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Natalka [10]
3 years ago
6

The absorbance of a chlorophyll a standard solution in ethanol (density = 0.785 g/mL) is measured in

Chemistry
2 answers:
Dmitry_Shevchenko [17]3 years ago
5 0
Let <span>A= ebc </span>
<span>     0.765 = 86,300*1.3*c </span>
<span>
Solve for c = approximately 7E-6 Molar
                  = mols/L soln. </span>
<span>g = 7E-6*893.49
   = about 0.006 g chlorophyll/L soln. </span>
<span>
1000 x 0.785 = 785 g ethanol. </span>
<span>Conc. = about 0.006g chlorophyll/785 g soln. </span>
<span>
Change that to ppm. by using formula:
(0.006/785)*1E6</span>
jasenka [17]3 years ago
5 0

Answer:

7.76 is the concentration of the solution in ppm.

Explanation:

Using Beer-Lambert's law :

Formula used :

A=\epsilon \times C\times l

where,

A = absorbance of solution = 0.765

C = concentration of solution = ?

l = path length = 1.3 cm

\epsilon = molar absorptivity coefficient = 86,300 M^{-1} cm^{-1}

0.765=86,300 M^{-1}cm^{-1}\times C\times 1.3 cm

C=6.82\times 10^{-6} M=6.82\times10^{-6} mol/L

\text{ppm}=\frac{\text{Mass of solute}}{\text{Mass of solution}}\times 10^6

Both the masses are in grams.

Mass of solute that is chlorophyll = 6.82\times 10^{-6}\times 893.49 g/mol=0.00609 g

Mass of ethanol = m

Density of the ethanol = d = 0.785 g/mL

Volume of the ethanol = 1 L = 1000 mL

m=0.785 g/mL\times 1000 mL=785 g

Mass of solution = 0.00609 g + 785 g = 785.00609 g

Concentration in ppm:

\frac{0.00609 g}{785.00609 g}\times 10^6=7.76

7.76 is the concentration of the solution in ppm.

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