Analytical Chemistry Flashcards
1
Q
Amount of one chemical specie reacting stoichiometrically with another chemical specie
A
Equivalents
2
Q
Equivalents per liter
A
Normality
3
Q
Why we grade chemicals?
A
Quality of chemicals must be consistent with its intended purpose
4
Q
Substances whose exact solution concentration can be determined by dissolving known weight of a reagent
A
Primary Standards
5
Q
Chemical with highest purity (>95%)
A
American Chemical Society Reagent (ACS)
6
Q
Chemical with high purity but no established specifications.
A
Reagent Grade /Analytical Reagent (AR)
7
Q
Chemicals not adequate for reagent use / unfit for analysis
A
USP / NF
(US Pharmacopoeia / National Formulary)
8
Q
Chemicals with high quality by unknown levels of impurities
A
Laboratory / Chemically Pure (CP)
9
Q
Chemicals with low quality (<90%) with no established standard set of quality
A
Commercial / Technical Reagents
10
Q
Sample Sizes
Hint: mass and volume
A
Ultra micro: < 1 mg
Micro: 1-10 mg ; < 50 uL
Semi micro: 10-100 mg ; 50-100 uL
Macro: >100 mg ; >100 uL
11
Q
Sample Constituents
Hint: %mass
A
Ultratrace: <1ppb
Trace: 1 ppb
Minor: 0.01% - 1%
Major: 1% - 100%
12
Q
Elimination of an interferent by converting it to a non-interfering form
A
Masking
13
Q
Explain Le Chatelier principle
A
“The position of an equilibrium always shifts in such a direction to relieve an applied stress.”
14
Q
Explain Common-Ion Effect
A
“The solubility of an ionic precipitate decreases when a
another solute containing a similar ion is added to the solution”
15
Q
Explain autoprotolysis
A
Self-ionization of a solvent to produce both a conjugate acid and a conjugate base
16
Q
Ideal Precipitate
A
Low solubility
Filterable
Inert
Known chemical composition
17
Q
Differentiate:
Occlusion, Inclusion, Adsorption
A
INCLUSION is an impurity that occupies lattice sites in a crystal.
OCCLUSION is impurity is trapped in a crystal.
ADSORPTION is impurity adsorbed to precipitate surface
18
Q
Why are many ionic precipitates washed with electrolyte solution instead of pure water?
A
To preserves the electric double layer and prevents peptization.
19
Q
Many ionic precipitates are washed with electrolyte solutions instead of pure water to avoid leaching of the electrolytes responsible for the coagulation, which is called:
A
Peptization
20
Q
Desiccants in general have which important property?
A
high chemical or physical affinity for water
21
Q
Heating of precipitates in the precipitation solution to give the crystals a chance to dissolve and re-precipitate under equilibrium conditions
A
Digestion
22
Q
3 Benefits of Digestion
A
- Redissolve colloids and reprecipitate them-crystal size grows
- Slow recrystallization (less impurities)
- Agglomeration occurs
23
Q
Supersaturation is an unstable state in which a solution contains higher solute concentration than a saturated solution. Supersaturation is relieved by ____
A
precipitation of excess solute
24
Q
Ratio used to predict if precipitate growth is more favored than nucleation.
A
Supersaturation Ratio
SR = (Q-S)/S
25
Defines the relationship between mass of sample and precipitate
Gravimetric factor
26
Gravimetric method results are directly calculated therefore ____
Gravimetric method does not required calibration or standardization
27
A _____ ionizes totally when dissolved in water.
strong electrolyte
28
The __ the pKa, the weaker the ___ and the stronger the ___
Higher pKa = weaker acid = stronger conjugate base
29
Calculation:
pH of Strong Acids and Bases
ACIDS: pH=-log(C,acid)
BASES: pH=14-log(C,base)
30
How to get pH of:
WEAK ACIDS and BASES
ACIDS: pH=-1/2 log(KaC,acid)
ACIDS: pH=14+1/2 log(KbC,base)
31
How to get pH of:
BUFFER SOLUTIONS
Henderson-Hasselbalch
pH=-log(Ka) - log(acid/basic component)
32
Buffer capacity is at a maximum when:
pH = pKa
Also, higher weak acid and conjugate base conc. = higher buffer capacity (more based needed to neutralize)
33
BUFFERS: Explain the effects of dilution on pH buffers
pH independent of dilution unless concentrations equal to Kw
34
Physical Characteristics of Acids and Bases
Acids:
sour, sticky, red litmus
Bases:
bitter/sweet, slippery, blue litmus
35
Water at room temperature usually has a slightly acidic pH. This is largely attributed to what compound(s)?
