chem whatarethemechanismsofchemicalchange
Reactivity 3.2.2 - half-equations separate the processes of oxidation and reduction, showing the loss or gain of electrons
electrons are included in both half-equations to balance the charges
steps in acidified solutions
- write unbalanced equations
- assign oxidation states to determine which elements are oxidised and which are reduced
- write separate half-equations for oxidation and reduction including the electrons needed to account for the changes
- balance atoms other than
and - balance each half-equation for
by adding as needed - balance each half-equation for
by adding as needed - check that each half-equation is balanced for atoms and for charge
- equalise the number of electrons in the two half-equations by finding a common factor and multiplying each appropriately
- add the two half-equations together, cancelling out anything that is the same on both sides, including electrons
redox titrations
titration method is the same as acid-base titrations, but the equivalence point is where the two reactants have reacted stoichiometrically by transferring electrons
examples
iodine-thiosulfate reaction
several different redox titrations use an oxidising agent to convert excess iodide ions to iodine
the liberated iodine,
starch can be added as an indicator before the equivalence point is reached. it forms a blue colour by forming a complex with free
analysis of iron with manganate(VII)
the manganate(VII) ion is purple, while the
challenge questions
- reactions in which the same element is simultaneously oxidised and reduced are known as disproportionation reactions. deduce the equation for the reaction when
reacts with to produce , , and , and show that this is a disproportionation reaction.
iodate ion: