Chang chemistry 9th edition solutions

Nov 16, Kruse page 1 of Lecture Material It contains the following sections: solutions manual, study guide, ARIS assessment, review and instruction system Physical and chemical properties of Matter; Measurement; Handling numbers; Dimensional analysis in solving In the Chang, Raymond. Physical Chemistry for the Biosciences. Sausalito, USA: University. Science Books, Student Solutions Manual by Brandon J. If you have a Distinguish between physical and READ: 1. DO: Questions and Chemistry Course Manual.

Fall Section B. Date Last Revised: Fall Chemical reactions in solution e. Thermochemistry f. Quantum theory, atomic and Chemistry, 12th Edition , by Raymond Chang.

Completion of all laboratory experiments, with the Week 3: Physical Properties of Solutions: solution nomenclature, concentration units, and solution Physical Science Department. Course Syllabus. Topics covered include intermolecular forces, properties of solutions, chemical kinetics, equilibrium, thermodynamics, acids and bases, and electrochemistry.

Goldsby; McGraw Hill, New. Raymond Chang. Chemistry 6th Edition. Rodney J. Physical Chemistry. Graduate Assistant, Chemistry Dept. District, Tucson, AZ. Chang, R. Student Solutions Manual to Accompany Raymond. Chang's General Chemistry. Course Syllabus Edition, Raymond Chang and Kenneth A. York; Chemistry, 5 th. Fay; Prentice Hall, New Jersey;. Engineering mahagement challengcs in the new millennium. Rebert Norlon. Chapter 18 The potential in the presence of base would be more negative because the nickel ion activity in this solution would be far less than 1 M.

Consequently the driving force for the reduction if Ni II to the metallic state would also be far less, and the electrode potential would be significantly more negative. Chapter 18 0. Chapter 19 Chapter 19 The electrode potential of a system that contains two or more redox couples is the electrode potential of all half-cell processes at equilibrium in the system. Equivalence refers to a particular equilibrium state when a stoichiometric amount of titrant has been added.

A specific indicator exhibits its color change as a result of reactions with a particular solute species. For points before the equivalence point, potential data are computed from the analyte standard potential and the analytical concentrations of the analyte and its reaction product.

Post-equivalence point data are based upon the standard potential for the titrant and its analytical concentrations. The equivalence point potential is computed from the two standard potentials and the stoichiometric relation between the analyte and titrant. In contrast to all other points on the titration curve, the concentrations of all of the participants in one of the half-reactions or the other cannot be derived from stoichiometric calculations.

Instead, the equivalence point potential is computed from the two standard potentials and the stoichiometric relation between the analyte and titrant.

An asymmetric titration curve will be encountered whenever the titrant and the analyte react in a ratio that is not An external source would be needed to force this reaction to occur. Chapter 19 Because Ecell is negative, the spontaneous reaction is not oxidation on the left and reduction on the right. Chapter 19 Because Ecell is negative, the reaction woulds not proceed spontaneously in the direction considered reduction on the left, oxidation on the right.

Note that in these calculations, it is necessary to round the answers to either one or two significant figures because the final step involves taking the antilogarithm of a large number. Chapter 19 0. Chapter 19 2. Eeq, V Indicator a 0. For example, at The results appear in the spreadsheet that follows. Equivalence Point, For example, Chapter 19 c The data points for this titration, which are found in the spreadsheet that follows, are obtained in the same way as those for parts a and b.

Chapter 19 d The results for this titration are obtained as in parts a and b. Chapter 19 Post-equivalence Point. Chapter 20 Chapter 20 Only in the presence of Cl— ion is Ag a sufficiently good reducing agent to be very useful for prereductions.

Standard solutions of reductants find somewhat limited use because of their susceptibility to air oxidation. Cerium IV precipitates as a basic oxide in alkaline solution. Chapter 20 permanganate ion. By removing the dioxide at the outset, a much more stable standard reagent is produced. Standard permanganate and thiosulfate solutions are generally stored in the dark because their decomposition reactions are catalyzed by light. The solution concentration of I3— becomes stronger because of air oxidation of the excess I—.

Starch decomposes in the presence of high concentrations of iodine to give products that do not behave satisfactorily as indicators. This reaction is prevented by delaying the addition of the starch until the iodine concentration is very small. Chapter 20 2. Chapter 20 0.

See spreadsheets on the following pages. Chapter 21 Chapter 21 This potential arises from dissimilarities between the inner and outer surface of the membrane.

