Revision_bch1049_07MCWC2b

Revision_bch1049_07MCWC2b - BCH 1049 Revision Lecture (Week...

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1 BCH 1049 Revision Lecture (Week 13, Semester B, 2007) Assessment ± Examination (2 hours) 70%. Examination (2 hours) 70%. Coursework 30%. Coursework 30%. ± Coursework: Continuous assessment in the form of tutorials and assignments (check Blackboard, Bb6) . ± Minimum Passing Requirement: “A minimum of 30% in A minimum of 30% in coursework and a minimum of 30% in examination, in addition to a minimum of 40% in coursework and examination taken together together ”.
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2 Atoms, Molecules, and Ions Common Cations Atoms, Molecules, and Ions Common Anions
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3 Aqueous Reactions Aqueous Reactions and Solution Stoichiometry (Chapter 4) What’s Ahead: 1. Nature of substances and reactants in water Nature of substances and reactants in water 2. Reaction types: precipitation, acid Reaction types: precipitation, acid -base and oxidation base and oxidation -reduction reduction 3. 3. Concentration of solutions Concentration of solutions 4. Using solution stoichiometry for analysis Using solution stoichiometry for analysis Dissociation • When an ionic substance dissolves in water, the solvent pulls individual ions from the bulk crystal and solvates them. • This process is called dissociation . Electrolyte • Substance that dissociates into ions (ionizes) when dissolved in water. •A non-electrolyte may dissolve in water but does not ionize (dissociate into ions).
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4 Electrolytes •A strong electrolyte dissociates completely when dissolved in water. weak electrolyte only dissociates partially when dissolved in water. • Do NOT confuse “dissociate” and “dissolve” : • Acetic acid, CH 3 CO 2 H readily dissolves in water but only partially dissociates, so CH 3 CO 2 H is a weak electrolyte. • Barium hydroxide, Ba(OH) 2 dissolves poorly in water, but the amount that dissolves readily dissociates, so Ba(OH) 2 is a strong electrolyte. Aqueous Reactions Oxidation-Reduction Reactions n oxidation occurs when an atom or ion loses electrons (e.g. Ca). reduction occurs when an atom or ion gains electrons (e.g. O 2 ). 2 Ca ( s ) + O 2 ( g ) ⎯→ 2 CaO ( s )
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5 Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity. Rules for assigning oxidation numb er (ON) : 1. Elements in their elemental form have an oxidation number of zero. 2. The oxidation number of a monatomic ion is the same as its charge. 3. Non-metals tend to have negative oxidation numbers, but can be positive in some compounds: ¾ Oxygen has ON of 2, except for the peroxide ion O 2 2 , where each oxygen exhibits ON of 1. ¾ Hydrogen is 1 when bonded to metal, +1 when bonded to a non-metal. ¾ Fluorine always has an oxidation number of 1. ¾ The other halogens mostly have an oxidation number of 1, but they can have positive oxidation numbers (most notably in oxyanions).
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This note was uploaded on 01/11/2011 for the course BCH 1049 taught by Professor Michaelcwchan during the Spring '06 term at City University of Hong Kong.

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Revision_bch1049_07MCWC2b - BCH 1049 Revision Lecture (Week...

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