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ChE LE Flashcards > Analytical Chemistry > Flashcards

Analytical Chemistry Flashcards

1
Q

Amount of one chemical specie reacting stoichiometrically with another chemical specie

A

Equivalents

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2
Q

Equivalents per liter

A

Normality

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3
Q

Why we grade chemicals?

A

Quality of chemicals must be consistent with its intended purpose

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4
Q

Substances whose exact solution concentration can be determined by dissolving known weight of a reagent

A

Primary Standards

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5
Q

Chemical with highest purity (>95%)

A

American Chemical Society Reagent (ACS)

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6
Q

Chemical with high purity but no established specifications.

A

Reagent Grade /Analytical Reagent (AR)

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7
Q

Chemicals not adequate for reagent use / unfit for analysis

A

USP / NF
(US Pharmacopoeia / National Formulary)

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8
Q

Chemicals with high quality by unknown levels of impurities

A

Laboratory / Chemically Pure (CP)

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9
Q

Chemicals with low quality (<90%) with no established standard set of quality

A

Commercial / Technical Reagents

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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

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11
Q

Sample Constituents
Hint: %mass

A

Ultratrace: <1ppb
Trace: 1 ppb
Minor: 0.01% - 1%
Major: 1% - 100%

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12
Q

Elimination of an interferent by converting it to a non-interfering form

A

Masking

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13
Q

Explain Le Chatelier principle

A

โ€œThe position of an equilibrium always shifts in such a direction to relieve an applied stress.โ€

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14
Q

Explain Common-Ion Effect

A

โ€œThe solubility of an ionic precipitate decreases when a
another solute containing a similar ion is added to the solutionโ€

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15
Q

Explain autoprotolysis

A

Self-ionization of a solvent to produce both a conjugate acid and a conjugate base

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16
Q

Ideal Precipitate

A

Low solubility
Filterable
Inert
Known chemical composition

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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

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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.

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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

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20
Q

Desiccants in general have which important property?

A

high chemical or physical affinity for water

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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

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22
Q

3 Benefits of Digestion

A
  1. Redissolve colloids and reprecipitate them-crystal size grows
  2. Slow recrystallization (less impurities)
  3. Agglomeration occurs
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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

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24
Q

Ratio used to predict if precipitate growth is more favored than nucleation.

A

Supersaturation Ratio
SR = (Q-S)/S

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25
Q

Defines the relationship between mass of sample and precipitate

A

Gravimetric factor

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26
Q

Gravimetric method results are directly calculated therefore ____

A

Gravimetric method does not required calibration or standardization

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27
Q

A _____ ionizes totally when dissolved in water.

A

strong electrolyte

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28
Q

The __ the pKa, the weaker the ___ and the stronger the ___

A

Higher pKa = weaker acid = stronger conjugate base

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29
Q

Calculation:
pH of Strong Acids and Bases

A

ACIDS: pH=-log(C,acid)
BASES: pH=14-log(C,base)

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30
Q

How to get pH of:
WEAK ACIDS and BASES

A

ACIDS: pH=-1/2 log(KaC,acid)
ACIDS: pH=14+1/2 log(KbC,base)

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31
Q

How to get pH of:
BUFFER SOLUTIONS

A

Henderson-Hasselbalch
pH=-log(Ka) - log(acid/basic component)

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32
Q

Buffer capacity is at a maximum when:

A

pH = pKa
Also, higher weak acid and conjugate base conc. = higher buffer capacity (more based needed to neutralize)

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33
Q

BUFFERS: Explain the effects of dilution on pH buffers

A

pH independent of dilution unless concentrations equal to Kw

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34
Q

Physical Characteristics of Acids and Bases

A

Acids:
sour, sticky, red litmus
Bases:
bitter/sweet, slippery, blue litmus

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35
Q

Water at room temperature usually has a slightly acidic pH. This is largely attributed to what compound(s)?

