titration 3

Redox Titration

is a laboratory method of determining the concentration of a given analyte by causing a redox reaction between the titrant and the analyte.

Redox Titration

require the use of a potentiometer or a redox indicator

potentiometer or a redox indicator

sometimes used during redox titrations

Redox titration

based on an oxidation-reduction reaction between the titrant and the analyte.

Redox titration

It is one of the most common laboratory methods to identify the concentration of unknown analytes

redox titrations i

involve a transfer of electrons between the given analyte and the titrant

treatment of an iodine solution with a reducing agent.

An example of a redox titration

Oxidizing agent

makes oxidation to happen

Reducing agent

makes reduction to happen

Oxidation

loss of electrons A loses electrons

Reduction

gain of electrons

reducing agent

The thing that is oxidized

oxidizing agent

The thing that is reduced

Iodometric titration

is used to determine oxidizing agents

Iodometric titration

is an indirect titration

Iodimetric titration

used to determin reducing agents

Iodimetric titration

is a direct titration method

Iodimetric titration

an iodine solution is directly titrated with a reducing soltuon

Iodometric titration

iodine (intermediary) that has been formed as a result of a prior redox reaction is titrated with a reducing agent

Iodometric titration

the total number of redox reactions is two

Iodometry

is commonly applied in several experiments

Iodimetry titration

only one redox reaction is involved

Iodometry

commonly applies in several experiments

Iodimetry method

is less commonly applied in experiments

Iodine solution

is easily standardized against Na2S2O3/ As2O3 solution

Oxidizing agents

CuSO4

K2Cr2O7

KMnO4

Fe3+

H202

Br2

CI2

Reducing Agents

Ascorbic acid

Iodimetric titrations

A reducing analyte

Iodimetric titrations

one reaction

Iodimetric titrations

standard solution: Iodine (I2)

Iodometric titrations

An oxidizing analyte

Iodometric titrations

Two reactions

Iodometric titrations

Standard solution: Sodium thiosulfate

PRECIPITATION TITRATION

is a titration method in which a precipitate is formed.

Precipitation titration

It is a quantitative analytic technique that determines the amount of the analyte by measuring volume

Precipitation Titration

It is a titrimetric method which involves the formation of precipitates during the experiment of titration

Precipitation Titration

The titrant reacts with the analyte and forms an insoluble substance.

Precipitation Titration

The titration is continued till the last drop of the analyte is consumed. When the titrant is excess it reacts with the indicator and signals to terminate the titration process

Precipitation

Is a combination of two ionic species to form a non soluble product which forms a precipitates.

solubility product

permits the calculation of an ion if the other is known

Reagents

trigger chemical reactions.

Types of precipitation titration

Mohr method, Adsorption method, Volhard method

Mohr method

Depends on differentia precipitation (with different solubilities)

Adsorption method

Depends on the adsorption process

Adsorption method

Fajan’s method

Volhard method

Depends on Back titration technique

Mohr’s method

argentometric

all precipitation titration methods

uses silver nitrate as a titrant

AgCI

white precipitate

AgBr

pale yellow precipitate

ag2CrO4

reddish brown precipitate

Volhard method

includes iodide

Volhard method

back titration (indirect titration) technique used to determine excess

Volhard method

precipitate halide ions

AgI

yellow precipitate

Fajan’s method

direct titration w/ silver nitrate

Adsorption Indicators

Fluorescein

Eosin

Dichlorofluorescein

Mohr method

Simple silver titration method

Mohr method

Alkaline solutions only

Mohr method

Not suitable for iodide

Mohr method

requires a blank

Fajans method

Capability for different pH ranges and selectivity with different indicators

Fajans method

Difficulty with dilute solutions

Fajans method

Should not be a high background ionic level

Volhard method

Capable of direct silver and indirect halide analyses

Volhard method

Very clear colour change

Volhard method

Must be 1M nitric acid solution

Volhard method

Some problem with specific anions

Complexometric Titration

The titrate combines with the titrant which results in the formation of complex salts in this type of titration.

complex salts in complexometric titration

may or may not be soluble.

Complexometric titrations

are used mainly to determine metal ions by use of complex-forming reactions.

Complexometric titrations

are used to titrate and analyze the concentration of unknown metal ions that are present in the sample solutions

EDTA

Ethylenediaminetetraacetic acid

Ethylenediaminetetraacetic acid

is a chemical that binds and holds on to (chelates) minerals and metals such as chromium, iron, lead, mercury, copper, aluminum, nickel, zinc, calcium, cobalt, manganese, and magnesium

Calmagite, Arsenazo I, Xylenol orange

Sample of Complexometric Indicators

Direct titration

is a way to determine the contents of a substance quantitatively. Scientists may be aware of a reactant, but not know the SU reactant’s quantity

Direct titration

is sometimes based on indicators that respond to the analyzed material, called the analyte.

Direct titration

Other times, the methods are based on the use of added metal ions, which are individual atoms or molecules of a specific type of metal

Direct Titrations

Is conducted by introducing a standard acid solution from a burette into a solution of the based being assayed until chemically equivalent amounts of each have reacted as shown by some change in properties of the mixture.

Assay of sodium bicarbonate titrant

1 N H2SO4

Assay of sodium bicarbonate Indicator

Methyl Orange

Assay of sodium hydroxide titrant

1 N H2SO4

Assay of sodium hydroxide indicator

Phenolphthalein or Methyl Orange

Assay of sodium salicylate titrant

0.1 N HCI

Assay of sodium salicylate Indicator

Bromophenol Blue

back titration

is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent.

back titration

The second titration's result shows how much of the excess reagent was used in the first titration, thus allowing the original analyte's concentration to be calculated

back titration

indirect titration

UNKNOWN SUBSTANCE, Volatile, Insoluble Salt, Reaction is too slow

USE OF RESIDUAL/BACK/INDIRECT TIRATRION

limiting reagent

determined reactant will limit the chemical reaction

limiting reagent

the one that produces less product

back titration

is generally a two-stage analytical technique

direct titration

involves a weak acid - weak base titration

Back titration

is used when the molar concentration of an excess reactant is known but the need exists to determine the strength or concentration of an analyte

Back titrations

are applied, more generally, when the endpoint is easier to see than with a normal titration , which applies to some precipitation reactions.

Kjeldahl method or Kjeldahl digestion

a method for the quantitative determination of nitrogen contained in organic substances plus the nitrogen contained in the inorganic compounds ammonia and ammonium (NH3/NH4+)

blank titration

we titrate the titrant (soln in burette) against the blank solvent in which a sample of unknown concentration (analyte) is dissolved.

Blank Titration

This is done to ensure that either there are no substances in the solvent which can react with the titrant, or to estimate the amount of titrant that would react with the pure solvent

Blank Titration

In this way, we can estimate the error that can be produced when the actual titration experiment is conducted.

Blank Titration

carried out without the analyte and is used to correct titration error