Precipitation Titration

Precipitation

• formation of a solid in a solution

• occurs when water solutions of two different ionic compounds are mixed and an insoluble solid separates out of solutions

Precipitation Titration

• a titration method based on the formation of precipitate, which is slightly soluble

Precipitation Titration

• not so popular in present-day routine analysis

• SLOW

• involving periods of digestion, cooling, filtration etc

• Tends to limit the reactions that are available for titration

Argentometric Titration

• titrations involving silver

Halides and Pseudohalides

Argentometric Titration:

• the major precipitation reaction used is that of silver with a range of anions. These anions include:

Mohr’s Method, Fajan’s Method, Volhard’s Method

Argentometric methods involving precipitation titrimetry

Mohr’s Method

Nature of Titration

• Direct method of titration

Potassium Chromate

Mohr’s Method - Indicator

Silver Nitrate

Mohr’s Method - Titrant

Chloride Ion Solution

Mohr’s Method - Analyte

Reddish Brown complex/ Red ppt of Silver Chromate

Mohr’s method - End Point

Neutral/Alkaline (pH 6.5 to 9)

Medium

Mohr’s Method

Use

• Can be used to determine bromide and chloride

• titration of iodide and cyaneate is not possible

Mohr’s Method

• carried out at room temperature because solubility of silver chromate is increased with rising temperature

Volhard Method

Nature of Titration

• an indirect method of titration

Volhard’s Method

• in this method, chlorides are first precipitated with excess silver nitrate then excess silver nitrate is titrated with potassium thiocyanate

Ferric Ammonium Sulphate

Volhard’s Method - Indicator

Wine red color

Volhard’s Method - End point

Acidic Condition

Volhard’s Method - Medium

Volhard’s Method

Titration can be used to determine Iodide, Bromide, and chloride

Volhard’s Method

• titration is carried out below 20 C to prevent the color of ferric thiocyanate complex form fading

Redox Reaction

• involved oxidation and reduction reaction between the analyte and the titrant

Permanganimetric, Dichromatometric, Iodometry, Iodimetry

Classifications of Redox Titration

Permanganimetric

Titrant - KMnO4

Dichromatometric

Titrant - K2Cr2O7

Iodimetry

• it is a direct titration method

Iodometry

• it is an indirect titration method

Iodometric

• two redox reaction occur in this titration

Iodimetry

• one redox reaction occurs in this titration

Iodometry

• used to quantify the oxidizing agent

Iodimetry

• used to quantify the reducing agent

Determination of Sulfites and Hydrogensulfites

reduces iodine readily in acidic medium to iodide

Determination of Sulfides and Hydrogensulfides

• the excess arsenic trioxide is then determined by titrating against standard iodine solution using starch indicator