To determine the relationship between absorbance versus conc

To determine the relationship between absorbance versus concentration of crystal violet, a Beer’s law calibration curve of absorbance versus concentration of crystal violet, [CV+], was prepared in the pre-lab exercise. Linear regression analysis of the calibration curve data yielded the equation: Absorbance = 48983 x M + 0.00148. During the investigation, the absorbance of a crystal violet solution in the presence of hydroxide ions was monitored at 565 nm until a value of 0.200 was reached. The next step in the investigation was to convert the linear range absorbance values into concentrations using the Beer’s law calibration curve equation. Show how you would calculate the concentration of the crystal violet solution corresponding to an absorbance of 0.548.

Solution

Ans. The standard curve equation) is in form of y = mx + c , where m = slope , c = intercept.

In the graph, Y-axis indicates absorbance and X-axis depicts concentration. That is, according to the trendline (linear regression or standard curve equation) equation y = 48983x - 0.00148 obtained from the graph, 1 absorbance unit (1 Y = Y) is equal to 48983 units on X-axis (concentration) plus 0.00148.

# Given, absorbance of the unknown = 0.548

Putting the value of y = 0.548 in trendline equation-

            0.548 = 48983x + 0.00148

            Or, x = (0.548 - 0.00148) / 48983

            Hence, x = 1.1157 x 10^-5

Therefore, [CV] corresponding to an Abs of 0.548 = 1.1157 x 10^-5 M