A

Carbonic acid

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36
Q

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?

A

Hydronium ions

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37
Q

Define a salt in terms of acid and base.

A

Salt - compound (other than water) produced by the reaction of an acid and a base.

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38
Q

Different Ways to Classify Acids and Bases

A
  1. Arrhenius: Acids donates H+, Bases donates OH-
  2. Bronsted Lowry: Acids donates proton to Bases
  3. Lewis: Bases donates e- to Acids
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39
Q

Acids donates H+, Bases donates OH-

A

Arrhenius Acid and Base

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40
Q

Acids donates proton to Bases

A

Bronsted Lowry Acid

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41
Q

Type of Acid-Base pair in terms of โ€œconjugatesโ€

A

Bronsted Lowry

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42
Q

The stronger acid / base the ___ the conjugate base / acid

A

weaker

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43
Q

Bases donates e- to Acids

A

Lewis Base

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44
Q

Type of Acid-Base pair explaining the formation of complex ions

A

Lewis acids and bases

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45
Q

Differentiate Electrolytes and Nonelectrolytes

A

Electrolytes: can conduct electricity when dissolved in water. Lightbulb lights up
Nonelectrolytes: CANNOT conduct electricity when dissolved in water. Lightbulb does not light up

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46
Q

When a can of soda is opened and CO2 is released to the atmosphere, what is the resultant pH of the soda?

A

Increases

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47
Q

Natural rainfall is slightly acidic at a pH of about 5.5. Why is the pH of natural rain acidic?

A

H2CO3 forms when CO2 dissolves in rainwater

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48
Q

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

A

pH at equivalence point

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49
Q

For a strong acid/strong base titration, the pH at the equivalence point is ___

A

pH is equal to 7 (becomes completely neutral)

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50
Q

For a weak acid/strong base titration, the pH at the equivalence point is ___

A

pH is more than 7 (becomes conjugate base)

51
Q

For a weak base/strong acid titration, the pH at the equivalence point is ___

A

pH is less than 7 (becomes conjugate acid)

52
Q

The best indicator for the titration of a weak acid and a strong base

A

Phenolphthalein

53
Q

Differentiate endpoint and equivalence point

A

Both are the same thing.
Endpoint = color change
Equivalence point = all analyte reacted

54
Q

Standard Molarities:
HCl
H2SO4
NaOH

A

a) HCl - 12.1 M
b) H2SO4 - 18 M
c) NaOH - 19.4 M

55
Q

Titrant pH Transitions:
Bromocresol Green
Methyl Red
Methyl Orange
Phenolphthalein

A

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
Q

Titrant pH Transitions:
Bromocresol Green

A

Bromocresol Green: 3.8 to 5.4

57
Q

Titrant pH Transitions:
Methyl Red

A

Methyl Red: 4.2 to 6.3

58
Q

Titrant pH Transitions:
Methyl Orange

A

Methyl Orange: 3.1 to 4.4

59
Q

Titrant pH Transitions:
Phenolphthalein

A

Phenolphthalein: 8.3 to 10

60
Q

Titrant pKaโ€™s:
Bromocresol Green
Methyl Red
Methyl Orange
Phenolphthalein

A

Bromocresol Green - 4.66
Methyl Red - 5.00
Methyl Orange - 3.46
Phenolphthalein - 9.00

61
Q

Titrant pKaโ€™s:
Bromocresol Green

A

Bromocresol Green - 4.66

62
Q

Titrant pKaโ€™s:
Methyl Red

A

Methyl Red - 5.00

63
Q

Titrant pKaโ€™s:
Methyl Orange

A

Methyl Orange - 3.46

64
Q

Titrant pKaโ€™s:
Phenolphthalein

A

Phenolphthalein - 9.00

65
Q

Measure of acid-neutralizing capacity of water

A

Alkalinity

66
Q

Sources of alkalinity

A

OH-, HCO3- and CO3,2-

67
Q

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

A

HF and NaF

68
Q

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.

