Chemistry {analytical chemistry} can have analyses. Chemistry techniques are chromatography, conductivity, diffraction, electrolysis, gas pressure, gravimetry, potentiometry, radioactivity, reflectance, resonance, spectrophotometry, spectroscopy, titrimetry, and volumetry.
error types
Error types are measured-value and true-value difference {absolute error}, absolute-error average {mean error}, measured value as percent of true value {relative error, analysis}, and absolute error divided by true value {percent error}. Bad or uncalibrated instruments, careless or suspect operations, incomplete reactions, co-reactions, and material impurities cause error {determinate error}. Errors {indeterminate error} can be random.
Burning {ashing}| requires 400 C to 700 C in furnace, followed by dissolving sample in hydrochloric acid. Lead, zinc, cobalt, antimony, chromium, molybdenum, strontium, and iron evaporate at 500 C. Low-temperature ashing uses microwaves to make oxygen radicals and oxidizes sample at less than 100 C. Oxygen combustion can find carbon and hydrogen amounts. Ascarite absorbs carbon dioxide. Dehydrite absorbs water.
Computer analysis of measurements from many points can display 3D images {Computerized Tomography} (CT) (CAT) from MRI, x-rays, and PET.
Boiling and then condensing liquid {distillation}| can remove impurities.
Frequency spectrum {hyperfine structure, molecule} indicates molecular-orbital type.
In Kjeldahl digestion, nitrogen {nitrogen analysis} makes ammonium sulfate, using potassium sulfate, sulfuric acid, and mercury, copper, or selenium catalyst. Adding sodium hydroxide ends reaction. Distilling into hydrochloric acid finishes analysis.
Experimenters can study surfaces {surface analysis} by low-energy electron diffraction, reflected-light polarization {ellipsometry}, high-curvature electron emission {field-emission microscopy}, edge helium-atom ionization {field-ionization microscopy}, and crystal-hole atom ionization with mass spectroscopy {atom-probe field-ionization microscopy}.
Analysis {chemical analysis} can be qualitative or quantitative. Analysis method depends on speed, cost, instrument availability, and required results.
Analysis {ultramicroanalysis} can be on very small samples, less than 1 milligram.
Analysis {microanalysis} can be on small samples, 1 to 10 milligram or less than 50 microliter.
Analysis {semimicro analysis} can be on medium samples, 10 milligram to 100 milligram or 50 microliter to 100 microliter.
Analysis {macroanalysis} can be on large samples, greater than 100 milligram or 100 microliter.
Analysis {qualitative analysis}| can be about which atoms and molecules are reactants and products, how fast reactions are, or how easy reactions are.
Analysis {quantitative analysis}| can measure reactant and product amounts.
Quantitative analysis tests candidate compounds {sample, chemistry}. Time, randomness, proper conditions, amount needed, and number needed affect sampling. Storing and preserving samples depends on temperature, pressure, dust, gas, evaporation, leakage, light, preservatives, and container material.
Sample parts {constituent, sample} {sample constituent} can be more than 1% {major constituent}, 0.1% to 1% {minor constituent}, or less than 0.1% {trace constituent}.
Samples {sample preparation} can have ashing, centrifugation, chromatography, crystallization, dissolution, distillation, drying, oxidation, precipitation, and reduction.
Apparatus {laboratory equipment} includes glassware and metalware. Apron. Balance. Beaker. Bunsen burner. Cover slip. Crucible. Dissecting needle. Dropper. Dropper bottle. Flask. Forceps. Funnel. Goggles. Graduated cylinder. Lens paper. Petri dish. Pipet or pipette. Razor blade. Ring. Ring stand. Scalpel. Scissors. Slide. Stirring rod. Test tube. Test tube holder. Test tube rack. Thermometer. Thistle tube. Tongs. Watch glass. Wire gauze.
Laboratory heating devices {Bunsen burner}| can provide hot steady smokeless flame. Bunsen burners have short, vertical metal tube, connected to gas source. Tube has perforations at bottom to admit air. Michael Faraday designed Bunsen burner, but the German chemist Robert Wilhelm Bunsen modified it [1855].
Containers {container} can be glass or ceramic. Borosilicate glass, called Pyrex or Kimax, has yellow tinge, melts at high temperature, and resists rapid temperature change. Soft glass has green tinge, and alkali attacks it. Porcelain is inert. Teflon is inert and has high melting point.
Recorders, transducers, alarms, specialized quality-control devices, and test instruments {controller device} can monitor and control chemical processes.
Containers {crucible}| used for heating to high temperature are Gooch, sintered, and porcelain filter.
Machines {dessicator}| {vacuum dessicator} can be for drying.
Paper {filter paper}| can be ashless for burning.
Ovens {furnace, chemistry}| can be for ashing and ignition, up to 1200 C.
Technical grade or commercial grade is lowest grade {grade, chemical} {chemical grade}. U.S.P. is safe for humans. Reagent grade or A.C.S. is high quality. Primary standard is highest quality.
Covered areas {hood}| can conduct fumes to outside building.
Flasks {Kjeldahl flask} can be for digestion and dissolving, with no splattering or bumping.
Furnaces {oven, chemistry} can be for drying.
Bottles {wash bottle} can have spouts for rinsing.
High-speed spinning {centrifugation}| can separate substances by density or particle size. Solid pellet can form at tube end. Sucrose solutions or cesium chloride have a density gradient.
mass
Centrifugation can find molecule mass. Terminal-velocity sedimentation rate through medium depends directly on particle molecular weight. Machine reaches sedimentation rate when molecule cross-sectional size and viscosity balance centrifugal force. Sedimentation rate also depends on temperature and solvent.
polymer
Polymer sedimentation rate depends on volume divided by acceleration. In density gradient, centrifugal force balances polymer diffusion at equilibrium density.
Terminal velocity {sedimentation rate} through medium depends directly on particle molecular weight. Machine reaches sedimentation rate when molecule cross-sectional size and viscosity balance centrifugal force. Sedimentation rate also depends on temperature and solvent. Polymer sedimentation rate depends on volume divided by acceleration.
Two phases in contact, one moving and one stationary, dissolve solute with different solubilities or adsorb solute at different rates {chromatography}|.
purposes
Chromatography is non-destructive, separates mixtures into groups, and can be quantitative.
phases
Stationary phase is starch or diatomaceous earth on columns or plates {chromatograph}. Solid substrate saturates with solvent. Moving phase is solvent at constant pH and salt concentration.
process
Solute in solution starts at saturated-substrate edge. Solvent flows through saturated substrate. Molecules transfer back and forth between mobile and stationary phases.