Carbonic acid
36
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
37
Define a salt in terms of acid and base.
Salt - compound (other than water) produced by the reaction of an acid and a base.
38
Different Ways to Classify Acids and Bases
1. Arrhenius: Acids donates H+, Bases donates OH-
2. Bronsted Lowry: Acids donates proton to Bases
3. Lewis: Bases donates e- to Acids
39
Acids donates H+, Bases donates OH-
Arrhenius Acid and Base
40
Acids donates proton to Bases
Bronsted Lowry Acid
41
Type of Acid-Base pair in terms of "conjugates"
Bronsted Lowry
42
The stronger acid / base the ___ the conjugate base / acid
weaker
43
Bases donates e- to Acids
Lewis Base
44
Type of Acid-Base pair explaining the formation of complex ions
Lewis acids and bases
45
Differentiate Electrolytes and Nonelectrolytes
Electrolytes: can conduct electricity when dissolved in water. Lightbulb lights up
Nonelectrolytes: CANNOT conduct electricity when dissolved in water. Lightbulb does not light up
46
When a can of soda is opened and CO2 is released to the atmosphere, what is the resultant pH of the soda?
Increases
47
Natural rainfall is slightly acidic at a pH of about 5.5. Why is the pH of natural rain acidic?
H2CO3 forms when CO2 dissolves in rainwater
48
What is the primary basis in choosing the best indicator for an acid-base titration?
a. acid strength
b. base strength
c. pH at equivalence point
d. temperature
pH at equivalence point
49
For a strong acid/strong base titration, the pH at the equivalence point is ___
pH is equal to 7 (becomes completely neutral)
50
For a weak acid/strong base titration, the pH at the equivalence point is ___
pH is more than 7 (becomes conjugate base)
51
For a weak base/strong acid titration, the pH at the equivalence point is ___
pH is less than 7 (becomes conjugate acid)
52
The best indicator for the titration of a weak acid and a strong base
Phenolphthalein
53
Differentiate endpoint and equivalence point
Both are the same thing.
Endpoint = color change
Equivalence point = all analyte reacted
54
Standard Molarities:
HCl
H2SO4
NaOH
a) HCl - 12.1 M
b) H2SO4 - 18 M
c) NaOH - 19.4 M
55
Titrant pH Transitions:
Bromocresol Green
Methyl Red
Methyl Orange
Phenolphthalein
Bromocresol Green: 3.8 to 5.4
Methyl Red: 4.2 to 6.3
Methyl Orange: 3.1 to 4.4
Phenolphthalein: 8.3 to 10
56
Titrant pH Transitions:
Bromocresol Green
Bromocresol Green: 3.8 to 5.4
57
Titrant pH Transitions:
Methyl Red
Methyl Red: 4.2 to 6.3
58
Titrant pH Transitions:
Methyl Orange
Methyl Orange: 3.1 to 4.4
59
Titrant pH Transitions:
Phenolphthalein
Phenolphthalein: 8.3 to 10
60
Titrant pKa's:
Bromocresol Green
Methyl Red
Methyl Orange
Phenolphthalein
Bromocresol Green - 4.66
Methyl Red - 5.00
Methyl Orange - 3.46
Phenolphthalein - 9.00
61
Titrant pKa's:
Bromocresol Green
Bromocresol Green - 4.66
62
Titrant pKa's:
Methyl Red
Methyl Red - 5.00
63
Titrant pKa's:
Methyl Orange
Methyl Orange - 3.46
64
Titrant pKa's:
Phenolphthalein
Phenolphthalein - 9.00
65
Measure of acid-neutralizing capacity of water
Alkalinity
66
Sources of alkalinity
OH-, HCO3- and CO3,2-
67
Which of the following pairs will form a buffer when mixed together in an aqueous solution?
a. KCl and KH2PO4
b. HCl and KOH
c. Ca(OH)2 and NaOH
d. HF and NaF
HF and NaF
68
When mixed together, all of the following pairs can form buffers EXCEPT
a. H3PO4 and NaH2PO4.
b. NaH2PO4 and Na2HPO4.
c. CH3CO2H and NaOH.
d. HCl and NaCH3CO2.
e. NaI and NaOH.
