Co(II) was used as an internal standard to analyze a sample of Ti(IV) with atomi

Question

Co(II) was used as an internal standard to analyze a sample of Ti(IV) with atomic absorption spectroscopy (AAS). A standard mixture containing 1.38 g Co/mL and 2.35 g Ti/mL measured by AAS produced a signal-to-signal ratio of 2.15 Ti: 1.00 Co. A mixture was prepared by combining 4.00 mL of a Ti(IV) solution of unknown concentration with 3.50 mL of a 11.1 g/mL solution of Co(II). The absorbance of the mixture at the Ti(IV) wavelength was 0.155 and the absorbance at the Co(II) wavelength was 0.191. Determine the concentration, in moles per liter, of Ti(IV) in the original unknown solution.

Please solve and explain.

Explanation / Answer

From standard,

1.38 ug/ml Co gave absorbance = 1.0

2.35 ug/ml of Ti gave absorbance = 2.15

Response factor (F) = (2.15 x 1.38/(1.00 x 2.35)) = 1.26

For mixture,

concentration of Co = 14.5 ug/ml of 4 ml solution = 11.1 x 3.5/7.5 = 5.18 ug/ml

So concentration of Ti in solution = (0.155 x 5.18/1.26 x 0.191) = 3.34 ug/ml in 10 ml solution

Concentration of Ti in 4 ml solution = (3.34 x 7.5/4)/(47.867 g/mol x 1000) = 1.308 x 10^-7 mol/L

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