The Determination of Rate Constant “K” for second order of the reaction

Determination of Rate Constant “K” for Hydrolysis of Ester(CH3COOCH3) in the presence of Strong Base(NaOH)


Glassware:

Required Glasswares:
⦁ 2 Measuring Flask(100 ml)
⦁ A Conical Flask
⦁ A Burette
⦁ 2 Beakers(100&250 ml)
⦁ A Pipette
⦁ A Measuring cylinder
⦁ A Funnel

Apparatus:

Required apparatus:
⦁ A Thermostat
⦁ An Electrical Balance
⦁ Iron Stand
⦁ Clamp
⦁ Ice-vibes

Chemicals Required:

The chemicals required are:
⦁ An Ester solution(10 ml)
⦁ A Sodium Hydroxide Solution(1M in 100 ml)
⦁ A Hydro Chloric Acid Solution(1M in 100 ml)

Indicator:

An indicator is a substance that shows the completion of reaction by changing its color.
(Some Miss Please Download Word File)
Theory:
The study of rates and mechanism of chemical reactions is called Chemical Kinetics. (Miss Line)
⦁ Instantaneous Reaction
⦁ Moderate Reaction
⦁ Slow Reaction

Instantaneous Reaction:

The reactions which are completed at once (in no time) are called Instantaneous Reactions.
For Example:
⦁ Reaction between AgNO3 and NaCl, white precipitate of AgCl are formed
De-coloration of acidified KMnO4 solution with FeSO4 Solution

Moderate Reaction:

The reactions which proceed at moderate speed and accurate measurements of their rates are possible are known as Moderate Reactions.

For example:

Hydrolysis of ester is a moderate reaction.

Slow Reaction:

The reaction that proceeds at extremely slow rate is known as Slow Reaction.

For example:

Rusting of Iron
⦁ Fixation of atmospheric Nitrogen

Rate Constant:

The rate constant can be defined as
( Miss Line Please Download Word File)
The value of K varies from reaction to reaction and also with temperature of a given reaction.

Order of Reaction:

(Miss Line Please Donload Word File ) It cannot be calculated from balance chemical equation but is determined through experiments.
It can be:
⦁ Zero order of reaction
⦁ First order of reaction
⦁ Second order of reaction
⦁ Third order of reaction
⦁ Pseudo-order of reaction
⦁ Mixed order of reaction
Here our concern if second order of reaction
Second Order of Reaction:
If the rate of reaction is directly proportional to the product of the concentration of the two species of the reactants whose concentration is changed during the reaction is known as Second Order of Reaction.

For example:

Hydrolysis of ester in the presence of a base
CH3COOCH3+NaOH→CH3COONa+CH3OH

Units:

For second order of the reaction units are dm3/mol s

Hydrolysis of Ester:

The breakdown of an ester in the presence of water is known as hydrolysis of ester. It can be carried out in both acidic and basic medium.
A known volume of standard NaOH solution is added to the known volume of the ethyl acetate respectively. Let “a” and “b” are the initial concentrations respectively. The formula determining the rate constant K for hydrolysis of ester in the presence of a base:

           K=2.303/t log V∞-Vo/V∞-Vt

Where
Vο is volume of standard acid required for neutralization at start of the reaction
Vt is the volume of acid required for neutralization at time “t”
V∞ is the volume required for neutralization after completion of reaction

Procedure:

⦁ The glassware was washed properly and dried completely
⦁ 1 molar solution of HCl was prepared by taking 10 ml HCl in measuring flask and diluted it up to the mark
⦁ 1 molar NaOH solution was prepared by taking 4g of NaOH on watch glass and poured into the measuring flask and diluted up to the mark
⦁ Reaction mixture was prepared by mixing 100 ml NaOH and 10 ml of ester
⦁ When time is zero second ( suddenly after mixing) then 5ml of the reaction mixture was taken in conical flask and ice-vibes were added to stop the reaction
⦁ 2-3 drops of phenolphthalein indicator were added in conical flask
⦁ Sample solution was titrated with standard solution of HCl (filled in burette with the help of funnel) till pink solution becomes colorless , which is the end point
⦁ The volume of HCl used for neutralization was noted which’s Vo
⦁ Similarly reaction mixture was taken in conical flask after intervals and titrated against the standard HCl solution to find Vt
⦁ 25-30 ml from reaction mixture was taken in a beaker and was heated at 60-70 Co for 35 minutes in thermostat
⦁ 5 ml of this reaction mixture was taken in conical flask and titrated against standard solution in burette to find volume V∞.
⦁ Put the values in the given formula
K=2.303/t log V∞-Vo/V∞-Vt


Observations and calculations:

Preparation of 1M NaOH solution in 100ml

Amount of NaOH in 1M solution in 1000ml=40g
Amount of NaOH in 1M solution in 1ml=40/1000 g
Amount of NaOH in 1M solution in 100ml=40×100/1000g
=4g

So, 4g of NaOH was weighed on an electrical balance and dissolved in distilled water taken in measuring flask. The flask was filled up to the mark.

Preparation of 1M HCl in 100 ml

%age purity=31.5%
Density =1.16 g/cm3
Molarity= %age purity × density/molecular mass×10
= 31.5×1.16/36.5×10
= 10.01M
So stock molarity is 10.01
Stock = Required
M1V1=M2V2
V1 = 1× 100/10.01
V1=9.99 ml
V1=10ml

10 ml of HCl was taken with the help of measuring cylinder and poured into the flask and diluted up to the mark.

Sr.no Time Vo V∞ Vt K
( s) (ml) (ml) (ml)

(dm3mol-1s-1)
1 0 0.1 3.7 0.1 0
2 600 0.1 3.7 2 0.00123
3 1200 0.1 3.7 2.7 0.00114
4 1800 0.1 3.7 2.8 0.00076
5 2400 0.1 3.7 2.9 0.00057
6 3000 0.1 3.7 3.7 0

Graph:Determination of Rate Constant

The Determination of Rate Constant “K” for second order of the reaction

Result:

From graph it is cleared that hydrolysis of ester shows second order of reaction in basic conditions.

Precautions:

⦁ Glass ware should be washed carefully and dried properly to avoid impurities
⦁ Lab-coat and gloves should be necessary
⦁ Don’t use broken glassware because it can damage and can affect readings
⦁ HCl and NaOH solution should be handled carefully because both in concentrated form are corrosive.

Determination of Rate Constant “K” for Hydrolysis of Ester(CH3COOCH3) in the presence of Strong Base(NaOH)

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