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A set of slides created to teach Redox to learners at Bishops Diocesan College in Cape Town.

A set of slides created to teach Redox to learners at Bishops Diocesan College in Cape Town.

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Redox Presentation Transcript

  • 1. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Redox and Oxidation Numbers K Warne
  • 2. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net _ _ _ _ _ _ _ _ Metal Electrodes. • Metal atoms can leave their outer electrons (weakly held) and go into solution. _ M _ _ + + + + + + + + + + + + + + + + + M(s)  M+ (aq) + e- e- e- e- e- e- e- e- M+ M+ An electric potential develops between the solution(+)and electrode(-). M+ M+ - +
  • 3. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net _ _ _ _ _ _ _ _ Direct Contact. _ Zn _ _ + + + + + + + + + + + + + + Zn(s)  Zn2+ (aq) + 2e- e- e- e- e- e- e- e- Cu2+ Cu2+ The copper ions are reduced to copper metal and the zinc metal is oxidised to zinc ions. Cu2+ Cu2+ (SO4 2-) Cu2+ (aq) + 2e-  Cu(s) • The zinc rod would become layered with copper • The blue solution would become colourless Copper has a STRONGER attraction for electrons than Zinc.
  • 4. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Oxidation - Reduction Zn(s)  Zn2+ (aq) + 2e- ...........of electrons = ....................... Cu2+ (aq) + 2e-  Cu(s) ........of electrons = ....................... • A REDOX reaction always includes BOTH these processes. • OILRIG – Oxidation Is Loss – Reduction Is Gain • The element ......................the Oxidation is the ........................ AGENT! (itself reduced) • The element ......................the REDUCTION is the ....................... AGENT! (itself oxidised)
  • 5. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Oxidation numbers Oxidation numbers can be used to identify oxidation and reduction as well as balance equations – particularly when it is difficult to identify e- transfer. Oxidation numbers are …………… charges that an atom of an element ……………. in a compound, if all bonds were …………... O H H + - H = …., O = ….. NH3 H = ….., N = …..
  • 6. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Electronegativity
  • 7. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Oxidation number Rules OXIDATION STATE DETERMINED BY MOST ELECTRONEGATIVE ELEMENT Oxidation Number Pure Element: ZERO – no electrons lost or gained! COMPOUNDS Oxidation numbers add up to zero. NaCl: Na.... , Cl ... Compound Ions: Oxidation numbers add up to the charge on the ion. MnO4 - Mn ...., O ...... Metals: Ox No = group no GI - Na, K ... and Hydrogen (except Hydrides; NaH,) GII - Mg, Ca etc GIII – Al Non Metals: Ox no. = group number - 8 GVII: (Halides): F, Cl, Br G VI: Oxygen O, Sulphur: S (except O in H2 O2 O=-1) GV: Nitrogen N Other elements worked out from these. Assign oxidation numbers in the following order: .................................................................................................................
  • 8. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net OXIDATION NUMBER EXAMPLES Calculate the oxidation states of the underlined elements. 1. Na2S Na +1 x2 = +2 .: S = -2 2. FeCl3 Cl -1 x3 = -3 .: Fe = +3 3. H2SO4 H +1x2 = +2, O -2x4= -8 .: S = +6 4. MnO4 – O = -2x4 = -8 .: Mn = +7 +7 -8 = -1 5. ClO4 - O = -2x4 = -8 .: Cl = +7 +7 -8 = -1 6. NaClO Na +1, O = -2 .: Cl = +1 +1 -2 +1 = 0 7. PO4 3- O -2 x4 = -8 .: P = +5 +5 -8 = -3
  • 9. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Redox Reactions • Involve electron ……….. • Oxidation is loss Reduction is ………… OILRIG • Na Na+ + e- Cl2 + 2e-  2Cl- • Both processes ALWAYS occur together. • Oxidation is caused by OXIDIZNG AGENTS – who are ……………………!! Na Na+ + e-, Na oxidised .: ……………..agent!! (Good one) • Reduction is caused by REDUCING AGENTS – who are ……………………………! Cl2 + 2e-  2Cl-, Cl2 reduced .: ……………….. agent! (Good) …………………………………. … … ….. ….. ………………………. OVERALL: 2Na + Cl2  Na+ + 2Cl-
