Question

Determination of the Calcium Content of Beer and Water Using Atomic Absorption Spectroscopy

1. Assuming the wort is saturated with Ca3(PO4)2(s), what would happen to the concentration of Ca2+ions in the wort if: (i) More HPO42-ions were added? PO43- Concentration will increase (ii) Ca3(PO4)2 (s) was added? (iii) The pH of the solution was decreased by addition of a suitable acid?

2. Why is LaCl₃ utilized? What changes would be needed in set up of the AAS if LaCl₃ was not used

3. If your two highest concentrations for the calibration both have an absorbance of about 2, what is the problem and how you would correct it?

Answer 1

1)3)

If pH of the solution is decreased, then the protonated form will arise...So, the conversion of

will be facilitate...

Thus, instead of Ca3(PO4)2 , we will get soluble CaHPO4 . So , then as it is soluble, it will dissotiate into -

So, concentration of Ca2+ will increase.

3)

The absorbance is too high ( 2 ), that means, the concentration of target is too high.

Now, in such high concentration , the deviations of Bear's Law is observed due to assotiation etc. Then , we cannot accurately calculate oncentration just by using the callibration formula . So, at such high absorbance , we should not take the results for calculation . What we can do , is - We can quantitatively dilute the samples . Let say , exact 5 times dilution . Then if we record the absorbance , it will be good . Using that absorbance value, we can get the concentration of the diluted species . Now , as we had diluted quantitatively , so , by multiplying with the dilution factor ( here 5 ) , we can get the initial concentration of the sample .