Oxidation and Reduction

Question 1

What is oxidation?

Answer 1

OIL RIG

• Oxidation is Loss of electrons.
• Oxidation: Increases Oxidation #. (Gain charge)
• Combustion is an example of oxidation, adding oxygen

Question 2

What is reduction?

Answer 2

OIL RIG

• Reduction is the gain of electrons.
• Reduction decreases the oxidation #. (Lose charge.)

Question 3

What are the rules (in order) for counting oxidation numbers?

Answer 3

1. Each atom in a free element has ox # = 0.
2. Simple monatomic ions have ox # = charge on the ion.
3. The sum of all ox #’s in a molecule or a polyatomic ion = the overall charge.
   
   1. So the nonmetals have to match the metals, you know what it should be.
4. Flourine (F) has ox # = -1.
5. Hydrogen (H) has ox # = +1.
   
   1. Except in hydrides with metals, ox# = -1. (Ex: NaH, H= -1.)
6. Oxygen (O) has ox # = -2.
   
   1. Except in peroxides, when there are two oxygens bonded together, O = -1.

Question 4

What are redox reactions?

Answer 4

• Single replacement reaction
• Transfer of electrons
• Recognize change in oxidation number, transfer of O or H

Question 5

What are the rules for balancing redox reactions?

Answer 5

1. Separate into half reactions.
2. Balance all elements besides H and O.
3. Balance O by adding H₂O to opposite side.
4. Balance H by adding adding H+ to opposite side.
5. Count up net charge and balance with electrons
6. Multiply by an integer to get electrons to cancel
7. Add half reactions and cancel species on both sides
8. In a BASIC solution, then cancel H+ by adding as many OH- as H+ to both sides. Combine H+ and OH- to make H₂O, cancel out.
9. Check that charges AND atoms are balanced.

Question 6

What is the oxidizing agent?

Answer 6

• The susbtance that accepts electrons and is reduced
  
  • It allows the other to lose electrons and be oxidized
• It’s the full substance in the equation. (Not just the element)

Question 7

What is the reducing agent?

Answer 7

• The substance that gives electrons and is oxidized
  
  • It allows something else to be reduced
• It’s the full substance in the equation. (Not just the oxidized element)

Question 8

What is a redox reaction?

Answer 8

• Electron transfer reactions
• Changes in oxidation numbers occur
• Something is oxidized and something is reduced
• Occurs in an excess of acid or base
• Includes single replacement reactions and combustion reactions (NOT double replacement)
  
  • The reaction of an acid with a metal is a redox reaction in which the metal is oxidized and the acid is reduced

Question 9

Describe hydrogen as an oxidizing reagent

Answer 9

• Hydrogen is only strong enough to oxidize some metals
  
  • A metal more active than hydrogen will dissolve
  • A metal less active than hydrogen won’t dissolve

Question 10

What are nonoxidizing acids vs. oxidizing acids?

Answer 10

• Non-oxidizing: if the anion is a weaker oxidizing agent than hydrogen
  
  • HCl, H₂SO₄, H₃PO₄ - exception for phosphoric acid if hot & concentrated
• Oxidizing: if the anion is a stronger oxidizing agent than the hydrogen
  
  • HNO₃, H₃PO₄ (if hot and concentrated)

Question 11

What is a single replacement reaction?

Answer 11

• When one element replaces another in a compound
• Type of redox reaction

Question 12

What is the activity series?

Answer 12

• Use it to see which metals are “active” / more easily oxidized
  
  • A metal is active if it’s more active than hydrogen
  • A more active metal will give up its electron
• More active metals can dissolve in nonaxidizing acids, where H is the oxidizing agent (ex; HCl, H3PO4, H2SO4)
• Less active metals (gold, mercury, silver, copper) need oxidizing acids where something other than H acts as oxidizing agent (ex: HNO3, H2SO4 hot, conc)
• Predict the outcome of single replacement redox reactions
  
  • The element that is more easily oxidized will replace the one that is less easily oxidized.
    
    • Ex: In HCl, an active metal like lithium will displace hydrogen and produce H₂ gas and a metal salt. Whereas copper is less active than hydrogen, so nothing will happen to copper in HCl.

Question 13

What are ionic and metal oxides?

Answer 13

• Oxides are the products after combination with oxygen
• Metal –> ionic oxides
• Nonmetals –> molecular oxides

Question 14

Combustion

Answer 14

• Fast combination with O2
• O2 with organic compounds –> CO₂ + H₂O
  
  • When a hydroxarbon is combusted without enough oxygen, carbon monoxide instead of CO2. With even less oxygen, just elemental C.
  • If sulfur is in the compound, sulfur dioxide SO₂ is an additional product
• O2 with metals –> metal oxides
  
  • Fast = combustion, slow = corrosion/tarnishing
• O2 with nonmetals –> nonmetal oxides