A

NaI and NaOH.

69
Q

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.

A

Buffer capacity

70
Q

All half-cell potential (โˆ†E) use the _________ as the reference

A

hydrogen electrode

71
Q

Enumerate Weak Acids

A

Acetic Acid, Hydrofluoric (HF), Cyanic (HCN), Sulfuric (H2SO4), Phosphoric (H3PO4) and organic acids

72
Q

What are Weak Bases

A

Ammonia and its derivatives
[NH3, etc]

73
Q

Chemicals that acts as an acid or base

A

Amphoteric or Amphiprotic

74
Q

Determination of nitrogen

A

Kjeldahl Method

75
Q

OH-, HCO3- and CO3- Solโ€™n:
Write Sample Composition and Titrant Volumes

A

Na2CO3: Vph = Vbcg
NaOH: Vbcg = 0
NaHCO3: Vph = 0
Na2CO3 + NaOH: Vph > Vbcg
Na2CO3 + NaHCO3: Vph < Vbcg

76
Q

Equivalents:
Acetic acid

A

1 eq

77
Q

Equivalents:
Ammonium Sulfate (NHโ‚„)โ‚‚SOโ‚„

A

2 eq

78
Q

Equivalents:
CN- : Ni

A

4 eq / mole Ni
Tetracyanonickelate

79
Q

Equivalents:
For Liebig
CN- : Ag+

A

2 CN- : 1 Ag,+
[Ag(CN)2],-1
Dicyanosilver ion

80
Q

OH-, HCO3- and CO3- Solโ€™n:
NaOH Titrant

A

Phenolphthalein

81
Q

OH-, HCO3- and CO3- Solโ€™n:
NaHCO3 Titrant

A

Bromocresol Green / Methyl Orange

82
Q

Start and Endpoints:
Volhard Method
Fajans Method
Mohr Method

A

Mohr Method: White to Brick Red PPT
Fajans Method: White to Pink PPT
Volhard Method: White to Bloody Red PPT

83
Q

Indicators:
Mohr Method
Fajans Method
Volhard Method

A

Mohr Method: Na2CrO4
Fajans Method: Dichlorofluorescein
Volhard Method: FeSCN2+

84
Q

Titrants:
Mohr Method
Fajans Method
Volhard Method

A

Mohr Method: AgNO3 (direct)
Fajans Method: AgNO3 (direct)
Volhard Method: SCN-

85
Q

What sets Volhard Method apart from other precipitation titrations?

A

a) Excess SCN- titrant
b) AgNO3 back-titration
c) Needs filtration

86
Q

Why EDTA has its own kind of precipitation reaction?

A

EDTA forms stable 1:1 complexes with virtually all multivalent metal ions.

87
Q

Explain chelating agent

A

Organic compound that contains electron-donor groups to complex a cation.

88
Q

Explain ligand or coordinating agent

A

Molecule or ion containing the donor atom in coordination chemistry

89
Q

Product resulting from the reaction between a metal ion and a ligand

A

coordination compound or complex ion

90
Q

Difference between Galvanic and Electrolytic Cells

A

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
Q

Oxidation occurs at the _____
While reduction occurs at the ____

A

Anode, Cathode

92
Q

What is the role of graphite in dry cell?

A

Cathode materials in the dry cell

93
Q

Describe salt bridges

A

Device that provides electrical contact but prevents mixing of dissimilar solutions in an electrochemical cell.

94
Q

Describe reductants

A

AKA reducing agents
Brings about the reduction of another substance while the reductant is oxidizing.

95
Q

Why do we bubble H2 in electrochemical cells?

A

1) Make solโ€™n saturated with H2
2) Hence results are reproducible

96
Q

Electrode Potential VS Titration:
When are either one used?

