Experiment 5. Preparation and Standardization of KSCN Solution

volumetric precipitimetry or saturation method

Precipitation Method is also known as:

Precipitation Method

This is a type of titration where an amount of sample is titrated with STD. solution of a precipitating agent in the presence of a suitable indicator.

AgNO3, NH4SCN, KSCN

common standard solutions

photosensitive

All common standard solutions are a.______________ so there is a specialized apparatus such as b.____________ or if unavailable, you should c.__________ or d.______________

a = ?

amber burette

All common standard solutions are a.______________ so there is a specialized apparatus such as b.____________ or if unavailable, you should c.__________ or d.______________

b = ?

turn off the lights

All common standard solutions are a.______________ so there is a specialized apparatus such as b.____________ or if unavailable, you should c.__________ or d.______________

c = ?

cover the burette with aluminum foil

All common standard solutions are a.______________ so there is a specialized apparatus such as b.____________ or if unavailable, you should c.__________ or d.______________

d = ?

AgNO3

The common precipitating agent of this group is:

Argentometric Titration

If we are to use AgNO3 as a precipitating agent, the method of titration we are performing is ______________________________

Halides, Halogenoids (CN-,SCN-), Fatty acids, Mercaptans (Thiols), divalent inorganic anions (BaCl2)

Common analytes:

internal indicators

If we are conducting a precipitation method of titration, we call our indicators as _________________.

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2)

TYPES OF INDICATORS:

• usually used for thiocyanate reactions

• After the thiocyanate ion has been precipitated by Ag/Hg, the thiocyanate reacts with ferric alum to form red ferric thiocyanate.

FeSCN^-2

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2) Complexes:

a. formed in high ferric ion concentration (high concentration of indicator)

b. formed in equivalence point

c. formed if there is a high amount of SCN concentration

a = ?

Fe(SCN)3

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2) Complexes:

a. formed in high ferric ion concentration (high concentration of indicator)

b. formed in equivalence point

c. formed if there is a high amount of SCN concentration

b = ?

Fe(SCN)4^-1

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2) Complexes:

a. formed in high ferric ion concentration (high concentration of indicator)

b. formed in equivalence point

c. formed if there is a high amount of SCN concentration

c = ?

blood red

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2)

• color of the complex formed

flesh

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2)

• endpoint color

Volhard

TYPES OF INDICATORS:

Ferric Ammonium Sulfate/Ferric alum (NH4Fe(SO4)2)

• Used if the method of volumetric precipitimetry is:

brownish-red ppt

TYPES OF INDICATORS:

Chromates/Dichromates

• forms a ______________________ (Ag2CrO4) with AgNO3

Mohr

TYPES OF INDICATORS:

Chromates/Dichromates

• Used if the method of volumetric precipitimetry is _______.

Adsorptive

TYPES OF INDICATORS:

• Adheres to the surface of the precipitates

• just sticks to the surface and does not chemically react

Fluorescent Indicators

TYPES OF INDICATORS:

Adsorptive

• other name

Fajans

TYPES OF INDICATORS:

Adsorptive

• Method used:

Dichlorofluorescein (DCF), Eosin Yellow T.S (also known as TBF or Tetrabromofluorescein), Tetrabromophenolphthalein ethylester (TEE)

TYPES OF INDICATORS:

Adsorptive

• examples

greenish/yellow fluorescent

TYPES OF INDICATORS:

Adsorptive (Colors)

a. with excess Cl-

b. with excess Ag+

c. endpoint

a = ?

reddish pink

TYPES OF INDICATORS:

Adsorptive (Colors)

a. with excess Cl-

b. with excess Ag+

c. endpoint

b = ?

reddish pink

TYPES OF INDICATORS:

Adsorptive (Colors)

a. with excess Cl-

b. with excess Ag+

c. endpoint

c = ?

KSCN/NH4SCN

PRECIPITIMETRIC METHODS OF ANALYSIS

Thiocyanate

Standard Solution: ?

