IA on investigating the concentration of active ingredient salicylic acid from aspirin, measured using visible spectrophotometer.

1. Determine the conc of active ingredient salicylic acid from aspirin, measured using visible spectrophotometer.
Aspirin hydrolysis
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:
Standard calibration plot done using SA ranging from (1.56 – 25.0)mg/100
0.025g SA dissolve in 100ml water. (25mg/100). Half fold serial dilution was done.
1ml SA of diff conc added to cuvette.
100ul of Fe3+ added and mix.
Abs was done at 565nm
Mechanism of aspirin hydrolysis to produce SA Aspirin 500mg was turn
into powder

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
Determine the conc of active ingredient salicylic acid from aspirin, measured using visible spectrophotometer.

3. y = 0.0945x + 0.016
R² = 0.9999
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14
Abs
conc/mg/100
conc vs abs
Line best fit Abs = 0.0945 (Conc) + 0.016
Std calibration plot. Conc vs Abs at 565nm
Conc
mg/100ml
Abs
0.781 0.086
1.56 0.168
3.125 0.315
6.25 0.600
12.5 1.199
25.0 1.904
Data collected.
500mg aspirin dissolved in 100ml water/ethanol mix.
Expected conc – 382mg/100ml.
Abs from aspirin found to be 0.938
Determine the conc of active ingredient salicylic acid from aspirin, measured using visible spectrophotometer.
Abs = 0.0945 (Conc) + 0.016
0.938 = 0.0945 (Conc) + 0.016
Conc = 9.75mg/100
% error =
(𝐸𝑥𝑝𝑒𝑐𝑡𝑒𝑑 −𝐸𝑥𝑝𝑡)
𝐸𝑥𝑝𝑒𝑐𝑡𝑒𝑑
x100%
% error =
(382−9.75)
382
x100%=97%
Hydrolysis of aspirin is very slow in water/ethanol mix
1 mol aspirin produces - 1 mol SA
500mg aspirin contain 0.00277mol
0.00277 mol aspirin produces 0.00277 mol SA
RMM SA – 138.
0.00277 mol x 138 = 382mg SA