The absorbance of a chlorophyll a standard solution in ethanol (density = 0.785 g/mL) is measured in
a 1.3 cm cuvette or path length. The absorbance is 0.765 and the molar absorptivity coefficient is 86,300 M–1cm–1.
The molecular weight for chlorophyll a is 893.49 g/mol.
What is the concentration of the solution in ppm?
A= ebc
0.765 = 86,300*1.3*c
Solve for c = approximately 7E-6 Molar = mols/L soln.
g = 7E-6*893.49 = about 0.006 g chlorophyll/L soln.
1000 x 0.785 = 785 g ethanol.
Concn = about 0.006g chlorophyll/785 g soln.
Change that to ppm. The easy way to do that is (0.006/785)*1E6 = ?
Check my work carefully.
To determine the concentration of the chlorophyll a solution in parts per million (ppm), we need to follow these steps:
Step 1: Calculate the concentration in molarity (M).
We can use the Beer-Lambert Law to relate the absorbance (A), molar absorptivity coefficient (ε), path length (l), and concentration (C) of the solution:
A = εcl
Rearranging the equation to solve for concentration (C), we have:
C = A / (εl)
Substituting the given values:
A = 0.765 (absorbance)
ε = 86,300 M–1cm–1 (molar absorptivity coefficient)
l = 1.3 cm (path length)
Plugging in these values, we get:
C = 0.765 / (86,300 * 1.3)
Step 2: Convert the concentration to molarity from the given molecular weight.
We know the molecular weight (MW) of chlorophyll a is 893.49 g/mol. We need to convert the concentration from moles per liter (M) to grams per liter (g/L) using the molecular weight as a conversion factor:
1 M = MW g/L
Multiplying the concentration (C) by the molecular weight (MW), we have:
C = C * MW
C = (0.765 / (86,300 * 1.3)) * 893.49
Step 3: Convert the concentration to ppm.
To convert the concentration from grams per liter (g/L) to parts per million (ppm), we use the following conversion factor:
1 ppm = 1 mg/L = 1 μg/mL
Since the given density of ethanol is 0.785 g/mL, the concentration in ppm can be calculated as:
C_ppm = (C * 0.785) * 1000
C_ppm = ((0.765 / (86,300 * 1.3)) * 893.49 * 0.785) * 1000
By completing these calculations, you should be able to find the concentration of the chlorophyll a solution in parts per million (ppm).