Redox Reactions

Class 11 · Chemistry

4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.

Oxidation, Reduction and Electron Transfer

Part of: Electron Transfer and Oxidation Numbers

Oxidation loses electrons; reduction gains them. The donor reduces and is the reducing agent; the acceptor oxidises and is the oxidising agent. Metals compete to donate: zinc beats copper, copper beats silver, with cobalt and nickel nearly tied.

Why it matters. Batteries, rust and bleaches all run on electron trade. Naming donor and acceptor correctly starts every redox analysis.

Formulas

Oxidation is loss of electrons; reduction is gain of electrons.
Zn + Cu2+ yields Zn2+ + Cu, as zinc displaces copper ions.
Cu + 2Ag+ yields Cu2+ + 2Ag, as copper displaces silver ions.

Key words

Oxidation: : Losing electrons raises oxidation state and marks the substance oxidised.
Reduction: : Gaining electrons lowers oxidation state and marks the substance reduced.
Reducing agent: : The electron donor that reduces another species while being oxidised.
Oxidising agent: : The electron acceptor that oxidises another species while being reduced.
Redox couple: : The oxidised and reduced forms of one species in a half reaction.
Displacement reaction: : A more reactive metal donates electrons and displaces a weaker metal ion.

Try it in two minutes

Dip zinc in blue solution and watch copper appear.
Name who lost and who gained.
Rank three metals by donating power.

Try at home. Compare nail rust in dry versus salty air.

Oxidation Numbers

Part of: Electron Transfer and Oxidation Numbers

Oxidation numbers pretend full electron transfer to the greedier atom. Rules fix fluorine at minus one, oxygen usually at minus two, and free elements at zero. Rising numbers mean oxidation; falling mean reduction; unchanged means no redox.

Why it matters. Numbers track electron shifts even in covalent tangles. They flag redox, disproportionation and balance needs.

Formulas

Free elements and uncombined atoms have oxidation number 0.
A single-atom ion has oxidation number equal to its charge.
Alkali metals are +1, alkaline earth metals are +2, aluminium is +3.
Oxygen is usually -2; peroxides -1; oxygen in OF2 is +2.
Hydrogen is +1, except -1 in metal hydrides like NaH.
Fluorine is always -1; other halogens are -1 as halide ions.
Oxidation numbers in a neutral compound add to 0; in an ion add to the charge.

Key words

Oxidation number: : A book-keeping charge assigned as if bonding electrons went to the greedier atom.
Free element: : An uncombined element whose atoms all carry oxidation number zero.
Oxidation state: : Another name for the oxidation number of an element in a compound.
Disproportionation: : One species oxidised and reduced at once into two different products.
Average oxidation number: : The mean value shared when identical atoms in one formula differ.

Try it in two minutes

Assign numbers to three salts.
Spot rise and fall in a reaction.
Find a disproportionation split.

Try at home. Assign numbers across a page of formulas.

Balancing Redox Reactions

Part of: Balancing and Cells

Split redox into oxidation and reduction halves, balancing atoms with water and H+ in acid, then charge with electrons. Equalise electron counts before adding halves; basic media add hydroxide to both sides.

Why it matters. Inspection fails on redox; halves never do. The method scales to any acidic or basic equation.

Formulas

Balance atoms other than O and H first, then O with H2O and H with H+ in acid.
Balance the charge by adding electrons to the more positive side.
Multiply the halves so electrons lost equal electrons gained, then add them.
In basic medium add one OH- for each H+ on both sides and combine to water.

Key words

Half reaction: : The oxidation or reduction half written as a separate balanced equation.
Oxidation half: : The half reaction that releases electrons as a species is oxidised.
Reduction half: : The half reaction that consumes electrons as a species is reduced.
Acidic medium: : Conditions where water balances oxygen and H+ balances hydrogen.
Basic medium: : Conditions where extra hydroxide balances the acid step first.

Try it in two minutes

Split a reaction into halves.
Balance atoms, then charge.
Equalise electrons and add.

