Question

Specifically, you are to prepare a graph of Absorbance versus [Co²⁺] for the following solutions -- prepared by diluting the specified volumes of 0.2500 M Co²⁺ stock solution to 25.00 mL each:

	volume Absorbance 0mL 0 2.50mL .165 5.00mL .320 7.50 mL .485 10.0mL .610 12.0mL .721 What is the slope? For an unknown solution whose absorbance was 0.330, what would be the corresponding value of [Co2+]?

Answer 1

Let's first calculate concentration of Co2+ in all the solutions:
Formula: M1V1 = M2V2
Solution-2
M1 = 0.2500 M, V1 = 2.50mL, V2 = 25mL
So M2 = (0.25*2.5)/25 = 0.025 M
Solution-3
M1 = 0.2500 M, V1 = 5.00mL, V2 = 25mL
So M2 = (0.25*5)/25 = 0.05 M
Solution-4
M1 = 0.2500 M, V1 = 7.50mL, V2 = 25mL
So M2 = (0.25*7.5)/25 = 0.075 M
Solution-5
M1 = 0.2500 M, V1 = 10mL, V2 = 25mL
So M2 = (0.25*10)/25 = 0.1 M
Solution-6
M1 = 0.2500 M, V1 = 12mL, V2 = 25mL
So M2 = (0.25*12)/25 = 0.12 M

A B C D E F G H I J 1 Concentration Absorbance The equation of best fit line is: o 0 Y = 6.012*X +0.012 0.025 0.165 0.05 0.32 Slope is = 6.012 0.075 0.485 Unkown solution absorbance is (Y=) 0.330 0.1 0.61 0.12 0.721 Then Concentration (X) = (0.330-0.012)/6.012 = 0.053 M Thus the concentration of unkown solution is 0.053 M. Conc. vs Absorbance y = 6.012x + 0.012 R2 = 0.997 0.02 0.04 0.06 0.08 Concentration (M) 0.1 0.12 0.14