The document describes an experiment to study the effect of temperature on the rate of aspirin hydrolysis. Aspirin solutions in 0.1N HCl were maintained at different temperatures from 40-80°C. The hydrolysis of aspirin was measured by removing aliquots over time and measuring the concentration of salicylic acid product using UV-Vis spectroscopy. Rate constants were determined from first-order plots at each temperature. Plotting the log of the rate constants against the inverse of temperature allowed determination of the activation energy based on the Arrhenius equation.

1. Kinetics
Effect of Temperature on the rate of
Aspirin Hydrolysis

2. COOH
OCOCH3
Aspirin
0.1N HCl

COOH
OH
+ CH3COOH
Salicylic acid
FeCl3
violet color
measured at 530 nm.

3. • The speed of many reactions increases about
2 or 3 times with each 10°c rise in
temperature.
• The effect of temperature on reaction rate is
given by Arrhenius equation:
K = A e –Ea RT
Or log K = log A – Ea 1
2.303 RT

4. log K = log A – Ea 1
2.303 RT
In which:
K : The specific reaction rate.
A : Constant called frequency factor.
Ea : activation energy.
R : Gas constant (1.987 calories /degree. mole).
T : absolute temperature.

5. Effect of Temperature
• Log K can be obtained from first order curve.
Slope = - K ∕ 2.303
t
Intercept = log Co
logC
log C = log C0 – Kt / 2.303

6. Effect of Temperature
• Determination of (K) at several temperatures.
Slope = - Ea / 2.303 R
1/ T
Intercept = log A
Log K
Slope = -Ea/2.303R
Intercept = Log A

7. 1- take 1 mL of aspirin soln.
in methanol.

in w.b. at 50 C
3-
°
4-after 10 min. take 5 mL of
soln , cool
5- add 0.5 mLFeCl3, then
complete to 10 mL with water
6- measure the absorbance at 530 nm
and calculate the Conc.
7- repeat steps 4 ,5, and 6 after 20 ,30
,40 ,50 and 60 min.
2- 9ml 0.1NHCl

8. Effect of Temperature
Procedures
1. One ml of aspirin solution in methanol is
transferred to each of six dry test tubes.
2. To each tube, 9 ml of 0.1N HCl solution is added
and maintained in a water bath at
40,50,60,70,80°C
3. At 10, 20, 30, 40, 50, 60 min time intervals, 5 ml is
withdrawn and cooled.
4. (0.5ml) of freshly prepared ferric chloride were
added and complete to 10 ml with distilled water.
5. The violet color obtained is measured at 530 nm.

9. Effect of Temperature
Procedures
6.Calculate the concentration of salicylic acid
equivalent to aspirin hydrolysis using Beer's and
Lambert's law:
Cu = Cs x Au x 2
As
Cs = 3.623 x 10-4 mole / liter.
As = 0.510
7.Determine the rate constant of the reaction (K).
8.Collect K values at different temperatures from
groups of the students.
9.Plot log K against 1/ T.
10.Calculate Log A from the intercept.

10. Log C
Remaining
conc. (A)
Cu
Abs.
Time (min.)
10
20
30
40
50
60
Cu = x (decomposed conc.)
a = 5.525 x 10-2 mole/ liter.
Draw Log C against Time (t)

11. Log K (+,-)
Log K
K
1/ T
T °k
Temp. °C
40
50
60
70
80
Draw Log K against 1/ T
T = t + 273