A) You begin preparation of the calibration curve to measure absorbance vs conce

Question

A) You begin preparation of the calibration curve to measure absorbance vs concentration of FeSCN2+. To do so, you add 4.128 mL of 0.150 M Fe(NO3)3 to a cuvette and then directly add 210.454 µL of 0.001 M KSCN. What is the resulting concentration of FeSCN2+, assuming complete conversion of SCN- to FeSCN2+? Provide your response to four digits after the decimal; be careful with your exponent, it must complete this expression: __________ x 10-3 M.

B) If the initial amount of Fe(NO3)3 transferred to the cuvette is 0.046 mol, and the absorbance measurements indicate that 0.024 mol of FeSCN2+ are present at equilibrium, what must be [Fe3+] at equilibrium? The total volume of solution in the cuvette is 2.451 mL. Provide your response to two digits after the decimal.

Explanation / Answer

A)

mmoles of Fe(NO3)3 = 4.128 x 0.150

= 0.6192 mmoles

mmoles of KSCN = 0.001 x 210.454 x 10^-3

= 0.000210454 mmoles

Thus, KSCN is the limiting reagent

we get 0.000210454 mmoles of Fe(NO3)3 in(4.128 +0.210454)mL of solution

Thus,0.0002104545 mmoles in 4.338454 mL of solution

concentration= 2.10454 x 10^-4 / 4.338454

= 4.85 x 10^-5 M

concentration = 0.0485 x 10-3 M

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