Therefore, if ppt accuracy is needed, a titration should be picked. Thus, pick potential measurements if activity is the desired quantity. Chapter 21 The potential arises from the difference in positions of dissociation equilibria on each of the two surfaces. This charge difference, or potential, serves as the analytical parameter when the pH of the solution on one side of the membrane is held constant.

In order for a glass membrane to be pH sensitive, it is necessary for the two surfaces to be hydrated so that the equilibria shown in the previous problem can be established. Uncertainties include 1 the acid error in highly acidic solutions, 2 the alkaline error in strongly basic solutions, 3 the error that arises when the ionic strength of the calibration standards differs from that of the analyte solution, 4 uncertainties in the pH of the standard buffers, 5 nonreproducible junction potentials with solutions of low ionic strength and 6 dehydration of the working surface.

Because of variables that cannot be controlled, it is necessary to calibrate the response of the electrode against one or more standards. Chapter 21 standard is replaced by the test solution. The uncertainty associated with this assumption translates into uncertainties in the second decimal place of the measured p-value. The alkaline error arises when a glass electrode is employed to measure the pH of solutions having pH values in the 10 to 12 range or greater.

In the presence of alkali ions, the glass surface becomes responsive to not only hydrogen ions but also alkali metal ions. Measured pH values are low as a result. A gas-sensing probe functions by permitting the gas to penetrate a hydrophobic membrane and altering the composition of liquid on the inner side of the membrane.

Thus, there is no direct contact between the electrodes and the test solution as there is with membrane electrodes. Chapter 21 this potential is the boundary potential.

It is caused by charge separation created by the differences in the rates at which ions migrate across the interface. The source of this potential is the same as described in part b. The direct potentiometric measurement of pH provides a measure of the equilibrium activity of hydronium ions in the sample.

A potentiometric titration provides information on the amount of reactive protons, both ionized and nonionized, in the sample.

Chapter 21 result is analyte concentration even though the electrode responds to activity, thus ionic strengths are not important. This relationship has been adopted throughout the world as the operational definition of pH. The result is shown in cell D22 of the spreadsheet. Chapter 21 For the titration curve, plot the potential in column D vs.

For the first derivative, plot the derivative in column H vs. For the second derivative, plot the derivative in column L vs. The plots follow.

As can be seen in the plots, the maximum of the first derivative does not coincide with the equivalence point, nor does the zero crossing of the second derivative.

Our slope is slightly higher than this as shown in the spreadsheet above, but the plot is linear. Hence, we conclude that the Nernst equation is obeyed with a slightly larger than theoretical slope. Theoretically the slope should be —0. Our slope is almost exactly this as shown in the spreadsheet above.

The plot is linear so we can conclude that the Nernst equation is obeyed with a nearly theoretical slope. Chapter 22 Chapter 22 In Kinetic polarization, the current is limited by the rate at which electrons are transferred between the electrode surfaces and the reactant in solution. For either type, the current is no longer linearly related to cell potential. Migration is the movement of an ion under the influence of an electrostatic attractive or repulsive force.

The reference electrode is an electrode of constant potential against which the potential of the working electrode is measured. The control circuit regulates the applied potential such that the potential between the working electrode and a reference electrode in the control circuit is constant and at a desired level. It is the difference between the theoretical cell potential and the actual cell potential at a given current.

Chapter 22 c In controlled-potential electrolysis, the potential applied to a cell is continuously adjusted to maintain a constant potential between the working electrode and a reference electrode. The time required to generate enough reagent to complete the reaction is measured.

Diffusion arises from concentration differences between the electrode surface and the bulk of solution. Migration results from electrostatic attraction or repulsion. Convection results from stirring, vibration or temperature differences. A current in an electrochemical cell always causes the cell potential to become less positive or more negative.

Variables that influence concentration polarization include temperature, stirring, reactant concentrations, presence or absence of other electrolytes and electrode surface areas. Both kinetic and concentration polarization cause the potential of an electrode to be more negative than the thermodynamic value. Concentration polarization results from the slow rate at which reactants or products are transported to or away from the electrode surfaces.

Kinetic polarization arises from the slow rate of the electrochemical reaction at the electrode surfaces. Chapter 22 Kinetic polarization is often encountered when the product of a reaction is a gas, particularly when the electrode is a soft metal such as mercury, zinc or copper. It is likely to occur at low temperatures and high current densities. High concentration of an inert electrolyte, called the supporting electrolyte, are used to minimize the contribution of migration to concentration polarization.