Depending on relative solubility, molecules spend different times in phases. Molecules that are more soluble in moving phase than in stationary phase move faster. Molecule polarity, size, shape, and charge in solution affect movement rate. Smaller compounds elute faster.
diffusion
Molecules diffuse, so peaks can be wide if flow rate is slow and time is long.
types
Gas or liquid mixtures can separate using gas chromatography, liquid chromatography, supercritical fluid chromatography, or capillary electrophoresis.
At constant pH and salt concentration, liquid or gas solvent {moving phase} flows through stationary phase.
Solvents {eluant} can flow past solid and carry molecules to analyze.
Column efficiency {height equivalent of theoretical plate} (HETP) is column length divided by theoretical plate number, which depends on retention volume divided by baseline peak width. High volume means good resolution, so small HETP is good. HETP depends on sideways diffusion, longitudinal diffusion {band spread}, mass transfer from phase to phase, and flow rate, which depend on viscosity. Optimum flow rate keeps diffusion minimal. Equations {von Deemster equation} can relate these quantities.
Starch or diatomaceous earth {stationary phase} on column or plate chromatographs has solvent at constant pH and salt concentration.
Fluid chromatography {supercritical fluid chromatography} {supercritical fluid extraction} can use carbon dioxide or water above critical point, to analyze labile and low-volatility compounds.
Plots {total ion chromatogram} (TIC) can show retention time versus ion amount.
Molecules in solution, at constant pH and salt concentration, can bind to substrate, coenzyme, or inhibitor attached to agarose resin, as solution flows past resin {affinity chromatography}. After solution passes through resin, solvent at different pH and salt concentration passes through, to remove molecules from resin.
Chromatography {column chromatography} can use column with stationary solid adsorbent, such as cellulose, and moving liquid solvent.
Chromatography {gas-liquid chromatography} (GLC) can use stationary liquid phase and moving gas phase.
purpose
GLC can separate high-volatility substances, such as molecules with carbon, nitrogen, and hydrogen atoms, and determine amounts, with no decomposition. GLC needs only small sample.
process: column
Columns are polyester, silicone polymer, or diatomaceous earth, with varying mesh sizes. Mesh size determines surface area. Columns are 1 to 3 meters long.
process: solvent
Solvent saturates column material. Inert, thermally stable liquids with low vapor pressure can be solvents. Typical solvents are naphthalene or anthracene. Squalene is for non-polar molecules. Amides are for polar molecules.
process: solution
Solution starts at column end.
process: gas
Inert helium or nitrogen gas, at high pressure, is mobile phase.
process: flow
Volatile molecules in solution can separate between gas and liquid phases. More-volatile molecules spend more time in moving gas phase and move faster. High flow-rate minimizes diffusion. Heating makes molecules more volatile. Temperature is 25 C to 150 C. Lower temperature gives better resolution.
volume
Gas volumes {retention volume} elute samples.
time
Columns take time {retention time, column} to elute samples. Retention time depends on number of carbons. Bigger molecules are slower. First sample takes minimum time {dead time}.
detection
To detect sample, use Wheatstone bridge to measure conduction {thermal conductivity} (TCD).
Ionize in flame {flame ionization} (FID), if sample is solid or liquid organic but not carbonyl.
Measure decrease in electron flow {electron capture} (ECD) for halogens, oxygen, nitrogen, and sulfur compounds but not for hydrocarbons, amines, or ketones.
Chromatography {gas-solid chromatography} (GSC) can separate and determine amount, using alumina, silica, charcoal, zeolite, or polymer beads like Porapak as solid.
Liquid-liquid chromatography {high-pressure liquid chromatography} (HPLC) can use high pressure. The 100-atmosphere pressure requires special packing materials, such as Zipax or Coracil bonded beads, with porous-material coatings. Beads can have different sizes. Solvent, pH, ionic strength, and temperature affect HPLC.
purposes
HPLC separates molecules with low vapor pressure and high molecular mass or easily decomposed materials, such as nucleic acids, amino acids, bile acids, drugs, pesticides, herbicides, surfactants, and anti-oxidants. It is fast, is sensitive, and has high resolution.
Molecules or ions in solution can exchange with molecules or ions bound to polymer resin, at constant pH and salt concentration, as solution flows past resin {ion-exchange chromatography}. After solution passes through resin, solvent at different pH and salt concentration, or different solvent, passes through resin to remove bound molecules or ions.
ion types
Polystyrene or CM-cellulose sulfonated groups bind hydrogen ions or sodium ions {cation exchange}. DEAE-cellulose amine groups bind anions {anion exchange}. Anion-exchange resins, such as DEAE Sephadex, can have surface depressions for size separation.
clay
Besides polymer resins, ion-exchange chromatography can use clays, as in water softening, or sodium aluminum silicate zeolites.
chemical activity
Debye-Hückel theory relates potential-energy and chemical-potential lowering to ion solubility. Low chemical potential means solution is more random and more soluble. Ions in solution have more potential energy than uncharged molecules. Ion chemical potential depends on molecule concentration, size, and charge. Other ions go faster or slower as they pass charge. Opposite-charge counterions surround ions, making ions closer together than in random arrangements and lowering potential energy and chemical potential. Counterions shield ions and reduce effective charge, lowering potential energy and chemical potential.
chemical activity: solvent polarization
Solvent has dielectric constant and polarization. Polarization decreases attraction between ions, lowering potential energy and chemical potential. Water lowers chemical potential most, because it has highest dielectric constant.
chemical activity: factors
Lower concentration, higher temperature, higher solvent dielectric constant, lower ion charge, and larger ion size cause lower chemical potential, because potential energy is lower.
chemical activity: field
External electric field increases chemical potential. Negative voltage decreases positive-ion chemical potential, because ions have less-directed motion. Low chemical potential makes low current. Electric field can come from two different ion concentrations or two different phases. At equilibrium, potentials are equal in all phases.
Chromatography {liquid-solid chromatography} {adsorption chromatography} can separate non-polar molecules with different steric or spatial configurations. Adsorption chromatography can separate large amounts. Solid phase is silica, calcium carbonate, charcoal, or alumina, which all adsorb liquid solvents well. Eluant solvent flows past solid, carrying molecules to analyze. Bigger molecules and more polar molecules adsorb better and move slower. Second eluant can elute high-polarity molecules that stay in solid.
