Find molar absorptivity given the following

  • Thread starter Thread starter ssb
  • Start date Start date
Click For Summary
SUMMARY

The discussion focuses on calculating the molar absorptivity of potassium dichromate (K2Cr2O7) at a wavelength of 455 nm, given a concentration derived from 36.5 mg dissolved in 500.0 mL and a transmittance of 12.0% in a 2.000 cm cell. The user successfully calculated the concentration as 2.482 x 10^-4 mol/L using the atomic mass of K2Cr2O7 (294.07 g/mol). The relationship between transmittance and absorbance is clarified through Beer's Law, leading to the calculation of absorbance (A) as 0.0921, which is then used to find the molar absorptivity (E) as 185.5359 L/(mol·cm).

PREREQUISITES
  • Understanding of Beer's Law (E = A/bc)
  • Knowledge of molar concentration calculations
  • Familiarity with absorbance and transmittance concepts
  • Basic skills in significant figures and unit conversions
NEXT STEPS
  • Study the implications of transmittance on absorbance in spectrophotometry
  • Learn about the significance of significant figures in chemical calculations
  • Explore the applications of Beer's Law in various chemical analyses
  • Investigate the properties and uses of potassium dichromate in laboratory settings
USEFUL FOR

Chemistry students, laboratory technicians, and professionals involved in analytical chemistry and spectrophotometry who seek to understand the calculation of molar absorptivity and its applications.

ssb
Messages
119
Reaction score
0

Homework Statement



Calculate the molar absorptivity of K2Cr2O7 at 455 nm given that 36.5 mg disolved in 500.0 mL exhibits 12.0% transmittance at 455 nm in a 2.000 cm cell.

Homework Equations



Beers law E = A/bc

The Attempt at a Solution



I was able to do the following part ( i solved for concentration of K2Cr2O7 )
I found the atomic mass of K2Cr2O7
[(0.0365 g)/(294.07 g/mol)] / (0.5000 L) = 2.482 x 10^-4

Now I plug this into beers law but the question asks for something about a 12.0% transmittance. I am stuck here. How does transmittance relate to molar absorptivity?

I basically have 2 unknowns in one equation... what do I need to do next?

E = A / [(2.000 cm)(2.482 x 10^-4)] and I need to solve for A.
 
Physics news on Phys.org
Does A = -log(.12)= .0921 ?

and if this is the case

E = 0.0921 / [(2.000 cm)(2.482 x 10^-4)] = 185.5359 ? are sig figs correct as well?
 
Last edited:
Which number in your calculation has the fewest sig figs? How many are there? How many are in your answer?
 

Similar threads

How Do You Calculate Molar Absorptivity?
  • · Replies 11 ·
Replies
11
Views
5K
Calculating Radionuclide (243 Am3+) in a solution
  • · Replies 1 ·
Replies
1
Views
2K
Chemistry Beers Law, maximum molar absorptivity of carbonyl molecule
  • · Replies 4 ·
Replies
4
Views
5K
Engineering Light absorption in a semiconductor
  • · Replies 7 ·
Replies
7
Views
3K
What is the difference between absorptance and absorbance in spectrophotometry?
  • · Replies 11 ·
Replies
11
Views
11K
Finding mixture concentration using Beer's Law
  • · Replies 3 ·
Replies
3
Views
13K
Molarity given percent solution and density.
  • · Replies 5 ·
Replies
5
Views
9K
Calculating the molar concentration of H3O+ and pH of solutions
  • · Replies 4 ·
Replies
4
Views
6K
Chemistry Using data (Pressure vs. density) to find molecular mass .
  • · Replies 7 ·
Replies
7
Views
8K
Find molarity, seemingly simple but I can't do it.
  • · Replies 3 ·
Replies
3
Views
5K