Question

1)    The procedure stated “benzoate is protonated to make benzoic acid. Caffeine has no appreciable basicity, so it is neutral at pH 2” – what does it mean to protonate? Why would it be important to protonate benzoate? Why is caffeine not affected the same way? Cite and interact

2)    UV, fluorescence and luminescence: Does Beers law hold true for all three? What dictates what kind of chemical compound will demonstrate as a UV chromophore or naturally fluoresce or naturally luminesce? Cite and interact: remember that I only want about 4-5 sentences, so be concise.

3)    What do you think would have happened if we had used a diluent that was just water or was 0.010 N NaOH for this experiment? Predict what would happen to the calibration curves and the final results in each situation.

Answer 1

1. protonation: it means putting in an acid mean a salt. The benzoate is soluble in water, but benzoic acid does not. Caffeine can not be protonated or deprotonated. Then it will not be soluble.

2. Beer law is most suitable for uv. Other methods as fluorescence and luminescence we can use atomic or molecular spectrocopy.

Fluorescence occurs when an orbital electron of a molecule, atom, or nanostructure, relaxes to its ground state by emitting a photon from an excited singlet state:

Excitation:

Fluorescence (emission):

Here is a generic term for photon energy with h = Planck's constant and = frequency of light. The specific frequencies of exciting and emitted light are dependent on the particular system.

3. The experiment you did is needed.

What might have happened is related to the separation of the compound within a chemical matrix. Also the compound might have reacted with NaOH and their product is not a colored molecule. Which in the calibration curve can be seen as a non linear relation between concentration and absorbance.