Liquid-liquid chromatography {paper chromatography} can separate barbiturates, antibiotics, amino acids, hormones, indoles, and ions. Paper chromatography is cheap, fast, and sensitive. Paper is stationary phase and saturates with solvent. Paper draws mobile phase along by capillary action. Fluorescent dyes stain separated molecules. Ninhydrin stains amino acids.
Chromatography {liquid-liquid chromatography} {partition chromatography} can be for polar molecules. It has high resolution, uses small batches, is more reproducible, and uses lower concentration than adsorption chromatography. Stationary phase is deactivated silica gel, diatomaceous earth, or cellulose, which absorb water. Organic solvents, such as octanol, slightly soluble in water are mobile phase. Solute has relative concentrations in octanol and water. Polarity, hydrogen bonding, and molecule size affect partition. Concentration ratio {partition coefficient} determines mobility.
Solid-liquid chromatography {thin-layer chromatography} can separate amino acids, food colorings, drugs, sugars, dyes, insecticides, ions, and salts. It is cheap, fast, and sensitive. Stationary phase is silica or alumina layer on glass plate. Solvent typically is strong acid or base.
To precipitate salt {crystallization}|, reduce salt solubility. Slow precipitation makes larger crystals, because they can form and reform. Crystals have fewer impurities, because area is smaller. Maintaining low supersaturation, keeping pH low, holding temperature high, and using the most-dilute precipitating agents promotes slow crystallization. After precipitation, add excess agent, lower temperature, and raise pH to ensure complete precipitation. Precipitated crystals adsorb ions. Timed washing can remove impurities. Water washing can dissolve crystal or make colloid. Washing with volatile reagent or with solution with common ion does not dissolve crystal or make colloid.
Other salts can also precipitate {coprecipitation}, trapping or occluding solvent-molecule impurities. Using optimum conditions for reducing solubility minimizes trapped and occluded molecules. Re-precipitation can remove more impurities.
To prevent colloid formation, solutions do not move {Ostwald ripening} while crystals start to form.
X-rays {x-ray crystallography}| {x-ray diffraction} can find atom positions and electron densities. X-rays have wavelength 0.1 nanometers, the same as atom spacing in crystals. Crystal planes reflect x-rays. Large ions polarize easily. Small ions have large field. Cations are less polarizable than anions, because positive charge holds electrons better. Transition metals have bigger fields.
process
Powder rotates for instrument to check all interplanar distances and make one line for each plane, on film. Alternatively, one crystal rotates for instrument to make differing intensity-point patterns, on film.
Interference pattern can calculate spacing between crystal planes: path-length difference = 2 * d * sin(A) {Bragg condition}, where d is distance between planes, and A is angle.
Compounds can dissolve {dissolution, compound}| in fluids. Solid or liquid solute in liquid solvent tends to break into molecules through collisions with surrounding solvent molecules. Solubility depends on melting point and fusion enthalpy. If both are low, solute is easy to disrupt and dissolve, and solubility is high. Solubility is low if chemical potential is high, because solute order is high.
flux
Inorganic compounds can fuse with acid flux, such as hydrochloric acid, nitric acid, or dry perchloric acid. Inorganic compounds can fuse with base flux, such as sodium carbonate. Ratio is 1:10 to 1:20. Flux and compound melt in crucible for 30 minutes until clear, and then cool and dissolve in dilute acid or water.
digestion
Organic materials can dissolve by oxidizing in boiling acid {wet digestion}: nitric and sulfuric acids, or nitric, perchloric, and sulfuric acids.
Adding solvent that does not dissolve well to mixture, and letting mixture and solvent separate, puts solute in new solvent {extraction}|. Extraction solvent can be ammonium chloride, acetic acid, or other salt. In two solvents, equilibrium solute-concentration ratio equals solute-solubility ratio {distribution coefficient}.
Techniques {conductivity measurement} {conductance measurement} can measure total electrolytes in solution.
purposes
Conductivity can detect bath and electrolyte acidity, scrubbing-tank basicity, and water, soil, milk, biological tissue, and ion-exchange-chromatography ions. Conductivity is fast, accurate, and non-destructive.
AC current
AC current prevents decomposition. Low frequency is for high resistance, and high frequency is for low resistance, to keep capacitance low.
ions
Conductivity in solutions depends on solute-ion transport. If ion charge is low, velocity is high, and conductivity is high. Proton goes from water molecule to water molecule directly and so is fast. Big ions have small hydration and small effective size. Ion hydration and ionic interactions affect conductivity.
ions: electrolyte
Strong electrolytes slightly reduce conductivity as concentration increases, because there are more collisions. Weak electrolytes have low molar conductivity, because they do not dissociate. Weak electrolyte causes more variation.
standard
Potassium chloride is standard.
solvent
Solvent-ion collisions affect solute-ion velocity through solvent.
solvent: viscosity
Higher viscosity makes more-random flow and resists conduction.
temperature
High temperature increases conductance.
Techniques {coulometry} can measure charge that has flowed, by weighing metal or gas produced by electrolysis. 1 Faraday = 96487 Coulomb = 1 mole of electrons.
Instruments {coulometer} can have silver anode and platinum cathode in silver perchlorate solution, in series with cell to test. Deposited silver weight indicates total charge that flowed.
Two platinum electrodes can be in iodine and potassium iodide solution. Titration with reducing agent finds iodide-concentration change.
Two platinum electrodes in potassium sulfate solution can produce hydrogen and oxygen gas.
Opposite-charge ions {counterion} surround ions. Opposite charges attract and make ions closer together than in random arrangements, lowering potential energy and chemical potential. Counterions shield ions and reduce effective charge, lowering potential energy and chemical potential.
Potential-energy and chemical-potential lowering depend on ion solubility {Debye-Hückel theory}.
Electric current can reduce metal ion to make metal, separating metal from solution or mixture, for weighing {electrogravimetry}.
Voltage can separate charged molecules in solution {electrophoresis}|. Electrophoresis can use pH gradient.
purposes
Electrophoresis can separate nucleic acids and peptides by size and charge.
process
Solution at constant, buffered pH is in paper or gel. Voltage applied across paper or gel moves charged molecules. The most-highly-charged molecules move most. Molecular size and shape also affect movement.
gel
Gel can be polyacrylamide {polyacrylamide gel electrophoresis} (PAGE). Gel can be agarose sugar, which can have different concentrations to separate different size ranges. Thinner gels allow more resistance and so more voltage compared to current.
detergent
During electrophoresis {SDS-gel electrophoresis}, detergent can coat molecules. Molecules then have same shape and charge, so only molecule size determines separation.
pH
During electrophoresis {zone electrophoresis} {moving boundary electrophoresis}, solution pH can change as solution moves. During electrophoresis {disc electrophoresis}, solution pH in gels can change over time in one direction. During electrophoresis {slab electrophoresis}, solution pH in gels can change over time in two directions.
