Category Archives: Essay Question

Titrimetric Analysis of Amino Acids

The quantitative titrimetric analysis of amino acids often is complicated by the high pKa of the —NH4+ group, which produces a titration break that is too small for the effective use of a visual indicator. There are several ways to … Continue reading

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Complexometric Titration of CaO in Limestone: Analysis of Procedure

In the EDTA titration for CaO in limestone, the pH of the sample is made sufficiently basic so any magnesium thatis present will precipitate as Mg(OH)2. The adjustment of pH is fairly critical, as complications  arise if the solution is … Continue reading

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Gravimetric Method for Analysis of Phosphorous: Analysis of Procedure

Once upon a time, a common method for determining phosphorous was to convert it to phosphate, precipitate it as magnesium ammonium phosphate, MgNH4PO4, and ignite it to form magnesium pyrophosphate, Mg2P2O7.  The solubility reaction for MgNH4PO4 is MgNH4PO4(s) ↔ Mg2+(aq) … Continue reading

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Sampling Plan for Cadmium Leeching from Strip Mine

One of the hazards of strip mining is that water passing through the mine’s “tailings” (the piles of discarded material) is often very acidic and contains high concentrations of metal ions, such as Pb2+ and Cd2+. (a) Suppose you are … Continue reading

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Extraction and Analysis of Gingko Leaves

You may know that there is a growing interest in the ginkgo tree because herbal supplements using extracts of ginkgo are believed to aid in fighting memory loss.  A recent paper [Lang, G.; Wai, C. M. Anal. Chem. 1999, 71, … Continue reading

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Developing a Sampling Plan for Lead in Soil

When leaded gasoline was available, automobiles were a significant source of the total yearly environmental emission of Pb.  During internal combustion lead in gasoline, which was present as tetraethyl lead, was vaporized.  The lead, now present as Pb0, adsorbed to … Continue reading

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Separating a Weakly Acidic Analyte from a Weakly Basic Interferent

Imagine  you have an aqueous sample containing a weak acid analyte, HA, and a weak base interferent, HI.  The following information about HA, HI, the method of analysis, and the sample are available to you: Ka,HA = 1.00 x 10-3 … Continue reading

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External Standardization for Copper

To determine the concentration of Cu2+ in a sample of water obtained from a local pond, the following solutions were prepared: Solution I: 5.00 mL of sample diluted to 10 mL in a volumetric flask Solution II: 5.00 mL of … Continue reading

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Analysis of Pb in Biological and Environmental Samples

A paper by Yan, et. al. [Yan, X.-P.; Sperling, M.; Welz, B. Anal. Chem. 1999, 71, 4216-4222] describes a newly developed analytical method for the analysis of biological and environmental samples containing Pb2+ in the presence of a variety of … Continue reading

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Analysis of a Digital Pipet

Mechanical micropipets are commonly used to dispense small (μL) volumes of reagents.  A recent “Application Note” [Am. Lab. June 1999] contains the following data for 50 replicate deliveries of a reagent using a 5.0-μL micropipet. Average volume delivered = 4.967 … Continue reading

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