Question

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

Answer 1

Let 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. 
Conc. = about 0.006g chlorophyll/785 g soln. 

Change that to ppm. by using formula:
(0.006/785)*1E6

Answer 2

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.