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

Question

o(II) was used as an internal standard to analyze a sample of Ti(IV) with atomic absorption spectroscopy (AAS). A standard mixture containing 1.66 g Co/mL and 1.38 g Ti/mL measured by AAS produced a signal-to-signal ratio of 1.76 Ti: 1.00 Co. A mixture was prepared by combining 4.50 mL of a Ti(IV) solution of unknown concentration with 3.00 mL of a 10.6 g/mL solution of Co(II). The absorbance of the mixture at the Ti(IV) wavelength was 0.140 and the absorbance at the Co(II) wavelength was 0.207. Determine the concentration, in moles per liter, of Ti(IV) in the original unknown solution.

Explanation / Answer

A standard mixture containing 1.66 g Co/mL and 1.38 g Ti/mL measured by AAS produced a signal-to-signal ratio of 1.76 Ti: 1.00 Co.

ratio of concentration is

1.38/1.66 = 0.8313 ratio of absorbance is 1.76

The absorbance of the mixture at the Ti(IV) wavelength was 0.140 and the absorbance at the Co(II) wavelength was 0.207. so the signal-to-signal ratio is 0.14/.207 = 0.676 : 1

So when ratio of absorbance is 0.677 ratio of concentration should be 0.3198

when the measured sample was 1 the concentration was (10.6 ug/mL x 3mL)/(3mL + 4.5 mL) = 4.24 ug Co/mL

Concentration of Ti would be 4.24 x 0.3198 = 1.355 ug Ti/Ml this is in 7.5 mL so in the 4.5 mL added it would be

1.355 x 7.5 /4.5 = 2.26 ug Ti/mL = 2.26 mg/L

47.87 g/mol is the mol wt of Ti

2.26 mg is 2.26 x 10-3/47.87 moles = 4.72 x 10-5 moles/L

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