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Quick Review

Quick Review.

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Quick Review

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  1. Quick Review • Basic Ideas about solubility in wateras mentioned last weak-ionic materials generally dissociate in waterTwo quick rules (shortened from p. 120) cations: all salts of Group I ions and NH4+ are soluble anions: salts of Cl-,Br-,I- ,nitrate,perchlorate, acetate and sulfate are soluble • MX(aq) + M’X’(aq) => would ppt form? • Possibilities MX’ or M’X for a ppt to form both parts must not be on the list • Suppose MX’ meets that criterion and will ppt • MX + M’X’ => MX’ + M’X molecular • M+(aq) + X-(aq) + M’+(aq) + X’-(aq) => MX’(s) + X-(aq) + M’+(aq) total ionic • M+(aq) + X’-(aq) => MX’(s) • Acids and bases • HA + B => A- + BH+

  2. Oxidation and reduction Oxidation-loss of one or more electrons-the species being oxidized is the reducing agent • Reduction-gain of one or more electrons-the species being reduced is the oxidizing agent • redox process-transfer of electrons from the reducing agent to the oxidizing agent • Tracking electrons is far more complex than tracking protons, as they don’t appear explicitly in the chemical formula • Oxidation numbers are used to follow electrons

  3. Oxidation Numbers • You should be aware that oxidation numbers are designed to track electron changes, not the actual distribution of electrons in a complex species • General Rules • Elements in their elemental forms have ON=0 • A monoatomic ion has an oxidation number equal to its charge • In an ionic compound, the oxidation numbers equal the ion charges. • In chemical compounds or polyatomic ions(there is a hierarchy here, a higher rule trumps a lower one) • fluorine is always 1- • H is 1+ except in metal hydrides where it is 1- • oxygen is 2- except in peroxides(1-) or bound to F • other halogens are 1- except for interhalogen compounds or when bound to oxygen • the sum of the oxidation numbers must equal the charge on the compound or ion. • What are the oxidation numbers in the following: • CO2, MnO4-, HClO4, H2CO, FeSO4

  4. Redox Reactions • It is usually possible to separate a redox process into half reactions based upon oxidation number changes MnO4- + Fe 2+ => MnO2 + Fe 3+ CH3OH + Cr2O72- => H2CO + Cr3+ We can write “generic” equations of the type RA + OA => OA + RA similar to that done for acids and bases

  5. Looking from both sides • In the areas of precipitation, acids-bases and redox, the processes can be viewed either left to right or right to left. • M+(aq) + X-(aq)  MX(s) • HA(aq) + B(aq)  A-(aq) + HB+(aq) • RA + OA  OA + RA

  6. A few acid-base details In the reaction below HA and A- is a conjugate acid-base pair as is B and HB+ HA(aq) + B(aq)  A-(aq) + HB+(aq) Neutral acid-base species alkali metals and alkaline earths and the conjugate bases of the strong monoprotic acids Cl-, Br-, I-, NO3- and ClO4-

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