AP Chemistry Due Next Class: Oxidation Numbers Packet Determination % H2O Lab + Conclusion Upcoming Dates: MC Ch. 1-4 & 4 (9/20 @ MIDNIGHT) Ch. 1-4 Test (9/21)

Warm Up Write the balanced molecular and net ionic equation for the following reactions: HBr(aq) + Ca(OH)2(aq)  Aqueous acetic acid is neutralized by aqueous barium hydroxide Solid magnesium carbonate reacts with aqueous hydrochloric acid

Warm Up Write the balanced molecular and net ionic equation for the following reactions: 2HBr(aq) + Ca(OH)2(aq)  2H2O(l) + CaBr2(aq) 2H+(aq) + 2OH-(aq)  2H2O(l)

Warm Up Aqueous acetic acid is neutralized by aqueous barium hydroxide 2 HC2H3O2(aq) + Ba(OH)2(aq)  2H2O(l) + Ba(C2H3O2)2(aq) 2H+(aq) + 2OH-(aq)  2H2O(l)

Warm Up Solid magnesium carbonate reacts with aqueous hydrochloric acid MgCO3(s) + 2HCl(aq)  H2O(l) + MgCl2(aq) + CO2(g) MgCO3(s) + 2H+(aq)  H2O(l) + Mg2+(aq) + CO2(g)

Chapter 1-3 Notes Buddy up (no more than three, preferably just two of you) Share/Compare your notes on these chapters What did they have that you didn’t? (add as you like) What did you both make sure to include? On the half sheet of paper List 3 topics that you would like Ms. Bryce to mini-lecture next class

Add to yours, or begin yours… your choice! LEO the lion says GER! Notes 4.4 GER! Add to yours, or begin yours… your choice!

Oxidation-Reduction Reactions Loss of Electrons is Oxidation. Gain of Electrons is Reduction. Always happen together, if one is losing… the other is gaining! The reactions are often called redox reactions.

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

When Zn(s) reacts with HCl(aq) to produce H2(g) and ZnCl2(aq), the zinc is _____ because it _____ electrons. reduced; gains reduced; loses oxidized; gains oxidized; loses Answer: d

Activity Series Phone Batteries Elements higher on the activity series are more reactive. The more reactive the metal, the more it wants to lose it’s electrons (to stabilize) The elements above hydrogen will react with acids to produce hydrogen gas. Jewelry

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.

Ionic Compounds In ionic compounds elements transfer electrons and form ions. A cation has lost electrons and has a positive charge. An anion has gained electrons and has a negative charge. The balanced chemical formula of an ionic compound is written by finding the smallest number of ions it takes to balance the charges, which is why we reduce when possible.

Covalent Compounds In covalent compounds elements share electrons to bond. Whichever element has the highest electronegativity, or attraction for electrons, pulls the shared pair of electrons towards it. (The closer an element is to Fluorine the greater its electronegativity.) We assign an oxidation number to elements based on the “apparent charge” on the element due to the pull of electrons (or unequal sharing.) Since elements can have more than one oxidation number we can use the Stock System to name these compounds.

Oxidation Number or Charge? To distinguish between a charge and an oxidation number we place the sign either before or after the number. For a charge we place the sign after the number. For example, the charge on sulfate is a 2- . For an oxidation number we place the sign before the number. For example, the oxidation number of N in the compound NO2 is +4 .

Examples H2O H = _____ O = _____ N2 N = _____ SO42- S= _____ O= _____ H3PO4 H = _____ P = _____ O = _____

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. 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. 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. 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.

What is the oxidation number of nitrogen in aluminum nitride, AlN? +1 –1 –2 –3 Answer: d

What is the oxidation number of nitrogen in nitric acid, HNO3? +6 +5 +4 –1 Answer: b

For the rest of class… Chapters 1-4 Test on 9/21! Work on… Oxidation Numbers Packet (Due next class) Lab & Conclusion (Due next class) Register for Mastering Chemistry if you haven’t already! Mastering Chemistry Assignments (Due 9/20 @ midnight) Chapters 1-4 Test on 9/21!