Analytical Chemistry Flashcards
Dilution Formula
C1V1=C2V2
V2=V1+V(H2O)
f for Redox Reaction
Number of lost or gained electrons
f for Acid-Base Reactions
Number of participating OH- or H+
Cr2 (SO4)3 • 18 H2O is precipitated as hydroxide. What is the value of f?
f=3 for Cr (OH)3
f=6 for Cr2 (SO4)3
Gravimetric Factor Formula
(MW unknown/ MW given residue) • (mol unknown/ mol given residue)
Percent element in a sample for gravimetry
%X = (mass of residue × GF × 100%) / mass of sample
Aliquot is a portion of the sample. How to relate mass of aliquot to mass of sample?
Use ratio and proportion. Aliquot has the same properties as the sample.
If given total mass of two compounds in a mixture, how to attain their individual masses?
Set up two equations.
Eq 1: X+Y=total mass
Eq 2: set up reactions for X and Y to get the products
Gravimetry where mass of precipitate is the signal
Precipitation Gravimetry
Arrhenius Acid and Base
Acid - produces hydronium ion in aqueous solution
Base - produces hydroxide ion in aqueous solution
Bronsted-Lowry Acid and Base
Acid - proton donor
Base - proton acceptor
Lewis Acid and Base
Acid - electron pair acceptor
Base - electron pair donor
Product of neutralization reaction aside from water
Salt
When benzoic acid is dissolved in water, it partially ionizes forming benzoate and hydronium ion.
Name the parts of the reaction
Benzoic acid - Weak acid
Water - Base
Benzoate - Conjugate base
Hydronium Ion - Conjugate acid
Water at room temperature is more basic. True or False?
False, it is more acidic due to formation of carbonic acid
Differentiate strong acids and weak acids in terms of ionization
Strong acids - 100℅ ionization
Weak acids - partial ionization
Acids that yield more than 1 hydronium ion
Polyprotic Acids
For polyprotic compounds that yields two hydronium ions, K1 is _____ than K2?
smaller? larger? or equal?
smaller
Kn»_space;> … K2 > K1
A mixture of ammonia and potassium hydroxide is considered a ____ base.
Strong or Weak?
Strong Base
pOH = -log (concentration of solution)
pH computation for strong acids and bases
pH = -log [H+]
pOH = -log [OH-]
pH + pOH = 14
pH means…
potential of hydrogen
computation of pH for weak acids
Ka = x² / (Cao - x)
Cao = [(Va)(Ca) / Va+Vt]
a - analyte
t - titrant added
Kw at 25°C
1x10^-14 = [H+][OH-]
Kw at 50 °C
5.5x10^-14
Formula of Kw in terms of equilibrium constants
Kw = Ka•Kb
How to solve equivalence volume
Veq = [(Va)(Ca) / Ct]
At end point = Veq = V(titrant)
Formula for pka, pkb, and pkw
pka = -log (Ka)
pkb = -log (Kb)
pka + pkb = pKw
Combination of weak acid and base and their respective conjugates.
Buffer system
Explain buffer
Weak analyte + Strong titrant = Conjugate + water
Buffer is the mixture of the weak analyte and its conjugate
Equation used when dealing with buffer solutions
Henderson-Hasselbalch Equation
ph = pKa + log (conjugate base/ weak acid) (both at equilibrium)
Increased in buffer capacity will result to…
ratio of base and acid components approaching 1
pH = pKa happens when…
Vt = Veq/2
A-/HA = 1
at maximum buffer capacity
Which of the following acids would be most suitable to prepare a buffer with pH of 4?
a. Alex acid pKa= 2.565
b. Xander acid pKa = 4.150
c. Busto acid pKa = 7.004
c. Harvard acid pKa = 10.000
B. Choose an acid with a pH close to the desired pH of the buffer solution
Kjeldahl Method
Determination of Nitrogen from the conversion of organic Nitrogen to Ammonia, which is separated by distillation and quantified using titration
NH3 + HCl = NH4+ + Cl-
How to get %N in the sample using Kjeldahl method?
NH3 reacted with HCl = HCl used - HCl reacted with NaOH
1 mol of N/ 1 mol of NH3
%N (used gravimetric procedure)
In saponification, esters react with hydroxide to form what products?
Carboxylate ions (RCOO-)
Alcohol (R’OH)
Why does hydroxide and bicarbonate can’t coexist in a solution?
