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Gravimetric Analysis Flashcards

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1
Q

are quantitative methods that are based
on determining the mass of a pure compound to which the
analyte is chemically related

A

Gravimetric Methods

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2
Q

the analyte is separated from a
solution of the sample as a precipitate and is then converted
to a compound of known composition that can be weighed.

A

Precipitation Gravimetry

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3
Q

the analyte is separated from
other constituents of a sample by conversion to a gas of
known chemical composition. The weight of this gas then
serves as a measure of the analyte concentration

A

Volatilization Gravimetry

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4
Q

the analyte is separated by deposition of
an electrode by an electrical current. The mass of this product
then provides a measure of the analyte concentration

A

Electrogravimetry

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5
Q

the mass of a reagent of known concentration required to
react completely with the analyte provides the information
needed to determine the analyte concentration

A

Gravimetric Titrimetry

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6
Q

uses a mass spectrometer to separate the gaseous ions formed
from the elements making up a sample of matter. The
concentration of the resulting ions is then determined by
measuring the electrical current produced when they fall on
the surface of an ion detector

A

Atomic Mass Spectrometry

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7
Q

The process of precipitation involves three steps which are

A

supersaturation, nucleation, and particle growth

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8
Q

________ occurs upon addition of the first drops of the precipitating agent

A

supersaturation

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9
Q

then starts to occur
wherein a minimum number of atoms, ions, or molecules
aggregate together to form a stable solid.

A

Nucleation

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10
Q

then starts to occur
wherein a minimum number of atoms, ions, or molecules
aggregate together to form a stable solid.

A

Nucleation

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11
Q

Further
precipitation then involves a competition between additional
nucleation and growth on existing nuclei

A

particle growth

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12
Q

[Factors That Determine the Particle Size of Precipitates]

are invisible to
the naked eye (10^-7 to 10^-4 cm in diameter).

show no tendency to settle from
solution and are difficult to filter

A

Colloidal suspensions

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13
Q

[Factors That Determine the Particle Size of Precipitates] The temporary dispersion of particles in the liquid
phase

tend to settle
spontaneously and are easily filtered

A

Crystalline suspension

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14
Q

The net effect of these variables can be accounted for, at least
qualitatively, by assuming that the particle size is related to a
single property of the system called

states that the particle size of
precipitates is inversely proportional to
the relative saturation of the solution
during the precipitation process

A

Relative Supersaturation / Von Weirman Equation

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15
Q

a minimum
number of atoms, ions, or molecules aggregate together to form a
stable solid.

A

nucleation

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16
Q

Often, these nuclei form on the surface of suspended
solid contaminants, such as dust particles. Further precipitation then
is governed by the competition between additional nucleation and
growth of existing nuclei

A

particle growth

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17
Q

Control of Particle size

A

Increasing the solubility of the precipitate S
Precipitation using dilute solutions to minimize Q
Slow addition of the precipitating agent with good stirring to
keep the concentration of solute Q low

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18
Q

Brownian motion prevents their settling out of solution under the influence of gravity. However, we can coagulate, or agglomerate, the individual particles of most colloids to give a filterable, amorphous mass that will settle out of solution

A

Colloidal Precipates

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19
Q

Coagulation can be hastened by:

A

Heating
Stirring
Adding an electrolyte to the medium

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20
Q

Coagulation can be hastened by:

A

Heating
Stirring
Adding an electrolyte to the medium

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21
Q

a substance (gas, liquid, or solid) is held on the
surface of a solid.

A

Absorption

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22
Q

is the process by which a coagulated colloid reverts to its original dispersed state

A

Peptization

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23
Q

is the process by which a coagulated colloid reverts to its original dispersed state

A

Peptization

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24
Q

are more easily filtered and purified than
coagulated colloids.

A

Crystalline precipitates

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25
Q

The particle size of crystalline solids can often be
improved significantly by

A

minimizing Q or maximizing S, or
both.

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26
Q

of crystalline precipitates (without stirring) for
some time after formation often yields a purer, more
filterable product.

A

Digestion

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27
Q

The amount of impurities depends on nature of
precipitate and condition of precipitation
It may be due to

A

-coprecipitation
-post-precipitation

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28
Q

is the process in which normally soluble
compounds are carried out of the solution. It leads to an increase
in the mass of precipitate

A

Coprecipitation

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29
Q

four types of coprecipitation

A

surface absorption
mixed-crystal formation
occlusion
mechanical entrapment

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30
Q

Is likely to cause significant contamination of
precipitates with large specific surface areas, that is,
coagulated colloids.

A

Surface Absorption

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31
Q

How to minimize absorbed impurities on colloids

A

Washing of colloidal particles

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32
Q

is a drastic but an effective way to minimize the effects of absorption.

A

Reprecipitation

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33
Q

one of the ions in the crystal lattice
of a solid is replaced by an ion of another element

A

Mixed Crystal Formation

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34
Q

is a type of coprecipitation in which a compound is
trapped within a pocket formed during rapid crystal growth

A

Occlusion

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35
Q

occurs when crystals lie close together
during growth. Several crystals grow together and in so doing
trap a portion of the solution in a tiny pocket

A

Mechanical entrapment

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36
Q

________may occur in both colloidal and
crystalline precipitates, but _________ are confined to crystalline precipitates.