The supporting electrolyte also reduces the cell resistance, which decreases the IR drop. Potentiometric methods are carried out under zero current conditions and the effect of the measurement on analyte concentration is typically undetectable.

In contrast, electrogravimetric and coulometric methods depend on the presence of a net current and a net cell reaction i. Unlike potentiometric methods where the cell potential is simply the difference between two electrode potentials, two additional phenomena, IR drop and polarization, must be considered in electrogravimetric and coulometric methods where current is present.

Finally, the final measurement in electrogravimetric and coulometric methods is the mass of the product produced electrolytically, while in potentiometric methods it is the cell potential. A depolarizer is a substance that is reduced or oxidized more readily than a potentially interfering species. For example, the codeposition of hydrogen is prevented through the introduction of nitrate ion as a cathodic depolarizer. The species produced at the counter electrode are potential interferences by reacting with the products at the working electrode.

Isolation of one from the other is ordinarily required. As a titration proceeds, the potential of the working electrode will inevitably rise as concentration polarization of the analyte begins. Unless an auxiliary reagent is present to terminate this rise by producing a species that reacts with the analyte, some other species will be oxidized or reduced thus lowering the current efficiency and producing erroneous results. Chapter 22 0.

That is, 0. Eapplied 0. Chapter 22 d 0. Thus, if the cathode is maintained between —0. Thus, if the right electrode is maintained between —0. Deposition of A is complete when 0. Thus, 0. Chapter 22 1 mol Tl 1 mol e 1F 96, C 0. Chapter 22 60 s 1C 1 mol e 1 mol H 2S For sample 1, 1F 1 mol e 1 mol CCl4 4 For sample 1, 0. See spreadsheet, following page. Chapter 23 Chapter 23 Amperometry is a technique in which the limiting current is measured at a constant potential.

In pulse voltammetry, an excitation signal is used that consists of a series of voltage pulses that increase in size linearly as a function of time. The ring- disk-electrode is a modified rotating disk with a second ring-shaped electrode isolated electrically from the center disk.

These electrodes are shown in Figure A diffusion current is a limiting current when analyte transport is solely by diffusion. It is characterized by a parabolic flow profile. Turbulent flow is a type of liquid flow that has no regular pattern. When these are approximately the same, the half-wave potential and the standard potential are essentially equal.

The deposited analyte is later stripped from the working electrode and determined by an electroanalytical method, often voltammetry. In standard voltammetry, the electrode current is measured as a function of applied potential. A high supporting electrolyte concentration is used in most electroanalytical procedures to minimize the contribution of migration to concentration polarization.

Chapter 23 The reference electrode is placed near the working electrode to minimize the IR drop that can distort voltammograms. Most organic electrode processes consume or produce hydrogen ions. Unless buffered solutions are used, marked pH changes can occur at the electrode surface as the reaction proceeds.

In stripping methods, the electrodeposition step preconcentrates the analyte on the surface of the working electrode. Because of this preconcentration step, stripping methods are more sensitive than ordinary voltammetric methods. The purpose of the electrodeposition step in stripping analysis is to preconcentrate the analyte on the surface of the working electrode and to separate it from many interfering species.

The advantages of a hanging mercury drop electrode compared with platinum or carbon electrodes include 1 the high overvoltage of hydrogen on mercury, 2 the ability to form fresh electrode surfaces of reprodcuble area and 3 the reproducible currents that are achieved on a mercury electrode. The disadvantages include 1 its poor anodic potential range, 2 its relatively large residual current, 3 its inconvenience. A plot of Eappl versus log should yield a straight line having a slope of.

The corresponding volumes of titrant are calculated in cells B8:B18 of the spreadsheet. Applying a current of 6. Problems can also arise if the electrode dimensions become comparable to the double-layer thickness or to molecular dimensions.

In some cases for nanoelectrodes, new theories and experimental approaches may be necessary. Chapter 24 Chapter 24 The yellow color comes about because the solution absorbs blue light in the wavelength region nm and transmits its complementary color yellow. The purple color comes about because green radiation nm is absorbed and its complementary color purple is transmitted. Molar absorptivity has the units of L mol—1 cm—1. Deviations from linearity can occur because of polychromatic radiation, unknown chemical changes such as association or dissociation reactions, stray light, and molecular or ionic interactions at high concentration.

