Assignment: Spectrophotometry and Equilibrium Intro

1) Calculate the energy and frequency of a photon with a wavelength of 573.8 nm.

2. (0.4 each) Define the following terms:

a. Transmittance

b. Pathlength

c. Molar absorptivity

d. Absorbance

e. Beer's Law

3) A 3.7 × 10^-4 M solution of compound X has an absorbance of 0.5342 when measured at 740 nm. Assuming a pathlength of 1 cm, calculate compound X's molar absorptivity.

4) The iron content of a well water sample must be quantified. A 10.00 mL aliquot of well water is transferred to a 100.0-mL volumetric flask and 20 mL of 0.10 M nitric acid is added to oxidize iron(II) to iron(III). Next 30 mL of a 0.1 M sodium thiocyanate solution is added to form the deep red complex iron(III) thiocyanate. The solution is diluted to volume with distilled deionized water. A reagent blank is similarly prepared. If the absorbance of the iron thiocyanate solution is 0.5483 and the reagent blank absorbance is 0.0282, calculate the iron concentration for the water sample. The molar absorptivity for iron(III) thiocyanate is 3200 M^-1 cm^-1. Assume a pathlength of 1 cm and a 100% yield.

Fe³⁺ (aq) + SCN^- (aq) (↔- ) FeSCN²⁺ (aq)

5) Using the first 2 columns of data in Table 4-8 on p. 85 of your text, determine the µg of protein in an unknown sample if the absorbance is measured to be 0.401. Prior to the analysis 25 mL of sample was diluted to 100.0 mL in a volumetric flask. In addition find the uncertainty (u_x or s_x) in µg as well as the 95% confidence interval in the unknown sample.

6) Calculate the molar solubility for calcium fluoride in deionized water and in a 0.10 M NaF solution. (2 separate problems)

7) Find the [H⁺] and pH of a solution that is 3.98 × 10^-4M in OH^- ion.

8) Identify the conjugate acid-base pairs and label each species as a Bronsted-Lowry acid or base in the following reaction:

CN^- + HI ↔ HCN + I^-

9) Make a list of the common strong acids and bases, memorize it!

10) Find the K_b value for CN^-.

(0.2 each) Given the following compounds identify the resulting aqueous solution as acidic, basic, or neutral.

NaOH

HCl

Cl^-

NH₃

NH₄Cl

CH₃CO₂H

CH₃CO₂Na