, where aspirin's hydrolysis was monitored, with results suggesting a maximum concentration of about 21 mg/100 ml of SA by day 5. A clear linear relationship was established between absorbance and concentration, indicated by an R² value of 0.9999.

1. Aspirin hydrolysis (Standard calibration plot)
Aspirin undergo hydrolysis to produce salicylic acid (SA) and acetic acid.
SA, active ingredient will react with Fe3+ to form violet product.
Standard calibration plot was done using SA.
Conc range from (1.56, 3.125, 6.25, 12.5, 25.0) in mg/100
1% FeCI3 solution was prepared.
Violet colorization monitored with colorimeter.
Fe3+ reacts with SA to produce
violet substance which can be measure with colorimeter
Procedure:
500mg aspirin dissolve in 100ml water.
1ml aspirin sol added to cuvette. (Duration Day 1)
300ul of Fe3+ added and were mix together.
Abs was done at 565nm.
Process repeat over 7 days, to investigate the extend of
aspirin hydrolysis in water.
Mechanism of aspirin hydrolysis to produce SA Aspirin 500mg was turn
into powder
Hydrolysis of aspirin in water, duration over 5 days, measured using visible spectrophotometer.

2. Go to expt – press calibrate Insert cuvette (violet sol), press collect
Insert a blank containing water
Press stop, and click on rainbow icon. Select abs vs conc. λ max at 565nm will
be automatically chosen
Type in concentration and press keep
Type in concentration and press keep
for 5 diff conc
Standard calibration plot is generated
Hydrolysis of aspirin in water, duration over 5 days, measured using visible spectrophotometer.

3. Hydrolysis of aspirin is water over 5 days
y = 0.0945x + 0.016
R² = 0.9999
0
0.5
1
1.5
0 2 4 6 8 10 12 14
Abs
Conc SA/mg/100
Conc SA vs abs
Line best fit Abs = 0.0945 (Conc) + 0.016
1mol aspirin produces - 1mol SA
500mg aspirin contain 0.00277mol
0.00277mol aspirin produces 0.00277mol SA
RMM SA – 138.
0.00277mol x 138 = 382mg SA
Duration Abs Conc
SA/mg/100ml
Day 1 0.702 7.25
Day 2 1.76 18.45
Day 3 2.02 21.20
Day 4 2.04 21.41
Day 5 2.08 21.84
Abs = 0.0945 (Conc) + 0.016
0.702 = 0.0945 (Conc) + 0.016
Conc = 7.25mg/100
Hydrolysis of aspirin seems to reach max after 5 days.
Conc SA is around 21mg/100ml
Hydrolysis of aspirin in water, duration over 5 days, measured using visible spectrophotometer.
0
5
10
15
20
25
0 1 2 3 4 5 6
Conc
SA/mg/100ml
Duration/days
duration vs conc SA