INTRODUCTION:
The rate of a chemical reaction is mainly a function of the rate constant and the concentration of the reacting constituents of these the reaction rate constant is highly sensitive to temperature the values of k increase in hundreds of times over ordinary ranges of temperature. The study of effect of temperature on k (an thus on the reaction rates) is hence of very wide theoretical and practical interest.
The influence f temperature on the rate constant is generally expressed in terms of an empirical equation known as arrhenious equation.
K = A e-E/RT
Where A is frequency factor and E is called energy of activation.
Aim:
The aim of the experiment is to establish the nature of temperature dependency of the reaction rate constant for the saponification of ethylacetate with sodium hydroxide in dilute aqueous solutions.
Materials required:
Ethyl acetate (freshly prepared)0.1 N 100ml
Sodium hydroxide (aqueous) 0.05 N 250ml
Sodium hydroxide (aqueous) 0.1 N 50ml
Hydrochloric acid (aqueous Standard oxalic acid phenolphthalein indicator 100ml stoppered conical flasks)
Procedure:
1. Adjust the setting of thermostat so as to obtain a constant temperature of 200 / 250 / 30 0/ 350C ( + or 0.50C).
2. Take 25 ml of the 0.1 N NaOH solution in stoppered flask (1) and mount it in the thermostat.
3. Similarly take 25 ml of 0.1 N Ethyl acetate solution in another flask (2) and mount it in the thermostat.
4. Allow about 25 minutes for thermal equilibrium to attain.
5. Standardise the given NaOH solutions with oxalic acid (given) standardise the HCl solution using NaOH.
6. Keep a clean 20 ml pipette and a stop clock handy.
7. Pipette 20 ml of 0.1 N HCl into each of two 100 ml titration flasks.
8. Carefully add the contents of conical flask (1) to contents of conical flask (2) and immediately transfer the contents of (2) into (1) place the conical flask (1) in the thermostat.
9. At t = 1.5 min. and t = 3 min pipette 20 ml of the reaction mixture and transfer that into conical flasks containing HCl
Important:
After the first addition gently stir the contents of the flask for a few seconds before transferring them back to flask.
(i) Also gently stir contents of flask (1) finally before placing it back in the thermostat
(ii) As soon as the first addition is over start the stop clock.
(iii) Try to accomplish these operations as quickly as possible without causing any spillage.
10. Back titrate the contents of the two-titration flasks with
0.05 N NaOH
11. Repeat the experiment at two other temperatures with an
interval of not less than 5C.
Readings and calculations:
1. (a) Standardization of 0.1 N NaOH
volume of oxalic acid taken =………………………………ml
titrate value =………………………………ml
normality of NaOH =………………………………ml
(b) Standardization of 0.05 NaOH
volume of oxalic acid taken =…………………………………ml
titrate value =…………………………………ml
normality of NaOH N3 = ………………………………N
(c) Standardization of 0.1 N HCl
volume of Hcl taken (V1) = ……………………………………ml
titrate value =………………………………………ml
normality of HCl N1 =………………………………………N
volume of sample = V2 ml
2.EVALUATIONS OF CA:
________________________________________________________________
Vol. of NaOH
Used for back
titration CA(g mole/Lit) 1/CA
-----------------------------------------------------------------
V3 (V1N1 – V3N3)/V2
Temperature T1= 0K
Time, t1 = 1.5 min -------------- ----------- -----
Time, t2 = 3.0 min -------------- ----------- -----
Temperature T2 = 0K
Time, t1 = 1.5 min -------------- ---------- ----
Time, t2 = 3.0 min -------------- ---------- ---
Temperature T3= 0K
time, t1 = 1.5 min --------------- --------- ----
time, t2 = 3.0 min --------------- --------- ---- ________________________________________________________________
3. Evaluation of KC:
Plot 1/CA Vs time (inclusive of initial readings) at each of the temperatures. Obtain the slopes of the three straight-line plots.
T0K KC liters/(gm. mole) (min.)
---------- ----------
----------- -----------
4. Plot ln kC Vs 1/T. Obtain the values of the frequency factor
and energy of activation from the straight line plot.
A = ---------------litters/(gm mole)(min)
E = ----------------cal/gm. mole.
