Hydrolysis of methyl acetate in aqueous solution has been studied by titrating the liberated acetic acid against sodium hydroxide. The concentration of the ester at different times is given below:
Time $(t)$ $\text{min}$ $0$ $30$ $60$ $90$
Conc. of ester $(C)$ $\text{mol L}^{-1}$ $0.850$ $0.800$ $0.754$ $0.710$

Show that it follows a pseudo first-order reaction as the concentration of $H_2O$ remains nearly constant $(54.2 \text{ mol L}^{-1})$ during the course of the reaction. What is the value of $k'$ in this reaction?

Vedclass pdf generator app on play store
Vedclass iOS app on app store
(N/A) For a pseudo first-order reaction,the rate constant $k'$ is given by the formula:
$k' = \frac{2.303}{t} \log \frac{C_0}{C_t}$
Given $C_0 = 0.850 \text{ mol L}^{-1}$.
At $t = 30 \text{ min}$,$C_t = 0.800 \text{ mol L}^{-1}$:
$k'_1 = \frac{2.303}{30} \log \frac{0.850}{0.800} = 0.07677 \times \log(1.0625) \approx 0.07677 \times 0.0263 = 0.00202 \text{ min}^{-1}$.
At $t = 60 \text{ min}$,$C_t = 0.754 \text{ mol L}^{-1}$:
$k'_2 = \frac{2.303}{60} \log \frac{0.850}{0.754} = 0.03838 \times \log(1.1273) \approx 0.03838 \times 0.0520 = 0.00200 \text{ min}^{-1}$.
At $t = 90 \text{ min}$,$C_t = 0.710 \text{ mol L}^{-1}$:
$k'_3 = \frac{2.303}{90} \log \frac{0.850}{0.710} = 0.02559 \times \log(1.1972) \approx 0.02559 \times 0.0781 = 0.00200 \text{ min}^{-1}$.
Since the values of $k'$ are nearly constant,the reaction follows pseudo first-order kinetics.
The average value of $k' \approx 2.00 \times 10^{-3} \text{ min}^{-1}$.

Explore More

Similar Questions

$A$ first order reaction has a rate constant $1.15 \times 10^{-3} \, s^{-1}$. How long will $5 \, g$ of this reactant take to reduce to $3 \, g$?

Difficult
View Solution

In the following graphs,which graph$(s)$ belong to a first-order reaction?

The half-life for the decomposition of gaseous compound $A$ is $240 \ s$ when the initial gaseous pressure is $500 \ Torr$. When the initial pressure is $250 \ Torr$,the half-life is found to be $4.0 \ min$. The order of the reaction is....... (Nearest integer)

For the decomposition of $N_2O_5$ according to the equation $2N_2O_5(g) \to 4NO_2(g) + O_2(g)$,the reaction is of first order. After $30 \, \min$ from the start of the reaction in a closed vessel,the total pressure is $305.5 \, mm \, Hg$,and at the end of complete decomposition,the total pressure is $587.5 \, mm \, Hg$. Calculate the rate constant of the reaction.

For a first order reaction,the graph between $\log \frac{a}{(a-x)}$ (on $y$-axis) and time (in $min$,on $x$-axis) gave a straight line passing through origin. The slope is $2 \times 10^{-3} \ min^{-1}$. What is the rate constant (in $min^{-1}$)?

Vedclass Products

For Students

Vedclass Test Series

Mock tests in real JEE/NEET style with performance analysis. 5-day free trial.

Start Free Trial
For Teachers

Exam Paper Generator

Generate Set A/B/C/D exam papers from 7.5L+ questions in 2 minutes. 3 chapters free.

Try Free
For Institutes

Online Exam Module

Live online exams with unlimited students, 360° analytics & white-label branding.

See Demo