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PH 105 > Volumetric Precipitimetry > Flashcards

Volumetric Precipitimetry Flashcards

1
Q

These are class of reactions that deal with the formation of relatively insoluble substances (or precipitates)

A

Volumetric Precipitation Methods

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2
Q

In Volumetric Precipitation Methods the completion (endpoint) of the reaction is determined through the following

A
  • Adsorption indicators
  • Turbidity Method
  • Colored precipitate (color depends on species)
  • Soluber colored compound
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3
Q

Adsorption indicators used in the official volumetric Precipitation of assays:

A
  • Dichlorofluorescein (DCF) TS
  • Eosin Y TS
  • Tetrabromophenolphthalein ethyl Ester (TEE) TS
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4
Q

Other indicators used in the official volumetric Precipitation assays:

A

Ferric Ammonium Sulfate (NH4Fe(SO4)2·12H2O) (Ferric alum)
Potassium Chromate (K2CrO4 TS)

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5
Q

used both in direct and residual titrations employing standard ammonium thiocyanate (NH4SCN) solution.

A

Ferric Ammonium Sulfate

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6
Q

used in the analysis of chloride (and
other halides).

A

Potassium chromate

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7
Q

After precipitation, thiocyanate ion (SCN-) reacts with ferric

ammonium sulfate to form?

A

Red ferric thiocyanate

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8
Q

what analytes are used in ferric Ammonium sulfate?

A

Mercury and Silver

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9
Q

What is the precipitate of silver Chromate against the background of silver chloride?

A

Red precipitate

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10
Q

Why does precipitation occur?

A

precipitate has low solubility product constant (Ksp) than the other species in the solution

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11
Q

is the product of the concentration of ions in a solution.

A

Ksp

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12
Q

What is the Ksp expression of each species

A

it is the product of the (molar) concentration of [cations] and [anions]

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13
Q

What are the factors that affect the values of Ksp, which solubility of a compound is affected by different factors:

A

Common-ion effect
Complex formation
Temperature
Interference Ion
Solvent

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14
Q

What are the substances analyzed in Volumetric Precipitation methods

A

Halides
Halogenoids (pseudohalides)
Mercaptans
Fatty acids
Divalent inorganic compounds

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15
Q

F, Cl, Br, I

A

Halides

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16
Q

CN-, SCN, OCN- N^3-, Fe(CN)6^3-

A

Halogenoids

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17
Q

Organic thiol (R-SH) derivatives

A

Mercaptans

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18
Q

Metal^2+

A

Divalent inorganic compounds

19
Q

What are standard solutions employed in the official assays by precipitation methods?

A

0.1 N Silver Nitrate
0.1 N Ammonium Thiocyanate

20
Q

any titration that uses silver Nitrate as standard is termed as?

A

Argentometry

21
Q

in the standardization of silver Nitrate what is the use of acetic acid?

A

It is used to sharpen the endpoint

22
Q

It provides a Shar endpoint in acidic media (the color change is sharpest in an acetic acid solution)

A

Eosin Y

23
Q

What happens the Eosin Y reacts first with silver?

A

Premature determination of the endpoint

24
Q

In standardization of silver Nitrate why is methanol added?

A

to prevent competition of Eosin Y and nacl

25
Q

in standardization of silver nitrate, it is used in the assay to help keep the precipitated silver chloride in a colloidal state and thus give sharpness to the color change which occurs on the precipitate surface

A

Alcohol

26
Q

What is the color of the precipitate of Eosin Y with Silver

A

Magenta

27
Q

Rules on the use of adsorption indicator

A

The precipitate should separate as far as possible in the solution.
The indicator ion must have an opposite charge to the ion of the precipitating agent
The indicator ion should not be adsorbed before the particular compound has been completely precipitated

28
Q

Based on the cessation of precipitation

A

Gay-Lussac Method

29
Q

Direct Titration - Silver Nitrate
Analyte - Halides

A

Gay-Lussac Method

30
Q

what is the characteristics of AgF

A

Clear, Colorless (Silver Fluoride is soluble)

31
Q

what is the characteristics of AgCl

A

White, Curdy Precipitate

32
Q

What is the characteristics of AgBr

A

Pale yellow, Curdy precipitate

33
Q

What is the characteristics of AgI

A

Yellow, Curdy precipitate

34
Q

Based on the formation of a second highly colored precipitate

A

Mohr Method

35
Q

Direct Titration - Silver Nitrate
Analyte: Halides
Indicator: Potassium Chromate (K2CrO4)

A

Mohr method

36
Q

What are some important conditions in Mohr’s Method

A

pH : neutral (pH 8)
Temperature
Concentration of the indicator Potassium Chromate

37
Q

based on the formation of a soluble, colored complex

A

Volhard

38
Q

Titration with Silver Nitrate as excess and Ammonium Thiocyanate as backtitrant
Analyte: Halides
Indicator: Ferric Ammonium Sulfate

A

Residual Titration of Volhard Method

39
Q

Titration with ammonium thiocyanate
Analyte Mercury (Hg)
Indicator: Ferric Ammonium Sulfate

A

Direct titrate of Volhard Method

40
Q

Based on the appearance of turbidity

A

Liebig Method

41
Q

Direct Titration - Silver Nitrate
Analyte: Cyanides (CN-)

A

Liebig Method

42
Q

Direct Titration - Silver Nitrate
Analyte: Cyanides (CN-)
Addition of NH3

A

Modified Liebig’s method (Denige’s modification)

43
Q

Based on the adsorption of the indicator on the surface of the precipitate

A

Fajan Method

PH 105 (6 decks)

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