Hello! I am unsure how to calculate the molarity of my orginal unknown and I am

Question

Hello! I am unsure how to calculate the molarity of my orginal unknown and I am unsure if my values for part C are correct. The lab is "solution concentration by spec.analysis." The diluted unknown solution was made using an unknown solution of Erythosin B (MM 879.87 g/mol). 5mL of the unknown solution was diluted with 45.00mL of DI water for a total volume of 50.00mL. The data I have gathered is as follows:

Known Solutions:

Molarity of standard solution: 8.342x10^-4 g/L

Molarity of stock solution 3.34 x 10^-5 g/L

Solution A: 1.67x10^-6 M, 0.123 absorbance

Solution B: 3.34 x 10^-6 M, 0.248 absorbance

Solution C: 4.68x10^6 M, 0.338 absorbance

Solution D: 6.68 x 10^-6 M, 0.489 absorbance

B. Unknown Solution

0.095 absorbance

1.30x10^-6 M of diluted unknown

Molarity of original unknown: ??

C. Molar absorptivity constant (E) of Erythrosin B at max wavelength (525 nm)

Slope: 7.31 x 10^4 M^-1cm^-1

Value of E: 7.37 x 10^4 M^-1cm^-1

Thank you!

Explanation / Answer

molarity of unknown = absorbance of unknown x molarity of known/absorbance of unknown

C1 = A1 x C2/A2

Taking one of the values from above

B. molarity of unknown = 0.095 x 1.67 x 10^-6/0.123 = 1.3 x 10^-6 M

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