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 2.24 g Co/mL and 2.28 g Ti/mL measured by AAS produced a signal-to-signal ratio of 2.06 Ti: 1.00 Co.

A mixture was prepared by combining 6.00 mL of a Ti(IV) solution of unknown concentration with 4.00 mL of a 14.5 g/mL solution of Co(II). The absorbance of the mixture at the Ti(IV) wavelength was 0.142 and the absorbance at the Co(II) wavelength was 0.187.

Determine the concentration, in moles per liter, of Ti(IV) in the original unknown solution.

Explanation / Answer

From standard,

2.24 ug/ml Co gave absorbance = 1.0

2.28 ug/ml of Ti gave absorbance = 2.06

Response factor (F) = (2.06 x 2.24/1.00 x 2.28) = 2.024

For mixture,

concentration of Co = 14.5 ug/ml of 4 ml solution = 14.5 x 4/10 = 5.8 ug/ml

So concentration of Ti in solution = (0.142 x 5.8/2.024 x 0.187) = 1.966 ug/ml in 10 ml solution

Concentration of Ti in 6 ml solution = (1.966 x 10/6)/47.867 g/mol x 1000 = 6.845 x 10^-8 mol/L

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