NaI and NaOH.
69
The number of moles of a strong acid (or a strong base) that causes 1.00 L of a buffer to undergo a 1.00-unit change in pH.
Buffer capacity
70
All half-cell potential (∆E) use the _________ as the reference
hydrogen electrode
71
Enumerate Weak Acids
Acetic Acid, Hydrofluoric (HF), Cyanic (HCN), Sulfuric (H2SO4), Phosphoric (H3PO4) and organic acids
72
What are Weak Bases
Ammonia and its derivatives
[NH3, etc]
73
Chemicals that acts as an acid or base
Amphoteric or Amphiprotic
74
Determination of nitrogen
Kjeldahl Method
75
OH-, HCO3- and CO3- Sol'n:
Write Sample Composition and Titrant Volumes
Na2CO3: Vph = Vbcg
NaOH: Vbcg = 0
NaHCO3: Vph = 0
Na2CO3 + NaOH: Vph > Vbcg
Na2CO3 + NaHCO3: Vph < Vbcg
76
Equivalents:
Acetic acid
1 eq
77
Equivalents:
Ammonium Sulfate (NH₄)₂SO₄
2 eq
78
Equivalents:
CN- : Ni
4 eq / mole Ni
Tetracyanonickelate
79
Equivalents:
For Liebig
CN- : Ag+
2 CN- : 1 Ag,+
[Ag(CN)2],-1
Dicyanosilver ion
80
OH-, HCO3- and CO3- Sol'n:
NaOH Titrant
Phenolphthalein
81
OH-, HCO3- and CO3- Sol'n:
NaHCO3 Titrant
Bromocresol Green / Methyl Orange
82
Start and Endpoints:
Volhard Method
Fajans Method
Mohr Method
Mohr Method: White to Brick Red PPT
Fajans Method: White to Pink PPT
Volhard Method: White to Bloody Red PPT
83
Indicators:
Mohr Method
Fajans Method
Volhard Method
Mohr Method: Na2CrO4
Fajans Method: Dichlorofluorescein
Volhard Method: FeSCN2+
84
Titrants:
Mohr Method
Fajans Method
Volhard Method
Mohr Method: AgNO3 (direct)
Fajans Method: AgNO3 (direct)
Volhard Method: SCN-
85
What sets Volhard Method apart from other precipitation titrations?
a) Excess SCN- titrant
b) AgNO3 back-titration
c) Needs filtration
86
Why EDTA has its own kind of precipitation reaction?
EDTA forms stable 1:1 complexes with virtually all multivalent metal ions.
87
Explain chelating agent
Organic compound that contains electron-donor groups to complex a cation.
88
Explain ligand or coordinating agent
Molecule or ion containing the donor atom in coordination chemistry
89
Product resulting from the reaction between a metal ion and a ligand
coordination compound or complex ion
90
Difference between Galvanic and Electrolytic Cells
Galvanic cells, chemical energy is converted to electrical energy to do electrical work such as running an electric motor.
Electrolytic cells require external electric source to bring about nonspontaneous redox reactions.
91
Oxidation occurs at the _____
While reduction occurs at the ____
Anode, Cathode
92
What is the role of graphite in dry cell?
Cathode materials in the dry cell
93
Describe salt bridges
Device that provides electrical contact but prevents mixing of dissimilar solutions in an electrochemical cell.
94
Describe reductants
AKA reducing agents
Brings about the reduction of another substance while the reductant is oxidizing.
95
Why do we bubble H2 in electrochemical cells?
1) Make sol'n saturated with H2
2) Hence results are reproducible
96
Electrode Potential VS Titration:
When are either one used?
