Question

A student used standard solutions of aspirin in a FeCl3-KCl-HCl mixture to plot a graph of molarity versus absorbance for diluted aspirin solutions of known concentration. The student determined the slope of the graph to be 4,862 M-1cm-1. Next the student measured out 0.219 grams of a headache medicine tablet and dissolved it in 10.0 ml of NaOH and then added enough water to make a 100 ml solution. Five ml of this solution was then added to another 100 ml flask and diluted to the mark with enough FeCl3-KCl-HCl mixture. The solution was then measured for absorbency as 0.301 Calculate the molarity of the diluted solution determined from the absorbency and the slope. Then use the molarity of the original solution, its volume and molar mass to calculate the grams of pure acetylsalicylic acid. Put your answer in 3 significant figures.

Answer 1

According to Beer-Lambert's law, absorbance (A) = cl

Where is molar absorption coefficient

'c' is the molar concentration of the solution

'l' is the path length = 1 cm

Therefore, A = c

The above equation is in the form of linear equation y = mx (y = A, m = slope = , and x = c)

Here, A = 0.301 and = 4862 M^-1cm^-1

Now, 0.301 = 4862 M^-1cm^-1 * c * 1 cm

i.e. c = 0.301/4862 M^-1 = 6.19*10^-5 M

Therefore, the concentraiton of the diluted solution = ​6.19*10^-5 M