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# What is mole fraction? What is oxidation number?

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## Mole fraction Mole fraction is a unit of concentration, defined to be equal to the number of moles of a component divided by the total number of moles of a solution. Because it is a ratio, mole fraction is a unitless expression. The mole fraction of all components of a solution, when added together, will equal 1. Mole Fraction Example In a solution of 1 mol benzene, 2 mol carbon tetrachloride, and 7 mol acetone, the mole fraction of the acetone is 0.7. This is determined by adding up the number of moles of acetone in the solution and dividing the value by the total number of moles of components of the solution: Number of Moles of Acetone: 7 moles Total Number of Moles in Solution = 1 moles (benzene) + 2 moles (carbon tetrachloride) + 7 moles (acetone) Total Number of Moles in Solutions = 10 moles Mole Fraction of Acetone = moles acetone / total moles solution Mole Fraction of Acetone = 7/10 Mole Fraction of Acetone = 0.7 Similarly, the mole fraction of benzene would be 1/10 or 0.1 and the mole fraction of carbon tetrachloride would be 2/10 or 0.2. Oxidation number Oxidation number, also called Oxidation State, the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. Each atom that participates in an oxidation-reduction reaction (q.v.) is assigned an oxidation number that reflects its ability to acquire, donate, or share electrons. The iron ion Fe3+, for example, has an oxidation number of +3 because it can acquire three electrons to form a chemical bond, while the oxygen ion O2− has an oxidation number of −2 because it can donate two electrons. In an electronically neutral substance, the sum of the oxidation numbers is zero; for example, in hematite(Fe2O3) the oxidation number of the two iron atoms (+6 in total) balances the oxidation number of the three oxygen atoms (−6).

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