Try at home. Balance permanganate with iron step by step.

Electrode Potentials and Cells

Part of: Balancing and Cells

Standard potentials rank electron hunger against hydrogen. Cell EMF is cathode minus anode; positive means spontaneous, converting to Gibbs energy by minus nF E. Fuel cells burn hydrogen and oxygen into water at 1.23 volts.

Why it matters. Tables predict batteries and corrosion without experiments. One subtraction decides direction and energy.

Formulas

Anode half: Zn yields Zn2+ + 2e-, oxidation at the negative electrode.
Cathode half: Cu2+ + 2e- yields Cu, reduction at the positive electrode.
The standard potential of the hydrogen electrode is 0.00 V.
A negative E0 marks a stronger reducing agent than hydrogen.
A positive E0 marks a weaker reducing agent than hydrogen.
O2 + 4H+ + 4e- yields 2H2O with E0 = 1.23 V.

Key words

Electrode potential: : The voltage tendency of a metal rod in its salt solution to lose or gain electrons.
Standard electrode potential: : Electrode potential measured at unit concentration and 298 K against hydrogen.
Hydrogen reference: : The H+ and H2 couple fixed at 0.00 V for ranking all electrodes.
Salt bridge: : Jelly with potassium chloride that completes the cell without mixing solutions.
Daniell cell: : Zinc in zinc sulphate paired with copper in copper sulphate through a bridge.
Anode: : The negative zinc electrode where oxidation releases electrons to the circuit.
Cathode: : The positive copper electrode where ions gain electrons from the circuit.

Try it in two minutes

Pair zinc with copper and subtract.
Convert EMF into Gibbs energy.
Rank three metals by potential.

Try at home. Compare lemon, potato and salt batteries.

What your child will practise

Balancing Redox Reactions: Desert Quick Fire (Quick Fire)
Electrode Potentials and Cells: Space Puzzle (Clue Puzzle)
Electrode Potentials and Cells: Space Quick Fire (Quick Fire)
Oxidation Numbers: Ocean Quick Fire (Quick Fire)
Oxidation, Reduction and Electron Transfer: Jungle Puzzle (Clue Puzzle)

Quiz: Balancing Redox Reactions (8 questions)
Quiz: Electrode Potentials and Cells (8 questions)
Quiz: Oxidation Numbers (8 questions)
Quiz: Oxidation, Reduction and Electron Transfer (8 questions)

Redox Reactions

Class 11 · Chemistry

4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.

Oxidation, Reduction and Electron Transfer

Part of: Electron Transfer and Oxidation Numbers

Why it matters. Batteries, rust and bleaches all run on electron trade. Naming donor and acceptor correctly starts every redox analysis.

Formulas

Oxidation is loss of electrons; reduction is gain of electrons.
Zn + Cu2+ yields Zn2+ + Cu, as zinc displaces copper ions.
Cu + 2Ag+ yields Cu2+ + 2Ag, as copper displaces silver ions.

Key words

Oxidation: : Losing electrons raises oxidation state and marks the substance oxidised.
Reduction: : Gaining electrons lowers oxidation state and marks the substance reduced.
Reducing agent: : The electron donor that reduces another species while being oxidised.
Oxidising agent: : The electron acceptor that oxidises another species while being reduced.
Redox couple: : The oxidised and reduced forms of one species in a half reaction.
Displacement reaction: : A more reactive metal donates electrons and displaces a weaker metal ion.

Try it in two minutes

Dip zinc in blue solution and watch copper appear.
Name who lost and who gained.
Rank three metals by donating power.

Try at home. Compare nail rust in dry versus salty air.

Oxidation Numbers

Part of: Electron Transfer and Oxidation Numbers

Why it matters. Numbers track electron shifts even in covalent tangles. They flag redox, disproportionation and balance needs.

