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Chemistry 5.9

Chemistry 5.9. Oxidation-Reduction. Oxidation- Loss of electrons by an atom or ion . Reduction- Gain of electrons by an atom or ion . Neither reduction or oxidation can take place alone. LEO the lion says GER !. +1 or 1+?. The charge of a sodium ion is +1

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Chemistry 5.9

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  1. Chemistry 5.9

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

  3. +1 or 1+? • The charge of a sodium ion is +1 • The oxidation number of sodium in NaCl is 1+. • Don’t sweat this, it’s not a big deal!

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

  5. …more rules • 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.

  6. 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. • Double displacement rxs are not redox.

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

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

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

  10. The Voltaic Cell

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

  12. Electrolytic Cells

  13. The action of electrolysis in an electrolytic cell: • In the aqueous solution copper sulphate dissociates into its respective ions. • 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.

  14. Acids and Bases • An Arrhenius acid is one that produces Hydrogen (H+) or Hydronium (H3O+) ions in solution. • An Arrhenius base is one that produces Hydroxide (OH-) ions in solution.

  15. HCl + NaOH • HCl → H+(aq) + Cl-(aq) • NaOH → Na+(aq) + OH-(aq) • Neutralization reaction: HCl + NaOH → NaCl + H2O

  16. Naming Acids & Bases • 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].

  17. Reactions with Acids and Metals • If the metal is higher than H2 on the activity series table, than it will react with the acid (H+) to produce H2 and a salt. • Zn(s) + HCl(aq)→ H2(g) + ZnCl2(aq)

  18. 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.

  19. Solving Titration Problems: • Use the formula: M1V1 =M2V2 • Find the molarity of a HCl solution if 50.0 ml of a 0.250 M KOH are needed to neutralize 20.0 ml of HCL.

  20. The pH scale • Measures the negative log of the hydronium concentration [H+] or [H3O]. • Measured between 0 and 14.

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

  22. 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.

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