Determination of reaction rate constant second order
BP407P Physical Pharmaceutics II Practical
To determine the reaction rate constant and half-life period of ethyl acetate in 0.025N sodium hydroxide solution at room temperature.
The alkaline hydrolysis of an ester (ethyl acetate) is irreversible and follows the second-order kinetics.
CH3COOC2H5 + NaOH CH3COONa + C2H5OH
Ethyl acetate sodium Sodium acetate ethyl alcohol hydroxide
The molecularity of the reaction is two and the order is also two. The second-order reaction is defined as the reaction in which the rate of reaction depends upon the concentration of two reactants with each term raised to the first power.
Apparatus and chemicals:
• Conical flask (250 ml)
• Water bath
• Burette (50 ml)
• Ethyl acetate solution (0.05N)
• Hydrochloric acid solution
• Ice cold water
• Phenolphthalein indicator
Preparation of ethyl acetate solution (0.05N)
The molecularity weight of ethyl acetate is 88.10 density is 0.90g/ml. percentage purity is 99%. Measure 50 ml of Ethyl acetate and transfer into 1000ml volumetric flask dilute to 1000ml with distilled water.
Preparation of hydrochloric acid solution (0.02N)
Solutions of any normality XN may be prepared by diluting 85 xml of hydrochloric acid to 1000ml with water. Measure 850 ml of distilled water into 1000ml volumetric flask. Add 1.7ml of concentrated hydrochloric acid slowly and shake. Finally make up the volume to the mark.
Preparation of sodium hydroxide solution (0.05N)
Weigh 2.0gm of sodium hydroxide in water and transfer into 1000ml volumetric flask. Add water slowly with continuous stirring, while cooling the flask under running tap water. Add sufficient water to make 1000ml. allow it to stand overnight and pour off the clear liquid into a bottle. This clear solution is used.
- Measure 50ml of 0.05N sodium hydroxide solution and transfer into a conical flask. Keep it in a water bath for equilibrium at room temperature.
- Measure 50ml of 0.05N of the given ester and transfer into a conical flask. Keep it in above water bath for equilibrium. Normally it takes about 10 minutes.
- Mix the alkali and ester solution thoroughly and keep in same water bath.
- Immediately after mixing, withdrawn a 10ml sample of the mixture with pipette and transfer into a conical flask containing 10ml ice cold water
- Add few drops of Phenolphthalein indicator
- Titrate against 0.02N hydrochloric acid. This titter value times t=0 corresponds to the original concentration “a” report the results
- Periodically withdrawn samples at 5, 10, 15, 20, 25, 30 minutes time periods. Repeat the steps 4 to 6. These titter values denote the amount of sodium hydroxide or ethyl acetate remain unreacted ie, (a-x) at time. Record the results
- Substitute the values in integral equation and calculate the reaction rate constant (K2). These values will more or less constant
- Calculate the average of the reaction rate constant (K2)
- Draw a plot by taking x/a (a-x) on y-axis and time on x-axis
- Estimate the slope. This slope same as K2 value.
The reaction rate constant (K2) of the given ester (methyl acetate or ethyl acetate) in 0.025N NAOH at room temperature
From graphical method= minutes From substitution method= minutes
The half -life (t1/2) of the given ester (methyl acetate or ethyl acetate) in 0.025N NAOH at room temperature
From graphical method= From substitution method=
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