Indicator:

Endpoint:

Ferric alum

PRECIPITIMETRIC METHODS OF ANALYSIS

Thiocyanate

Standard Solution:

Indicator: ?

Endpoint:

blood red

PRECIPITIMETRIC METHODS OF ANALYSIS

Thiocyanate

Standard Solution:

Indicator:

Endpoint: ?

AgNO3 and KSCN

PRECIPITIMETRIC METHODS OF ANALYSIS

Volhard’s (Residual)

Standard Solution: ?

Indicator:

Endpoint:

Ferric alum

PRECIPITIMETRIC METHODS OF ANALYSIS

Volhard’s (Residual)

Standard Solution:

Indicator: ?

Endpoint:

blood red

PRECIPITIMETRIC METHODS OF ANALYSIS

Volhard’s (Residual)

Standard Solution:

Indicator:

Endpoint: ?

AgNO3

PRECIPITIMETRIC METHODS OF ANALYSIS

Mohr’s

Standard Solution: ?

Indicator:

Endpoint:

Chromates

PRECIPITIMETRIC METHODS OF ANALYSIS

Mohr’s

Standard Solution:

Indicator: ?

Endpoint:

brownish red

PRECIPITIMETRIC METHODS OF ANALYSIS

Mohr’s

Standard Solution:

Indicator:

Endpoint: ?

AgNO3

PRECIPITIMETRIC METHODS OF ANALYSIS

Fajan’s

Standard Solution: ?

Indicator:

Endpoint:

Adsorptive

PRECIPITIMETRIC METHODS OF ANALYSIS

Fajan’s

Standard Solution:

Indicator: ?

Endpoint:

reddish pink

PRECIPITIMETRIC METHODS OF ANALYSIS

Fajan’s

Standard Solution:

Indicator:

Endpoint: ?

Silver Nitrate

stable primary standard that can be prepared directly as a primary standard solution (though it is photosensitive, it is non-hygroscopic, therefore stable.)

16.4g of pure silver nitrate crystals

PREPARATION OF STD. AgNO3 SOLUTION:

1. Weigh accurately _______________________________ in a tared beaker.

2. Dissolve the silver nitrate in _________________________ and pour into a 1000-mL volumetric flask.

3. ______________ with distilled water and transfer the rinsing to the volumetric flask.

4. Add ____________________ to complete the volume.

5. Store the solution in an _________________________ and labeled properly.

1 = ?

200 mL of distilled water

PREPARATION OF STD. AgNO3 SOLUTION:

1. Weigh accurately _______________________________ in a tared beaker.

2. Dissolve the silver nitrate in _________________________ and pour into a 1000-mL volumetric flask.

3. ______________ with distilled water and transfer the rinsing to the volumetric flask.

4. Add ____________________ to complete the volume.

5. Store the solution in an _________________________ and labeled properly.

2 = ?

Rinse the beaker

PREPARATION OF STD. AgNO3 SOLUTION:

1. Weigh accurately _______________________________ in a tared beaker.

2. Dissolve the silver nitrate in _________________________ and pour into a 1000-mL volumetric flask.

3. ______________ with distilled water and transfer the rinsing to the volumetric flask.

4. Add ____________________ to complete the volume.

5. Store the solution in an _________________________ and labeled properly.

3 = ?

enough distilled water

PREPARATION OF STD. AgNO3 SOLUTION:

1. Weigh accurately _______________________________ in a tared beaker.

2. Dissolve the silver nitrate in _________________________ and pour into a 1000-mL volumetric flask.

3. ______________ with distilled water and transfer the rinsing to the volumetric flask.

4. Add ____________________ to complete the volume.

5. Store the solution in an _________________________ and labeled properly.

4 = ?

amber colored stock bottle

PREPARATION OF STD. AgNO3 SOLUTION:

1. Weigh accurately _______________________________ in a tared beaker.

2. Dissolve the silver nitrate in _________________________ and pour into a 1000-mL volumetric flask.

3. ______________ with distilled water and transfer the rinsing to the volumetric flask.

