Info Tsl
h 0.762 abs units, ta 14.1 s, T 15.8 s, t 1.7 s, At 15.2 s, T' 13.5 s, sensitivity 7.62 x 10-3 ppm-1, about 260-270 samples h 13,700 ppm Cl-0.071 M HCl a 2.52 b 68 samples h c 94.8 w w cocaine 6.27 x 10-4 M H2SO4
M References
1. Goedhart, M. J. Verdonk, A. H. J. Chem. Educ. 1991, 68, 1005-1009. 2. Rousseeuw, P. J. J. Chemom. 1991, 5, 1-20. 3. Ellison, S. Wegscheider, W. Williams, A. Anal. Chem. 1997, 69, 607A-613A. 4. Shoemaker, D. P. Garland, C. W. Nibler, J. W. Experiments in Physical Chemistry, 5th ed. McGraw-Hill New York, 1989, pp. 55-63. 5. Lam, R. B. Isenhour, T. L. Anal. Chem. 1980,52, 1158-1161. 6. Mark, H. Workman, J. Spectroscopy, 1988,3 1 , 44-48. 7. Winn, R. L. Statistics for Scientists and Engineers,...
SOLUTION Trb
Using equation 12.1, we find that the resolution is The time required for unretained solutes to move from the point of injection to the detector tm . The volume of mobile phase needed to move an unretained solute from the point of injection to the detector. The separation between two chromatographic bands R .
Info Arg
gives a value for n of 1.97, or 2 electrons. Combining equations 11.40 and 11.41 shows that the y-intercept for a plot of E versus log i ilim - i is equal to the half-wave potential. Thus, E1 2 for the reduction reaction is -0.391 V versus the SCE. Graphical determination of electrochemical reversibility, n, and half-wave potential in linear scan hydrodynamic voltammetry. Effect of complexation on voltammograms. More Potential More - Effect of complexation on voltammograms. Determining...
P References
1. a Runo, J. R. Peters, D. G.J. Chem. Educ. 1993, 70, 708-713 b Vale, J. Fernandez-Pereira, C. Alcalde, M. J. Chem. Educ. 1993, 70, 790-795. 2. Van Slyke, D. D. J. Biol. Chem. 1922, 52, 525-570. 3. a Bower, V. E. Bates, R. G. J. Res. Natl. Bur. Stand. U. S. 1955, 55, 197-200 b Bates, R. G. Ann. N. Y. Acad. Sci. 1961, 92, 341-356 c Bates, R. G. Determination of pH, 2nd ed. Wiley-Interscience New York, 1973, p. 73. 4. Lambert, W. J. J. Chem. Educ. 1990, 67, 150-153. 5. Kolthoff, I. M. Lingane,...
Volatilization Gravimetry
A second approach to gravimetry is to thermally or chemically decompose a solid sample. The volatile products of the decomposition reaction may be trapped and weighed to provide quantitative information. Alternatively, the residue remaining when decomposition is complete may be weighed. In thermogravimetry, which is one form of volatilization gravimetry, the sample's mass is continuously monitored while the applied temperature is slowly increased. A form of volatilization gravimetry in which...
Nr Nr W
22. A solid sample is known to consist of approximately equal amounts of two or more of the following soluble salts. AgNO3 ZnCl2 K2CO3 MgSO4 Ba C2H3O2 2 NH4NO3 A sample of the solid, sufficient to give at least 0.04 mol of any single salt, was added to 100 mL of water, yielding a white precipitate and a clear solution. The precipitate was collected and rinsed with water. When a portion of the precipitate was placed in dilute HNO3, it completely dissolved, leaving a colorless solution. A second...
Suggested EXPERIMENTS Yqc
The following experiments may be used to illustrate the application of spectroscopy to quantitative or characterization problems. Experiments are divided into four groups those using UV Vis absorption, those using IR absorption, those using atomic absorption or atomic emission, and those using fluorescence. Other experiments are described in the highlighted method sections. A brief description is included with each experiment providing details such as the type of sample analyzed and the method...
