OXIDATION AND REDUCTION

Oxidation Losing electrons The higher positive oxidation number the more the atom has loss control over the electrons, therefore the more oxidized it is.

Reduction Gaining electrons The higher negative oxidation number the more it has gain electron control, therefore the more reduced it is.

Redox Redox reaction is a chemical reaction in which changes in the oxidation numbers occur Oxidation and reduction always occur together

Oxidation Number Oxidation number is a measure of the electron control that the atom has

Redox or Not? 2H 2 + O 2 2H 2 O Mg + O 2 MgO CH 4 + O 2 CO 2 + H 2 O Pb(NO3) 2 + 2KI PbI 2 + 2KNO 3 Na 2 CO 3 Na 2 O + CO 2 NaOH + KNO 3 NaNO 3 + KOH

Half-Equation 2Mg(s) + O 2 (g) 2MgO(s) 2Mg(s) 2Mg 2+ (s) + 4e - O 2 (g) + 4e - 2O 2- (s) This redox reaction is broken down into half- equations to show the electron transfer. Magnesium loses two electrons, which means it becomes oxidized. Oxygen gains two electrons, which means it becomes reduced.

Half-Equation 3Mg(s) + N 2 (g) Mg 3 N 2 (s) 3Mg(s) 3Mg 2+ (s) + 6e - N 2 (g) + 6e - 2N 3- (s) This redox reaction magnesium, shown in the half- equation, losing six electrons, therefore being oxidized. Nitrogen is gaining six electrons, therefore being reduced.

Oxidizing Agent Oxidizing agent is the reactant that accepts electrons

Reducing Agent Reducing agent is the reactant that supplies the electrons

Oxidation Number Number with plus or minus defining the relative charge Predict number H 2 S, S, SCl 2, SO 2, SO 3 -2, SO 3, H 2 SO 4, Mg, O 2, I 2

Name using oxidation state FeO = Iron (II) oxide Fe 2 O 3 = Iron (III) oxide Cu 2 O = Copper (I) oxide CuO = Copper (II) oxide MnO 2 = Manganese (IV) oxide K 2 Cr 2 O 7 = Potassium dichromate (VI)

Reactivity Reducing Agent Oxidizing Agent Mg Strongest F 2 Al Cl 2 Zn Br 2 = O 2 Fe I 2 Pb Cu Ag Weakest

Who’s more likely to occur? ZnCl + 2Ag 2AgCl + Zn 2FeCl 3 + 3Mg 3MgCl 2 + 2Fe 2KI + Cl 2 2KCl + I 2 3Mg + N 2 Mg 3 N 2 2Mg + O 2 2MgO

Voltaic Cell aka Galvanic Cell Voltaic cell is an electrochemical cell that produces electrical energy from redox reactions taking place within the cell. To generate a current each cell or electrode must have a different electric potential The electrode where oxidation occurs is called the anode The electrode where reduction occurs is called the cathode To complete the circuit the metal plates are connected with a wire and solutions are connected with a salt bridge

Voltaic Cell Salt bridge completes the circuit Zn Zn+e - Standard Conditions: 298K, 1 atm, 1mol dm -3 Cell Potential is 1.10V = 0.34 – (- 0.76) Cu ions are converted to cupper metal on the electrode If the Zn rod was place in the Cu solution there will be a color change and heat released