Cobalt was used as an internal standard to analyze a sample of titanium with ato

Question

Cobalt was used as an internal standard to analyze a sample of titanium with atomic absorption spectroscopy. A mixture was prepared by combining a 4.00 mL Ti solution of unknown concentration with 1.00 mL of a 10.2 micro g/mL solution of Co. The atomic absorbances were measured as 0.116 and 0.201 for Ti and Co, respectively. As a reference, a standard mixture containing 2.06 micro g Co/mL and 1.71 microTi/mL was prepared and measured to have a signal-to-signal ratio of 2.33 Ti: 1.00 Co. Determine the concentration (moles/L) of titanium in the original unknown solution. Number MTi

Explanation / Answer

Standard Values:

CCo= 2.06 mcg Co/mL; ACo= 1.00 Co

CTi = 1.71 mcg Ti/mL; ATi= 2.33 Ti

Sample Values:

VCo= 1 mL; CCo= 10.2 mcg Co/mL; ACo= 0.201 Co

VTi = 4 mL; CTi = x mcg Ti/mL; ATi= 0.116 Ti

Concentration of Ti in original sample?

C(mx-Ti)/A(mx-Ti) = C(st-Ti)/A(st-Ti)

C(mx-Ti) = [C(st-Ti) x A(mx-Ti)]/A(st-Ti)

C(mx-Ti) = [1.71mcg.mL-1 x 0.116]/2.33

C(mx-Ti) = 0.085 mcg/mL

Molarity concentration in initial solution (Ti)?

M = 0.085 mcg/mL x (1000 mL/1L) x (1g/106mcg) x (1 moL Ti / 47.9g Ti)

M = 1.77x10-6 moL/L

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