Redox Reactions Redox Reactions n n n Redox

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Redox Reactions

Redox Reactions

Redox Reactions n n n Redox is the abbreviated way to write reductionoxidation reaction.

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

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

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

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

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. –

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

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,

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 +

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

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

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

Homework n Page 611: 6, 7, 8, 9