A real deviation occurs at high concentrations due to molecular or ionic interactions. Other deviations occur because of the imperfect manner in which measurements are made instrumental deviations or because of chemical changes that occur with concentration and are unknown to the user. Both electronic and vibrational transitions are quantized, that is they occur at specific wavelengths and energies.

Electronic transitions are much higher in energy, involving excitation or relaxation of electrons from one orbital to another, while vibrational transitions involve changes in the vibrational frequency of the atoms in a molecule. Chapter 24 atoms and molecules can undergo electronic transitions while only molecules can undergo vibrational transitions.

Chapter 24 Chapter 24 Plotting these data clearly shows the deviations from linearity that occur 1. Chapter 25 Chapter 25 They exhibit low dark current, but have no inherent amplification. Solid-state photodiodes are semiconductor pn-junction devices that respond to incident light by forming electron-hole pairs. They are more sensitive than phototubes but less sensitive than photomultiplier tubes. Photomultipliers have built-in gains and thus have very high sensitivities. They suffer from somewhat larger dark currents.

They provide low resolution wavelength selection suitable for quantitative work. Monochromators produce high resolution for qualitative and quantitative work. With monochromators, the wavelength can be varied continuously, whereas this is not possible with filters. This device can provide very high resolution wavelength selection, but is relatively slow when acquiring an absorption spectrum over a range of wavelengths due to the necessity of scanning the monochromator.

A diode-array spectrophotometer simultaneously monitors a range of wavelengths determined by the dispersion of the grating monochromator and the width of the diode-array. Chapter 25 wavelength resolution is limited by the dispersion of the monochromator and the separation between the detecting elements in the diode-array. The effective bandwidth of a monochromator is the width in units of wavelength of the band of transmitted radiation measured at one half the height of the band.

On the other hand, qualitative analyses require narrow slits so that any fine structure in the spectrum will be resolved. This can allow differentiation of one compound from another. Photons in the infrared region of the spectrum do not have sufficient energy to cause photoemission from the cathode of a photomultiplier. The iodine prolongs the life of the lamp and permits it to operate at a higher temperature. The iodine combines with gaseous tungsten that sublimes from the filament and causes the metal to be redeposited, thus adding to the life of the lamp.

While offering the advantage of multiple wavelength operation, spectrophotometers are substantially more complex and more expensive than photometers. Chapter 25 polychromator uses a diffraction grating to disperse the spectrum, but contains multiple exit slits, allowing several discrete wavelengths to be monitored simultaneously.

A monochromator can be used to monitor one wavelength at a time while a polychromator can monitor several discrete wavelengths simultaneously. In a double-beam instrument the solvent and solution are irradiated simultaneously or nearly so.

The advantages of the double- beam instruments are freedom from problems arising from fluctuations in the source intensity due to drift in electronic circuits and easier adaptation to automatic spectral recording. The single-beam instrument offers the advantages of simplicity and lower cost. Chapter 25 It compensates for any absorption or reflection losses in the cell and optics. Electrolyte concentration, pH, temperature. Fourier transform IR spectrometers have the advantages over dispersive instruments of higher speed and sensitivity, better light-gathering power, more accurate and precise wavelength settings, simpler mechanical design, and elimination of stray light and IR emission.

In a deuterium lamp, the input energy from the power source produces an excited deuterium molecule that dissociates into two atoms in the ground state and a photon of radiation. As the excited deuterium molecules relaxes, the quantized energy is distributed between the energy of the photon and the kinetic energies of the two deuterium atoms.

The latter can vary from nearly zero to the original energy of the excited molecule. Therefore, the energy of the radiation, which is the difference between the quantized energy of the excited molecule and the kinetic energies of the atoms, can also vary continuously over the same range. Consequently, the emission spectrum is a continuum. A photon detector produces a current or voltage as a result of the emission of electrons from a photosensitive surface when struck by photons.

A thermal detector consists of a darkened surface to absorb infrared radiation and produce a temperature increase. A thermal transducer produces an electrical signal whose magnitude is related to the temperature and thus the intensity of the infrared radiation.

An absorption spectrometer requires a separate radiation source and a sample compartment that holds containers for the sample and blank.

With an emission spectrometer, the sample is introduced directly into a hot plasma or flame where excitation and emission occur. Basically, an absorption photometer and a fluorescence photometer consist of the same components. The basic difference is in the location of the detector. The detector in a fluorometer is positioned at an angle of 90o to the direction of the beam from the source so that emission is detected rather than transmisson.

