Analytical Chemistry

Use KSP, Ka and Eo values from textbook

1. (a) An unknown solution contains only two absorbing species thymol blue and methylthymol blue. This sample had absorbance of 0.412 at 455 nm and 0.632 at 545 nm when measured using standard 1.000 cm cell, and the absorbance of blank at the same wavelengths as 0.003 and 0.005 respectively. The table below gives the molar absorptivities of the two

 molecules:

Calculate the concentration of thymol blue and ethylthymol blue in the unknown sample.

(b) If the unknown solution above contained thymol blue and an unknown compound Y instead of methylthymol blue, what are the concentrations of the thymol blue and Y given the molar absorptivities of the two molecules are:

2. The titration of  50.00 mL aqueous sample of Fe2+with 0.09533 M Ce⁴⁺gives the following cell potentials when using a platinum indicator electrode and silver-silver chloride reference electrode. Use a Gran plot to determine the concentration of Fe2+in this sample.

3. The following results were obtained for a spectrophotometric titration that was carried out at 600 nm to measure Cu2+in a water sample according to the reaction below:Cu2++ Trien → Cu(trien)2+

A 10.00 mL sample of water was used for this titration, and the following results were obtained upon the addition of increments of titrant to the sample:

(a) What was the concentration of Cu2+in the original sample?

(b) Explain the shape of the titration curve obtained for this analysis. What does this curve tell you about the ability of the analyte, titrant and product to absorb light at the wavelength used for this titration?

(c) Use the information provided to estimate the value of the molar absorptivities for the analyte, titrant and product at 600 nm.

4. Given the following spectra of ibuprofen and sulindac, in numbered bullet format explain how you would perform the analysis of a tablet sample containing unknown amounts of ibuprofen and sulindac. For full marks, you have to be very specific and describe all steps in detail. UVspectra are copyright photostability of drugs and drug formulations, 2ndedition, by H.H. Tonessen(p.11)

5. Calibration data for a F-ion-selective electrode using KF standard solutions prepared in buffer of 0.5 M ionic strength is given in the table below. This fluoride ion-selective electrode has selectivity coefficient of 0.001 for chloride ions. Construct calibration curve, perform least-squares linear regression as appropriate and determine the magnitude of β for this particular electrode.

 (b) An unknown sample of tap water as analyzed 5 hours after the above calibration data was collected. E measured was 341.0 mV. what is he concentration of F-in this tap water sample? How accurate is this concentration and explain your reasoning?

(c) An unknown sample of ocean water was analyzed immediately after the above alibration data was collected. E measured was 142.0 mV. What is the concentration of F-in this ocean water sample? How accurate is this concentration and explain your reasoning?

(d) What (if anything) would you do differently if you were performing the analyses described in (b) and (c) to increase the accuracy of the [F-] determination? For full marks, be very clear and specific

6. Compound P binds with X to form the complex PX. A series of solutions was prepared with the total P concentration remaining fixed at 1.00 x10-5M in all solutions. Both P and X do not absorb at 437 nm, but PX has an absorption maximum at 437 nm. The following table shows how the absorbance at 437 nm in a 5.00 cm cell depends of [X], using the assumption that [X]is approximately qual to XTbecause XT>>*P+.

Make a Scatchard plot of ΔA/*X+ versus ΔA in order to find the equilibrium constant K for this binding event.