Volumetric Precipitimetry

Question 1

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

Answer 1

Volumetric Precipitation Methods

Question 2

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

Answer 2

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

Question 3

Adsorption indicators used in the official volumetric Precipitation of assays:

Answer 3

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

Question 4

Other indicators used in the official volumetric Precipitation assays:

Answer 4

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

Question 5

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

Answer 5

Ferric Ammonium Sulfate

Question 6

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

Answer 6

Potassium chromate

Question 7

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

ammonium sulfate to form?

Answer 7

Red ferric thiocyanate

Question 8

what analytes are used in ferric Ammonium sulfate?

Answer 8

Mercury and Silver

Question 9

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

Answer 9

Red precipitate

Question 10

Why does precipitation occur?

Answer 10

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

Question 11

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

Answer 11

Ksp

Question 12

What is the Ksp expression of each species

Answer 12

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

Question 13

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

Answer 13

Common-ion effect
Complex formation
Temperature
Interference Ion
Solvent

Question 14

What are the substances analyzed in Volumetric Precipitation methods

Answer 14

Halides
Halogenoids (pseudohalides)
Mercaptans
Fatty acids
Divalent inorganic compounds

Question 15

F, Cl, Br, I

Answer 15

Halides

Question 16

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

Answer 16

Halogenoids

Question 17

Organic thiol (R-SH) derivatives

Answer 17

Mercaptans

Question 18

Metal^2+

Answer 18

Divalent inorganic compounds

Question 19

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

Answer 19

0.1 N Silver Nitrate
0.1 N Ammonium Thiocyanate

Question 20

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

Answer 20

Argentometry

Question 21

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

Answer 21

It is used to sharpen the endpoint

Question 22

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

Answer 22

Eosin Y

Question 23

What happens the Eosin Y reacts first with silver?

Answer 23

Premature determination of the endpoint

Question 24

In standardization of silver Nitrate why is methanol added?

Answer 24

to prevent competition of Eosin Y and nacl

Question 25

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

Answer 25

Alcohol

Question 26

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

Answer 26

Magenta

Question 27

Rules on the use of adsorption indicator

Answer 27

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

Question 28

Based on the cessation of precipitation

Answer 28

Gay-Lussac Method

Question 29

Direct Titration - Silver Nitrate Analyte - Halides

Answer 29

Gay-Lussac Method

Question 30

what is the characteristics of AgF

Answer 30

Clear, Colorless (Silver Fluoride is soluble)

Question 31

what is the characteristics of AgCl

Answer 31

White, Curdy Precipitate

Question 32

What is the characteristics of AgBr

Answer 32

Pale yellow, Curdy precipitate

Question 33

What is the characteristics of AgI

Answer 33

Yellow, Curdy precipitate

Question 34

Based on the formation of a second highly **colored precipitate**

Answer 34

Mohr Method

Question 35

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

Answer 35

Mohr method

Question 36

What are some important conditions in Mohr's Method

Answer 36

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

Question 37

based on the formation of a soluble, colored complex

Answer 37

Volhard

Question 38

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

Answer 38

Residual Titration of Volhard Method

Question 39

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

Answer 39

Direct titrate of Volhard Method

Question 40

Based on the appearance of turbidity

Answer 40

Liebig Method

Question 41

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

Answer 41

Liebig Method

Question 42

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

Answer 42

Modified Liebig's method (Denige's modification)

Question 43

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

Answer 43

Fajan Method