Formulas

Free elements and uncombined atoms have oxidation number 0.
A single-atom ion has oxidation number equal to its charge.
Alkali metals are +1, alkaline earth metals are +2, aluminium is +3.
Oxygen is usually -2; peroxides -1; oxygen in OF2 is +2.
Hydrogen is +1, except -1 in metal hydrides like NaH.
Fluorine is always -1; other halogens are -1 as halide ions.
Oxidation numbers in a neutral compound add to 0; in an ion add to the charge.

Key words

Oxidation number: : A book-keeping charge assigned as if bonding electrons went to the greedier atom.
Free element: : An uncombined element whose atoms all carry oxidation number zero.
Oxidation state: : Another name for the oxidation number of an element in a compound.
Disproportionation: : One species oxidised and reduced at once into two different products.
Average oxidation number: : The mean value shared when identical atoms in one formula differ.

Try it in two minutes

Assign numbers to three salts.
Spot rise and fall in a reaction.
Find a disproportionation split.

Try at home. Assign numbers across a page of formulas.

Balancing Redox Reactions

Part of: Balancing and Cells

Why it matters. Inspection fails on redox; halves never do. The method scales to any acidic or basic equation.

Formulas

Balance atoms other than O and H first, then O with H2O and H with H+ in acid.
Balance the charge by adding electrons to the more positive side.
Multiply the halves so electrons lost equal electrons gained, then add them.
In basic medium add one OH- for each H+ on both sides and combine to water.

Key words

Half reaction: : The oxidation or reduction half written as a separate balanced equation.
Oxidation half: : The half reaction that releases electrons as a species is oxidised.
Reduction half: : The half reaction that consumes electrons as a species is reduced.
Acidic medium: : Conditions where water balances oxygen and H+ balances hydrogen.
Basic medium: : Conditions where extra hydroxide balances the acid step first.

Try it in two minutes

Split a reaction into halves.
Balance atoms, then charge.
Equalise electrons and add.

Try at home. Balance permanganate with iron step by step.

Electrode Potentials and Cells

Part of: Balancing and Cells

Why it matters. Tables predict batteries and corrosion without experiments. One subtraction decides direction and energy.

Formulas

Anode half: Zn yields Zn2+ + 2e-, oxidation at the negative electrode.
Cathode half: Cu2+ + 2e- yields Cu, reduction at the positive electrode.
The standard potential of the hydrogen electrode is 0.00 V.
A negative E0 marks a stronger reducing agent than hydrogen.
A positive E0 marks a weaker reducing agent than hydrogen.
O2 + 4H+ + 4e- yields 2H2O with E0 = 1.23 V.

Key words

Electrode potential: : The voltage tendency of a metal rod in its salt solution to lose or gain electrons.
Standard electrode potential: : Electrode potential measured at unit concentration and 298 K against hydrogen.
Hydrogen reference: : The H+ and H2 couple fixed at 0.00 V for ranking all electrodes.
Salt bridge: : Jelly with potassium chloride that completes the cell without mixing solutions.
Daniell cell: : Zinc in zinc sulphate paired with copper in copper sulphate through a bridge.
Anode: : The negative zinc electrode where oxidation releases electrons to the circuit.
Cathode: : The positive copper electrode where ions gain electrons from the circuit.

Try it in two minutes

Pair zinc with copper and subtract.
Convert EMF into Gibbs energy.
Rank three metals by potential.

Try at home. Compare lemon, potato and salt batteries.

What your child will practise

Balancing Redox Reactions: Desert Quick Fire (Quick Fire)
Electrode Potentials and Cells: Space Puzzle (Clue Puzzle)
Electrode Potentials and Cells: Space Quick Fire (Quick Fire)
Oxidation Numbers: Ocean Quick Fire (Quick Fire)
Oxidation, Reduction and Electron Transfer: Jungle Puzzle (Clue Puzzle)

Quiz: Balancing Redox Reactions (8 questions)
Quiz: Electrode Potentials and Cells (8 questions)
Quiz: Oxidation Numbers (8 questions)
Quiz: Oxidation, Reduction and Electron Transfer (8 questions)