Question

When measuring your starch samples in a spectrophotometer, what sort of results would you expect to see if there were:

a. different concentrations of starch in two tubes?

b. How could you tell if there was the same concentrations of starch in two tubes?

c. How could you tell if there was no starch in a tube?

Answer 1

To determine starch concentration in samples, first one cuvette is left for blank(solvent used for preparing sample solution) as reference. Spectrophotometer uses this for making auto zero(Absorbance by solvent in sample solution is nullified). Samples are filled only in the 2nd cuvette and absorbance readings are taken running the spectrophotometer for all the samples to be determined.

This answer if you meant sample in cuvettes.

A) If both cuvettes are filled with sample starch solutions of different concentrations, we will get wrong values. As absorbance values we get are calculated using transmittance from 1st cuvette (I_o, intensity of incident light) and 2nd cuvette(I, intensity of light after passing through the sample).

A=log(I_o/I)

We get absorbance values lesser/ greater than expected.

B) If there are 2 same concentrations in the cuvettes we get A value zero.

The intensity of incident light is equal to the intensity of transmitted light.

I_o/I =1

log 1 = 0 absorbance.

A=0

C)If there is no starch in sample solution, it will be blank resulting zero absorbance same as above.

This answer if you meant samples in lab test tubes

A)If there are different concentrations of starch samples, we get 2 different absorbance values.

B) If there are same concentrations of starch samples, we get same absorbance values.

C)If there is no starch in sample solution, it will be blank resulting zero absorbance.

The intensity of incident light is equal to the intensity of transmitted light.

I_o/I =1

log 1 = 0 absorbance.

A=0