Unit 3.1 & 3.2 Redox

Reduction is gain of electrons (RIG)

Oxidation is loss of electrons (OIL)

The 'change' in charge of the atom in compound compared to its atomic form

An ion which plays no part in the reaction

To provide the H+ ions necessary to reduce oxygen to H₂O

The electrode where reduction occurs (Red cat)

The electrode where oxidation occurs (An ox)

A metal submerged in a solution of its own ions

A dynamic equilibrium $\mathit{(M \rightleftharpoons M^{n+} + ne^-)}$ which results in a potential diference (energy per coulomb of charge)

The reduction process (electrons on left: EOL)

The potential difference formed between an element's half cell and a standard electrode, under standard conditions

-All concentrations are 1$mol\ dm^{-3}$
-1 atm and 25°c (298k)
-All metals in their standard state

A strip of paper soaked in a saturated Potassium Nitrate solution

$Fe^{2+} and\ Fe^{3+}$

The reduction process will tend to occur

The oxidation process will tend to occur

A half cell where a platinum electrode is suspended in a 1$mol\ dm^{-3}$ solution of H$^+$ions with a supply of 1 atm Hydrogen gas

A strongly negative SEP (As this means its readily oxidised)

The polarity of the half cell electrode when connected to an SHE

A method of energy storage with no moving parts and only involving Hydrogen and Oxygen, making them particularly efficient, reliable, and clean

To minimise the flow of current, which would affect the reading

To allow the movement of ions and thus charge without causing cross contamination of the solutions

A way of representing half-cell systems using set notation

The more positive one will move forwards whilst pushing the more negative one backwards

The resulting potential diference when 2 half-cells are connected

The reaction will proceed

The oxidation process (OIL)

The one with the highest oxidation state

With the 2 species bracketed and separated by a comma (The electrode is still denoted, but by using "/Pt"

Deposition of material on the electrode surface

$KMnO_4$

+7 to +2 ($Mn^{2+}$)

$MnO_4^- + 5e^- + 8H^+\rightarrow Mn^{2+} + 4H_2O$

An excess of H$^+$ ions are required to fully "mop-up" the reduced oxygens, or else MnO is formed, which is a brown precipitate which obscures the end point.

Sulphuric acid, as the sulphur ions will usually remain as spectators in solution

No, as it has a tendency to deteriorate on standing

Using a primary standard (such as sodium ethanedioate)

No, as it is a self-indicating reaction

The first appearance of a permanent pink hue in the colourless flask reagent

$K_2Cr_2O_7$

+6 to +3 ($Cr^{3+}$)

$Cr_2O_7^{2-} + 6e^- + 14H^+ \rightarrow 2Cr^{3+} + 7H_2O$

Sulphuric acid or hydrochloric acid may be used, as dichromate isn't a strong enough of a oxidise agent to oxidis the Cl$^-$ ions

Yes, as it's available in a highly pure form and is stable enough to be stored long-term

Yes, as the colour change from orange to green is unclear, so complex organic indicators are required

$Na_2S_2O_3$

$2S_2O_3^{-2} \rightarrow S_4O_6^{2-} + 2e^-

Tetrathionate ($S_4O_6^{2-}$)

A starch indicator (blue-black to colourless)

Yellowish-brown

Very pale green