Chemistry 5.9

Oxidation-Reduction Oxidation- Oxidation- Loss of electrons by an atom or ion. Loss of electrons by an atom or ion. Reduction- Reduction- Gain of electrons by an atom or ion. Gain of electrons by an atom or ion. Neither reduction or oxidation can take place alone. Neither reduction or oxidation can take place alone. LEO the lion says GER! LEO the lion says GER!

+1 or 1+? The charge of a sodium ion is +1 The charge of a sodium ion is +1 The oxidation number of sodium in NaCl is 1+. The oxidation number of sodium in NaCl is 1+. Don’t sweat this, it’s not a big deal! Don’t sweat this, it’s not a big deal!

Ok, some rules of Redox: 1. Any element in pure form has an oxidation state of ‘zero’ (0). 2. Hydrogen has an oxidation number of +1 (HCl) when combined with a non-metal, and -1 when combined with a metal (NaH). 3. Oxygen has a charge of -2 in compounds except when combined with fluorine or in peroxide.

…more rules The sum of the oxidation numbers in all compounds must be zero. The sum of the oxidation numbers in all compounds must be zero. The sum of the oxidation numbers in polyatomic ions must be equal to the charge on the ion. The sum of the oxidation numbers in polyatomic ions must be equal to the charge on the ion.

To be, or not to be…Redox. If there is a change in oxidation numbers for any atom in a reaction, then redox must take place. If there is a change in oxidation numbers for any atom in a reaction, then redox must take place. Double displacement rxs are not redox. Double displacement rxs are not redox.

Oxidizing and reducing agents. The substance being oxidized is the reducing agent. The substance being oxidized is the reducing agent. The substance being reduced is the oxidizing agent. The substance being reduced is the oxidizing agent.

Half reactions A half reaction shows either the reduction or oxidation portion of a given redox reaction. A half reaction shows either the reduction or oxidation portion of a given redox reaction. Remember your laws of conservation! Remember your laws of conservation!

Electrochemical Cells 1. Galvanic (Voltaic) Cell- A chemical reaction is used to produce a flow of electrons (batteries). A chemical reaction is used to produce a flow of electrons (batteries). Requires a salt bridge to complete the circuit. Requires a salt bridge to complete the circuit. 2. Electrolytic cell- An electric current is used to force a chemical reaction (metal plating). An electric current is used to force a chemical reaction (metal plating). 3. Red cat, an ox.: Reduction takes place at the cathode, and oxidation takes place at the anode. Always. Reduction takes place at the cathode, and oxidation takes place at the anode. Always.

The Voltaic Cell

The half reactions of the Voltaic cell 1. Zn Zn2+ + 2e- 0.76v 2. Cu2+ + 2e- Cu +0.34v _________________________ Zn + Cu2+ Zn2+ + Cu 1.10v Look at table J the activity series. Look at table J the activity series. Remember the money metals do not easily oxidize (except Nickel. Why?) Remember the money metals do not easily oxidize (except Nickel. Why?)

Electrolytic Cells

The action of electrolysis in an electrolytic cell: 1. In the aqueous solution copper sulphate dissociates into its respective ions. 2. On passing electric current the copper ions (cations) move towards the cathode and get deposited as copper. Simultaneously the sulphate ions (anions) move towards the anode.

Acids and Bases An Arrhenius acid is one that produces Hydrogen (H+) or Hydronium (H 3 O+) ions in solution. An Arrhenius acid is one that produces Hydrogen (H+) or Hydronium (H 3 O+) ions in solution. An Arrhenius base is one that produces Hydroxide (OH-) ions in solution. An Arrhenius base is one that produces Hydroxide (OH-) ions in solution.

HCl + NaOH HCl → H+ (aq) + Cl- (aq) HCl → H+ (aq) + Cl- (aq) NaOH → Na+ (aq) + OH- (aq) NaOH → Na+ (aq) + OH- (aq) Neutralization reaction: Neutralization reaction: HCl + NaOH → NaCl + H 2 O

Naming Acids & Bases Binary acids begin with hydro and end with the ic ending. Ex/ hydrochloric acid (HCl) Binary acids begin with hydro and end with the ic ending. Ex/ hydrochloric acid (HCl) Bases use the true name of the positive ion with hydroxide ending. Ex/ calcium hydroxide [Ca(OH) 2 ]. Bases use the true name of the positive ion with hydroxide ending. Ex/ calcium hydroxide [Ca(OH) 2 ].

Reactions with Acids and Metals If the metal is higher than H 2 on the activity series table, than it will react with the acid (H+) to produce H 2 and a salt. If the metal is higher than H 2 on the activity series table, than it will react with the acid (H+) to produce H 2 and a salt. Zn (s) + HCl (aq) → H 2(g) + ZnCl 2(aq) Zn (s) + HCl (aq) → H 2(g) + ZnCl 2(aq)

Titration Titration is a procedure used in chemistry in order to determine the molarity of an acid or a base. A chemical reaction is set up between a known volume of a solution of unknown concentration and a known volume of a solution with a known concentration. Titration is a procedure used in chemistry in order to determine the molarity of an acid or a base. A chemical reaction is set up between a known volume of a solution of unknown concentration and a known volume of a solution with a known concentration. molarityacidbase molarityacidbase

Solving Titration Problems: Use the formula: Use the formula: M 1 V 1 =M 2 V 2 M 1 V 1 =M 2 V 2 Find the molarity of a HCl solution if 50.0 ml of a M KOH are needed to neutralize 20.0 ml of HCL. Find the molarity of a HCl solution if 50.0 ml of a M KOH are needed to neutralize 20.0 ml of HCL.

The pH scale Measures the negative log of the hydronium concentration [H+] or [H 3 O]. Measures the negative log of the hydronium concentration [H+] or [H 3 O]. Measured between 0 and 14. Measured between 0 and 14.

Acid-Base indicators Each indicator will change color when the solution falls within a certain pH range. Each indicator will change color when the solution falls within a certain pH range. Common indicators are phenolphthalein and methyl orange. Common indicators are phenolphthalein and methyl orange.

Conjugate Acid-Base pairs. When an acid gives up its proton, what remains is called the conjugate base of that acid. When a base accepts a proton, the resulting chemical is called the conjugate acid of that original base. HF and F- are a conjugate acid-base pair. H2O and H3O+ are a conjugate pair, where H3O+ is the acid and H2O is the base. When an acid gives up its proton, what remains is called the conjugate base of that acid. When a base accepts a proton, the resulting chemical is called the conjugate acid of that original base. HF and F- are a conjugate acid-base pair. H2O and H3O+ are a conjugate pair, where H3O+ is the acid and H2O is the base.