Ch. 11 - Oxidation-Reduction Reactions

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What is oxidation? reduction?

Oxidation = loss of electrons

Reduction = gain of electrons

OIL RIG

What is an oxidation–reduction (redox) reaction?

A reaction where oxidation and reduction occur simultaneously.

What is an oxidizing agent?

A substance that facilitates the oxidation of another compound and is itself reduced.

often contain Oxygen or a similarly electronegative element.

What is a reducing agent?

A substance that facilitates the reduction of another compound and is itself oxidized.

often contain Metal ions or hydrides (H-)

What is the oxidation number of any free element or diatomic species?

Zero.

What is the oxidation number of a monatomic ion?

Equal to the charge of the ion.

ex.

• Group IA metals = +1

• Group VIIA elements = +2

• hydrogen = +1, unless paired with a less electronegative element, in which case it is –1.

• oxygen = –2, except in peroxides (–1) or compounds with more electronegative elements

What must the sum of oxidation numbers in a compound equal?

The overall charge of the compound.

What is the most common method to balance redox reactions?

The half-reaction (ion–electron) method.

Steps for Balancing Redox Reactions:

1. Separate the two half-reactions.

2. Balance all atoms except H and O.

3. In acidic solutions: Balance H and O using water and H+.

4. In basic solutions: Balance H and O using water and OH−.

5. Balance charges by adding electrons as necessary.

6. Multiply half-reactions to equalize electron transfer.

7. Add half-reactions and cancel terms to ensure mass and charge balance.

What does a complete ionic equation show?

All ions present in the reaction.

What does a net ionic equation show?

Only species participating in the reaction (ignoring spectator ions).

Steps for Writing Net Ionic Equations:

1. Split aqueous compounds into ions.

2. Keep solid salts intact.

3. Subtract spectator ions (appear on both sides).

What is the net ionic equation for double displacement reactions without a solid salt?

There is no net ionic equation because ions remain in solution and do not change oxidation numbers.

What is a disproportionation (dismutation) reaction?

A redox reaction where one element is both oxidized and reduced, forming species with different oxidation states.

What do redox titrations follow?

Transfer of charge.

What do indicators in redox titrations do?

Change color when specific solution voltages are achieved.

What is a potentiometric titration?

A redox titration where a voltmeter measures the electromotive force (emf) of a solution

the equivalence point is determined by a sharp change in voltage instead of an indicator.