Info Hrp
The formation constant for a metal-ligand complex in which only one ligand is added to the metal ion or to a metal-ligand complex K . The formation constant for a metal-ligand complex in which two or more ligands are simultaneously added to a metal ion or to a metal-ligand complex P . This creates a problem since it no longer is clear what reaction is described by a formation constant. To avoid ambiguity, formation constants are divided into two categories. Stepwise formation constants, which...
C Beers Law and Multicomponent Samples
Beer's law can be extended to samples containing several absorbing components provided that there are no interactions between the components. Individual ab-sorbances, A, are additive. For a two-component mixture of X and Y, the total absorbance, Atot, is Atot Ax Ay 8xbCx 8 YbCY Generalizing, the absorbance for a mixture of n components, Am, is given as Calibration curves showing positive and negative deviations from Beer's law. Calibration curves showing positive and negative deviations from...
Info Lwp
Considering these results, discuss the optimum conditions for the determination of Mo by this method. Express your results for the precipitant as the minimum concentration in excess, as w v, needed to ensure a quantitative precipitation. 11. A sample of an impure iron ore is believed to be approximately 55 w w Fe. The amount of Fe in the sample is to be determined gravimetrically by isolating it as Fe2O3. How many grams of sample should be taken to ensure that approximately 1 g of Fe2O3 will be...
H Problems
1. In calibrating a 10-mL pipet, a measured volume of water was transferred to a tared flask and weighed, yielding a mass of 9.9814 g. a Calculate, with and without correcting for buoyancy, the volume of water delivered by the pipet. Assume that the density of water is 0.99707 g cm3 and that the density of the weights is 8.40 g cm3. b What are the absolute and relative errors introduced by failing to account for the effect of buoyancy Is this a significant source of determinate error for the...
O Urw
Oxidation with HNO3 in presence of Ag Combustion in O2 with Pt catalyst in presence of Ag Oxidation with HNO3 in presence of Ba2 Combustion in O2 with Pt catalyst to produce SO2 and SO3 which are collected in dilute H2O2 Reaction with HI to produce RI acidic solution acidified to pH 4.5-5.0 with HCl to prevent the possible precipitation of BaCO3 or Ba3 PO4 2 and performed near the solution's boiling point. The precipitate is digested at 80-90 C for at least 2 h. Ashless filter paper pulp is...
N-h-h Chemistry
When an acid and a base react, the products are a new acid and base. For example, the acetate ion, CH3COO-, in reaction 6.7 is a base that reacts with the acidic ammonium ion, NH4 , to produce acetic acid and ammonia. We call the acetate ion the conjugate base of acetic acid, and the ammonium ion is the conjugate acid of The equilibrium constant for a reaction in which an acid donates a proton to the solvent Ka . Strong and Weak Acids The reaction of an acid with its solvent typically water is...
Q Classifying Analytical Techniques
Analyzing a sample generates a chemical or physical signal whose magnitude is proportional to the amount of analyte in the sample. The signal may be anything we can measure common examples are mass, volume, and absorbance. For our purposes it is convenient to divide analytical techniques into two general classes based on whether this signal is proportional to an absolute amount of analyte or a relative amount of analyte. Consider two graduated cylinders, each containing 0.01 M Cu NC gt 3 2...
Info Rqn
What is the concentration of copper, in micrograms per gram FFDT, for a 11.23-mg FFDT tissue sample that yields an absorbance of 0.023 Linear regression of the calibration standards gives the relationship between absorbance and concentration as Substituting the sample's absorbance into the preceding equation gives the concentration of copper in solution as 0.351 ppm. The concentration in the tissue sample, therefore, is
Characterizing Experimental Errors
Realizing that our data for the mass of a penny can be characterized by a measure of central tendency and a measure of spread suggests two questions. First, does our measure of central tendency agree with the true, or expected value Second, why are our data scattered around the central value Errors associated with central tendency reflect the accuracy of the analysis, but the precision of the analysis is determined by those errors associated with the spread. Accuracy is a measure of how close a...
