Oxidation States and Rules

The video tutorial introduces the concept of oxidation numbers, explaining that they represent the total number of electrons an atom gains or loses to form chemical bonds. It outlines several rules for assigning oxidation numbers to elements, molecules, and ionic compounds, emphasizing that the sum of oxidation numbers must equal the charge of the molecule or ion. The tutorial provides examples, such as lithium oxide and carbon dioxide, to illustrate these rules. A complex example with perchlorate is also discussed, highlighting the importance of rule precedence. The video concludes with a student exercise on determining oxidation numbers in H3PO4.

What is the oxidation number of an element in its elemental form?

• Zero

• Depends on the element

• Varies with temperature

• One

Which group of elements typically has an oxidation number of +1?

• Group 1A metals

• Group 2A metals

• Group 7A elements

• Group 6A elements

What is the oxidation number of oxygen in most compounds?

• +2

• +1

• -2

• -1

In lithium oxide, what is the oxidation state of lithium?

• -1

• 0

• +2

• +1

How is the oxidation state of carbon determined in carbon dioxide?

• By balancing the oxidation states of oxygen

• By considering it as a polyatomic ion

• By assuming it is zero

• By using the oxidation state of hydrogen

In the perchlorate ion, which rule takes precedence when assigning oxidation numbers?

• Rule for halogens

• Rule for metals

• Rule for oxygen

• Rule for hydrogen

What is the oxidation number of chlorine in the perchlorate ion?

• -1

• +3

• +5

• +7

When there is a conflict between two oxidation number rules, what should be done?

• Use the average of both rules

• Apply the rule with the lower number

• Ignore both rules

• Apply the rule with the higher number

What is the overall charge of a polyatomic ion if the sum of oxidation numbers is zero?

• Depends on the ion

• Zero

• Negative

• Positive

In H3PO4, what is the oxidation number of phosphorus?

• -3

• +5

• +3

• +7