They react with each other forming carbonate ion and water
pH of Phenolphthalein and alkaline ions it detect
8.3
hydroxide and carbonate
pH of bromocresol green and alkalines it detect
4.5
Bicarbonate
Volume of Bromocresol green = 0
Hydroxide
Volume of Phenolphthalein = 0
Bicarbonate
Volume of BCG = Volume of Ph
Carbonate
Volume of BCG > Volume of Ph
Carbonate (Volume of ph)
Bicarbonate (Volume at the end point of BCG - 2 Volume of ph)
Volume of BCG < Volume of Ph
Hydroxide
Carbonate
Uses silver ion as titrant or analyte
Argentometric Titration (Precipitation Titration)
Mohr Method’s Indicator
Alkali Metal Chromate (e.g., K2CrO4)
Titration reaction of Argentometric process
Ag+ + Cl- = AgCl (white precipitate)
Ag+ is supplied in excess
Final indicator of Mohr Method
Ag2•CrO4
brick red precipitate
Favorable pH for Mohr Method
6.5 < pH < 10.3
lower than 6.5 - soluble complex
higher than 10.3 - insoluble hydroxide
Fajan Method’s Indicator
Dichlorofluorescein (DCF-) (green color)
Eosin
Final indicator product of Fajans Method
Ag+• AgCl • DCF- (Pink precipitate)
Indicator of Volhard’s Method
FeSCN^2+ from ferric alum
bloody red precipitate
Favorable condition for Volhard method
Acidic (pH 4-7) to avoid Fe^3+ precipitation
Nickel + Cyanide will form _____ and in what ratio?
Tetracyanonickelate
1 Ni^2+ : 4 CN^-
EDTA
Ethylenediaminetetraacetic acid
C10•H16•N2•O8
Who develop the metal ligand titration methods for determining CN- and Cl-?
Titrants used for the aforementioned ligands?
Julius von Liebig, 1850
Ag+ for CN-
Hg2+ for Cl-
EDTA in neutral form is …
H4Y (tetraprotic, meaning it can exist in variety of protonated protons)
Explain chelating effect
EDTA has a cleating effect, which is the ability to form more stable metal complexes than those formed by similar mono-dentate ligand
Direct titration method for determination of carbonates and hydroxides
Warder Method
Indirect titration method for determination of carbonates and hydroxide
Winkler Method
Titration method used to determine protein content of food products
Kjeldahl Analysis
Milk of magnesia, which is used for antacid and laxative
Mg(OH)2
Slaked lime used in mortar
Ca(OH)2
Titrants for standardization of potassium permanganate (KMnO4)
Sodium oxalate (Na2C2O4)
Pure iron wire (Fe)
Arsenic oxide
Reaction for standardization of KMnO4 using Na2C2O4
2 KMnO4 + 5 H2C2O4 + 6 H+ —
2 Mn2+ + 10 CO2 + 8 H2O
Permanganimetry Redox Couple (pH < 2)
MnO4^- (violet) — Mn^2+ (colorless)
Permanganimetry Redox Couple (5 < pH < 9)
KMnO4^- (violet) — MnO2 (brownish precipitate)
Redox Couple for Cerimetry
Ce^4+ (bright yellow) — Ce^3+ (colorless)
Titrant for cerimetry
Cerium (IV) Sulphate
Titrant for Dichromate Titrations
K2Cr2O7/Potassium Permanganate
Redox couple for dichromate titrations
Cr2O7^-2 — Cr^3+
Advantages of dichromate titration. What are the conditions maintained?
stable, low cost, available in primary standard grade purity
strongly acidic conditions (maintained by adding dilute H2SO4)
Iodimetry vs Iodometry
Iodimetry - use of I^2 (iodine) as oxidant
Iodometry - use of I^- (iodide ion) as reductant
Advantages and disadvantages of iodimetry
+++
1. Availability of excellent indicator, starch
- Iodine is a weaker oxidant
- Weak stability; thus, they need to be standardized regularly
Indicator that end point is reach in iodimetry
Iodide ion is dissolved in iodine solution to form I^3-, which creates dark blue complex with starch
Redox couple for Iodometry
S2O3^2- — S4O6^2-
(S +2). — (S +2.5)
Redox Couple for Ferrous Ion
Fe2+ — Fe3+
