chem 30 redox

Oxidizing Agent (OA)

A substance that undergoes reduction and causes another substance to be oxidized, meaning its oxidation number decreases.

Reducing Agent (RA)

A substance that undergoes oxidation and causes another substance to be reduced, meaning its oxidation number increases.

Reduction

The gain of electrons by a chemical species, resulting in a decrease in its overall oxidation number.

Oxidation

The loss of electrons by a chemical species, resulting in an increase in its overall oxidation number.

Hydrogen Oxidation Number in Metallic Hydrides

It is exactly -1 in compounds like $NaH$, $CaH_2$, or $BaH_2$, serving as a major exception to the standard +1 rule.

Dissociation Rule: Soluble Ionic Compounds

They completely dissociate into two separate ions in aqueous solution, identified by starting with a metal or the ammonium ion ($NH_4^+$).

Dissociation Rule: Molecular Compounds

They consist entirely of non-metals and stay completely together as whole molecules instead of dissociating in solution.

Dissociation Rule: Strong Acids

They fully split into two separate ions in solution, consisting of the 6 strong acids: $HClO_4$, $HI$, $HBr$, $HCl$, $H_2SO_4$, and $HNO_3$.

Dissociation Rule: Weak Acids

They do not fully ionize or dissociate in solution and must be listed intact as a single molecular compound.

Listing Species: "Acidic" Condition

You must explicitly list hydronium

Listing Species: "Basic" Condition

You must explicitly list hydroxide ions ($OH^-_{(aq)}$) as a species present in the mixture.

Listing Species: Aqueous Solutions

You must always list water ($H_2O_{(l)}$) as an available species since it serves as the solvent.

Typical Oxidizing Agents (OAs)

Chemical species including metallic cations, acidic solutions, and halogens.

Typical Reducing Agents (RAs)

Chemical species including neutral metals, basic solutions, and halide ions.

Amphoteric Redox Species (Both OA and RA)

Chemical species that can act as either an oxidizing agent or a reducing agent, specifically $Cr^{2+}$, $Sn^{2+}$, $Fe^{2+}$, and $H_2O$.

Empirical Evidence: Solid Reactant

The overall mass of the solid substance will decrease as it undergoes the reaction.

Empirical Evidence: Solid Product

The overall mass of the solid substance will increase as it plates out or deposits.

Empirical Evidence: Precipitate Formation

If you form a positive ion and a negative ion together on the product side, you must check the solubility table to watch for a precipitate.

Empirical Evidence: $H^+_{(aq)}$ as a Reactant

The total concentration of $H^+$ will decrease, causing the reaction mixture to become less acidic and the pH to increase.

Empirical Evidence: $H^+_{(aq)}$ as a Product

The total concentration of $H^+$ will increase, causing the reaction mixture to become more acidic and the pH to decrease.

Empirical Evidence: $OH^-_{(aq)}$ as a Reactant

The total concentration of $OH^-$ will decrease, causing the reaction mixture to become less basic and the pH to decrease.

Empirical Evidence: $OH^-_{(aq)}$ as a Product

The total concentration of $OH^-$ will increase, causing the reaction mixture to become more basic and the pH to increase.

Empirical Evidence: Coloured Ion as a Reactant

The intensity of the color in the solution will lighten, fade, or completely disappear during the reaction.

Empirical Evidence: Coloured Ion as a Product

The intensity of the color in the solution will darken, deepen, or brighten during the reaction.

Empirical Evidence: Coloured Ion as Both Reactant and Product

The color of the solution will directly shift from the original reactant color to the newly formed product color.

Titration Lab: Manipulated Variable

The exact volume of the sample being titrated, which functions as the independent variable.

Titration Lab: Responding Variable

The total volume of titrant added to reach the endpoint, alongside the specific color change of the endpoint.

Titration Lab: Controlled Variables

The concentration of the standard solution, the initial concentration of the unknown sample, and environmental parameters kept constant.