Mcq On Analytic Chemistry
Weighted normal calibration curve for the data in Example 5.13. The lines through the data points show the standard deviation of the signal for the standards. These lines have been scaled by a factor of 50 so that they can be seen on the same scale as the calibration curve. Weighted normal calibration curve for the data in Example 5.13. The lines through the data points show the standard deviation of the signal for the standards. These lines have been scaled by a factor of 50 so that they can...
Info Mva
Examining equation 6.31 tells us a great deal about the relationship between pH and the relative amounts of F- and HF at equilibrium. If the concentrations of F- and HF are equal, then equation 6.31 reduces to pH p a,HF -log Ka,HF -log 6.8 X 10-4 3.17 For concentrations of F- greater than that of HF, the log term in equation 6.31 is positive and This is a reasonable result since we expect the concentration of hydrofluoric acid's conjugate base, F-, to increase as the pH increases. Similar...
Quality Control
Quality control encompasses all activities used to bring a system into statistical control. The most important facet of quality control is a set of written directives describing all relevant laboratory-specific, technique-specific, sample-specific, method-specific, and protocol-specific operations.1 gt 3-6 Good laboratory practices GLPs describe the general laboratory operations that need to be followed in any analysis. These practices include properly recording data and maintaining records,...
Info Mli
Source Compiled from Parsons, M. L. Major, S. Forster, A. R., App. Spectrosc. 1983, 37, 411-418. Source Compiled from Parsons, M. L. Major, S. Forster, A. R., App. Spectrosc. 1983, 37, 411-418. In atomic emission, the decrease in emission intensity when light emitted by excited state atoms in the center of a flame or plasma is absorbed by atoms in the outer portion of the flame. much higher, background interferences due to molecular emission are less problematic. Emission from the plasma's core...
Fluorometer Diagram
Block diagram for molecular fluorescence spectrometer. Block diagram for molecular fluorescence spectrometer. An instrument for measuring fluorescence that uses filters to select the excitation and emission wavelengths. An instrument for measuring fluorescence that uses a monochromator to select the excitation and emission wavelengths. Two basic instrumental designs are used for measuring molecular fluorescence. In a fluorometer the excitation and emission wavelengths are selected with...
The Laboratory Notebook
Finally, we cannot end a chapter on the basic tools of analytical chemistry without mentioning the laboratory notebook. Your laboratory notebook is your most important tool when working in the lab, providing a complete record of all your work. If kept properly, you should be able to look back at your laboratory notebook several years from now and reconstruct the experiments on which you worked. Your instructor will probably provide you with detailed instructions on how he or she wants you to...
Info Jfa
Because values of aHA may depend on the concentration of HA, equation 10.10 may not be linear. A Beer's law calibration curve of A versus Ctot will be linear if one of two conditions is met. If the wavelength is chosen such that 8HA and SA are equal, then equation 10.10 simplifies to and a linear Beer's law calibration curve is realized. Alternatively, if aHA is held constant for all standards, then equation 10.10 will be a straight line at all wavelengths. Because HA is a weak acid, values of...
SOLUTION Efw
From Table 11.9 we see that the coulometric titration of S2O32- with I3- is 2S2O32- aq I3- aq t S4O62- aq 3I- aq Oxidizing S2O32- to S4O62- requires one electron per S2O32- n 1 . Combining equations 11.23 and 11.24, and making an appropriate substitution for moles of Na2S2O3 gives FW Na2S2O3 Solving for the grams of Na2S2O3 gives ite FW Na2S2O3 This represents the amount of Na2S2O3 in a 10.00-mL portion of a 100-mL sample, thus 0.1325 g of Na2S2O3 is present in the original sample. The purity...
flflB Potentiometric Methods of Analysis
In potentiometry the potential of an electrochemical cell is measured under static conditions. Because no current, or only a negligible current, flows while measuring a solution's potential, its composition remains unchanged. For this reason, poten-tiometry is a useful quantitative method. The first quantitative potentiometric applications appeared soon after the formulation, in 1889, of the Nernst equation relating an electrochemical cell's potential to the concentration of electroactive...
