Wednesday, December 28, 2011

Rules for Assigning Oxidation States; Oxidation and Reduction; Redox Reactions -- Chemistry HW 11/11/10

Rules for assigning oxidation states

1. Free elements (elements that are not combined with other elements) have an oxidation state of zero.

2. The oxidation state of any monatomic ion is equal to the charge on the ion.  
Example: The ion Fe3+ (ferric ion) has an oxidation state of +3.
3. The algebraic sum of all the individual oxidation states of all the atoms in a molecule, polyatomic ion, or formula unit is always equal to the net charge. 

4. The oxidation state of a neutral compound is zero.

5. the total oxidation numbers of all atoms in an ion equals the overall charge on the ion

6. the most electronegative element in the compound or ion carries the negative oxidation state

7. In compounds, the oxidation number of:
  • Hydrogen when combined with nonmetals is +1
  • Hydrogen when combined with metals is -1
  • Oxygen, except when combined with fluorine or in peroxides or superoxides, is -2
  • Oxygen when combined with fluorine is +2
  • Halogens (Cl, Br, I), except in combination with oxygen, is -1
  • Alkali metals is +1
  • Alkaline earth metals is +2
Oxidation Process
It is a process in which oxygen is caused to combine with other molecules. The oxygen may be used as elemental oxygen, as in air, or in the form of an oxygen-containing molecule which is capable of giving up all or part of its oxygen. Oxidation is an either an increase in positive valence or removal of electrons.

Most oxidations occur with the liberation of large amounts of energy in the form of either heat, light, or electricity. The stable ultimate products of oxidation are oxides of the elements involved. These oxidations occur in nature as corrosion, decay, and respiration and in the deliberate burning of matter such as wood, petroleum, sulfur, or phosphorus to oxides of the constituent elements. 

Reduction Process  
Reduction is a part of a reduction-oxidation (redox) reaction in which atoms have their oxidation number changed. They may either give off oxygen or take on electrons.

Oxidizing Agent / Oxidant / Oxidizer / Oxidiser
An oxidizing agent can be defined as either a chemical compound that readily transfers oxygen atoms, or a substance that gains electrons in a redox chemical reaction.They are usually paired with reducing agents. Oxidizing agents are substances that gain electrons in an oxidation-reduction (redox) chemical reaction. In the reaction, the oxidizing agent is reduced, and the reducing agent is oxidized.

Reducing Agent / Reductant / Reducer
A reducing agent is the element or compound in a reduction-oxidation (redox) reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized". This means that there must be an "oxidizer"; because if any chemical is an electron donor, another must be an electron recipient (oxidizer).

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