The molar of this class of dyes is about 50,000 (Liters/mol cm). The maximum abs

Question

The molar of this class of dyes is about 50,000 (Liters/mol cm). The maximum absorbance that you should have is about 1.5 for a reasonably precise measurement, with the ideal being less than 1.0.

A) Assuming a molar absorptivity of 50,000 (Liters/mol cm) calculate what molarity you would need to get an absorbance of 1.0, using Beers Law.

A = c l, where A is the absorbance; is the molar absorptivity in L/mol cm; c is the concentration in mol/liter; and l is the path length in cm, which, in our case, is 1.00 cm.

Algebraically rearranging gives c = A/ l =A/.

B) Start with 20 mg of your dye. Calculate what morality would result when this 20 mg of dye is dissolved in 50 ml (0.050 liters) of acetone.

C) Then calculate what volume of this solution would be required to dissolve in 50 ml of solvent to give a solution having an absorbance of 1.0, calculated in part A.

Remember, C1V1=C2V2, or V1 =(C2V2)/C1

Explanation / Answer

A )

A = c l

1.0 = 50,000 x C x 1.00

C = 2.0 x 10^-5 M

molarity = 2.0 x 10^-5 M

B)

in 1 Litre ------------> 2.0 x 10^-5 moles

moles = mass / molar mass

2 x 10^-5 = 20 x 10^-3 / molar mass

molar mass = 1000 g/mol

now molarity = (mass / molar mass ) x 1000 / 50

=( 20 x 10^-3 / 2 x 10^-5 ) x 1000 / 50

= 4 x 10^-4 M

C)

2.0 x 10^-5 x V1 = 4 x 10^-4 x 50

V1 = 1000 mL

volume = 1000mL

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