1. Reactions in Aqueous Solutions
Unit 4:
Reactions in Aqueous Solutions
Day 3: Oxidation Numbers and Study Guide

2. Oxidation-Reduction Reactions
Way to remember!!!!!!

3. Oxidation Numbers
To determine if an oxidation–reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.

4. Rules to Assign Oxidation Numbers
Elements in their elemental form have an oxidation number of zero.
The oxidation number of a monatomic ion is the same as its charge.

5. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Oxygen has an oxidation number of −2, except in the peroxide ion, in which it has an oxidation number of −1.
Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.

6. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Fluorine always has an oxidation number of −1.
The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, most notably in oxyanions (ex. Chlorate)

7. Rules to Assign Oxidation Numbers
The sum of the oxidation numbers in a neutral compound is zero.
The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.

8. Look at Oxidation Number Rules
What is the oxidation state of Phosphorous in P2O5?
What is the oxidation state of Hydrogen in NaH?
What is the oxidation state of Chromium in Cr2O72- ?
What is the oxidation state of tin in SnBr4?
What is the oxidation state of Oxygen in BaO2?

9. What is the oxidation state of Phosphorous in P2O5
What is the oxidation state of Phosphorous in P2O5? = +5, because each oxygen has a -2 charge.
What is the oxidation state of Hydrogen in NaH? = -1, because hydrogen bonded to a metal is -1, +1 when bonded to a non-metal
What is the oxidation state of Chromium in Cr2O72- ? = +6, because each oxygen is -2 and the charge of the ion is -2 overall
What is the oxidation state of tin in SnBr4? = +4, because Br oxidation state is -1
What is the oxidation state of Oxygen in BaO2? = +2, because O2 is the peroxide ion -1

10. What is the oxidation state of Phosphorous in P2O5?
= +5, because each oxygen has a -2 charge.

11. What is the oxidation state of Hydrogen in NaH?
= -1, because hydrogen bonded to a metal is -1, +1 when bonded to a non-metal

12. What is the oxidation state of Chromium in Cr2O72- ?
= +6, because each oxygen is -2 and the charge of the ion is -2 overall

13. What is the oxidation state of tin in SnBr4?
= +4, because Br oxidation state is -1

14. What is the oxidation state of Oxygen in BaO2?
= +2, because O2 is the peroxide ion -1

15. DISPLACEMENT REACTIONS and ACTIVITY SERIES

16. Displacement Reactions
In displacement reactions, ions oxidize an element.
In this reaction, silver ions oxidize copper metal:
Cu(s) + 2 Ag+(aq)  Cu2+(aq) + 2 Ag(s)
The reverse reaction does NOT occur. Why not?

17. Activity Series
Elements higher on the activity series are more reactive.
They are more likely to exist as ions.
Any metal on the list can be oxidized by the ions of the metal below it

18. Metal/Acid Displacement Reactions
The elements above hydrogen will react with acids to produce hydrogen gas.
The metal is oxidized to a cation.

19. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe?
Write the balanced molecular equation for one.
Write the net ionic equation

20. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe? Because Fe and Zn are above Pb on the activity series.
Write the balanced molecular equation for one:
Pb(NO3)2 (aq) + Zn(s)  Pb(s) + Zn(NO3)2 (aq)
Write the net ionic equation
Pb2+(aq) + Zn(s)  Pb(s) + Zn2+(aq)

21. Guided Inquiry: Oxidation Numbers
WITH YOUR TABLE PARTNERS: Work on Guided Inquiry Assignment TIME: Until the End of Class WHEN DONE: Work on Mid-term Study Guide