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 1.50 μgCo/mL and 1.40μg Ti/mL measured by AAS produced a signal-to-signal ratio of 2.15Ti:1.00Co, A mixture was prepared by combining 5.50 mL of a Ti(IV) solution of unknown concentration with 4.00 mL of a 14.9μg/mL solution of Co (II). The absorbance of the mixture at the Ti(IV) wavelength was 0.118 and the absorbance at the Co(II) wavelength was 0.217 . Determine the concentration, in moles per liter, of Ti(IV) in the original unknown solution.

Answer 1

The concentration of Ti(IV) in the unknown solution can be calculated by correlating the measured absorbance values to the standard signal ratio and accounting for dilution factors. This involves a multi-step process that includes comparing absorbances, calculating the concentration after dilution, and converting the final μg/mL value to molarity.

Step-by-step explanation:

Using atomic absorption spectroscopy (AAS), we can determine the concentration of Ti(IV) in an unknown solution. A standard mixture containing Co (II) as an internal standard showed the signal ratio of Ti to Co is 2.15:1. Given that a mixture of unknown Ti(IV) solution and known Co(II) concentration produced absorbance values at their respective wavelengths, we can calculate the unknown Ti(IV) concentration by using the absorbance ratio obtained from AAS.

The process involves the following steps:

1. Calculate the absorbance ratio of Ti to Co in the mixed solution according to their measured values (0.118 for Ti and 0.217 for Co).
2. Correlate this absorbance ratio to the standard ratio to determine the concentration of Ti in the mixed solution (after combining with Co).
3. Obtain the concentration of Ti in the original unknown by considering the dilution factor from mixing.

We are given that the concentration of Co in the mixed solution is 14.9μg/mL. The volume of the Co solution added is 4.00mL, and the volume of the unknown Ti solution added is 5.50mL. To get the concentration of Ti in μg/mL, we multiply the ratio of the absorbances of Ti and Co in the mixed solution by the concentration of Co, then divide that product by the standard ratio.

Using the formula C1V1 = C2V2 (where C1 and V1 are the concentration and volume of the original Ti solution and C2 and V2 are the concentration and volume after dilution), we can then calculate the concentration C1 of Ti in the original unknown solution.

Finally, to express this concentration in moles per liter (M), we divide the concentration in μg/mL by the molar mass of Ti and convert μg/mL to g/L.