Analytical Chemistry

-Analysis
-determination of quality and quantity of a sample
-steps of chemical analysis
-determine objective
-determine a method
-acquire sample
-sample preparation
-quantitation (experiment)
-interpretation of results
-evaluation of error
-Errors
-determinate errors
-affect accuracy
-can be constant or proportional
-are controllable (errors in procedure)
-lead to differences between the obtained results and the truth
-detection of constant error
-compare to a norm value
-standards made by National Institute of Standards and Technology
-vary sample weight
-results of common error differ with different sample sizes
-use a different method
-the more different the methods, the more reliable the difference
-indeterminate error
-affects precision
-errors occur in rounding
-determination of a shade of a color
-transfers
-error determined by repetition of experiment
-report mean (average), median, range, or standard deviation (s)
-for small data sets with lots of scatter, the median can be more accurate than the mean
-Data Analysis
-data is easily viewed in a graph
-bell curve
-y = e-[x-m)(x-m)]/2s(s)/s 2p

-s = [S(x-x)2/n-1]1/2 (standard deviation)

-m = Sixi/n (average)
-on the bell curve, m-s to m+s incorporates 68.3% of the area
-Relative Standard Deviation
-s/m (standard deviation/average)
-unitless
-from m + 1.96s to m - 1.96s integrates 90%
-x (+/-) s = m
-m = xbar (+/-) ts/n1/2
-where s is an approximation of s
-degrees of freedom is number of trials - 1
-Central Tendency Theory
-as the number of replicates increases, the average becomes increasingly close to the true value
-Accuracy Determination
-xbar - xaccepted (><) ts/n1/2
-ts/n1/2 represents how much error could have occurred solely on variability
-if ts/n1/2 > xbar - xaccepted, the range falls into random variability and therefore the difference between xbar - xaccepted is insignificant
-if using 2 averages
-s = S(xbarA - xAinitial)2 + (xbarB - xBinitial)2/n-m
-m = number of sets
-Precision Tests
-Fcrit (<>) SA2/Sb2
-rejection of data
-Q = êxq - xn ê/w
-xq = suspect value
-xn = closest neighbor
-w = range of entire set
-Propagation of Error
-s = (sa2 + sb2)1/2
-regression analysis
-difference between the line with the longest difference and the actual data points
-Gravimetric Analysis
-precise, slow, useful
-best when analyte is in high percentage of sample
-components of a mixture
-major
-10% or more
-minor
-.5-10%
-trace
-<.5%
-ultratrace
-100 ppm or lower
-saturation
-Q = value of concentration of solute at instant of addition
-S = solubility of solute
-Q - S = extent of super-saturation
-if Q - S is small, large crystals will form
-Q - S/S = relative super-saturation
-to keep number of precipitant particles low, the relative super- saturation should be small
-size of crystals a S/Q - S
-gravimetric analysis are more successful with substances that have greater solubility
-electrostatic repulsion of crystals causes peptidation
-many small particles
-electrical double layer
-two layers in vaccinity of a phase boundary
-electrostatic interaction between two layers
-isomorphous replacement
-replacement of an ion with an interferent
-strategies
-PFHS
-precipitant forming homogenous substance
-organic precipitant
-not very soluble in water
-heavy
-Titrimetric Analysis
-addition of a titrant with a known morality to determine something about the analyte
-fast reaction, must have large Keq-, hard to detect color change
-types
-acid-base reactions
-precipitation reactions
-titration of Cl- in Ag+
-three types of indicators
-Fajan\'s
-absorption/fluorometric dye
-Mohr
-CrO4- ion in sample solution
-CrO4- turns red when bonded with Ag+
-Valhard
-SCN- + Fe+ ions in solution
-excess added to Cl- solution along with Fe+, then titrate SCN- solution into AgCl solution, and where equilibrium is reached the red Fe(SCN)2 is present
-mercurimetric titration
-Cl- + Hg2+ à Hg2Cl2
-redox reactions
-Moles
-weight units
-percent
-per thousand
-per million
-chemical units
-morality
-formality
-1 mole of solute/ L of solution but solute does not stay associated
-Solubility Equilibrium
-k = [A]n[B]m/[AB]
-ksp = [A]n[B]m
-determination of solubility
-s = M of dissolving stuff
-s = M of formed stuff
-s = (ksp)1/2 (in a 1:1 ratio)
-solubility with indifferent ions
-affected by concentration of indifferent ions
-ions with higher charge have greater effect
-ionic strength (m)
-m = ½Sicizi2
-ci = concentration
-zi = charge type (+1, +2)
-reactivity
-activityx < [x]
-ax = gx[x]
-gx = activity coefficient
-Derive\'s Equation
-(-log)g = .51z2m1/2/1 + 3.3axm1/2
-a = ion size parameter
-ksp/gagb = [a][b]
-pH
-pH = -log[H+]
-pH = -log[H+]gH+
-measurement of pH is (+/-).02 off
-when strong acid or base is dilute
-water serves as a weak electrolyte and will dissociate to a degree
-Cacid = initial concentration
-[H+] = Cacid + [OH-]
-[H+] = Cacid + 10-14/[H+]
-[H+] = Cacid (+/-) (Cacid2 - 4kw)1/2/2
-pH of a weak acid or base
-NH3 + H2O ó NH4+ + OH-
-kb = [NH4+][OH-]/[NH3]
-kb = 1.75 x 10-5
-CNH3 = instantaneous number