Quality Check for Titration Trials

Good trials must have volumes within 0.2 mL of each other, measured as the difference between the largest and smallest accepted trial volumes.

Voltaic Cell

An electrochemical cell that spontaneously converts chemical energy into electrical energy, acting as a functional battery with a positive net voltage.

Electrolytic Cell

An electrochemical cell that uses an external power supply to non-spontaneously convert electrical energy into chemical energy, possessing a negative net voltage.

Electrode

A solid piece of conducting material where half-reactions take place that must be able to conduct electricity.

Cathode

The site of the reduction half-reaction in an electrochemical cell, always located in the half-cell containing the strongest oxidizing agent (SOA); attracts cations.

Anode

The site of the oxidation half-reaction in an electrochemical cell, always located in the half-cell containing the strongest reducing agent (SRA); attracts anions.

Direction of Electron Flow

Electrons always travel through the external wire from the anode to the cathode, moving from negative to positive in a voltaic cell.

Salt Bridge

Porous Cup

Direction of Anion Migration

Negative ions (anions) always move through the salt bridge or porous boundary directly towards the anode.

Direction of Cation Migration

Positive ions (cations) always move through the salt bridge or porous boundary directly towards the cathode.

Inert Electrode

A solid metal or carbon

Standard Cell Notation Format

Electrode (s) | Electrolyte (aq) || Electrolyte (aq) | Electrode (s), where single lines denote phase boundaries and double lines denote a porous boundary or salt bridge.

Cell Potential Formula ($\Delta E$)

$\Delta E = E_{r(\text{cathode})} - E_{r(\text{anode})}$ or $\Delta E = E_{r(\text{SOA})} - E_{r(\text{SRA})}$.

Sign-Reversal Rule for Oxidation Potential

The oxidation potential of any given substance is exactly equal to its standard reduction potential with the mathematical sign reversed.

Chloride Anomaly

When chloride ions ($Cl^-$) and water ($H_2O$) compete to act as the strongest reducing agent (SRA) in an electrolytic cell, chloride ions win out and oxidize instead of water.

KI Electrolysis: Cathode Half-Reaction

$2H_2O_{(l)} + 2e^- \rightarrow H_{2(g)} + 2OH^-_{(aq)}$ with an standard reduction potential ($E^\circ_r$) of -0.83 V.

KI Electrolysis: Anode Half-Reaction

$2I^-{(aq)} \rightarrow I{2(aq)} + 2e^-$ with an standard reduction potential ($E^\circ_r$) of +0.54 V.

KI Electrolysis: Minimum Voltage Required

A total minimum applied voltage of +1.37 V is required, calculated from a net cell potential ($E^\circ_{\text{net}}$) of -1.37 V.

Corrosion Prevention: Paint

A barrier method that prevents rust by shielding the metal from direct physical exposure to oxygen and moisture.

Corrosion Prevention: Galvanizing

Coating a metal structure with a layer of zinc ($Zn_{(s)}$), which reacts with oxygen to build a protective $ZnO_{(s)}$ coating over the underlying metal.

Corrosion Prevention: Sacrificial Anode

Deliberately installing a highly reactive metal (such as magnesium, $Mg$) to act as the SRA and corrode first, ensuring the protected metal is no longer the SRA.

Corrosion Prevention: Impressed Current

Applying an external DC electrical power supply that continuously delivers electrons to environmental oxidizing agents so the valuable metal is not oxidized.

Moles of Electrons Formula ($n_e$)

$n_e = \frac{It}{F}$, a critical equation that is not in your standard chemistry data booklet and must be completely memorized.

Faraday's Law: Variable $I$

Represents the current measured in Amperes (A) or Coulombs per second (C

Faraday's Law: Variable $t$

Represents the total elapsed time, which must always be mathematically converted into seconds (s).

Faraday's Law: Variable $F$

Represents the Faraday constant, which possesses a standard value of $9.65 \times 10^4\text{ C

Faraday's Law Formula Rearranged for Current ($I$)

$I = \frac{n_e F}{t}$.