A

Mixed-crystal formation; occlusion and mechanical
entrapment

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37
Q

may cause either negative or
positive errors in an analysis. If the contaminant is not a compound of the ion being determined, a positive error will always result. In contrast, when the contaminant does contain the ion being determined, either positive or negative errors may occur

A

Coprecipated Impurities

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38
Q

is a process in which a
precipitate is formed by slow generation of a
precipitating reagent homogeneously throughout a
solution

A

Homogeneous precipitation

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39
Q

Solids formed by homogeneous precipitation are?

A

generally purer and more easily filtered

40
Q

Steps in gravimetric analysis

A

Preparation of the Solution
Precipitation
Digestion
Filtration
Washing
Drying or Ignition
Weighing
Calculation

41
Q

Preliminary separation of potential
interferences before precipitating the
analyte
Adjustment of solution condition (pH /
temperature / volume / concentration of
test substance) to maintain low solubility of
precipitate and maximum precipitate
formation

A

Preparation of the Solution

42
Q

The precipitating reagent is added at a
concentration that favors the formation of a
“good” precipitate
This may require low concentration, extensive
heating (often described as“digestion”), or careful
control of the pH

A

Precipitation

43
Q

Also known as Ostwald ripening, the small
particles tend to dissolve and precipitate on
the surfaces of the larger crystals

A

Digestion

44
Q

Precipitate is separated from mother liquor (the
solution from which a precipitate was formed.
Choice depends on the nature of precipitate, cost of
media, and heating temperature required for
drying

A

Filtration

45
Q

Coprecipitated impurities, especially those
on surface, are removed by

A

Washing

46
Q

its purpose is to remove the
remaining moisture
It is done by heating about 120-150℃ for 1-2
hours

A

Drying

47
Q

Its purpose in a
muffle furnace at temperatures ranging from
600-1200℃ is to get the material with exactly
known chemical structure so that the amount
of analyte can be determined accurately.
The precipitate is converted to a more
chemically stable form

A

Ignition

48
Q

After the precipitate is allowed to cool
(preferably in a desiccator to keep it from
absorbing moisture), it is

A

Weighed (Process: Weighing)

49
Q

The combined constant factors in a
gravimetric calculation are referred to as
the

A

Gravimetric Factor

50
Q

Volumetric Analysis is also known as

A

Titration

51
Q

Involve measuring the volume of a solution
of known concentration that is needed to
react completely with the analyte

A

Volumetric Analysis / Titration

52
Q

A reagent of known concentration that is used to carry out volumetric titration

A

Titrants or titrators

(Standard solution/ Standard Titrant)

53
Q

A theoretical point reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample

A

Equivalence point

54
Q

Is a point in titration that signifies the completion of the titration by a change in the colour or intensity of the solution

A

End point

55
Q

Are often added to the analyte solution to produce observable physical change (which signals end point) at or near the equivalence point

A

Indicators

56
Q

Refers to the mass difference in volume or mass between the equivalence point and the end point

A

Titration error

57
Q

Highly purified compound that serves as a reference
material in titrations

A

Primary Standards

58
Q

[Primary Standards] Acid-base reactions

A

sodium carbonate Na2CO3
- sodium tetraborate Na2B407
- potassium hydrogenphthalate KH(C8H404)
- constant boiling point hydrochloric acid
- potassium hydrogeniodate KH(IO3)2
- benzoic acid (C6H5COOH).

59
Q

[Primary Standards] Complex formation reactions

A

silver, silver nitrate, sodium chloride, various metals and salts, depending upon the
reaction used.

60
Q

[Primary Standards] Precipitation reactions

A

silver, silver nitrate, sodium chloride, potassium
chloride, and potassium bromide (prepared from
potassium bromate).

61
Q

[Primary Standards] Oxidation-reduction reactions

A
  • potassium dichromate K2Cr2O7
  • potassium bromate KBrO3
  • potassium iodate KIO3
  • potassium hydrogeniodate KH(IO3)2
  • sodium oxalate Na2C204
  • arsenic(II) oxide As2O3
  • pure iron.
62
Q

are widely used to determine the amounts of acids
and bases and to monitor the progress of reactions that produce or consume
hydrogen (H+) ions.

A

Neutralization titrations

63
Q

Standard reagents used in acid-base titrations are always strong acids or
string bases such as:

A
  • Hydrochloric (HCL) acid;
  • Perchloric acid (HCLO4) acid;
  • Sulfuric (H2SO4) acid;
  • Sodium hydroxide (NaOH); and
  • Potassium hydroxide (KOH)
64
Q

There are 3 types of indicators of Acids and Bases

A
  1. Natural
  2. Synthetic
  3. Olfactory
65
Q
  • these are indicators that can be organically found in nature
A

Natural indicators

66
Q

the most
common and well-known
acid/base indicator

A

Litmus paper

67
Q

naturally yellow in color
and turns red when it comes into
contact with a basic solution

A

Turmeric

68
Q

indicators which are synthesized and created by the chemical process.

