Help with number 2 Lab 5: Spectrophotometric Analysis of Permanganate solutions

Question

Help with number 2 Lab 5: Spectrophotometric Analysis of Permanganate solutions suggest something the student could do with the second sample that would make the determination of the concentration of permanganate ion more accurate. 2. is a compound that forms red complex with ironaD. The molar absorptivity a for the complex is 22,350 L 1 at A 535 nm. a) Determine the molar concentration range of the enanthroline complex that can be analyzed directly with a spectrophotometer, using a 1-cm cuvette. 95 Now chan se mole IL tu L by by rs a melav mass F A A 32 Y 2) convert molar concentrations determined in to grams of ironan per liter of solution the the method determining ironoID. Comment on the sensitivity of

Explanation / Answer

Question 2. 1. The concentration of the Iron can be found from absorption studies. For that purpose, the useful range of the absorbance scale is from 0-2 (1 % light is transmitted at absorbance 2) but it is better to keep within the range 0-1 because, above 1, the results become unreliable due to scattering of light.

Thus minimum concentration is 0, then we can increase the concentration which gives absorbance 1

Given that extinction coefficient at 535 nm is 22350 L mole -1.cm-1 .

Thus using Beer - Lamberts law

Absorbance = extinction coefficient x concentration x pathlength.

1= 22350 *1* x

Thus x = 0.447 x 10 -6M

Thus we can find the range of iron complex from 0 to 0.447 x 10 -6M using spectrophotometer.

Question 2. 2 From the absorption studies we got the concentration in Molarity.

As per definition, molarity is the number of moles of solute in one liter.

Amount substance can be found by multiplying the number of moles with its atomic/molecular weight.

In our case one complex contains one Fe atom. Thus for eg:

Mass of iron for absorbance 1 situation is

0.447 x 10 -6M * 55.85g/mole = 24.96 g/L

This technique can be used to detect iron present in very low concentrations also since the extinction coefficient at this wavelength is high.

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