4. Add ____________________ to complete the volume.

5. Store the solution in an _________________________ and labeled properly.

5 = ?

Lunar caustic, Lapiz infernularis (infernalis), Indelible ink

What are the other names of silver nitrate?

99.8-100.5%

What is the acceptance criteria for AgNO3 USP?

Primary Standardization

What is the method of standardization in silver nitrate?

10 g of potassium thiocyanate

PREPARATION OF POTASSIUM THIOCYANATE SOLUTION

1. Weigh roughly ___________________________ which is weighed in excess, because it is deliquescent

2. Dissolve the potassium thiocyanate in enough ____________ to make 1000 mL.

3. Store the solution in a ____________________.

1 = ?

distilled water

PREPARATION OF POTASSIUM THIOCYANATE SOLUTION

1. Weigh roughly ___________________________ which is weighed in excess, because it is deliquescent

2. Dissolve the potassium thiocyanate in enough ____________ to make 1000 mL.

3. Store the solution in a ____________________.

2 = ?

stock bottle (flint)

PREPARATION OF POTASSIUM THIOCYANATE SOLUTION

1. Weigh roughly ___________________________ which is weighed in excess, because it is deliquescent

2. Dissolve the potassium thiocyanate in enough ____________ to make 1000 mL.

3. Store the solution in a ____________________.

3 = ?

20.0 mL of standard silver nitrate solution

STANDARDIZATION OF POTASSIUM THIOCYANATE SOLUTION

1. Run down __________________________________ from an acid buret into an Erlenmeyer flask.

2. Add _____________________.

3. Add _________________________.

4. Add ___________________________.

5. Titrate with potassium thiocyanate solution to a _____ color endpoint.

1 = ?

50 mL of distilled water

STANDARDIZATION OF POTASSIUM THIOCYANATE SOLUTION

1. Run down __________________________________ from an acid buret into an Erlenmeyer flask.

2. Add _____________________.

3. Add _________________________.

4. Add ___________________________.

5. Titrate with potassium thiocyanate solution to a _____ color endpoint.

2 = ?

2 mL of concentrated nitric acid

STANDARDIZATION OF POTASSIUM THIOCYANATE SOLUTION

1. Run down __________________________________ from an acid buret into an Erlenmeyer flask.

2. Add _____________________.

3. Add _________________________.

4. Add ___________________________.

5. Titrate with potassium thiocyanate solution to a _____ color endpoint.

3 = ?

2 mL of ferric alum indicator

STANDARDIZATION OF POTASSIUM THIOCYANATE SOLUTION

1. Run down __________________________________ from an acid buret into an Erlenmeyer flask.

2. Add _____________________.

3. Add _________________________.

4. Add ___________________________.

5. Titrate with potassium thiocyanate solution to a _____ color endpoint.

4 = ?

flesh

STANDARDIZATION OF POTASSIUM THIOCYANATE SOLUTION

1. Run down __________________________________ from an acid buret into an Erlenmeyer flask.

2. Add _____________________.

3. Add _________________________.

4. Add ___________________________.

5. Titrate with potassium thiocyanate solution to a _____ color endpoint.

5 = ?

Secondary standardization

What is the method of standardization in potassium thiocyanate solution?

Volhard method

What is the principle of titration employed?

To prevent hydrolysis of ferric salts (ferric alum)

Why do we have to acidify with nitric acid?

AgNO3

it is non-hygroscopic

KSCN

it is hygroscopic (deliquescent)

Liebig method

The conventional a.________ does not use an indicator but its modified version uses b._____________________ as an indicator.

a = ?

bromophenol blue

The conventional a.________ does not use an indicator but its modified version uses b._____________________ as an indicator.

b = ?