A

Synthetic indicators

69
Q

Examples of synthetic indicators

A

Methyl Orange
Phenolphthalein

70
Q

these are substances whose smell changes in acidic or basic solutions

A

Olfactory indicator

71
Q

have a characteristic sharp smell. In a basic medium, the smell
cannot be detected, but in an acidic medium it retains its strong smell

A

Onions

72
Q

this occurs which the indicator changes color
differs from the pH at the equivalence point
- usually minimized by choosing the indicator carefully or by making a
blank correction

A

Determinate error

73
Q

originates from the limited ability of the
human eye to distinguish reproducibly the intermediate color of the
indicator

A

Indeterminate error

74
Q

The pH interval over which a given indicator exhibits a color change is
influenced by:

A

a. Temperature
b. Ionic strength of the medium
c. Presence of organic solvents and colloidal particles

75
Q

Two Sources of Hydronium (OH-) ions in an aqueous solution of strong
acids:

A
  1. Reaction of the acid with water; and
  2. The dissociation of water itself
76
Q

at this stage we compute the concentration of the acid
from its starting concentration and the amount of base that has been added.

A

Pre-equivalence

77
Q

hydronium and hydroxide ions are present in equal
concentrations, and the hydronium ion concentration is derived directly
from the ion-product constant for water.

A

Equivalence

78
Q

analytical concentration of the excess base is
computed, and the hydroxide ion concentration is assumed to be equal to or
a multiple of the analytical concentration.

A

Post equivalence

79
Q

it is the measurements of physical
properties of analytes, such as current, electrode potential, the absorption or
emission of light, and mass-to-charge ratios, and fluorescence, used for
quantitative analysis of a variety of inorganic, organic, and biochemical
analyte.

A

Instrumental methods of analysis

80
Q

quantitative method used to measure the potential of an
electrochemical cell under static condition.

A

Potentiometry

81
Q

in the Potentiometry is when the pair of
electrodes is placed in the sample solution, it shows the potential difference
by the addition of the titrant or by the change in the concentration of the
ions.

A

Principle

82
Q

a device for measuring the potential of an electrochemical
cell without drawing a current or altering the cell’s composition.

A

Potentiometer

83
Q

the electrode which contains its own potential value
and it is stable when dipped into sample solution.

A

Reference electrode

84
Q

commonly used to establish a
reference potential for measuring other electrode’s potentials.
It is dependable but large, bulky, and affected by temperature.

A

Calomel Reference Electrodes or mercury sulfate electrode
and mercury oxide electrode

85
Q

The most
widely marketed reference electrode system consists of a
silver electrode immersed in a solution of potassium chloride
that has been saturated with silver chloride.
- Widely used because it is simple, inexpensive, very stable
and non- toxic.
- More compact– overall better and faster

A

Silver- silver Chloride Reference Electrodes

86
Q

consists of a platinized
platinum electrode in HCl solution with hydrogen at
atmospheric pressure bubbled over the platinum surface.

A

Normal Hydrogen Electrode

87
Q

the electrode which responds to change in the
potential of analyte solution.

A

Indicator electrode

88
Q

It is convenient to classify
metallic indicator electrodes as electrodes of the first kind,
electrodes of the second kind, and inert redox electrodes.

A

Metallic Indicator Electrodes

89
Q

is a pure metal electrode that is in direct
equilibrium with its cation in the solution. A single
reaction is involved.

A

Electrodes of the First Kind

90
Q

Metals not only
serve as indicator electrodes for their own cations but
also respond to the activities of anions that form
sparingly soluble precipitates or stable complexes
with such cations.

A

Electrodes of the second Kind

91
Q

Several relatively inert conductors respond to redox
systems. Such materials as platinum, gold, palladium,
and carbon can be used to monitor redox systems.

A

Inert Metallic Electrodes for Redox Systems

92
Q

the most convenient
method for determining pH has involved measurement of the
potential that appears across a thin glass membrane that
separates two solutions with different hydrogen ion
concentrations.

A

Membrane Indicator Electrodes

93
Q

a type of
ion-selective electrode made of a doped glass membrane that
is sensitive to a specific ion.

A

The Glass Electrode for measuring pH

94
Q

Also known as the liquid junction, used to prevent the mixing
or interference of the analyte solution with that of the reference solution.

A

Salt bridge

95
Q

are potentiometric sensors that include a selective membrane to
minimize matrix interferences.

A

Ion – selective Electrode (ISE) or specific ion electrode (SIE)

96
Q

Most common ISE:

A

pH electrode, which contains a thin glass
membrane that responds to the H+ concentration in a solution.

97
Q

TYPES OF ION SELECTIVE ELECTRODE (ISE):
Any electrode that preferentially responds to one ion species.

A
  1. Glass Membrane Electrode: H+
  2. Solid State Electrode
  3. Liquid Membrane Electrode
  4. Gas Sensing Electrode
  5. Enzyme electrodes

anal chem (4 decks)

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