Battery and Fuel Cell Quiz

Oxidation Numbers (States)

• An oxidation number is the apparent charge of an atom in a neutral molecule or charged polyatomic ion.
• Oxidation numbers are used to identify if oxidation or reduction is occurring in a molecular compound without ion charges.
• A decrease in oxidation number represents reduction.
• An increase in oxidation number represents oxidation.

Rules for Assigning Oxidation Numbers

• Pure elements: The oxidation number is zero.
• Simple ions: The oxidation number is equal to the ion charge.
• Hydrogen in most compounds: The oxidation number is +1. (Exception: metal hydrides, eg, LiH, where hydrogen is -1.)
• Oxygen in most compounds: The oxidation number is -2. (Exception: peroxides eg, H₂O₂, Na₂O₂, where oxygen is -1.)
• Sum of oxidation numbers: The sum of oxidation numbers of all atoms in a substance must equal the substance's net charge (zero for compounds and the charge of the polyatomic ion).
• Molecular compounds (no H or O): The more electronegative element is assigned an oxidation number equal to the negative charge it usually has in ionic compounds.

Example Calculations

• N in N₂O: Individual oxidation numbers are +1 and -2; the sum is zero.
• C in C₂H₂OH: Individual oxidation numbers are -2, +1, -2, and +1 which sum to zero.
• P in P₂O₅: Individual oxidation numbers are +5 and -2; the sum is zero.

Redox Reactions

• Oxidation numbers help identify if a reaction is a redox reaction.
• A redox reaction involves both an increase and a decrease in oxidation numbers.
• Example (Ag(s) + NaNO₃(aq) → Na(s) + AgNO₃(aq)): Silver (Ag) is oxidized because its oxidation number increased, and Sodium (Na) is reduced because its oxidation number decreased.

Electrochemistry

• Electrochemistry: The branch of chemistry studying electron transfer in chemical reactions.
• Oxidation: Loss of electrons (LEO).
• Reduction: Gain of electrons (GER).
• Oxidation and reduction always occur together in redox reactions.
• Half-reactions describe the oxidation and reduction processes.
• Spectator ions do not change in a redox reaction.
• The substance reduced is the Oxidizing Agent (OA).
• The substance oxidized is the Reducing Agent (RA).

Spontaneous Redox Reactions

• Spontaneous redox reactions occur without external energy input.
• The strongest oxidizing agent (SOA) is on top-left of the table.
• The strongest reducing agent (SRA) is on bottom-right of the table.
• A redox reaction is spontaneous if the oxidizing agent (OA) is above the reducing agent (RA) in the table of half reactions.

Predicting Redox Reactions

• List all reactants
• Dissociate soluble ionic compounds and acids
• Do not dissociate molecular compounds
• Include H⁺ ions if acidic
• Always include water (H₂O)

Short-Hand Notation

• A shorthand notation is used to represent a voltaic or electrolytic cell.
• A line (/) separates items in different phases (solid, liquid, gas, or aqueous solution).
• A double line (//) represents a salt bridge or porous cup.
• Commas separate items in the same phase.

Drawing Electrochemical Cells

• When drawing a cell, label the cathode, anode, positive terminal, negative terminal, electrolytes, and the directions of cation and anion flow.
• Show and label reduction half-reaction, oxidation half-reaction, net reaction, Eº values, Eº net, and spontaneity.

Commercial Cells (Batteries)

• Batteries are made of multiple voltaic cells connected in series.

Dry Cells

• 1.5V and 9V batteries in clocks, remote controls, etc.

Nickel-Cadmium Batteries

• Rechargeable.

Lead Storage Batteries

• Typical car batteries.

Fuel Cells

• Continuous supply of reactants.
• Example: Hydrogen-oxygen fuel cells.

Electrolytic Cells (Basics)

• Use electrical energy to force a nonspontaneous chemical reaction to occur.
• Typically used to electroplate metals, recharge batteries, and split compounds into useful gases.

Quantitative Study of Electrolysis

• Stoichiometry is applied to electrolytic reactions.
• Charge (q) is in Coulombs(C).
• One mole of electrons carries 9.65 x 10⁴ C (Faraday Constant, F).
• Moles of electrons (nₑ) = (current(I) x time(t)) ÷ (Faraday constant(F)).

Titrations

• A titration is a procedure to determine the volume of one substance needed to completely react with another.
• Common oxidizing agents in redox titrations are permanganate and dichromate ions (because of their color change).
• The equivalence point is reached when the titrant (oxidizing agent) has completely reacted with the sample (reducing agent).
• The concentration of the titrant must be accurately known and standardized against a primary standard.

Test your knowledge on battery types, their components, and fuel cells with this quiz. Questions cover dry cell batteries, lead storage batteries, and hydrogen-oxygen fuel cells. Perfect for students and enthusiasts in the field of electrochemistry.