An unknown amount of a compound with a molecular mass of 257.23 g/mol is dissolv

Question

An unknown amount of a compound with a molecular mass of 257.23 g/mol is dissolved in a 10-mL volumetric flask. A 1.00-mL aliquot of this solution is transferred to a 25-mL volumetric flask and enough water is added to dilute to the mark. The absorbance of this diluted solution at 327 nm is 0.561 in a 1.000 cm cuvette. The molar absorptivity for this compound at 327 nm is E327-6503 M-1 cm-1. What is the concentration of the compound in the cuvette? Number 8.63x 10-5 (b) What is the concentration of the compound in the 10-mL flask? Number 2.16% 10-3 (c) How many milligrams of compound were used to make the 10-mL solution? Incorrect. First determine the moles of the compound in the 10-mL solution by multiplying the concentration in part (b) by the volume of the solution in Number 0.569 mg iters. Then use the molecular mass of the compound to find the mass of the compound.

Explanation / Answer

Solution :-

Apply Beer's Law

A = e*l*C

A = absorbanc, e = molar absorptivity, l = length of cuvette

so

from the cuvette concentation

A = e*l*C

C = A/(e*l) = 0.561/(1*6503 ) = 0.0000862679M

this value is A) concentration of compound in the cuvetet

b)

concentration of compound in th 10 mL flask:

0.0000862679 M at 25 mL

find concentation at V = 1 mL

M1*V1 = M2*V2

M1*1 = 0.0000862679*25

M1 = 0.002156697 M @1 mL

note that the concentration at 1 mL is the same of that in V = 10 mL

so this is B) M1 = 0.0021566975 M

c)

find mass in mg for compound

moles = C*V = 0.0021566975 M * 10 mL= 0.021566975 mmol

1 mmol = 273.67 mg

0.021566975 mg = 0.021566975 *273.67 = 5.9022 mg of sample

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