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Module 5 - Chapter 23 - Redox and electride potentials - Coggle Diagram
Module 5 - Chapter 23 - Redox and electride potentials
Redox titrations
Manganate titrations
Procedure
Standard solution of potassium mangante is added to burette
Add a measured volume of the solution being analysed to the conical flask - excess of dilute sulfuric acid is added to provide H+ ions required for reduction of MnO4-
Reaction is self indicating so no inidicator is added
Add the mangante(VII) solution, it will decolourise and the end point is the first permanent pink colour
Repeat until you have two concordant results
Due to the deep purple colour of the potassium manganate, you read from the top of the meniscus
Iodine/ thiosulfate titration
Thiosulfate ions are oxidised
Iodine is reduced
Procedure
Add sodium thiosulfate to burette
Add solution of oxidising agent to conical flask and then add potassium iodide which produces iondine and turns the solution yellow brown
Titrate the solution, iodine is reacted back to I- ions and brown colour fades
When end point is near (solution turns yellow) small amount of starch is added and blue black forms
As more sodium thiosulfate is added, blue black colour fades, end point is when solution is colour less
Copper analysis
Iodine thiosulfate is used to determine the copper content of copper(II) salts or alloys
For salts, Cu2+ ions are produced by dissolving the compount in water
Insoluble copper compouns can be reacted with acits to form Cu2+ ions
Copper alloys are reacted and dissolved in nitric acid
Cu2+ reacts with I- to form iodine solution and white precipitate of copper iondide
Iodine is tirated with a standard solution of soium thiosulfate
2 molues of Cu2+ forms 1 mole of iodine and reacts with 2 molues of thiosulfate ions
2 mole of Cu2+ is equivalent to 1 mol of thiosulfate ions
Cells
Electrochemical cell
Voltatic cell - cell that converts chemical energy into electrical energy
Half cells
Two separate halves of the reaction are contained in half cells
Metal/ metal ions half cells
Metal rod dipped into solution of its aqueous metal ion
Vertical line shows the phase boundary between aqueous solution and the metal
Equilibrium is present at the phase bounary
Ion/ ion half cells
Contains same element in different oxidation states
No metal to transport electrons in or out of the half cell, so an intert metal electrode made from platinum is used
Chemicals in two half cells must be kept apart (if they mixed, electrons would flow in an uncontrolled way and heat energy would be released