Iodine in potassium iodide solution is oxidizing agent {iodimetry}. I3- [3 is subscript and - is superscript] ion is at pH 6 to 8. Starch is indicator.
Iodide ion is reducing agent {iodometry}. Sodium thiosulfate titrates iodine. Starch is indicator.
Ion solutions have charge concentration {ionic strength} depending on ion charge and concentration: I = 0.5 * z1^2 * c1 + 0.5 * z2^2 * c2, where z = charge and c = concentration.
pH gradient across solution can move molecules to minimum-charge point {isoelectric point} {isoelectric focusing}.
Charge separation at electrode makes voltage {overvoltage} above standard potential.
Oxidation or reduction voltage change {oxidation-reduction titration} can indicate compound amount. Indicator oxidation increases voltage, by millivolts. Indicator reduction decreases voltage. Indicators and samples can change color.
types
Potassium permanganate is oxidizing agent, which standardizes with sodium oxalate or iron (II) sulfate. Potassium chromate is standard oxidizing agent. Cerium +4 ion in acid is standard oxidizing agent, with ferroin as indicator.
Thiosulfate is reducing agent, which oxygen in water does not oxidize and which standardizes with perchloric acid. Fe+2 ion titrates cerium, chromium, and vanadium ions, with ferroin as indicator. Tin (II) chloride reduces iron.
reactions
Carbon dioxide or acid removes sodium sulfate and sulfur dioxide reducing agents. Acid removes metals like zinc and lead. Phenol removes bromine and chlorine. Hydrazine boiling removes permanganate and peroxide.
Measuring galvanic-cell potential {potentiometry} can find ion concentration.
purposes
Potentiometry measures body-fluid, column-effluent, waste-water, pool, detergent, silver-thiocyanate solution, iodide, bromide, chloride, calcium, nitrate, copper, lead, sulfate, aluminum, phosphate, metal-plating cyanide wastes, bleach-chlorine, paper-bleach, water-pollution, and sewage ions. Titration by potentiometer is accurate.
Potentiometry is for redox reactions, precipitations, acid-base reactions, complexing, or indicators. pH meters and ion detectors use direct potentiometry or potential change followed by titration.
potentiometer
Potentiometers measure voltage at zero current, to eliminate internal resistance. Potentiometer has reference electrode and indicator electrode. Circuit has equal and opposite voltage.
Exact-voltage cells {Weston cell} can calibrate potentiometers.
At halfway to equilibrium, potential equals sample potential. At equivalence, potential is half sum of sample potential and titration ions, if valences are equal. Otherwise, it is weighted average. On graph, steepest slope is equivalence point.
potentiometer: reference electrode
Reference electrodes can change voltage by salt-bridge ion-flow-rate change, temperature change, pH change, electrical-resistance change, and mercury, potassium, or chloride sample contamination.
potentiometer: indicator electrode
Indicator electrodes are for redox reactions. Indicator electrodes must be rapid and exact. If both molecules are ions, electrodes are platinum. If ions are strong reducing agents, electrodes are gold. Strong reducing agents are chromium, titanium, or vanadium. If system uses metal and ion, and metal does not react in water, electrodes are gold. Silver, cadmium, mercury, and copper do not react in water. If system uses metal and low-solubility salt, electrodes are gold. Hydrogen electrode is for pH.
Voltage can determine solution metal concentration {voltametry}.
Techniques {polarography} can measure solution concentration, by diffusion-controlled oxidation or reduction at electrode surface. Voltage relates to metal-ion concentration.
purposes
Polarography measures transition metal ions, inorganic ions, water and blood oxygen levels, and ion resonance in organic compounds, aldehydes, acids, ketones, nitrogen compounds, and halides. Inorganic ions are sulfide, oxide, hydroxide, and chromate. Polarography is sensitive, with ion concentrations from 0.01 M to 0.000001 M.
process
A small electrode receives potential that depletes ions near it. With no stirring, electrode and solution have a concentration gradient. Polarized electrodes block ion flow, so nearby ion concentration is due only to ion diffusion from solution. Diffusion rate depends on concentration, if concentration gradient is constant. Potassium chloride minimizes electrostatic effects. Impurities and capacitances can cause other currents.
types
In electrodes {dropping mercury electrode} (DME), mercury can oxidize, removing oxygen gas from solution. Dropping mercury electrodes, rotating disk electrodes, or ring-disk electrodes remove surface layer.
Polarography methods {amperometry} can measure oxidation or reduction by titration, instead of directly.
Metals {electrode}| can contact solutions. Corrosion, electrolysis, electroplating, and batteries involve electrodes.
oxidation
At anode, ions enter solution, so anode is negative, and solution is positive. Oxidation is at anode surface, and reduction is at cathode surface. Opposite charges surround electrode charges, and solution ions solvate, with high attraction at surfaces. Charge gradient is higher for higher concentration and higher ion mobility. Higher temperature reduces attraction, by breaking up surface layer. Applied electric force reduces attraction.
current
Ion formation or discharge rate is current density, which is 0 at equilibrium. Ion far from electrode feels net force. At 10^-7 meters, ion sees widely distributed charges, as it enters ion layer around electrode and feels constant voltage. When ion reaches electrode surface, voltage changes rapidly to opposite sign. Finally, ion reaches electrode pure metal.
At high current, potential can be constant, such as at hydrogen electrode or calomel electrode. If high overvoltage causes high current density, diffusion can be too slow, and electrode can become polarized. Adding extra potential or moving electrodes reduces polarization. Solution friction causes slower cation flow than electron flow, causes ohmic resistance, and decreases current. Power generation maximizes if concentration polarization is just below limiting current.
Reference electrodes {calomel electrode} can use mercury and saturated mercury chloride. Potassium chloride reduces variation with temperature and can be salt bridge.
Electrodes {glass electrode} can pair with calomel electrodes or silver/silver chloride electrodes. Glass electrodes have silver and silver chloride in 0.1 M hydrochloric acid, in thin glass membrane. Temperature, acidity, and sodium contamination affect it. It requires storage in 0.1 M potassium chloride. It requires cleaning.
Reference electrodes {hydrogen electrode} can use platinum electrodes, with hydrogen gas at one atmosphere and hydrogen ion at one-molar concentration. Hydrogen electrodes can have platinum-surface changes and can vary hydrogen-gas pressure and hydrogen-ion concentration, so they are hard to control.
