1. Statistics

A) Determine whether or not the 22.56 value should be rejected from the following data set;

20.49, 20.95, 20.43, 20.39, 21.23, 22.56

Show your work.

• Using the Q-test, calculate Q = Gap/Range and compare the result to the table value.
• If Q > Q_TABLE, then the datum may be rejected.
• Gap = |22.56 – 21.23| = 1.33, Range = |22.56 – 20.39| = 2.17, Q = 1.33/2.17 = 0.613
• The Table value for 6 data is Q_TABLE = 0.56
• Since Q>Q_TABLE, the datum, 22.56, is rejected from the set.

B) Based on the above results, calculate the 95% confidence interval and report the statistically probable mean value at 95% confidence. Show your work using appropriate formulas.

The resulting data set consists of N = 5 points; {20.49, 20.95, 20.43, 20.39, 21.23}

Student’s t for 5 – 1 degree of freedom at 95% confidence level is t = 2.776

C) For each patterned target below, indicate whether the result is; accurate, precise, both, or neither.

3. Gravimetric Analysis

A) State four desirable properties of a gravimetric precipitate.

1- Complete reaction. Formed from low K_sp reaction.

2- Large precipitate particles for easy filtration.

3- Definite and known final chemical composition.

4- High molecular weight for increased measurement precision.

B) A 0.773 g sample containing Ni (F.W. 58.693) was dissolved in acid and subsequently treated with dimethylglyoxime (F.W. 116.12) precipitating all Ni as bis(dimethylglyoximate) nickel(II) complex (F.W. 288.91). Find the weight % of Ni in the sample if the precipitate weighed 2.990 g.

First, calculate the weight of Ni in the sample

Second, calculate the wt % in the sample,

3. Precipitation Titrations/Chemical Activity

(a) What volume (mL) of 0.100 F potassium iodide, KI, titrant is needed to reach the equivalence point for 25.0 mL of a solution of 0.050 F Hg₂(NO₃)₂ if the reaction is Hg₂²⁺ + 2I^- ® Hg₂I₂(s)?

(b) Using activities, calculate the molar solubility of Hg₂I₂ (K_sp=4.5´ 10^-29) in 0.050 F KNO₃

The solubility for Hg₂I₂ is found from

We need the activity coefficients for Hg₂²⁺ and I^-. The ionic strength is due to the soluble 0.050 F KNO₃ solution.

At this ionic strength, the table values for the activity coefficients are

The molar solubility is found by considering the change in concentrations starting with the solid

From the K_sp equation

Since x=[Hg₂²⁺], it is the molar solubility.

4. Acid-Base Titrations/Advanced Acid-Base Chemistry

The amino acid, methionine, is diprotic with a carboxylic acid pK_a1=2.20 and an ammonium pK_a2=9.05. In this problem, 10 mL of a 0.1 F solution of this amino acid is titrated with 0.1 F NaOH titrant.

(a) Below is the resulting titration curve. Indicate the two points where the solution has the maximum buffer capacity by A and C, and indicate the first and second equivalence points as B and D. Label the Titrant Volume axis markers.

(b) There are simple expressions for the pH at points A, B, and C. What are the pH's at these points? Give the equations below and put numbers on the pH axis on the above plot.

(c) At what pH would you want your indicator color change to occur at in order to titrate to the first equivalence point? Around the first equivalence point, the pH~6. This would be a good choice for the indicator pK_a

5. Electrodes

A) Calculate the electrode potential of the electrode, Ag/AgI/I^- (A = 0.001)// given

The overall electrode reaction is

It is easiest solved starting with the Nernst equation for silver reduction

B) Give two sources of error associated with pH measurements using the glass membrane electrode.

1- Alkali error (at high pH)

2- Acid error (at low pH).

Also valid: calibration errors, temperature errors. etc. (errors due to poor calibration or environmental drift)

6. Analytical Separations

A solute with a partition coefficient of 5.0 is extracted from 20 mL of phase 1 into phase 2.

A) What volume of phase 2 is needed to extract 99% of the solute in a single extraction?

B) What total volume of phase 2 is needed to remove 99% of the solute in three equal extractions?

C) Write the number of the type of chromatography after the appropriate description. 1-absorption chromatography, 2-partition chromatography, 3-ion-exchange chromatography, 4-molecular size exclusion chromatography, 5-affinity chromatography

Solute equilibrates between mobile phase and film of liquid attached to stationary phase 2

Different-sized solutes penetrate voids in stationary phase to different extents 4

Solute equilibrates between mobile phase and surface of stationary phase 1

Mobile phase ions attach to counter-ions covalently attached to stationary phase 3

Solute is attracted to specific groups covalently attached to stationary phase 5

D) Which column is more efficient, one with HETP=0.1 mm or one with HETP = 1 mm? The one with HETP=0.1 mm has more separation plates per unit length and is thus the more efficient.