> Chemical Reactions : Oxidation Numbers Quiz
Chemical Reactions : Oxidation Numbers Quiz
An oxidation number is a positive or negative number assigned to an atom according to a set of rules. Redox reactions can be balanced by the use of oxidation numbers. A simple way to remember a monatomic ion’s oxidation number is to recall the number of electrons it gains or loses, which is based on its group number.
Following are the list of rules that determine how oxidation numbers are assigned.
1. The oxidation number of a monatomic ion is equal in magnitude and sign to its ionic charge. For example, sodium’s charge is +1, so its oxidation number is +1.
2. The oxidation number of hydrogen in a compound is +1, except in metal hydrides such as NaH, when it is -1.
3. The oxidation number of oxygen in a compound is -2, except in peroxides when it is -1.
4. The oxidation number of an atom in elemental form is 0.
5. For any neutral compound, the sum of the oxidation numbers must equal 0.
6. For a polyatomic ion, the sum of the oxidation numbers must equal the ionic charge of the ion.
Example: What is the oxidation state of sulfur in SO2?
Rule 5 says that the sum of oxidation numbers for neutral compounds must be 0. There are two oxygens, and oxygen has an oxidation number of -2, according to rule 3.
Therefore, sulfur should have an oxidation number of +4, because +4 + (2 * (-2)) = 0.
For the following quiz, please read each question carefully. Use the above summary and example to help you determine the answer. Select the best answer from the choices.
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