In addition, a filter is often positioned in front of the detector to remove radiation from the excitation beam that may result from scattering or other nonfluorescence processes. In a transmission photometer, the detector is positioned in a line with the source, the filter, and the detector. The performance characteristics of an interference filter include the wavelength of its transmittance peak, the percent transmission at the peak, and the effective bandwidth.

Chapter 25 d The majority carrier in a semiconductor is the mobile charge carrier in either n-type or p-type materials. For n-type, the majority carrier is the electron, while in p-type, the majority carrier is a positively charged hole. Majority carriers are drawn away from the junction leaving a nonconductive depletion layer. Its wavelength usually differs from that of the radiation reaching the slit from the dispersing element. Chapter 26 Chapter 26 The advantages of spectrophotometers are greater versatility and the ability to obtain entire spectra.

The advantages of photometers are simplicity, ruggedness, higher light throughput and low cost. Conventional spectrophotometers require several minutes to scan the spectrum. Accordingly, diode- array instruments can be used to monitor processes that occur on fast time scales. Their resolution is usually lower than that of a conventional spectrophotometer. Electrolyte concentration, pH, temperature, nature of solvent, and interfering substances.

Chapter 26 Absorbance End Point Volume MnO4- A green filter should be used because the red permanganate solution absorbs green light. After the end point the absorbance becomes independent of titrant volume. The data must be corrected for dilution so Vol, mL A Acorr 0 0 0 1. Chapter 26 The point of intersection of the linear portion of the plot can be determined graphically or evaluated by performing least-squares on the linear portions and solving the two linear simultaneous equations.

Least-squares analysis gives the following results. Chapter 26 We can substitute numerical values to give 0. Applying the equation we developed in Solution we write 0. The data are plotted in the figure that follows. The isosbestic point is estimated to be at nm. We may assume at pH 1.

The approach is identical to that of Solution Plotting the data in the problem gives 0. Chapter 27 Chapter 27 The transition is from the lowest lying excited singlet state to the ground singlet state. The energy of the excited species is decreased by an amount equal to the quantity of vibrational energy transferred. An excited triplet state is produced and the transition is from the excited triplet state to the ground singlet state. Chapter 27 The magnitude of F, and thus sensitivity, can be enhanced by increasing the source intensity, P0, or the transducer sensitivity.

Thus, the ratio does not change nor does the analytical signal. Consequently, no improvement in sensitivity accompanies such changes. Compounds that fluoresce have structures that slow the rate of nonradiative relaxation to the point where there is time for fluorescence to occur. Compounds that do not fluoresce have structures that permit rapid relaxation by nonradiative processes. Organic compounds containing aromatic rings often exhibit fluorescence. Rigid molecules or multiple ring systems tend to have large quantum yields of fluorescence while flexible molecules generally have lower quantum yields.

Excitation of fluorescence usually involves transfer of an electron to a high vibrational state of an upper electronic state. Relaxation to a lower vibrational state of this electronic state goes on much more rapidly than fluorescence relaxation. Fluorescence almost always occurs from the lowest vibrational level of the excited electronic state to various vibrational levels of the ground electronic state. Such transitions involve less energy than the excitation energy.

Therefore, the emitted radiation is longer in wavelength than the excitation wavelength. See Figure A spectrofluorometer has two monochromators that are the wavelength selectors. Most fluorescence instruments are double beam to compensate for fluctuations in the analytical signal due to variations in source intensity. Fluorometers are more sensitive because filters allow more excitation radiation to reach the sample and more emitted radiation to reach the transducer.

Thus, a fluorometer can provide lower limits of detection than a spectrofluorometer. In addition, fluorometers are substantially less expensive and more rugged than spectrofluorometer, making them particularly well suited for routine quantitation and remote analysis applications. Chapter 28 Chapter 28 In atomic emission spectroscopy the radiation source is the sample itself.

The energy for excitation of analyte atoms is supplied by a plasma, a flame, an oven, or an electric arc or spark. The signal is the measured intensity of the source at the wavelength of interest. In atomic absorption spectroscopy the radiation source is usually a line source such as a hollow cathode lamp, and the signal is the absorbance.

The latter is calculated from the radiant power of the source and the resulting power after the radiation has passed through the atomized sample. In atomic fluorescence spectroscopy, an external radiation source is used, and the fluorescence emitted, usually at right angles to the source, is measured. The signal is the intensity of the fluorescence emitted. These collisions lead to slight changes in the energies of the states involved in emission or absorption and thus broadening of the spectral line.