Titration: to determine amount of analyte in sample
Electrode potential: to determine activity of analyte in sample
97
Recite Thermodynamics of Redox Reactions
dG0=-n*F*E0,cell = -RT lnK
E = E0 - (RT lnQ)/nF
98
Complete Description (Titrants, Analytes, Equivalents)
Permanganimetry
Iodometry
Iodimetry
Titrants:
- Permanganimetry: Potassium Permanganate (KMnO4)
- Iodometry: Sodium Thiosulfate (Na2S2O3)
- Iodimetry: Iodine (I2)
Analytes:
- Permanganimetry: analytes oxidizable by KMnO4
- Iodometry: I2 oxidized by analyte (I3- liberated ang tina-titrate)
- Iodimetry: analytes oxidizable by I2
Equivalents:
*Permanganimetry (MnO4-permanganate):
--𝑝𝐻 < 2: 5 eq (acidic condition)
--5<𝑝𝐻<9: 3 eq (basic condition)
*Iodometry (S2O3,2- thiosulfate) : 1 eq
*Iodimetry (I2 iodine) : 2 eq
*Fe,2+ and Ce,4+: 1 eq
*Dichromate Process (Cr2O7,2-): 6 eq
99
Titrants:
Permanganimetry
Iodometry
Iodimetry
Permanganimetry: Potassium Permanganate (KMnO4)
Iodometry: Sodium Thiosulfate (Na2S2O3)
Iodimetry: Iodine (I2)
100
Analytes:
Permanganimetry
Iodometry
Iodimetry
Permanganimetry: analytes oxidizable by KMnO4
Iodometry: I2 oxidized by analyte (I3- liberated ang tina-titrate)
Iodimetry: analytes oxidizable by I2
101
when used as a titrant in strongly acidic solution, can serve as its own indicator
Permanganate KMnO4
102
Standard electrode potential equation
E0 = E,cathode - E,anode
(Tip: reduced-oxidized)
103
Explain standard reduction potential, E0
Voltage associated with reduction reaction at an electrode when all solutes are 1M and all gases are at 1atm.
104
Explain cell potential
- The electric current between anode and cathode with difference in electric potential energy
- Measure of tendency of cell reaction to take place
105
Explain Ion-electron calculation
1. Write eqns of the two half-reactions including elections
2. Balance reactions, add H2O to balance O&H.
106
Why changing the stoichiometric coefficients of a half-cell reaction does not affect the value of E0?
Electrode potentials are intensive properties
107
The more positive standard electrode potential E0 is, the _____
The more positive E0 is, the greater the tendency for the substance to be reduced.
108
Dumas Method
Jean Bapiste Dumas
Determination of N (crude protein) in food
109
Winkler's Method
Determination of Dissolved Oxygen (DO) in water
110
Wij's Method
Determination of Iodine number in oils and fats
111
Metallic reductor:
Jones reductor
- Clemens Jones
- zinc-mercury amalgam
- reduce metal ions to very low oxidation state
112
Metallic reductor:
Walden reductor
- George Walden
- metallic silver with HCl
- reduce metal (except Cr and TiO) to lower oxidation state
113
Redox Titrations:
Differentiate Jones and Walden Reduction
Walden reductor is weaker but more selective than Jones reductor
Jones and Walden:
Fe3+ to Fe2+
Ce4+ to Ce3+
MnO4- (Permanganate) to Mn2+
Cr2O7- (Dichromate) to Cr3+
Jones only (Walden can't):
Cr3+ to Cr2+
114
Redox Titrations:
Equivalents of the following titrants
Permanganimetry
Iodometry
Dichromate Process
Fe,2+ and Ce,4+
MnO4- (permanganate for Permanganimetry):
--𝑝𝐻 < 2: 5 eq (acidic condition)
--5<𝑝𝐻<9: 3 eq (basic condition)
S2O3,2- (thiosulfate for Iodometry) : 1 eq
I2 (iodine for Iodimetry) : 2 eq
Fe,2+ and Ce,4+: 1 eq
Cr2O7,2- (Dichromate Process): 6 eq
115
Metallic reductor:
Devarda's Alloy
- Arturo Devarda
- reduce NO3- to NH3+
116
When a molecule absorbs/emits a photon, it ____
It is promoted/demoted to an excited/ground state.
117
Relationship between
absorbance and transmittance?
A = -log T = -log (P/P0)
118
Relationship between concentration and molar absorptivity
A = 𝜺*𝒄*b
119
Which of the following statements is/are correct?
(I) oxidation occurs at the anode
(II) reduction occurs at the cathode
(III) a reducing agent during a redox reaction
all
120
Which of these 0.1 M solution will give the highest boiling at 1 atm.
(a) table salt solution
(b) sugar solution
(c) barium chloride
(d) potassium chloride
barium chloride
121
The best conductor of electricity is ____
silver
122
When ferromagnets are heated above a critical temperature, its ability to posses permanent magnetism disappears. This temperature is called
Curie temperature
123
Acids donates H+, Bases donates OH-
Arrhenius Acid