Half Equivalence Point
See Section 2B.2 for a review of chemical equivalents and equivalent weights. The possible formula weights for the unknown weak acid are for n 1 FW EW 58.78 g mol for n 2 FW 2 x EW 117.6 g mol for n 3 FW 3 x EW 176.3 g mol If the weak acid is monoprotic, then the FW must be 58.78 g mol, eliminating ascorbic acid as a possibility. If the weak acid is diprotic, then the FW may be either 58.78 g mol or 117.6 g mol, depending on whether the titration was to the first or second equivalence point....
Info Pnw
Block diagrams for a a turbidometer and b a nephelometer. A method in which the intensity of scattered radiation is measured at an angle of 90 to the source. decrease in the radiation's transmitted power is measured. In nephelometry, scattered radiation is measured at an angle of 90 to the radiation source. The similarity of the measurement of turbidimetry to absorbance, and of nephelometry to fluorescence, is evident in the block instrumental designs shown in Figure 10.54. In fact, turbidity...
G Evaluation
Scale of Operation Molecular photoluminescence can be used for the routine analysis of trace and ultratrace analytes in macro and meso samples. Detection limits for fluorescence spectroscopy are strongly influenced by the analyte's quantum yield. For analytes with Of gt 0.5, detection limits in the picomolar range are possible when using a high-quality spectrofluorometer. As an example, the detection limit for quinine sulfate, for which Of is 0.55, is generally between 1 ppb and 1 ppTr part per...
I Suggested Readings 1
The following general references provide a broad introduction to electrochemical methods of analysis. Bard, A. J. Faulkner, L. R. Electrochemical Methods. Wiley New York, 1980. Faulkner, L. R. Electrochemical Characterization of Chemical Systems. In Kuwana, T. E., ed., Physical Methods in Modern Chemical Analysis, Vol. 3. Academic Press New York, 1983, pp. 137-248. Kissinger, P. T. Heineman, W. R. Laboratory Techniques in Electroanalytical Chemistry. 2nd ed. Marcel Dekker New York, 1996....
Info Byd
accuracy and precision. Detection limits for normal pulse polarography generally are on the order of 10-6-10-7 M, whereas those for differential pulse polarography, staircase, and square-wave polarography are between 10-7 M and 10-8 M. Precon-centrating the analyte in stripping voltammetry lowers the detection limit for many analytes to as little as 10-10 M. On the other hand, the current in stripping voltammetry is much more sensitive than pulse polarography to changes in experimental...
J Suggested Readings 1
For a general history of titrimetry, see the following sources. Kolthoff, I. M. Analytical Chemistry in the USA in the First Quarter of This Century, Anal. Chem. 1994, 66, 241A-249A. Laitinen, H. A. Ewing, G. W., eds. A History of Analytical Chemistry. The Division of Analytical Chemistry of the American Chemical Society Washington, DC, 1977, pp. 52-93. The use of weight instead of volume as a signal for titrimetry is reviewed in the following paper. Kratochvil, B. Maitra, C. Weight Titrations...
D OxidationReduction Reactions
In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are redox reaction not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation...
D Instrumentation
Frequently an analyst must select, from several instruments of different design, the one instrument best suited for a particular analysis. In this section we examine some of the different types of instruments used for molecular absorption spec-troscopy, emphasizing their advantages and limitations. Methods of sample introduction are also covered in this section. Instrument Designs for Molecular UV Vis Absorption The simplest instrument currently used for molecular UV Vis absorption is the...
