Analytical Chemistry Flashcards
Methods of Analyses
Classical Methods
1. Gravimetric Method
2. Volumetric Method
Modern Methods
1. Spectroscopic Method
2. Electroanalytic Method
deals with measurement of the mass of a substance that is chemically related to the analyte
Gravimetric Method
measures the volume of solution necessary to react completely with the analyte
Volumetric Method
measures the electromagnetic radiation produced by the analyte or its interactions with it
Spectroscopic Method
measures the electrical properties of the analyte such as current (A), potential (V), resistance (Ω), and amount of charge (coul)
Electroanalytic Method
Steps on Gravimetric Method
Gravimetric Factor = (MW of analyte / MW of ppt) × (x analyte / y ppt)
%analyte = (m_ppt × GF) / m_sample × 100
[Volumetric Method of Analysis]
solution of known concentration
Standard Solution
[Volumetric Method of Analysis]
process of determining the concentration of an unknown solution
Standardization
[Volumetric Method of Analysis]
a substance of high purity used for standardization
Primary Standard
[Volumetric Method of Analysis]
Characteristics of Good Primary Standard
- high purity and eq. wt.
- stable towards air, high T, humidity
- soluble in water
type of titration
the analyte reacts with the standard solution directly
Direct Titration
type of titration
an excess standard solution is added and the excess is determined by the addition of another standard solution
Back Titration
type of titration.
the analyte is converted to a product chemically related to it and the product of such reaction is titrated with a standard solution
Replacement Titration
type of titration
the analyte is converted to a product chemically related to it and the product of such reaction is titrated with a standard solution
Lewis Acid and Base
Lewis Acid = electron-pair acceptor
Lewis Base = electron-pair donor
Bronsted-Lowry Acid and Base
Bronsted-Lowry Acid = proton donor
Bronsted-Lowry Base = proton acceptor
Arrhenius Acid and Base
Arrhenius Acid = produces H+ in soln
Arrhenius Base = produces OH- in soln
reaction involving formation of ions
Ionization Reaction
Strong Acids (completely ionized in solution)
HI, HCl, HBr
HNO3, HClO4, H2SO4 (1st ion)
Strong Bases (completely ionized in solution)
Group 1A and 2A bases
Weak Acids (partially ionized in solution)
HF, HCN
H2SO3, H3PO4, organic acids
Weak Bases (partially ionized in solution)
ammonia and derivatives
Autoprotolysis of Water
H2O + H2O ↔️ H3O+ + OH-
Kw = 1×10-¹⁴ at 25°C
pH calculation of Strong Acids
pH = -log [A]
pH calculation of Strong Bases
pH = 14 + log (n_OH × [OH])
pH calculation of Weak Acids
pH = -1/2 log (Ka × [A])
pH calculation of Weak Bases
pH = 14 + 1/2 log (Kb × [B])
strong acid + weak base
acidic salt
strong base + weak acid
basic salt
strong acid + strong base
neutral salt
pH calculation of Acidic Salts
pH = 7 - 1/2 log ( Csalt / Kb )
pH calculation of Basic Salts
pH = 7 + 1/2 log ( Csalt / Ka )
solutions that contain weak acid/base and its conjugate salt; these tend to resist changes in pH
Buffer Solutions
pH calculation of a Buffer Solution
Henderson-Hasslebalch Equation
pH = pKa - log [acid]/[base]
pH = 14 - pKb - log [acid]/[base]
Primary Standards for Bases
Benzoic Acid, C6H5COOH
Oxalic Acid, H2C2O4•2H2O
Potassium Biiodate, KH(IO3)2
Potassium Hydrogen Phthalate (KHP), C6H4(COOH)(COOK)
Sulfamic Acid, HSO3NH2
Primary Standards for Acids
CaCO3
HgO
Na2CO3
THAM, (CH2OH)3CNH2
[Indicators for Acid-Base Titration]
Bromocresol Green
- pH transition range
- color change
- pKa
Bromocresol Green
- pH transition range: 3.8-5.4
- color change: yellow to blue
- pKa = 4.66
[Indicators for Acid-Base Titration]
Methyl Red
- pH transition range
- color change
- pKa
Methyl Red
- pH transition range: 4.2-6.3
- color change: red to yellow
- pKa = 5
[Indicators for Acid-Base Titration]
Bromothymol Blue
- pH transition range
- color change
- pKa
Bromothymol Blue
- pH transition range: 6.2-7.6
- color change: yellow to blue
- pKa = 7.1
[Indicators for Acid-Base Titration]
Methyl Orange
- pH transition range
- color change
- pKa
Methyl Orange
- pH transition range: 3.1-4.4
- color change: orange to yellow
- pKa = 3.46
[Indicators for Acid-Base Titration]
Phenolphthalein
- pH transition range
- color change
- pKa
Phenolphthalein
- pH transition range: 8.3-10
- color change: colorless to pink
- pKa = 9
application of acid-base titration
for determination of organic nitrogen
Kjeldahl Method
Kjeldahl Method Catalysts
K2SO4 - increases BP of H2SO4
HgO - increases rate of reaction
H2SeO3 - best catalyst
formula for %protein in sample
%protein = %N × f
f = 5.7 (cereal)
f = 6.25 (meat)
f = 6.38 (dairy)
precipitation titration is also called _____ titration since _____ is commonly employed in such technique
argentometric, AgNO3
indicators in precipitimetry
Mohr Method
Volhard Method
Fajans Method
Differentiate oxidation and reduction reactions
OIL RIG
Oxidation Is Loss of electrons / RA
Reduction Is Gain of electrons / OA
Balancing Redox Reactions
Write half cell reactions
Determine no. of electrons based on oxidation state
Balance by adding H2O to O-deficient side and H/OH on other side
cathode, anode, reduction, oxidation
AN OX
anode is where oxidation occurs
RED CAT
reduction occurs in cathode
electrochemical cell that stores electrical energy; reaction occurs spontaneously
galvanic/voltaic cell
requires an external source of electrical energy to operate
electrolytic cell
high positive reduction potential means…
good oxidizing agent
thermodynamic potential of an electrochemical cell
Ecell = Ecathode - Eanode
Nernst Equation
E = E° - (RT/nF) ln [C]^c[D]^d / [A]^a[B]^b
at 25°C:
E = E° - (0.0592/n) ln [C]^c[D]^d / [A]^a[B]^b
R = 8.314 J/mol-K
T [=] K
F = 96500 coul/mol e-
n = no. of e- in half cell reaction
describes absorption of radiant energy by matter
Beer’s Law
Beer’s Law formula
A = εbc = log Po/P = log 1/T
T = transmittance
A = absorbance
P = emergent radiation
Po = entering radiation
ε = molar absorptivity
b = thickness
c = concentration
