Q&A for How to Calculate Molar Absorptivity

Return to Full Article

Coming soon

Add New Question

Question

What is Beer Lambert's law?

Mohsin257

Community Answer

In simple words it states that light absorbed by the sample is directly proportional to the path length (l or x) and concentration.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 13 Helpful 34
Question

Is the molar absorptivity constant, or does it change as the length of the cuvette changes?

Community Answer

It is constant. Units of molar absorptivity constant is in M^-1 cm^-1, which is essentially how much is absorbed per unit length. As the length of cuvette increases, more is absorbed as a whole, but the constant is independent of length of cuvette!

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 9 Helpful 20
Question

How do I know the path length?

Mohsin257

Community Answer

It is known by sample compartment. Path-length is the area of the cell/sample compartment. It is mostly 1cm and depends on that compartment may be .5cm etc.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 19 Helpful 21
Question

How do I calculate the concentration of the unknown?

Community Answer

Concentration is molarity. So you use Mol's/solute, which is the M=Mol's/ml.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 85 Helpful 48
Question

How do I calculate molar concentrations?

Community Answer

Molarity is expressed in moles/liters. So find the number of moles using dimensional analysis, and then divide that by a volume measured in liters.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 6 Helpful 14
Question

How do I find the absorbance of radiation?

Community Answer

Use the formula A = ebc, where A is absorbance, e is molar extinction coefficient, b is path length (cm), and c is concentration (mol/L).

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 8 Helpful 2
Question

Shouldn't the slope be multiplied by path length and not divided in the 4th method? The absorptivity will be more at 1 cm path length than at 0.5 cm, won't it?

Community Answer

The formula is A = ɛlc. To solve for ɛ you use the formula A/lc, but the slope or gradient is A/c. So solving for ɛ would be the gradient multiplied by 1/l or the gradient divided by l.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 15 Helpful 2
Question

How do I calculate the absorbance?

Community Answer

In this procedure the absorbance is measured on a spectrophotometer. If, for some reason, you know all values except absorbance you can solve for it as A=e*l*c.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 4 Helpful 3
Question

How do I calculate the concentration of an extract if I don't know the molar absorbity?

Community Answer

In this procedure, you're preparing solutions of known concentration for analysis. You can't solve for the molar absorptivity if you don't know the concentration.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 12 Helpful 3
Question

How do I calculate the concentration from absorbance?

Community Answer

If you know the value of all variables except concentration, you can rearrange the equation as c = A/le.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 7 Helpful 3
Question

How do I calculate the molar absorptive if the concentration value is in PPM? How do I get the slop in moles per liter?

Community Answer

You must convert your units from ppm to mol/L. To do this, look up the molar mass (g/mol) of the compound of interest. Also, 1 ppm can be equated to 1 mg/L (or 0.001 g/L). For example, nitrate (NO3) is 62 g/mol. If you have a 62,000 ppm NO3 solution, it is equal to 1 mol/L NO3. (62,000 ppm = 62,000 mg/L * 1g/1000mg * 1mol/62g = 1 mol/L) The slope will not be in mol/L. It will be in your units for molar absorptivity (L mol^-1 cm ^-1).

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 0 Helpful 0
Question

What is the maximum wavelength of absorption for each dye?

Community Answer

You would have to run a scan of the wavelength spectrum rather than at a single wavelength to determine this.

Thanks! We're glad this was helpful.
Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
Yes No

Not Helpful 0 Helpful 0