Silver and silver chloride reference electrode {silver electrode} has saturated silver chloride on silver surrounded by saturated potassium-chloride solution as salt bridge. It is stable at high temperature. It can be internal reference for glass electrode.
Membrane that allows smaller particles to pass but not larger ones can separate larger substances from smaller ones {filtration}|. Filtering {ultrafiltration} can use pressure and membranes with smaller pores.
Porous-material membranes allow small solute and solvent molecules to pass {dialysis}| but stop larger molecules, such as proteins, starches, and nucleic acids. For example, cellophane membranes allow molecules less than 1000 daltons to pass.
purpose
Dialysis dilutes impurities from solutions. Dialysis concentrates large-molecule solutions.
dilution
For example, on one membrane side is salt and large-molecule solution. On other side is water. Net ion flow enters water, because concentration is higher on salt side, so more ions reach membrane each second from concentrated side. Net water flow enters salt solution, because water concentration is higher on water side, so more water molecules reach membrane each second from water side.
concentration
On one membrane side is large-molecule solution. On other side is concentrated-salt solution. Net salt-ion flow enters large-molecule solution, because concentration is higher on salt side, so more ions reach membrane each second from salt side. Net water flow enters salt solution, because water concentration is higher on large-molecule side, so more water molecules reach membrane each second from large-molecule side.
Molecules can separate by size, using agarose, Sephadex, or Biogel beads {gel filtration}. Beads have surface depressions. Same-size or smaller-size molecules stay in depressions and slow, but larger molecules flow past and so exit faster.
Porous-material sheets {membrane, filter}| allow smaller solute and solvent molecules to pass through but stop larger molecules, such as proteins, starches, and nucleic acids.
Techniques {actinometry} can measure incident radiation using a thermopile.
For solution light absorbance, molecule and solvent extinction coefficient A times solution light-path length L times molecule concentration c equals logarithm of transmitted-light percent T {Beers law} {Beer-Lambert law}: A*L*c = log(T). Molecule and solvent extinction coefficient is molar absorptivity. Outer-shell electron transitions are at ultraviolet and visible wavelengths. People know substance extinction coefficients and molar absorptivities, which depend on outer-shell electron-transition energies and probabilities. If molar absorptivity is high, sensitivity is high. Method can also use integrated absorption coefficient or oscillator strength.
Reaction vibrations and rotations can make light {chemiluminescence}.
Molecule structures {chromophore} determine color. For example, retinal visual pigment molecules have chromophore group. Hydroxyl, amine, and halogen groups do not make UV or visible light, but they can affect nearby-chromophore intensity or wavelength. However, groups separated by two single bonds do not affect each other.
Techniques {densitometry} can use UV or visible light to measure absorbance. Absorbance is linear with concentration. Densitometry measures staining in gels.
Absorbed light can re-emit at lower frequency {fluorescence}|.
purpose
Re-emission can measure concentration. Fluorescent dyes can bind to molecules to trace them. Fluorescence is 100 times more accurate than UV-visible methods and is more sensitive. Fluorescence has no interference, because instrument can choose band.
cause
Molecules with rigid co-planar structures, like anthracene and naphthalene, have fluorescence. Electrons can jump to high orbital, fall back to lower excited orbital by short vibration-induced jumps, and then fall to lowest band by spontaneous emission, giving visible light. Lowest band can have vibrational levels. Fluorescence is fast.
compounds
Substances, such as amino acids tyrosine, phenylalanine, and tryptophan, can absorb ultraviolet light and emit visible light.
concentration
If concentration is less than 0.01 M, Beer's law applies.
factors
Solvent, pH, molecule interactions, and temperature affect fluorescence. Higher temperatures cause less intensity, because more jump types are possible. Nitrates quench fluorescence.
phosphorescence
Excited electrons can fall from excited singlet to triplet and then from triplet to singlet ground state if heavy atom collision is available to change angular momentum. In solids, process is slow, so phosphorescence lasts several seconds.
Visible-light detectors {fluorimetry} can be at right angles to exciting radiation from mercury or xenon arc lamps.
Techniques {nephelometry} can measure light scattered at right angles to light path. At dilute concentrations, absorbance is directly proportional to scattering coefficient, path length, and concentration, as in Beer's law. Particle sizes, particle shapes, solution pH, temperature, and mixing can change scattering. Scattering is more if wavelength is less, so UV light causes more scattering. Nephelometry is 10 times more sensitive than turbidimetry.
Techniques {phosphorescence}| can use absorbed-light re-emission. Orbital ground state is singlet with spins paired. Lower excited orbital state is triplet with spins parallel. Higher excited orbital state is singlet with spins paired. Electron can fall from excited singlet to triplet if heavy atom is available to change angular momentum. Electron can fall from triplet to singlet ground state if heavy atom is available to change angular momentum. Electron fall requires heavy-atom collision. In gas, process is fast. In liquids, process is moderate. In solids, process is slow, so phosphorescence lasts several seconds. Electron-gun TV screens and fluorescent lights have phosphor coatings.
fluorescence
Fluorescence uses ultraviolet light to put electrons in high orbitals, from which they fall back to lower excited orbitals, by short vibration-induced jumps, from which they fall to lowest band by spontaneous emission, giving visible light. Fluorescence does not require collisions because momentum does not change, so fluorescence is fast.
Techniques {reflectance analysis} can compare surface refractive-index differences. Reflectance tests paint, fabric, paper, plaster, drugs, glass, food, and ink. Integrating sphere or ellipsoid mirror receives reflected light.
Reflectance {specular reflectance} can be mirror-like. Reflectance {diffuse reflectance} can be from rough surfaces, which have absorption and scattering.
Methods {turbidimetry} can measure light that passes through suspension compared to total light. Suspensions scatter light. Turbidimetry measures air and water particle pollution, finds wine and drug clarity, measures clear-fluid protein, measures bacteria counts, finds sulfur and sulfate levels, and measures plastic polymerization amount.
Methods {x-ray fluorescence} can detect all elements with mass greater than atomic number 12, by bombardment with x-rays. It can find trace elements in ore, blood, art, alloys, soils, and cultural artifacts. Secondary x-rays come from lithium chloride, sodium chloride, or ammonium dihydrogen phosphate. X-rays can excite inner electrons. Proportional counter with pulse-rate analyzer counts only pulses of specific energy ranges. Spectrum identifies atom. Voltage, matrix, wavelength, time, and absorption affect non-linear measurement.