A

Titration: to determine amount of analyte in sample
Electrode potential: to determine activity of analyte in sample

97
Q

Recite Thermodynamics of Redox Reactions

A

dG0=-nFE0,cell = -RT lnK
E = E0 - (RT lnQ)/nF

98
Q

Complete Description (Titrants, Analytes, Equivalents)
Permanganimetry
Iodometry
Iodimetry

A

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):
โ€“๐‘๐ป < 2: 5 eq (acidic condition)
โ€“5<๐‘๐ป<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
Q

Titrants:
Permanganimetry
Iodometry
Iodimetry

A

Permanganimetry: Potassium Permanganate (KMnO4)
Iodometry: Sodium Thiosulfate (Na2S2O3)
Iodimetry: Iodine (I2)

100
Q

Analytes:
Permanganimetry
Iodometry
Iodimetry

A

Permanganimetry: analytes oxidizable by KMnO4
Iodometry: I2 oxidized by analyte (I3- liberated ang tina-titrate)
Iodimetry: analytes oxidizable by I2

101
Q

when used as a titrant in strongly acidic solution, can serve as its own indicator

A

Permanganate KMnO4

102
Q

Standard electrode potential equation

A

E0 = E,cathode - E,anode
(Tip: reduced-oxidized)

103
Q

Explain standard reduction potential, E0

A

Voltage associated with reduction reaction at an electrode when all solutes are 1M and all gases are at 1atm.

104
Q

Explain cell potential

A
  • The electric current between anode and cathode with difference in electric potential energy
  • Measure of tendency of cell reaction to take place
105
Q

Explain Ion-electron calculation

A
  1. Write eqns of the two half-reactions including elections
  2. Balance reactions, add H2O to balance O&H.
106
Q

Why changing the stoichiometric coefficients of a half-cell reaction does not affect the value of E0?

A

Electrode potentials are intensive properties

107
Q

The more positive standard electrode potential E0 is, the _____

A

The more positive E0 is, the greater the tendency for the substance to be reduced.

108
Q

Dumas Method

A

Jean Bapiste Dumas
Determination of N (crude protein) in food

109
Q

Winklerโ€™s Method

A

Determination of Dissolved Oxygen (DO) in water

110
Q

Wijโ€™s Method

A

Determination of Iodine number in oils and fats

111
Q

Metallic reductor:
Jones reductor

A
  • Clemens Jones
  • zinc-mercury amalgam
  • reduce metal ions to very low oxidation state
112
Q

Metallic reductor:
Walden reductor

A
  • George Walden
  • metallic silver with HCl
  • reduce metal (except Cr and TiO) to lower oxidation state
113
Q

Redox Titrations:
Differentiate Jones and Walden Reduction

A

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 canโ€™t):
Cr3+ to Cr2+

114
Q

Redox Titrations:
Equivalents of the following titrants
Permanganimetry
Iodometry
Dichromate Process
Fe,2+ and Ce,4+

A

MnO4- (permanganate for Permanganimetry):
โ€“๐‘๐ป < 2: 5 eq (acidic condition)
โ€“5<๐‘๐ป<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
Q

Metallic reductor:
Devardaโ€™s Alloy

A
  • Arturo Devarda
  • reduce NO3- to NH3+
116
Q

When a molecule absorbs/emits a photon, it ____

A

It is promoted/demoted to an excited/ground state.

117
Q

Relationship between
absorbance and transmittance?

A

A = -log T = -log (P/P0)

118
Q

Relationship between concentration and molar absorptivity

A

A = ๐œบ๐’„b

119
Q

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

A

all

120
Q

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

A

barium chloride

121
Q

The best conductor of electricity is ____

A

silver

122
Q

When ferromagnets are heated above a critical temperature, its ability to posses permanent magnetism disappears. This temperature is called

A

Curie temperature

123
Q

Acids donates H+, Bases donates OH-

A

Arrhenius Acid

ChE LE Flashcards (20 decks)

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