The amount of broadening increases with the increasing concentration pressure of the collision partners and with increasing temperature.

The reverse effect is observed for atoms moving away from the detector. Chapter 28 d Nebulization is the process that converts a liquid into a mist or an aerosol by the flow of gas around the end of a capillary tube the other end of which is immersed in the liquid.

The cathode is constructed from or supports the element whose emission spectrum is desired. It could be eliminated with a perfect blank solution. It is an example of an additive interference. Chapter 28 l A radiation buffer is a substance that is added in large excess to both standards and samples in atomic spectroscopy to prevent the presence of that substance in the sample matrix from having an appreciable effect on the results.

It protects the analyte from forming non-volatile, but less stable interfering compounds. In this way, interference due to ionization of the analyte is minimized. In atomic emission spectroscopy, the analytical signal is produced by the relatively small number of excited atoms or ions, whereas in atomic absorption the signal results from absorption by the much larger number of unexcited species. Any small change in flame conditions dramatically influences the number of excited species, whereas such changes have a much smaller effect on the number of unexcited species.

Ionization interference effects are less severe in the ICP because the large concentration of electrons from the ionization of argon maintains a more-or-less constant electron concentration in the plasma. In the flame, ionization of matrix elements can change the electron concentration and thus the extent of ionization of the analyte.

In atomic absorption spectroscopy the source radiation is modulated to create an ac signal at the detector. The detector is made to reject the dc signal from the flame and measure the modulated signal from the source.

Chapter 28 and atomic emission from the analyte is discriminated against and prevented from causing an interference effect. The resolution and selectivity in ICP emission comes primarily from the monochromator. As a result, a high resolution monochromator can isolate the analyte spectral line from lines of concomitants and background emission.

It can thus reduce spectral interferences. In atomic absorption spectrometry, the resolution comes primarily from the very narrow hollow cathode lamp emission.

The monochromator must only isolate the emission line of the analyte element from lines of impurities and the fill gas, and from background emission from the atomizer. A much lower resolution is needed for this purpose. The temperature and pressure in a hollow cathode lamp are much less than those in an ordinary flame.

As a result, Doppler and collisional broadening effects are much less, and narrower lines results. Thus, the concentration of iron atoms is lower in the presence of sulfate.

A higher temperature flame could be used. The temperatures are high which favors the formation of atoms and ions. Sample residence times are long so that desolvation and vaporization are essentially complete. The atoms and ions are formed in a nearly chemically inert environment. The high and relatively constant electron concentration leads to fewer ionization interferences. Chapter 28 longer path length flames. Also, the high temperature of the plasma reduces the population of atoms in the ground state substantially.

The radial geometry provides better stability and precision while the axial geometry can achieve lower detection limits. Many ICP emission systems allow both geometries. Deviations from linearity at low concentrations are often the result of significant ionization of the analyte. When a high concentration of an easily ionized metal salt is added, the ionization of the analyte is suppressed because of the electrons produced by ionization of the metal. By linear interpolation 0. Chapter 28 Chapter 29 Chapter 29 In a double-focusing spectrometer, an electic sector precedes the magnetic sector.

The time required for an ion to reach a detector at the end of the field-free region is inversely proportional to the mass of the ion. These electrons are attracted to dynodes that are each held at successively higher positive voltage and collisions with the dynodes yields additional cascading electrons.

The temperatures are high which favors the formation of ions. Spectra consist of a simple series of isotope peaks for each element present along with some background ionic peaks. Chapter 29 The ICP torch serves both as an atomizer and ionizer. In an ordinary mass spectrum, the ordinate is ion abundance number of ions, ion current, or counts and the abscissa is the mass-to-charge ratio or sometimes just mass assuming singly charged ions.

Interferences fall into two categories: spectroscopic interferences and matrix interferences. In a spectroscopic interference, the interfering species has the same mass- to-charge ratio as the analyte. Matrix effects occur at high concentrations where interfering species can interact chemically or physically to change the analyte signal.

Internal standards are used in ICP-MS to compensate for instrument drifts, instabilities, and matrix effects when performing quantitative analysis. The higher resolution of the double focusing spectrometer allows the ions of interest to be better separated from background ions than with a relative low resolution quadrupole spectrometer.

The higher signal-to-background ratio of the double focusing instrument leads to lower detection limits than with the quadrupole instrument. With a gaseous ionization source, the sample is first vaporized and then ionized. With a desorption source, the solid or liquid sample is converted directly into gas-phase ions.

