Redox Reactions Redox Reactions n n n Redox
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Redox Reactions
Redox Reactions n n n Redox is the abbreviated way to write reductionoxidation reaction. Redox reactions are a very broad type of reaction and many of the types we have already discussed can also be classified as a redox reaction. In a redox reaction, reduction and oxidation must occur together. But what is reduction and oxidation? Reduction – chemical change in which electrons are gained. Oxidation – a chemical change in electrons are removed.
So, we need to Review Oxidation Numbers n What is the oxidation number? n Book definition – the number of electrons that must be added to or removed from an atom in a combined state to convert the atom into the elemental form. n In other words, the number of electrons gained or lost when a chemical bond is made. n Where can we find possible oxidation numbers? The Periodic Table
Assigning Oxidation Numbers – The steps from page 606 Identify the chemical formula If no formula is provided, write the formula of the formula or ion from the name. 2. Assign known oxidation numbers - The oxidation number of an atom of any free element in atomic or molecular form is zero. Examples: Cu, H 2, Ag, Na, S 8 - The oxidation number of monatomic ion is equal to the charge of the ion 1.
Assigning Oxidation Numbers – Continued - Fluorine always has an oxidation number of -1 since it is the most electronegative element. - In a compound: Group 1 atoms = +1 Group 2 atoms = +2 Aluminum = +3 - Hydrogen = +1, unless it is with a metal, then it is -1
Assigning Oxidation Numbers – Continued - Oxygen is usually -2, exceptions: - If combined with Fluorine, Oxygen’s oxidation number becomes +2 - In peroxides, H 2 O 2, Oxygen’s oxidation number becomes -1 - When comparing nonmetals, the more electronegative atom (page 194) gets the negative charge based on the column it is located in on the periodic table. - Group 17 = -1 , Group 16 = -2 , Group 15 = -3 __
Assigning Oxidation Numbers – Continued n Calculate any remaining numbers, and verify results. – Use the total oxidation number of each element’s atoms = oxidation number times subscript – The sum of the oxidation numbers for all the atoms in a molecule is zero. – The sum of the oxidation numbers for all the atoms in a polyatomic ion is equal to the charge on that ion.
Examples -3 +4 = +1 +2 +6 -8= 0 +2 -2 = 0 -3 +1 +2 +6 -2 +1 -2 NH 4+ Pb. SO 4 0 0 Al H 2 Ca(OH)2 +6 +12 -18 = 0 +3 +4 -2 Fe 2(CO 3)3 +2 -2 = 0 +1 +5 -6 = 0 +2 +5 -8 = -1 +1 -2 +1 +5 -2 H 2 O +2 Pb+2 KCl. O 3 H 2 PO 4 -1 +3 -3 = 0 +12 -14 = -2 +3 -1 +6 -2 BF 3 S 2 O 7 -2
Now that we reviewed oxidation numbers, what do we do with them? n Remember, in a redox reaction, something has to be oxidized (loses electrons, oxidation number increases) and something else has to be reduced (gains electrons, oxidation number decreases). n If we assign oxidation numbers to all atoms in a chemical equation, we can determine whether it is a redox reaction.
Are the following redox reactions? 2 H 3 O+ + Zn H 2 + 2 H 2 O + Zn+2 C 3 H 8 + 5 O 2 3 CO 2 + 4 H 2 O 2 KI + Pb(NO 3)2 Pb. I 2 + 2 KNO 3 2 K + Cl 2 2 KCl
Some other terms n Oxidizing agent – the substance that gains electrons in an redox reaction and is reduced. n Reducing agent - the substance that loses electrons in an redox reaction and is oxidized. n Notice that the oxidation agent oxidizes another substance and becomes reduces in the process and visa versa n Also note that these refer to the whole compound or ion.
Let’s look at the following redox reaction First, write the oxidation number for each atom: 8 H 3 O+ + Mn. O 4 - + 5 Fe+2 Mn+2 + 5 Fe+3 + 12 H 2 O What was reduced? Mn What was oxidized? Fe What is the oxidizing agent? Mn. O 4 What is the reducing agent? Fe+2
Homework n Page 611: 6, 7, 8, 9
- 20 examples of redox reaction
- How to write redox half reactions
- Chapter 19 review oxidation-reduction reactions
- Balance redox
- What are redox reactions
- Balancing redox reactions
- Oxidative phosphorylation concept map
- Reduction half reaction example
- Rules for balancing redox reactions
- Building redox tables
- Types of chemical reactions redox
- Redox reactions ncea level 2
- Activity series oxidation
- Khan academy balancing equations