Redox Reactions: High-Yield Short Notes

Comprehensive vocabulary flashcards covering core redox theory, n-factor calculations, high-yield reagents, structural exceptions, and titration formulas.

Oxidation state (O.S.)

A hypothetical charge assuming complete ionic cleavage of bonds.

Maximum Oxidation State

The maximum oxidation state an element can achieve is equal to its number of valence electrons (Group Number).

$$C_{3}O_{2}$$

Carbon Suboxide; average oxidation state is $+4/3$, real states are $+2, 0, +2$ based on structural logic where the middle $C$ is bonded only to $C$.

$$Br_{3}O_{8}$$

Tribromo-octaoxide; average oxidation state is $+16/3$, real states are $+6, +4, +6$ where terminal $Br$ have 3 bonds to $O$ and the middle has 2.

$$S_{4}O_{6}^{2-}$$

Tetrathionate ion; average oxidation state is $+2.5$, real states are $+5, 0, 0, +5$ where the middle $S$ is bonded only to $S$.

n-factor (Acids)

Determined by Basicity, or the number of replaceable $H^{+}$.

n-factor (Bases)

Determined by Acidity, or the number of replaceable $OH$.

n-factor (Salts)

Determined by the total cationic OR anionic charge.

n-factor (Redox Agent)

Calculated as $|\text{Change in O.S.}| \times \text{Number of atoms per molecule}$.

$KMnO_{4}$ (Acidic Medium)

The product formed is $Mn^{2+}$ with an n-factor of $5$ ($+7 \rightarrow +2$).

$KMnO_{4}$ (Neutral / Faintly Basic)

The product formed is $MnO_{2}$ with an n-factor of $3$ ($+7 \rightarrow +4$).

$KMnO_{4}$ (Strongly Basic)

The product formed is $MnO_{4}^{2-}$ with an n-factor of $1$ ($+7 \rightarrow +6$).

$K_{2}Cr_{2}O_{7}$ (Acidic Medium)

The product formed is $2Cr^{3+}$ with an n-factor of $6$ ($2 \times 3$).

Oxalic Acid ($H_{2}C_{2}O_{4}$)

A reagent that forms $2CO_{2}$ in acidic medium with an n-factor of $2$ ($2 \times 1$).

Hypo ($Na_{2}S_{2}O_{3}$)

Reaction with $I_{2}$ produces Tetrathionate ion ($S_{4}O_{6}^{2-}$) with an n-factor of $1$.

Peroxy Linkage Exception

Occurs when calculated O.S. exceeds maximum group valence; indicates an $O-O$ linkage where Oxygen is $-1$.

Caro's Acid ($H_{2}SO_{5}$)

Contains 1 peroxy linkage; calculated $S = +8$ is false; real $S = +6$.

Marshall's Acid ($H_{2}S_{2}O_{8}$)

Contains 1 peroxy linkage; calculated $S = +7$ is false; real $S = +6$.

Chromium Pentoxide ($CrO_{5}$)

Features a butterfly structure with 2 peroxy linkages; calculated $Cr = +10$ is false; real $Cr = +6$.

$n_{total}$ (Disproportionation)

Calculated using the formula $\frac{n_{1} \times n_{2}}{n_{1} + n_{2}}$ where $n_{1}$ is oxidation and $n_{2}$ is reduction.

Equivalent Weight ($E$)

Calculated as $\frac{\text{Molar Mass (M)}}{\text{n-factor}}$.

Normality ($N$)

Calculated as $\text{Molarity (M)} \times \text{n-factor}$.

Phenolphthalein ($HPh$)

Indicator used in double titration to detect completion of $NaOH \rightarrow NaCl$ ($n=1$) and $Na_{2}CO_{3} \rightarrow NaHCO_{3}$ ($n=1$).

Methyl Orange ($MeOH$)

Indicator used to detect completion of all bases down to $CO_{2}$, specifically for $Na_{2}CO_{3} \rightarrow CO_{2}$ ($n=2$) and $NaHCO_{3} \rightarrow CO_{2}$ ($n=1$).

Disproportionation Reaction

A reaction where the same element in an intermediate oxidation state is simultaneously oxidized and reduced.

$$F_{2}$$

The most electronegative element; it never undergoes disproportionation.

$$ClO_{4}^{-}$$

Contains $Cl$ in its maximum $+7$ oxidation state; it cannot disproportionate.

Reducing Agent Limit

Species in minimum oxidation states (e.g., $N^{3-}, S^{2-}, Cl^{-}$) can only lose electrons and act only as reducing agents.

Oxidising Agent Limit

Species in maximum oxidation states (e.g., $MnO_{4}^{-}, Cr_{2}O_{7}^{2-}, SO_{4}^{2-}$) can only gain electrons and act only as oxidising agents.

Halogen Displacement Logic

The order of displacement strength is $F_{2} > Cl_{2} > Br_{2} > I_{2}$.

Standard Electrode Potential ($E^{\circ}$)

A higher $E_{\text{reduction}}^{\circ}$ indicates a stronger oxidizing agent; a lower (negative) $E_{\text{reduction}}^{\circ}$ indicates a stronger reducing agent.