Analytical Chemistry Flashcards
It is a branch of chemistry involved with the analysis of a chemical substance.
Analytical Chemistry
It establishes the chemical identity of the species in a sample.
Qualitative Analysis
It determines the relative amounts of these species, or analytes, in numerical terms.
Quantitative Analysis
Determination of mass of the analyte or some compound chemically related to it.
Gravimetric Methods
Measurement of the volume of a solution containing sufficient reagent to react completely with the analyte.
Volumetric Methods
Measurement of electrical properties (potential, current, resistance, quantity of electric charge, etc.), emission of radiation by analytes, etc.
Instrumental Methods
A general expression for an amount of solute in a given amount of material.
Concentration
Molarity (M)
amount of solute (mol) / volume of solution (L)
molality (m)
amount of solute (mol) / mass of solvent (kg)
Allows for simplified calculations involved with certain types of problems
Normality
Based on measuring the amount of a substance required to react with an analyte completely.
Normality
The reaction ratio still must be taken into account, but it is done by combining it with the molarity to produce a new unit of concentration called
“normal”
Normality (N)
amount of solute (eq) / volume solution (L)
Normality = Molarity × h
h = number of electrons lost or gained in the reaction
Redox Reactions
h = number of participating H+ or OH− ions
Neutralization Reactions
Water, as an amphiprotic solvent, undergoes
self-ionization or autoprotolysis
Strong acids and bases ionize completely in
water
Weak acids and bases ionize only partially in
water
extent of ionization depends on the dissociation constants, which are
equilibrium constants
Mixtures of weak acids or bases and their conjugate.
pH Buffers
Have the ability to resist changes in pH upon dilution or addition of small amounts of acid or base.
pH Buffers
Henderson-Hasselbalch Equation:
pH = pKa - log [acid]/[base]
the quantity of strong acid or strong base needed to cause 1L of the buffer to undergo a pH change of 1.
Buffer capacity
The buffer capacity increases as the concentration ratio approaches
1
A solution is basic if:
[OH-] > [H+]
Water at room temperature usually has a slightly acidic pH. This is largely attributed to what compound(s)?
Carbonic Acid
When benzoic acid dissolves in water, it partially reacts with water and ionizes to form benzoate and hydronium ions. In this reaction, what is the conjugate acid?
Hydronium Ions
Define a salt in terms of acid and base.
A salt is a compound (other than water) produced by the reaction of an acid and a base.
When a can of soda is opened and CO2 is released to the atmosphere, what is the resultant pH of the soda?
Increases
Which of the following pairs will form a buffer solution in the course of a titration?
Acetic acid, sodium hydroxide
Buffer capacity is maximum when:
pH = pKa
Which of the following acids would be most suitable for preparing a buffer of pH 3.1?
Sulfanilic acid, pKa = 3.232
Determination of nitrogen based on the conversion of organic nitrogen to ammonia, which is then separated by distillation and determined by titration.
Kjeldahl Method
Bases that can be titrated with a strong acid such as HCl.
Carbonate, bicarbonate, and hydroxide ions
There are 5 possible sample compositions:
Na2CO3 alone, NaOH alone, NaHCO3 alone,
Na2CO3+NaOH, and Na2CO3+NaHCO3.
Titrations based on reactions that produce sparingly soluble substances (precipitates).
Precipitation Titrations
Among the oldest titrations known, but are limited in scope because it is sometimes non-stoichiometric, has a slow reaction rate, and has issues of co-precipitation.
Precipitation Titrations
Only procedures using silver ion (Ag+, argentometric titrations) as the titrant or analyte have remained competitive with newer analytical methods.
Precipitation Titrations
Analyte: Cl-, Br-, CN-
Titrant: AgNO3 (Ag+)
Indicator: Na2CrO4
Titration reaction: Ag+ + Cl− ↔ AgCl (s)
Indicator reaction: 2Ag+ + CrO2− ↔ Ag2CrO4 (s)
Carried out at 6.5<pH<10.3 to prevent formation of a soluble complex (pH<6.5) or an unwanted insoluble hydroxide or oxide (pH>10.3).
Mohr Method
Analyte: Cl-, Br-, I-, SCN-
Titrant: AgNO3 (Ag+)
Indicator: Dichlorofluorescein (Cl-, Br-, I-, SCN-), eosin (Br-, I-, SCN-)
Titration reaction: Ag+ + Cl− ↔ AgCl(s)
Indicator reaction: AgCl ∙ Ag+ + DCF− ↔ AgCl ∙ Ag+ ∙ DCF−(s)
Done with vigorous shaking to avoid coagulation.
Addition of dextrin inhibits undesired coagulation of the AgCl.
Fajans Method
Analyte: Cl-, Br-, I-
Titrant: SCN-
Indicator: FeSCN2+ (comes from ferric alum)
Analyte reaction: Ag+ + Cl− ↔ AgCl(s)
Titration reaction: Ag+ + SCN− ↔ AgSCN(s)
Indicator reaction: Fe3+ + SCN− ↔ FeSCN2+(s)
Nitrobenzene may be added to mask AgCl from reacting with SCN-
Volhard Method
bonds where both bonding electrons come from one of the two atoms involved.
coordinate covalent bonds
the molecule or ion containing the donor atom.
Ligand or coordinating agent
the product resulting from the reaction between a metal ion and a ligand
Coordination compound or complex ion
the number of pairs of electrons accepted by a particular metal ion (at least 4, often 6)
Coordination number
can be classified according to how many donor atoms it contains (dentate)
Ligands
When polydentate ligands coordinate with metal ions, ring structures known as ______ are formed.
chelates
A hexadentate, containing 4 oxygen and 2 nitrogen donor atoms.
Ethylenediaminetetraacetic Acid (EDTA)
EDTA
Ethylenediaminetetraacetic Acid
can exist in a variety of protonated forms
tetraprotic acid
Any or all of its protonated forms may react with a given metal to yield a metal
EDTA complex
Theory of Complexation Indicators
M + In ↔ MIn
MIn + Y ↔ MY + In