E Instrumentation
Atomic absorption spectrophotometers Figure 10.37 are designed using either the single-beam or double-beam optics described earlier for molecular absorption spec-trophotometers see Figures 10.25 and 10.26 . There are, however, several important differences that are considered in this section. Atomization The most important difference between a spectrophotometer for atomic absorption and one for molecular absorption is the need to convert the ana-lyte into a free atom. The process of converting...
F Ladder Diagram for OxidationReduction Equilibria
Ladder diagrams can also be used to evaluate equilibrium reactions in redox systems. Figure 6.9 shows a typical ladder diagram for two half-reactions in which the scale is the electrochemical potential, E. Areas of predominance are defined by the Nernst equation. Using the Fe3 Fe2 half-reaction as an example, we write Fe2 Fe2 - 0.05916log--- 0.771V - 0.05916log- J For potentials more positive than the standard-state potential, the predominate species is Fe3 , whereas Fe2 predominates for...
Common Analytical Problems
In Section 1A we indicated that analytical chemistry is more than a collection of qualitative and quantitative methods of analysis. Nevertheless, many problems on which analytical chemists work ultimately involve either a qualitative or quantitative measurement. Other problems may involve characterizing a sample's chemical or physical properties. Finally, many analytical chemists engage in fundamental studies of analytical methods. In this section we briefly discuss each of these four areas of...
Classification of Electrochemical Methods
Although there are only three principal sources for the analytical signal potential, current, and charge a wide variety of experimental designs are possible too many, in fact, to cover adequately in an introductory textbook. The simplest division is between bulk methods, which measure properties of the whole solution, and interfacial methods, in which the signal is a function of phenomena occurring at the interface between an electrode and the solution in contact with the electrode. The...
Answers to Selected Problems
1. a quantitative analysis b qualitative or quantitative analysis c qualitative analysis d characterization analysis e fundamental study f quantitative analysis. 1. a 3 b 3 c 5 d 3 e 4 f 3 2. a 0.894 b 0.893 c 0.894 d 0.900 e 0.0891 3. a 12.01 g mol b 16.0 g mol c 6.022 x 1023 mol-1 d 9.65 x 104 C mol 4. a 71.9 b 39.8 c 6.1 x 103 d 55 e 2.57 x 10-2 f -4.185 g 7.2 x 10-8 h 5.30 x 10-13 8. a 0.20 N b 0.10 N c 0.20 N 10. a 12.0 M b 31.1 g, 26.3 mL 12. 1.80 x 10-5 w v, 0.180 ppm, 1.80 x 102 ppb 15....
Implementing the Sampling Plan
After a sampling plan has been developed, it is put into action. Implementing a sampling plan normally involves three steps physically removing the sample from its target population, preserving the sample, and preparing the sample for analysis. Except for in situ sampling, the analysis of a sample occurs after removing it from the target population. Since sampling exposes the target population to potential contamination, the sampling device must be inert and clean. Once a sample is withdrawn...
G pH of a Polyprotic Acid or Base
A more challenging problem is to find the pH of a solution prepared from a polyprotic acid or one of its conjugate species. As an example, we will use the amino acid alanine whose structure and acid dissociation constants are shown in Figure 6.11. pH of 0.10 M H2L Alanine hydrochloride is a salt consisting of the diprotic weak acid H2L and Cl-. Because H2L has two acid dissociation reactions, a complete systematic solution to this problem will be more complicated than that for a mono-protic...
L Sly
Finally, quantitative problems involving multiple analytes and back titrations also can be solved by applying the principle of conservation of electron pairs. An alloy of chromel containing Ni, Fe, and Cr was analyzed by a complexation titration using EDTA as the titrant. A 0.7176-g sample of the alloy was dissolved in HNO3 and diluted to 250 mL in a volumetric flask. A 50.00-mL aliquot of the sample, treated with pyrophosphate to mask the Fe and Cr, required 26.14 mL of 0.05831 M EDTA to reach...
