Quiz Identify Type: 2H2O2 (l)  2 H2O (l) + O2 (g) Combustion, Synthesis Reaction, Decomposition reaction, Single replacement, Double replacement Identify Type: 2H2O2 (l)  2 H2O (l) + O2 (g) Identify Type: SiO2 (l) + 2C (s)  Si (l) + 2CO (g) Does this reaction take place? Al2(SO4)3 + 2 Fe  Fe2(SO4)3 + 2 Al List all spectator ions in the following equation. Ba(NO3)2(aq)+2NaSO4(aq) BaSO4(s)+2 NaNO3(aq)

Quiz Identify Type: 2H2O2 (l)  2 H2O (l) + O2 (g) Combustion, Synthesis Reaction, Decomposition reaction, Single replacement, Double replacement Identify Type: 2H2O2 (l)  2 H2O (l) + O2 (g) Identify Type: SiO2 (l) + 2C (s)  Si (l) + 2CO (g) Does this reaction take place? Fe2(SO4)3 + 2 Al  Al2(SO4)3 + 2 Fe List all spectator ions in the following equation. Ba(NO3)2(aq)+2NaSO4(aq) BaSO4(s)+2 NaNO3(aq)

5.3 Redox reaction

The charge of an ion are also known as oxidation numbers What is an ion? Any charged atoms or molecules How do you become ‘charged’? By losing or gaining electrons What is a cation? Did it lose or gain electrons? Positive ion, it LOST electrons What is an anion? Did it lose or gain electrons? Negative ion, it GAINED electrons The charge of an ion are also known as oxidation numbers

More Practice If a metal iron, Fe, becomes an ion, Fe3+, how many electrons did it lose or gain? It lost 3 electrons If a pure sulfur, S, becomes an ion, S2-, how many electrons did it lose or gain? It gained 2 electrons

Rules to find oxidation numbers Neutral elements and diatomic molecules have an oxidation number of zero. Ex. Na, Fe, H2, O2, F2 Monatomic ions have oxidation number equal to its charge. Ex, Na+ is 1, O2- is -2. Do you know how to use P.T to find oxidation #? Oxidation numbers in polyatomic ions add up to the total charge of the ion. Ex: shown NS

Example Sulfate is a polyatomic ion, with the formula of SO42- The oxidation number of sulfur and four oxygen must add up to -2 Since oxygen is -2, the total negative charge of it is -8 (-2 * 4) Sulfur must have an oxidation number of +6, to balance the oxygen, for the ion to have a charge of -2

(cations first, anions second) What are the oxidation number of the elements in a nitrate ion? NO3- Oxygen is -2 Nitrogen is 5

Redox Reactions We have covered 5 major types of chemical reactions Redox reaction is a totally different way to classify reactions, which can encompass all of the 5 major reactions As long as reactants and products are exchanging electrons, it is called a redox reaction

CuSO4(aq) + Zn  Cu + ZnSO4(aq) Copper(II) sulfate (CuSO4)is blue, zinc(II) sulfate (ZnSO4)is clear This is a redox reaction because copper is exchanging electrons with zinc

Copper sulfate (CuSO4) dissolves in water to form two ions, copper (II) ion and sulfate ion Cu2+ and SO42- How do we know copper is +2? Because we memorized sulfate(SO42-) a charge of -2, and so copper (II) ion needs to be +2 to make CuSO4 neutral A roman numeral in parentheses represents the charge, and are needed for ALL transitional metal ions!

The zinc metal gives the copper (II) ion (Cu2+) two electrons The zinc metal now becomes zinc (II) ion (Zn2+) while copper (II) ion (Cu2+) becomes copper metal (Cu) by gaining the two electrons Reminder: electrons are negatively charged!

When zinc lost the electrons (gave it away), the reaction, Zn Zn2+ + 2e-, is called oxidation reaction When copper (II) ion gained the electrons, the reaction, Cu2+ + 2e-  Cu, is called reduction reaction Oxidation and reduction reaction happens at the same time, which we call redox reaction

Cu2+ + 2e-  Cu Copper (II) ion Copper Copper (II) ion was reduced (gained e-)

Zn  Zn+2 + 2e- Zinc zinc (II) ion Zinc was oxidized (lost e-)

LEO the lion says GER Loss of Electrons is Oxidation Gaining Electrons is Reduction OIL RIG mOre positive (Oxi) lEss positive (rEduc)

Aluminium LOST 3 electrons. Which one is the correct equation? A) Al + 3e-  Al3+ Al  Al3+ + 3e- Is this Oxidation or Reduction?

Identify reduction and oxidation reaction AgNO3(aq)  + Cu → CuNO3(aq)  + Ag Ag+ NO3- Cu+ NO3- Silver (I) ion Copper (I) ion Ag+ gained, so reduction. Less positive. Cu lost, so oxidation. More positive

Identify reduction and oxidation reaction 2 Na + FeCl2 → 2 NaCl + Fe Fe2+ 2Cl- Na+ Cl- iron (II) ion sodium ion Reduction: Iron, gained e-, less positive Oxidation: Sodium, lost e-, more positive