Precipitation {precipitation test} uses tungstic acid, TCA, or barium hydroxide and zinc sulfate. Precipitation with silver ion tests for chloride, bromide, iodide, and thiocyanate ion, with chromate ion and ferric alum as indicators. Weak-acid anion dye, like fluorescein, can bind to precipitate.
Solution can precipitate into large lumps {coagulation}|. Stirring to separate colloidal particles, adding diverse ion to break layers, heating to break layers, and reducing concentration to make ions closer together hinder coagulation.
Cold temperature or organic solvent can precipitate solid from solution {gravimetry}. Precipitate dries in oven to remove water and burn filter paper off, before weighing. Organic precipitates can chelate. Ignition can make oxides or -ate compounds, for easier weighing.
Electromagnetism and radio waves can determine molecule electron configuration {electron spin resonance} (ESR). Unpaired electrons are in free radicals, transition-metal-complex d orbitals, and triplet-state molecules. Unpaired electrons can change spin state.
process
In molecules, net proton spin in nearby atomic nuclei causes magnetic field around electrons to differ. Applying magnetic field and shining microwaves resonates molecule unpaired electron spins, at specific frequencies. Frequency spectrum {hyperfine structure, frequency} can indicate molecular-orbital type.
intensity
Intensity increases as temperature increases, until numbers of ground-state and excited-state molecules are equal.
Techniques {nuclear magnetic resonance} (NMR) {magnetic resonance imaging} (MRI) can measure electron density around hydrogen nuclei and other nuclei that have magnetic fields.
purposes
NMR can detect proton transfers and isomer interconversions. Sample size is 0.1 ml to 0.4 ml. Accuracy is 1/10^8. MRI {functional MRI} (fMRI) can scan body or brain for regions where increased glucose containing oxygen-15 indicates high cellular activity. Blood-oxygen-level dependent (BOLD) method uses blood flow and volume increase with increased metabolism.
theory: spin
Atomic nuclei with odd atomic number or odd atomic mass number have an unpaired proton or neutron and so net spin. Hydrogen and nitrogen have atomic numbers 1 and 7, respectively, and have net spin. Radioactive elements carbon-11, nitrogen-13, and oxygen-15 have net spin.
theory: magnetic field
Charges with net spin make magnetic fields. Proton magnetic moment is small compared to electron magnetic moment, because proton mass is much larger. Applying strong 14000-gauss magnetic field aligns atomic-nucleus protons parallel or anti-parallel with field, because altering proton spin angle requires large torque. Spin and spin angle to applied magnetic field have quanta.
theory: microwave radiation
Parallel and anti-parallel alignments have energy difference at microwave energy levels. Applying microwave radiation can flip protons from parallel to anti-parallel, or vice versa. Microwave wavelength needed to flip indicates nucleus and neighboring-nuclei atomic mass.
theory: neighbor shielding
In molecules, neighboring atoms affect proton magnetic fields. More electrons near atomic nucleus shield it from outside magnetic fields, requiring more microwave energy to change field alignment. Different functional groups attached to hydrogen atom provide more or less shielding. Shielding from lowest to highest is methyl -CH3 [3 is subscript], methylene -CH2 [2 is subscript], methyne -CH, amine -NH2 [2 is subscript], and hydroxyl -OH. Polar molecules have greatest shielding, and non-polar molecules have smallest shielding. Trimethylsilane (TMS) is NMR standard compound, because it has silicon atom surrounded by three methyl groups and so minimum electron shielding.
theory: energy
Total energy of microwave frequency that changes alignment indicates number of hydrogens, or other magnetic nuclei, with same electron environment. For example, TMS has nine protons with same electron environment and has relative total energy nine. Frequency variations around microwave frequency can change alignment. Frequency-variation number indicates number of non-equivalent protons that affect shielding electrons. For example, TMS has zero variations, because all protons are equivalent.
theory: width
Peak width is greater for slow transitions, when inverse of time {relaxation time} in excited state is more, because transverse relaxation gives energy to neighboring nuclei. Transverse relaxation is rapid in solids, so proton NMR does not use solids. Longitudinal relaxation makes heat.
MRI {diffusion tensor imaging} (DTI) can measure water diffusion in tissues.
Ultraviolet, visible, or infrared absorption can determine chemical-bond concentrations {spectroscopy}|.
dipole
Molecules with permanent electric dipole moment have rotational spectra. Molecules with changing dipole moment have vibrational spectra, unless symmetry cancels dipole-moment change. Electronic transitions always cause vibrations through recoil.
Doppler effects
Spectral lines broaden by Doppler shifts. Shift is more if wavelength is bigger, because relativistic effects are greater. Shift is more if temperature is high, because molecular-speed range is wider. Shift is less if mass is more, because same-temperature velocities are lower.
Spectral lines broaden {lifetime broadening} by time {lifetime}| in excited state, because short lifetime means large energy. Lifetime can shorten by stimulated emission by other radiation or by electric-field vibration. Higher frequencies cause faster emission, because they have more energy available. Lifetime can shorten by collisions, because they carry energy away.
Light from lamp containing heavy metal can pass through heavy metals in solution in flame, so metal atoms absorb light to measure metal concentration {atomic absorption spectroscopy} {absorption flame spectroscopy}. Atomic absorption measures percent absorption. For atomic absorption, concentration can be 10 to 100 parts per million.
Metals in solution in flame emit light at strong emission wavelength lines, which can measure calcium, sodium, potassium, and low-molecular-mass-metal concentration {atomic emission spectroscopy} {emission flame spectroscopy}. Sample can be in graphite furnace, carbon-rod analyzer, boat, cup, or atomizer. Premixing is in mixing chamber or by baffles. Flame temperature is low enough not to ionize atoms. Flame excites electrons. Atomic emission detects emission-line intensity. For atomic emission, concentration must be 1%.
Techniques {emission spectroscopy} can detect emitted light. Emission spectroscopy can measure amounts of 80 metallic and metalloid elements in minerals, paint, air pollution, water pollution, and oil. Emission spectroscopy produces spectra in UV-visible range. AC spark is more intense and quantifiable. Laser can measure tiny impurities. Quartz tube with microwave coil can make inductively coupled plasmas.
problems
Emission spectroscopy has matrix effects and non-linear results. Emission spectroscopy detects the most-intense spectrum lines, which are also the most wandering. Emission spectroscopy is destructive, because DC arc ionizes metal atoms.