The rate of a chemical reaction is mainly a function of the rate constant and the concentration of the reacting constituents of these the reaction rate constant is highly sensitive to temperature the values of k increase in hundreds of times over ordinary ranges of temperature. The study of effect of temperature on k (an thus on the reaction rates) is hence of very wide theoretical and practical interest.
The influence f temperature on the rate constant is generally expressed in terms of an empirical equation known as arrhenious equation.
K = A e-E/RT
Where A is frequency factor and E is called energy of activation.
Aim:
The aim of the experiment is to establish the nature of temperature dependency of the reaction rate constant for the saponification of ethylacetate with sodium hydroxide in dilute aqueous solutions.
Materials required:
Ethyl acetate (freshly prepared)0.1 N 100ml
Sodium hydroxide (aqueous) 0.05 N 250ml
Sodium hydroxide (aqueous) 0.1 N 50ml
Hydrochloric acid (aqueous Standard oxalic acid phenolphthalein indicator 100ml stoppered conical flasks)
Procedure:
1. Adjust the setting of thermostat so as to obtain a constant temperature of 200 / 250 / 30 0/ 350C ( + or 0.50C).
2. Take 25 ml of the 0.1 N NaOH solution in stoppered flask (1) and mount it in the thermostat.
3. Similarly take 25 ml of 0.1 N Ethyl acetate solution in another flask (2) and mount it in the thermostat.
4. Allow about 25 minutes for thermal equilibrium to attain.
5. Standardise the given NaOH solutions with oxalic acid (given) standardise the HCl solution using NaOH.
6. Keep a clean 20 ml pipette and a stop clock handy.
7. Pipette 20 ml of 0.1 N HCl into each of two 100 ml titration flasks.
8. Carefully add the contents of conical flask (1) to contents of conical flask (2) and immediately transfer the contents of (2) into (1) place the conical flask (1) in the thermostat.
9. At t = 1.5 min. and t = 3 min pipette 20 ml of the reaction mixture and transfer that into conical flasks containing HCl
Important:
After the first addition gently stir the contents of the flask for a few seconds before transferring them back to flask.
(i) Also gently stir contents of flask (1) finally before placing it back in the thermostat
(ii) As soon as the first addition is over start the stop clock.
(iii) Try to accomplish these operations as quickly as possible without causing any spillage.
10. Back titrate the contents of the two-titration flasks with
0.05 N NaOH
11. Repeat the experiment at two other temperatures with an
interval of not less than 5C.
Readings and calculations:
1. (a) Standardization of 0.1 N NaOH
volume of oxalic acid taken =………………………………ml
titrate value =………………………………ml
normality of NaOH =………………………………ml
(b) Standardization of 0.05 NaOH
volume of oxalic acid taken =…………………………………ml
titrate value =…………………………………ml
normality of NaOH N3 = ………………………………N
(c) Standardization of 0.1 N HCl
volume of Hcl taken (V1) = ……………………………………ml
titrate value =………………………………………ml
normality of HCl N1 =………………………………………N
volume of sample = V2 ml
2.EVALUATIONS OF CA:
________________________________________________________________
Vol. of NaOH
Used for back
titration CA(g mole/Lit) 1/CA
-----------------------------------------------------------------
V3 (V1N1 – V3N3)/V2
Temperature T1= 0K
Time, t1 = 1.5 min -------------- ----------- -----
Time, t2 = 3.0 min -------------- ----------- -----
Temperature T2 = 0K
Time, t1 = 1.5 min -------------- ---------- ----
Time, t2 = 3.0 min -------------- ---------- ---
Temperature T3= 0K
time, t1 = 1.5 min --------------- --------- ----
time, t2 = 3.0 min --------------- --------- ---- ________________________________________________________________
3. Evaluation of KC:
Plot 1/CA Vs time (inclusive of initial readings) at each of the temperatures. Obtain the slopes of the three straight-line plots.
T0K KC liters/(gm. mole) (min.)
---------- ----------
----------- -----------
4. Plot ln kC Vs 1/T. Obtain the values of the frequency factor
and energy of activation from the straight line plot.
A = ---------------litters/(gm mole)(min)
E = ----------------cal/gm. mole.