Desorption sources have the advantage that they can be used to ionize nonvolatile and thermally unstable compounds. Gas-phase sources are often more reliable and reproducible. Many mass spectral libraries have spectra collected with gas-phase sources like the electron-impact source. The high energy of the beam of electrons used in EI sources is enough to break some chemical bonds and produce fragment ions. Such fragment ions can be useful in qualitative identification of molecular species.

A gas-phase sample is needed for mass spectrometry. The output of the LC column is a solute dissolved in a solvent, whereas the output of the GC column is a gas and thus directly compatible. When vaporized, however, the LC solvent produces a gas volume that is times greater than the carrier gas in GC.

Hence, most of the solvent must also be removed. The ion selected by the first analyzer is called the precursor ion. It then undergoes thermal decomposition, reaction with a collision gas, or photodecomposition to form product ions that are analyzed by a second mass analyzer. A hard ionization source, such as an EI source, is often more useful for structural elucidation because the many fragments provide information about bonding in the molecule.

A soft ionization source can provide accurate information about the molecular mass because the molecular ion is often the most abundant ion produced. Hard ionization sources provide many fragment ions which allows the mass spectrum to be used in qualitative identification. Most mass spectral libraries used in identifying compounds are based on electron-impact ionization, a hard ionization method. Chapter 30 Chapter 30 The rate of the reaction then depends upon the concentration of the isolated reactant A.

The term k2 is the rate constant for the dissociation of the complex to give products. Chapter 30 h An indicator reaction or follow-up reaction is one used to monitor the appearance of a reactant or the disappearance of a product. The indicator reaction must not affect the rate of the reaction of interest. Advantages would include; 1 measurements are made relatively early in the reaction before side reactions can occur; 2 measurements do not depend upon the determination of absolute concentration but rather depend upon differences in concentration; 3 selectivity is often enhanced in reaction-rate methods, particularly in enzyme-based methods.

Limitations would include; 1 lower sensitivity, since reaction is not allowed to proceed to equilibrium; 2 greater dependence on conditions such as temperature, ionic strength, pH and concentration of reagents; 3 lower precision since the analytical signal is lower.

Pseudo-first order conditions are used in kinetic methods because under these conditions the reaction rate is directly proportional to the concentration of the analyte. Chapter 30 k Chapter 30 We report the concentration of the unknown as 5. We would report the unknown concentration as 0. Chapter 31 Chapter 31 A collector ion is an ion added to a solution that forms a precipitate with the reagent which carries the desired minor species out of solution.

A high concentration of salt added to a solution that leads to precipitation of a protein is a salting-out effect. At low salt concentrations, protein solubility is often increased with increasing salt concentration, termed a salting-in effect. The two events are transport of material and a spatial redistibrution of the components.

Precipitation, extraction, distillation, ion exchange. The mobile phase then passes over or through the stationary phase. The variables that lead to band broadening include: 1 large particle diameters for stationary phases; 2 large column diameters; 3 high temperatures important only in gas chromatography ; 4 for liquid stationary phases, thick layers of the immobilized liquid; and 5 very rapid or very slow flow rates.

In gas-liquid chromatography, the mobile phase is a gas, whereas in liquid-liquid chromatography, it is a liquid. Determine the retention time tR for a solute and the width of the solute peak at its base, W. Two general methods for improving the resolution of a column are to increase the column length and to reduce the plate height.

So 3 extractions are needed. Chapter 31 The total volume would be 75 mL with 3 extractions. Wash with several hundred milliliters of water, collecting the liquid from the original solution and washings in a 2. Dilute to the mark and mix well.

Chapter 31 The following spreadsheet is a continuation of the previous spreadsheet. Chapter 32 Chapter 32 In gas-liquid chromatography, the stationary phase is a liquid that is immobilized on a solid.

Retention of sample constituents involves equilibria between a gaseous and a liquid phase. In gas-solid chromatography, the stationary phase is a solid surface that retains analytes by physical adsorption. Here separation involves adsorption equilibria. Gas-solid chromatography has limited application because active or polar compounds are retained more or less permanently on the packings. In addition severe tailing is often observed owing to the nonlinear character of the physical adsorption process.

Gas-solid chromatography is used primarily for separating low molecular mass gaseous species, such as carbon dioxide, carbon monoxide and oxides of nitrogen. Electronic, bubble, bubble with digital readout, digital mass or volume flow meters are used. A chromatogram is a plot of detector response versus time. The peak position, retention time, can reveal the identity of the compound eluting. The peak area is related to the concentration of the compound.