Spectroscopy {infrared spectroscopy} (IR) can detect functional groups and chemical-bond types. IR is simple, is cheap, uses infrared wavelengths 1 micrometer to 20 micrometers, and has narrow absorption bands. Infrared light source is Nernst glower or nichrome wire. Infrared light detector is thermocouple, thermister, or bolometer. Sodium-chloride prisms or reflection gratings select wavelength. Double beam allows scanning.
solvent
Solids, liquids, and gases have concentration 0.1% to 10%. Water absorbs infrared light, so it cannot be solvent. Carbon disulfide solvent is for wavelengths 7.5 micrometers to 16 micrometers. Carbon tetrachloride solvent is for wavelengths 2.5 micrometers to 7.5 micrometers.
container
Sodium chloride or potassium chloride windows hold sample. Path length is 0.1 millimeters to 1.0 millimeter.
theory
Organic-molecule functional groups have chemical bonds with rotations and vibrations. Rotations and vibrations have energies in infrared-light range. IR typically measures vibrations, rather than rotations, because vibrations have higher energies and frequencies. Rotations appear superimposed on vibrational spectral lines and make wider vibrational bands.
theory: dipole moment
The greater the dipole moment, the greater the infrared frequency. The longest chemical bonds and most-polarized functional groups have highest frequencies. Chemical-bond frequencies from highest to lowest are N-H, O-H, C-H, C=O, C=C, C-O, C-C, and H-H.
theory: rotations
Molecule rotation states depend on molecular symmetries. Spherical molecules have no rotational states. Linear molecules have one state, if they are symmetric along axis. Linear molecules with asymmetry have two states. Asymmetric molecules have three states, one for each axis.
Massive molecules have long dipole and have close rotational energy levels. Molecules with large bond distance have long dipole.
theory: vibrations
Chemical bond has stretching vibration. Two same-atom chemical bonds have bending vibrations. Vibrations involve simple harmonic motion, along bond axis or around bond angle. Vibrations give information about bond rigidity and bond-breaking energies. Strong bonds and long bond distances have more energy and make close energy levels. The most-polarized bonds have longest wavelength.
Bond bending is easier than bond stretching, because forces are less, so bending-vibration frequencies are less than stretching-vibration frequencies.
One bond has one less vibrational state, because rotation around bond makes vibrations cancel, because they have all directions. Homonuclear diatomic molecules have no stretching or bending vibrations, because they have no dipole. Heteronuclear diatomic molecules have only stretching vibrations along one bond.
Molecules with three atoms can have bending vibrations. n atoms can have 3*n vibrational states {degrees of freedom, atom}: three for translations and three or less for rotations. Pi-bond twisting is vibration.
problems
Vibrational energy levels get closer together nearer bond-dissociation energy. Liquids and solids have more vibration effects, because they have bonding and van der Waals forces.
Spectroscopy {mass spectroscopy} (MS) can find atomic and molecular mass. Mass spectroscopy is fast, reliable, expensive, and delicate.
sensitivity
Mass spectroscopy can detect masses from 1 to 400,000 daltons, at concentrations as low as 10^-12 M.
uses
Mass spectroscopy can find molecule functional groups by fragment mass differences. For example, methyl groups have mass 15, CO groups have mass 28, water has mass 18, ammonia has mass 17, and phenyl groups have mass 77.
Mass spectroscopy measures leak detection, blood gases, and tracers and analyzes petroleum, plastics, fertilizers, and insecticides. Mass spectroscopy can detect illegal drugs, impurities, pollutants, reaction products, and toxins in gases, liquids, and solids. Mass spectroscopy determines age, quantifies chemical composition, studies metabolism, detects molecular changes, and monitors chemicals. Mass spectroscopy can sequence peptides.
process
Mass spectroscopy measures mass-to-charge ratio of ionized atoms or molecules.
process: vaporization
A 350-C vacuum chamber heats sample to make gas, which expands into ionization chamber through pinhole.
process: ionization
70-eV electron beams ionize sample molecules to make ions with charge +1. Ionization can use proton transfer from ionized methane. Vaporized molecules can ionize {desorption, mass spectroscopy} by californium-252, secondary ions, lasers, high electric field on thin film, or electrospray from high-voltage needle.
process: electric field
Source positive charge repels positively charged ions into analyzer. Ions enter strong electric field and accelerate through slits to collimate.
process: magnetic field
Ions enter magnetic field and arc in semicircle. Typically, magnetic field or voltage sweeps. Big ions move slower and have big radius. Small ions move faster and have small radius.
process: detector
Ions hit surface with applied voltage, causing charge cascade {electron multiplier}. Ions make current, which can be as small as 10^-15 A. Detector measures ion energy and location. Location indicates ion mass. Energy, converted to electric current or light, indicates ion number.
process: types
Double-focusing mass spectroscopy separates masses first by radial electric field and then by radial magnetic field.
Sector detector uses electric field to focus ions, then magnetic field to spread ions. Larger masses need stronger fields to focus them on detector. Smaller masses need smaller field to bring them to detector. Detector plate converts collision energy into ions or electrons, detected as current, or photons, detected by photomultiplier.
Quadrupole mass filter uses four parallel plates or rods with constant direct-current electric field between two plates and varying radio-frequency electric field between two plates.
Ion traps use two parallel plates and ring electrode to trap ions that have mass range. Electric field increases to eject ions toward detector.
High-resolution detectors can measure dalton fractions. Fourier-transform ion-cyclotron resonance (FT-ICR) can trap ions between electrodes in a magnetic field. Radio-frequency electric field makes ions orbit. Orbiting ions create electromagnetic frequency measured by detector plates.
Time-of-flight (TOF) methods send ions accelerated to constant velocity across distance. Detector measures time and so mass.
Two-stage mass spectroscopy (MS/MS) can separate compound from mixture or separate compound constituents to analyze compound structure.
process: results
If electron-beam energy is high enough, sample has unique ion-fragment pattern {cracking, mass spectroscopy}. Highest-mass peak is original molecule with one electron missing. Pattern depends on chemical-bond strength, atoms, total molecular mass, and ionization potential. Chemical bonds break most easily where molecules branch. Double bonds can break. Saturated ring compounds break at side-chain alpha carbon. Carbonyls break so carbonyl ionizes. Aromatic compounds do not break.
process: isotopes
Isotopes cause peak doubling or tripling. Elements have definite peak-doubling or peak-tripling ratios. F, P, and I have no isotopes. 2H, 15N, and 18O [2, 15, and 18 are superscripts] have negligible amounts.
process: isotope ratios
First, find carbon number. 13C [13 is superscript] is 1.11% of total carbon, so first peak to second peak ratio shows carbon number. Next, find oxygen, sulfur, chlorine, and bromine numbers by isotope ratios. Find nitrogen number. If molecular mass is even, nitrogen number is 0 or even. If molecular mass is odd, nitrogen number is odd. You can also use compound spectra tables.