EE Precipitation Titrations
Thus far we have examined titrimetric methods based on acid-base, complexation, and redox reactions. A reaction in which the analyte and titrant form an insoluble precipitate also can form the basis for a titration. We call this type of titration a precipitation titration. One of the earliest precipitation titrations, developed at the end of the eighteenth century, was for the analysis of K2CO3 and K2SO4 in potash. Calcium nitrate, Ca NO3 2, was used as a titrant, forming a precipitate of CaCO3...
Classifying Separation Techniques
An analyte and an interferent can be separated if there is a significant difference in at least one of their chemical or physical properties. Table 7.4 provides a partial list of several separation techniques, classified by the chemical or physical property that is exploited. The simplest physical property that can be exploited in a separation is size. The separation is accomplished using a porous medium through which only the analyte or interferent can pass. Filtration, in which gravity,...
IG Quantitative Applications Using Molecular Luminescence
Molecular fluorescence and, to a lesser extent, phosphorescence have been used for the direct or indirect quantitative analysis of analytes in a variety of matrices. A direct quantitative analysis is feasible when the analyte's quantum yield for fluorescence or phosphorescence is favorable. When the analyte is not fluorescent or phosphorescent or when the quantum yield for fluorescence or phosphorescence is unfavorable, an indirect analysis may be feasible. One approach to an indirect analysis...
Info Tqy
The amount of ascorbic acid, C6H8O6, in orange juice was determined by oxidizing the ascorbic acid to dehydroascorbic acid, C6H6O6, with a known excess of I3-, and back titrating the excess I3- with Na2S2O3. A 5.00-mL sample of filtered orange juice was treated with 50.00 mL of excess 0.01023 M I3-. After the oxidation was complete, 13.82 mL of 0.07203 M Na2S2O3 was needed to reach the starch indicator end point. Report the concentration of ascorbic acid in milligrams per 100 mL.
C Limitations to Beers Law
According to Beer's law, a calibration curve of absorbance versus the concentration of analyte in a series of standard solutions should be a straight line with an intercept of 0 and a slope of ab or 8b. In many cases, however, calibration curves are found to be nonlinear Figure 10.22 . Deviations from linearity are divided into three categories fundamental, chemical, and instrumental. Fundamental Limitations to Beers Law Beer's law is a limiting law that is valid only for low concentrations of...
A 0.2521 G Sample Of An Unknown Diprotic Weak Acid
H2PO4- and HPO42- VPH gt 0 VMO 0 aVMO and VPH are, respectively, the volume of titrant needed to reach the methyl orange and phenolphthalein end points. bWhen no information is given, the volume of titrant needed to reach either end point is zero. aVMO and VPH are, respectively, the volume of titrant needed to reach the methyl orange and phenolphthalein end points. bWhen no information is given, the volume of titrant needed to reach either end point is zero. Two useful characterization...
D Detectors for Gas Chromatography
The final part of a gas chromatograph is the detector. The ideal detector has several desirable features, including low detection limits, a linear response over a wide range of solute concentrations which makes quantitative work easier , responsiveness to all solutes or selectivity for a specific class of solutes, and an insensitivity to changes in flow rate or temperature. Thermal Conductivity Detector One of the earliest gas chromatography detectors, which is still widely used, is based on...
Effect of Indeterminate Instrumental Errors on Relative Uncertainty in
Equation for Relative Uncertainty in Concentration T readout resolution, noise in thermal detectors positioning of sample cell, fluctuations in source intensity We can derive an expression between precision and transmittance by applying the propagation of uncertainty as described in Chapter 4. To do so we write Beer's law as Using Table 4.9, the absolute uncertainty in the concentration, sC, is given as where st is the absolute uncertainty for the transmittance. Dividing equation 10.27 by...