Temperature programming involves increasing the temperature of a gas-chromatographic column as a function of time. This technique is particularly useful for samples that contain constituents whose boiling points differ significantly. Low boiling point constituents are separated initially at temperatures that provide good resolution.

As the separation proceeds the column temperature is increased so that the higher boiling constituents come off the column with good resolution and at reasonable lengths of time. Chapter 32 In open tubular or capillary columns, the stationary phase is held on the inner surface of a capillary, whereas in packed columns, the stationary phase is supported on particles that are contained in a glass or metal tube.

Open tubular columns contain an enormous number of plates that permit rapid separations of closely related species. They suffer from small sample capacities. For satisfactory qualitative data, carrier gas flow rate, column temperature, injection port temperature, and injection volume sample size are among the most important variables. Sample injection volume, carrier gas flow rate and column condition are among the parameters which must be controlled for highest precision quantitative GC. The use of an internal standard can minimize the impact of variations in these parameters.

It is used primarily for detecting analytes that contain phosphorus or nitrogen. Disadvantage: low sensitivity. Disadvantage: destructive. Disadvantage: small linear range. Disadvantages: destructive, not applicable for many analytes. Disadvantages: not widely available, expensive. A hyphenated gas chromatographic method is a method in which the analytes exiting from a column are identified by one of the selective techniques such as mass spectrometry, absorption or emission spectroscopy or voltammetry.

Megabore columns can tolerate sample sizes similar to those for packed columns, but with significantly improved performance characteristics.

Thus, megabore columns can be used for preparative scale GC purification of mixtures where the compound of interest is to be collected and further analyzed using other analytical techniques. The inner surface of a PLOT column is lined with a thin film of a support material, such as a diatomaceous earth.

This type of column holds several times as much stationary phase as does a wall-coated column. Its inner walls are coated with a thin layer of the mobile phase. Bonding involves attaching a monomolecular layer of the stationary phase to the packing surface by means of chemical bonds. Cross linking involves treating the stationary phase while it is in the column with a chemical reagent that creates cross links between the molecules making up the stationary phase. The stationary phase liquid should have low volatility, good thermal stability, chemical inertness and solvent characteristics that provide suitable retention factor and selectivity for the separation.

Fused silica columns have greater physical strength and flexibility than glass open tubular columns and are less reactive toward analytes than either glass or metal columns. Film thickness influences the rate at which analytes are carried through the column, with the rate increasing as the thickness is decreased. Less band broadening is encountered with thin films. Chapter 32 b Band separation is enhanced by maintaining conditions so that k lies in the range of 1 to 10, using small particles for packing, limiting the amount of stationary phase so that particle coatings are thin, and injecting the sample rapidly.

The percentage of the analyte in the unknown by the method of external standards is 0. The internal standards compensate for variations in sample injection volume, carrier gas flow rate, and column conditions. Chapter 33 Chapter 33 Chapter 33 neutral ion-pair or as a result of electrostatic interactions between the ions in solution and charges on the stationary phase resulting from adsorption of the organic counter-ion.

It converts the ionized species used to elute analyte ions to largely undissociated molecules that do not interfere with conductometric detection. It is used for separating high molecular mass polar compounds. It is used for separating high molecular mass nonpolar species. In adsorption chromatography, separations are based on adsorption equilibria between the components of the sample and a solid surface. In partition chromatography, separations are based on distribution equilibria between two immiscible liquids.

In size-exclusion chromatography separations are based on the size, and to some extent the shape, of molecules with little interactions between the stationary phase and the sample components occurring. In ion-exchange chromatography, in contrast, separations are based on ion-exchange reactions between the stationary phase and the components of the sample in the mobile phase. Chapter 33 Gel filtration is a type of size-exclusion chromatography in which the packings are hydrophilic and eluents are aqueous.

Gel permeation chromatography is a type of size-exclusion chromatography in which the packings are hydrophobic and the eluents are nonaqueous.

Nonvolatile and thermally unstable compounds. In an isocratic elution, the solvent composition is held constant throughout the elution. Isocratic elution works well for many types of samples and is simplest to implement. In a gradient elution, two or more solvents are employed and the composition of the eluent is changed continuously or in steps as the separation proceeds.

Gradient elution is best used for samples in which there are some compounds separated well and others with inordinately long retention times.