Spectroscopy {Mössbauer spectroscopy} can study number of s orbitals involved in bonding and study valences. Atomic nuclei absorb gamma rays and then emit them, causing crystal recoil and vibration, which causes Doppler shift in electronic-transition wavelengths. Holding crystal in crystal lattice can minimize recoil. Decay is slow. Line width is small.
Spectroscopy {Near Infrared Spectroscopy} (NIRS) can detect glucose and oxygen by infrared reflection.
Spectroscopy {Raman spectroscopy} can study plastics, waxes, pure organic molecules, complex ions, or non-spherical molecules, by polarizing non-polar bonds with UV or visible light and analyzing infrared radiation.
scattering
UV or visible light scatters from molecules to polarize them, with +2 or -2 total angular momentum. Rayleigh scattering is elastic, with unchanged wavelength. Raman scattering is inelastic, because it makes dipoles, so vibration and rotation energy levels affect it.
polarization
Polarization causes infrared-light emission or absorption at vibration or rotation energies. Raman-scattering vibrations are not infrared. Raman-scattering rotations are infrared. Raman lines can have lower frequency {Stokes line} or higher frequency {anti-Stokes line}.
Spectroscopy {UV-visible spectroscopy} can find solution substance concentrations by measuring visible or ultraviolet light absorbance.
purposes
UV-visible spectroscopy can detect functional groups, bonds, and spatial configurations and so identify molecules. It can find equilibrium point, pH, or pK by comparing absorbance at two wavelengths. UV-visible spectroscopy is simple and cheap.
purposes: visible
Visible light can detect colored molecules, in concentrations down to 0.01 M, using standard curve for calibration.
technique
Extinction coefficient or molar absorptivity depends on outer-shell-electron transition energies and probabilities. Tables show values for most substances. Method can also use integrated absorption coefficient or oscillator strength. If molar absorptivity is high, sensitivity is high. Wavelength is maximum-absorbance wavelength. Bandwidth is broad, because energy is low. Path length through solution is typically one centimeter. Air absorbs light of less than 200-nanometer wavelength, so UV light path has vacuum. Glass absorbs all UV light, so containers are quartz.
theory: transition metal
Transition-metal ions have incomplete d orbitals, with three at lower energy and two at higher energy, which have electronic transitions in visible light. Central transition-metal ions can have two sets of low-energy d orbitals, with no symmetry center from metal-ion bonding orbitals to ligand antibonding orbitals or from metal-ion antibonding orbitals to ligand antibonding orbitals. Then intensity is low, because vibrations can also cause such transitions. High intensity is if charges transfer from ligand to ion, or vice versa.
theory: double bonds
Ultraviolet light can detect molecules with carbon-oxygen double or triple bonds or with carbon-carbon conjugated bonds. Unconjugated double bonds involve UV light. Pi-bond electrons jump to antibonding pi orbital to make UV light.
If double bond conjugates, electron delocalization causes small jump and visible light. Intensity is high.
Indicator color changes are large, because proton gain or loss changes conjugation. More conjugation makes longer wavelengths.
Molecules with lone electron pairs can make UV or visible light by jumping to antibonding pi orbitals, typically forbidden visible-light transitions.
theory: no light
Closed-shell electrons and sigma-bond electrons do not give UV or visible light. Hydroxyl, amine, and halogen groups do not give UV or visible light, but they can affect intensity or shift chromophore wavelengths.
Techniques {x-ray absorption} can find heavy atoms among lighter atoms, such as crystal impurities, gasoline lead, broken bones, barium enemas, body iodide, and steel and plastic faults. Absorption depends on molecular mass, density, and thickness. X-rays can come from electrons that hit metal anode at 80,000 V. X-rays hit target, whose ionization energy allows high primary x-ray absorption {absorption edge} and which emits lower-energy x-rays {secondary x-ray}. Detection is by film.
Electronic transitions cause spectra if asymmetric electron-distribution changes cause transient dipole moments {allowed transition}. Then angular momentum change is +1 or -1. Radiation intensity depends on electronic transition probability. Electric dipoles give highest intensity, because they have allowed transitions.
Symmetric electron-distribution changes {forbidden transition} do not change angular momentum. Electric quadrupoles and magnetic dipoles give low intensity, because they have forbidden transitions.
Reaction with high-concentration titrant {titration}| can measure concentrations in acid-base reactions, precipitations, oxidation-reductions, and complexometric reactions.
complexometric reaction
Reactions {complexometric reaction} can make water-soluble chelate from metal ion and EDTA.
volume
Titrants are at high concentration, so volume used is small.
titrant
Hydrochloric acid is for base titration. Sodium hydroxide is for acid titration.
process
Find acid or base concentration by reacting solution volume with known-concentration base or acid volume, until solution is neutral. pH or voltage changes fast at beginning, then rate becomes small as amounts become almost equal, and then rate becomes rapid again if past titration point. Find concentration by converting volume to mass.
Indicators typically change color at second rapid-rise beginning. Titrating weak acid or base slowly changes pH at pK. When pH = pK, salt and acid or base are equal.
standardization
Sodium carbonate standardizes strong-acid titrant. Find first sodium-carbonate endpoint with phenolphthalein at pH 8.0 to 9.5. Find second endpoint with methyl red at pH 4 to 6. Boiling removes carbon dioxide.
Potassium hydrogen phthalate (KHP) standardizes strong-base titrant. Phenolphthalein is indicator.
oxidation-reduction
For oxidation-reduction reactions, moles times valence {equivalent} depends on charge. Valence divides into molecular weight {equivalent weight}.
back titration
Methods {back titration} can add excess titrant to sample and then find excess titrant by titrating with another titrant.
Sample milligrams can be equivalent to one-milliliter titrant {titer}. Total weight m is titer t times number n of titrant milliliters: m = t*n.
Titration measures concentrations in acid-base reactions, precipitations, oxidation-reductions, and complexometric reactions by reaction with high-concentration solution {titrant}.
Analytical balances weigh dry substances {weighing, analysis}|. First, find weighing-paper, weighing-bottle, or weighing-dish tare weight. Find sample and container weight. Subtract tare weight to find sample weight. Weighing is at constant temperature, usually 24 C. No finger oil and no air drafts can affect sample. Analytical balances are not for sodium hydroxide, hydrogen iodide, hydrogen bromide, iodine, or bromine, which are corrosive.
empty container or holder weight {tare}|.
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0225