• Calibrate Buret  2G, 2H

• Prepare and Standardize Sodium Hydroxide Solution  37 C4, C7

• Determination of Potassium Hydrogen Phthalate (KHP) in an Impure Sample  37 C8

Notes: For the analysis of your unknown KHP, use the sample in the vial labeled "KHP Unk". There is enough for at least 4 trials.  Calculate your sample size assuming that your sample is about 50% KHP and plan to use about 40 mL of your standard NaOH solution.  For both of these titrations do an indicator blank.  Add 2 drops of indicator to 50 mL of water and titrate to the color change.  Titrate your samples to the same color (keep the blank) and correct your titrant volume for the amount needed to change the indicator color.  The complete color change should take no more than about 2 drops of titrant.

• Preparation of Standard EDTA Solution  37 E1, E2

• Determination of Magnesium by Direct Titration  37 E3

Notes: Although the EDTA is a primary standard, it is only 99.7% pure. Take this into account when doing your calculation of the concentration of the standard solution.  Use the sample labeled "Mg Titration Unk" and do not dry it.  Dissolve all of the sample in water and dilute to 500.00 mL in a volumetric flask.  Be sure it is thoroughly mixed.  Use a 50.00 mL pipet to transfer an aliquot for each trial.  For an indicator, use Calmagite instead of Eriochrome Black T. It will display the same color change but it is more stable.

Sep 30

• Preparation of Standard Silver Nitrate Solution  37 D1

• Potentiometric Titration of Chloride and Iodide in a Mixture  37 J1, J2

Notes: Use the solid AgNO₃ provided with the samples to prepare your standard solution.  Contrary to the instructions on the vial, dissolve approximately 4.2 grams of the silver nitrate, accurately weighed, and dilute to 250 mL.  This is a primary standard.  

Use the sample labeled "I-Cl Unk" for your analysis and do not dry it. All of the sample must be dissolved in a 250.00 mL volumetric flask. Use a 40.00 or 50.00 mL aliquot for your samples.  It is easiest to use a glass electrode as described in the text. The titration curve will show 2 end points. Do not stop until you have gone past both endpoints. It's a good idea to do a "quick and dirty" titration to determine approximately where the endpoints are before you do the drop wise additions.  For your accurate titrations it is most efficient and accurate to add larger amounts of titrant before and after each end point and successively smaller amounts through the steeper regions of your curve. In the steepest part you should be adding only 1 drop between measurements.  The goal is to measure the millivolts after each addition with many values through the equivalence points and, for efficiency, few in the regions bracketing the equivalence points.

Use second derivative plots, as described in class, to determine the endpoints and uncertainties.  

Oct 14

• Spectrophotometric Determination of pH  37 N4

Notes: Use the sample labeled "Spectro pH Unk." Measure the pH of 3 or 4 aliquots of the sample solution spectrophotometrically, as described in your text.  Using the diode-array spectrophotometer, measure and record the absorbance values at each of two wavelengths at, or near, the peaks for each of the two forms of the indicator.  This may not be as clear as intended so be sure to ask for clarification.  Do your measurements in duplicate.  Report the mean pH and the precision and uncertainty.  Note that the equilibrium constant for the indicator is strongly dependent on ionic strength.  Refer to H. Yamasaki, R. P. Sperliine, and H. Freiser, Anal. Chem. 1992, 64,2720-2725, for the appropriate value of Ka to best match your solution composition.

Oct 28

• Determination of Ethanol in a Beverage by Gas Chromatography  37 R1, 

Notes: Use the internal standard method.  Use the sample labeled "GC Alcohol Unk."  Be certain to record the brand and any other information provided.  Accurately prepare a set of 4 standard solutions containing 10%(vol) of propanol and 2, 5, 10 and 15%(vol) of ethanol, respectively. Prepare a diluted sample of your unknown containing 10.0% (vol) of propanol and an amount of unknown so that the solution contains between, approximately, 2 and 10%(vol) of ethanol.  Use the approximate value of your unknown sample to determine how much to use.  Prepare these solutions in 25 or 50mL volumetric flasks.

Use the gas chromatograph to determine the areas for the ethanol and propanol peaks from each solution.  Adjust the attenuation so that both of the peaks are at least 10% of full-scale and less than 100% of full-scale (not clipped at the top or bottom).  Be sure to record the instrument settings for each chromatogram.  This includes column temperature, flow rate and injection volume. Do at least one set of injections for your standards and three for your unknown solution.  Cut the labeled chromatograms into small sections and attach them in your notebook, together with the instrument settings for each.  

Plot the area ratios (A_etOH/A_prOH) for the standards vs. the volume of standard ethanol.  Use regression analysis to determine the concentration of ethanol in  the diluted sample.  Also use the regression calculations to determine  the uncertainty and precision of your results as described in the text  Report the corresponding values for the original sample.

Nov 6

• Potentiometric Determination of Solute Species in a Carbonate Mixture 16 B2, 37 J3

Notes: Use the sample labeled "Carbonate Mix Unk". Use 10.00 mL aliquots of your sample for each trial. Titrate one aliquot of your unknown solution with standardized HCl solution, measuring the pH of the solution as the HCl is added.  Be sure to adjust the HCl volume increments to determine the equivalence point efficiently, with reasonable accuracy, i.e., the smallest increments in the steepest regions of the curve.  Plot your data and compare to Figure 16-1.  Based on this comparison, determine the sample composition and the appropriate method of analysis. Note: you may need to prepare and standardize a solution of NaOH, depending on the sample composition.   Using the method identified for your sample, titrate the remaining samples to the indicator endpoints as described.  Report the mass (mg) of each carbonate-containing species in your original sample.  Also report the equilibrium constants as described. 

Nov 28

• Determination of Manganese in Steel   37 N3,  

• Checkout

Notes: Use the sample labeled "Steel Unk". Calculate the sample size based on the approximate percent of manganese. Prepare a series of standard addition solutions with volumes of 0.00, 1.00, 2.00, 3.00, 4.00 and 5.00 mL of the standard Mn solution. Each solution must also contain a constant volume of a diluted solution of your unknown.  Choose a sample solution dilution which will have a manganese concentration approximately equal to 1 -2 mL of standard manganese when mixed and diluted.  Please note: this is an extension of the solution set shown in the Table shown in the Procedure in the text.  Measure the absorbance of each standard solution at least once and your unknown at least twice.

Plot the absorbance of the solutions vs. the amount of Mn added to each.  Use regression analysis for the method of standard additions, as described in the text and in: Bruce, G. R.; Gill, P. S. J. Chem. Educ. 1999, 76, 805-807, to determine the concentration of Mn in the solution to which no standard Mn has been added, and also the uncertainty and precision.   From these results calculate the percent of Mn in the original sample along with the uncertainty and precision for your analysis of the original sample.