MCAT Redox

Question 1

What are redox reactions

Answer 1

Reactions that occurs by the transfer of electrons. Oxidation and reduction occurs in pairs as one species is reduced and the other is oxidized.

Question 2

What is oxidation? What is reduction?

Answer 2

Oxidation is the loss of electrons. Oxidizing agents oxidizes other compounds and so in return it’s reduced.
They tend to have oxygen or another electronegative element

Reduction is the gaining of electrons. Reducing agents reduces other compounds and so itself is oxidized. Reducing agents tend to have hydrides or metal ions.

Question 3

Describe the rules for assigning oxidation numbers?

Answer 3

1. Oxidation number for all free elements is zero ( i.e.N2= 0)
2. Oxidation number for group IA is +1 one.
3. Oxidation number for group IIA is +2.
4. Oxidation number for monoatomic ions is equal to the charge.
5. Oxidation number for group VIIA elements is -1 except when paired with a greater electronegative element in which it’s +1.
6. Hydrogen has a oxidation number of +1 except when paired with a least electronegative element in which it’s -1.
7. Oxygen has a oxidation number of -2 with two exceptions:
   - Oxygens of peroxides has a oxidation number of -1.
   -Oxygen combined with more electronegative elements has a charge of +2.
8. The sum of oxidation numbers equals zero for a neutral atom and to the charge of a polyatomic ion.

Question 4

Oxidation numbers for transition elements

Answer 4

They can have multiple oxidation states.

Question 5

Net ionic equation

Answer 5

When AQUEOUS compounds (NOT SOLIDS) are in a aqueous solution we draw the compounds in ionized form. We cross out ions that are on both sides of the equation as they’re inert. The remaining ions is our net ionic equation.

Question 6

Combintation reactions

Answer 6

Two or more species come together.

Question 7

Decomposition reactions

Answer 7

Species breaks down into it’s constituent parts.

Question 8

Combustion reactions

Answer 8

A hydrocarbon is reacted with oxygen forming carbon dioxide and water.

Question 9

Double- replacement (metathesis) and single replacement

Answer 9

Switching species to form new species.

Question 10

Disproportionation

Answer 10

When an element in a compound has both oxidized and reduced forms in the products.

Question 11

Oxidation- reduction titrations

Question 12

How to identify oxidation or reduction from the oxidation numbers?

Answer 12

Oxidation is the seen with an increase in oxidation number.

Reduction is the seen with a decrease in the oxidation number.

Each change in the oxidation state is accompanied with a gain (reduction) or loss (oxidation) of one electron.