Question

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 =ε c l, where **A** is the absorbance;
**ε** 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/ε l =A/ε.

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

Answer #1

C=(1)/(50000)= 2*10^-5 mol/L

let's assume the dye is the one described below, because it is necessary to know the molar mass to proceed:

FD&C Red 40 | Allura Red AC | 496.42 molar mass (g/mol) |

So the molarity of the solution proposed in part B would b

C=(0.020g/496.42g/mol)/0.05L= 8.06*10^-4 mol/L

Part C)

Using the Beers law, to get an absorbance equal to 1.0 is necessary a concentration of 2*10^-5mol/L as it was calculate previously. So in order to have this concentration starting from the previous solution it is necessary to use the following formula

C1*V1=C2*V2---->V1=(C2¨*V2)/C1

V1=(2*10^-5mol/L*0.05L)/ 8.06*10^-4 mol/L=0.0012L are needed in part C.

The molar absorptivity, ε, for the dye called xylenol
blue (C23H22O5S, molar mass =
410.49 g mol-1) was found by experiment to be
8.15×103 L mol-1 cm-1 at 424 nm.
The percent transmittance of a 960 mL solution of xylenol
blue was determined to be 30.9%. If the path length of the
cell is 2.19 cm, determine the mass (in g) of xylenol blue
present in the solution. Report your answer to 3 significant
figures in scientific notation.

The molar absorptivity of a dye is ε = 3.3 /M cm; what is the
concentration of the solution (C) if the path length is given as ℓ
= 1 cm and the absorption is A = 0.72? Beer-Lambert Law: A = εℓC
SHOW WORK
(a) 0.33 M
(b) 1.4 M
(c) 0.22 M
(d) 0.72 M

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(a) What is the concentration of the compound in the cuvet?
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