Question

At 565 nm wavelength, the Beer's Law is used to determine the rate of the reaction of crystal violet with sodium hydroxide at a particular temperature. Beer's Law Correlation Using the Absorbance of Crystal Violet in the Reaction -3 -4 k =-0.001726 s-1 at 9.9 °C In [Cv+] 5 -6 At 500 t (s) 250 750 1000 Beer's Law equation

The Beer's law equation parameters mean, A for abosrbance, c for conenctration (mol/L), b for the pathh of light (cm), and E for absoprtivity constance. Using the graph above, answer the following questions:

1. Briefly explain the relationship between the concentration and absorbance of crystal violet on the graph

2. Based on teh shape of the graph, write the applicable integrated rate law for the reaction

3. What is the rate constant of the reaction?

4. Write the complete rate law of the reaction at the observed temperature.

Answer 1

1.since absorbance A=ebC, C = concentration ,e = molar extinction coefficient

b =path length, so absorbance is directly proportional to concentration.

2. rate (-dC/dt)= K[C]ⁿ, n is the order of reaction and K is rate constant , C is concentration of reacting species

when n=1, the reaction is 1st order and hence -dC/dt= KC

or lnC= lnCO-Kt, where Co= initial concentration of reacting species and C= concentration at any time, t and K is rate constant. so the reaction is 1st order, since the plot of lnC vs t is a straight line. the slope is rate constant whose value is 0.001726/sec

rate law is given by -dC/dt= 0.001726*C