Presentation is loading. Please wait.

Presentation is loading. Please wait.

Redox Reactions Chapter 18 + O 2 . Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species.

Similar presentations


Presentation on theme: "Redox Reactions Chapter 18 + O 2 . Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species."— Presentation transcript:

1 Redox Reactions Chapter 18 + O 2 

2 Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species to another oxidation & reduction always occur simultaneously we use OXIDATION NUMBERS to keep track of electron transfers

3 Rules for Assigning Oxidation Numbers: 1) the ox. state of any free (uncombined) element is zero. Ex: Na, S, O 2, H 2, Cl 2, O 3

4 Rules for Assigning Oxidation Numbers: 2) The ox. state of an element in a simple ion is the charge of the ion. Mg 2+  oxidation of Mg is +2

5 Rules for Assigning Oxidation Numbers: 3) the ox. # for hydrogen is +1 (unless combined with a metal, then it has an ox. # of –1) Ex: NaOH (H bonded to O) v. NaH (H bonded to Na)

6 Rules for Assigning Oxidation Numbers: 4) the ox. # of fluorine is always –1.

7 Rules for Assigning Oxidation Numbers: 5) the ox. # of oxygen is usually –2. Why USUALLY? Not -2 when it’s in a peroxide, such as hydrogen peroxide: H2O2H2O2

8 Rules for Assigning Oxidation Numbers: 6) in any neutral compound, the sum of the oxidation #’s = zero.

9 Rules for Assigning Oxidation Numbers: 7) in a polyatomic ion, the sum of the oxidation #’s = the overall charge of the ion.

10 Rules for Assigning Oxidation Numbers: **use these rules to assign oxidation #’s; assign known #’s first, then fill in the #’s for the remaining elements:

11 Examples: Assign oxidation #’s to each element: a) NaNO 3

12 Examples: Assign oxidation #’s to each element: b) SO 3 2-

13 Examples: Assign oxidation #’s to each element: c) HCO 3 -

14 Examples: Assign oxidation #’s to each element: d) H 3 PO 4

15 Examples: Assign oxidation #’s to each element: e) Cr 2 O 7 2-

16 Examples: Assign oxidation #’s to each element: f) K 2 Sn(OH) 6

17 Definitions Oxidation: the process of losing electrons (ox # increases) Reduction: the process of gaining electrons (ox # decreases) Oxidizing agents: species that cause oxidation (they are reduced) Reducing agents: species that cause reduction (they are oxidized)

18 To help you remember… OIL RIG Oxidation Is Loss Reduction Is Gain

19 Are all rxns REDOX rxns? a reaction is “redox” if a change in oxidation # happens; if no change in oxidation # occurs, the reaction is nonredox.

20 Examples MgCO 3  MgO +CO 2

21 Examples Zn + CuSO 4  ZnSO 4 + Cu

22 Examples NaCl + AgNO 3  AgCl + NaNO 3

23 Examples CO 2 + H 2 O  C 6 H 12 O 6 + O 2

24 Balancing Redox Equations

25 In balancing redox equations, the # of electrons lost in oxidation (the increase in ox. #) must equal the # of electrons gained in reduction (the decrease in ox. #) There are 2 methods for balancing redox equations: 1. Change in Oxidation-Number Method 2. The Half-Reaction Method

26 1. Change in Oxidation-Number Method: based on equal total increases and decreases in oxidation #’s Steps: 1. Write equation and assign oxidation #’s. 2. Determine which element is oxidized and which is reduced, and determine the change in oxidation # for each. 3. Connect the atoms that change ox. #’s using a bracket; write the change in ox. # at the midpoint of each bracket. 4. Choose coefficients that make the total increase in ox. # = the total decrease in ox. #. 5. Balance the remaining elements by inspection.

27 Example S + HNO 3  SO 2 + NO + H 2 O

28 If needed, reactions that take place in acidic or basic solutions can be balanced as follows: Acidic:Basic: add H 2 O to the side needing oxygen balance as if in acidic sol’n then add H + to balance the hydrogen add enough OH - to both sides to cancel out each H + (making H 2 O) & then cancel out water as appropriate

29 Example: Balance the following equation, assuming it takes place in acidic solution. ClO 4 - +I -  Cl - +I 2

30 2. The Half-Reaction Method: separate and balance the oxidation and reduction half-reactions. Steps: 1. Write equation and assign oxidation #’s. 2. Determine which element is oxidized and which is reduced, and determine the change in oxidation # for each. 3. Construct unbalanced oxidation and reduction half reactions. 4. Balance the elements and the charges (by adding electrons as reactants or products) in each half-reaction. 5. Balance the electron transfer by multiplying the balanced half- reaction by appropriate integers. 6. Add the resulting half-reaction and eliminate any common terms to obtain the balanced equation.

31 Example: Balance the following using the half-reaction method: HNO 3 +H 2 S  NO +S+H 2 O


Download ppt "Redox Reactions Chapter 18 + O 2 . Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species."

Similar presentations


Ads by Google