  • 10. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net REDUCING AGENTS (Get oxidised!) • Cause OTHER THINGS to be REDUCED! • Are themselves OXIDIZED! Oxidizing & Reducing Agents OXIDIXZING AGENTS (Get reduced!) • Cause OTHER THINGS to be oxidised! • Are themselves REDUCED! (Estate AGENTS sell other peoples houses!) (Secret AGENTS (spies) spy on other people – the agent does the spying!) Na Na+ + e-, Na oxidised .: reducing agent!!Cl2 + 2e-  2Cl-, Cl2 reduced .: Oxidizing agent!
  • 11. For FULL presentation click HERE >> www.warnescience.net SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY Identifying Redox Reactions 1. Zn + CuSO4  ZnSO4 + Cu 2. N2 + H2  NH3 3. CaCO3+ H2SO4  CaSO4 + H2O + CO2 4. H2 + O2  H2O 5. Mg + O2  MgO 6. Ca + O2  CaO 7. H2 + I2  HI Using oxidation numbers determine which of the following reactions are redox reactions. In each case identify the reducing and oxidising agents.
  • 12. For FULL presentation click HERE >> www.warnescience.net SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY Identifying Redox Reactions 2. N2 + H2  NH3 0 0 -3+ 3(+1) = 0 OXIDIZING AGENT: Nitrogen REDUCING AGENT: Hydrogen Oxidised (O.N. increases) Reduction (O.N. decreases)
  • 13. For FULL presentation click HERE >> www.warnescience.net SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY Identifying Redox Reactions 1. Zn + CuSO4  ZnSO4 + Cu 0 RA +2OA +6 +((-2)4) = 0 +2 +6 +((-2)4) = 0 0 2. N2 + H2  NH3 3. CaCO3+ H2SO4  CaSO4 + H2O + CO2 4. H2 + O2  H2O 5. Mg + O2  MgO 6. Ca R. A + O2 O.A  CaO 7. H2 R.A + I2 O.A  HI
  • 14.  Reactions written as reductions.  Positive potentials ............... electrons are good .................... AGENTS.  Negative potentials .............. electrons are good ........................... AGENTS. ELECTROCHEMICAL SERIES Electrochemical half-cell potentials are listed from +ve to –ve Eθ values. Reactions take place
  • 15. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net BALANCING HALF REACTIONS 1. Identify the ½ reactions. 2. Balance oxygens by adding H2O 3. Balance hydrogens by adding H+ ions 4. Balance charges by adding electrons (to most + side) (Balanced M’s & NM’s first) To combine 1/2 reactions 1. Multiply by suitable factors to equal out the electrons. 2. Add the reactions and cancel things appearing on both sides. 3. Add spectator ions.
  • 16. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Redox Example An iron II solution can be standardised using a permanganate solution according to the reaction: FeCl2 + KMnO4  FeCl3 + Mn2+ Determine; • the oxidation states of all reacting species Fe: 2+ (2xCl- ), Mn: +7 (4xO2- )  Fe: 3+ (3xCl- ), Mn: 2+ • The forumula of the oxidising and reducing agents OA: MnO4 - (+7  +2 reduced) RA: Fe2+ (+2  +3 oxidised)
  • 17. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net FeCl2 + KMnO4  FeCl3 + Mn2+ Determine; the balanced overall (ionic) reaction Fe2+  Fe3+ + e- -- (1) MnO4 -  ........... MnO4 -  Mn2+ + ...................... MnO4 - + ......  Mn2+ + 4H2O MnO4 - + 8H+ ........  Mn2+ + 4H2O ----- (2) (1) x .....: .....Fe2+  .....Fe3+ + ....e- ----- (3) (2) + (3): ................................................................................ Ionic Eqn OVERALL REACTION INCLUDING SPECTATOR IONS ................................................................................................. worksheet>>
  • 18. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net QUESTION 7 – Redox 7.1.1 Define an oxidizing agent. (2) 7.1.2 What is the oxidation numbers of the underlined elements below? a) CO2 b) NO3 - (2) 7.1.3 Indentify the element which has been oxidized in the following reactions: a) Zn + 2AgNO3  Zn(NO3)2 + 2Ag (1) b) H2S + Br2  2HBr + S (1) 7.1.4 Using table 4A or 4B write a balanced ionic equation for the reaction between sulphur dioxide (SO2) and an acidified solution of permanganate ions (MnO4 - ). Clearly show all your working. (4) [10] Answers >>
  • 19. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Hi - This is a SAMPLE presentation only. My FULL presentations, which contain a lot more more slides and other resources, are freely available on my resource sharing website: www.warnescience.net (click on link or logo) Have a look and enjoy! WarneScience