Lecture Notes Week 03

Lecture Notes Week 03 - WEEK 3 ACIDS & BASES IN AQUEOUS...

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1 – WEEK 3 – (Refer to Chapters 16 & 17) Arrhenius Concept of Acids and Bases – based on H + and OH (Refer to section 16.1) Br ø nsted–Lowry Concept : (Refer to section 16.2) Acid is a _______________________ Base is a _______________________ ¾ Introduced CONJUGATE PAIRS e.g., HCl(aq) + H 2 O(l) H 3 O + (aq) + Cl (aq) acid base NOTE: To make a CONJUGATE BASE from its acid REMOVE H + To make a CONJUGATE ACID from its base ADD H + Example : Indicate conjugate acid/base pairs NH 4 + (aq) + H 2 O(l) NH 3 (aq) + H 3 O + (aq) CN (aq) + H 2 O(l) HCN(aq) + OH (aq) Lewis Concept: (Refer to section 16.3) Lewis Acid is a _______________________ Lewis Base is a _______________________ e.g., BF 3 + NH 3 BF 3 ·NH 3 acid base co–ordinate bond formed Note that with this definition, no proton needs to be involved. Review section 16.4 on relative strength of acids and bases and section 16.5 on molecular structure and acid strength.
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2 Self–Ionisation of Water (Refer to section 16.6) Water is AMPHOTERIC. This means it can act as BOTH an acid or as a base . Dissociation of Water: Pure water contains equal small amounts of both H 3 O + and OH ions. H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) K w = [H 3 O + ][OH ] = 1.00×10 –14 at 25 ° C K w – the ION PRODUCT for water Since there are equal amounts of H 3 O + and OH in PURE water: [H 3 O + ] = [OH ] = (1.0×10 –14 ) = 1.0×10 –7 M (at 25 ° C) NEUTRAL solution: [H 3 O + ] = [OH ] = ACIDIC solution: [H 3 O + ] [OH ] BASIC solution: [H 3 O + ] [OH ] STRONG ACIDS TOTALLY DISSOCIATE in water (ALL other acids only partially react.) STRONG ACIDS – there are only 6! HCl, HBr, HI, HNO 3 , HClO 4 2 SO 4 (1 st H only) ALL other acids are considered WEAK!! General equation is: HX(aq) + H 2 O(l) H 3 O + (aq) + X (aq) For a strong acid, the label on the bottle which represents the " stoichiometric " or " nominal " concentration is nonsense! e.g., C HCl = 0.10 M HCl You don't have ANY HCl molecules!!!!!! We only have: [H 3 O + ] = ] = Question : Determine the concentration of all the ions in a solution labelled "C HCl = 0.15 M" ? 1. RECOGNITION: What type of species? 2. [H 3 O + ] = [Cl ] = 3. Is that all the ions in the solution?
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3 Strong Acid, so [H 3 O + ] [OH ] STRONG BASES TOTALLY DISSOCIATE in water Alkali metals or alkaline earth Hydroxides. MOH(s) M + (aq) + OH (aq) M(OH) 2 (s) M 2+ (aq) + 2 OH (aq) Oxides also form base solutions: M 2 O(s) + H 2 O(l) 2M + (aq) + 2OH (aq) MO(s) + H 2 O(l) M 2+ (aq) + 2 OH (aq) QUESTION : What are all the ION concentrations in a solution labelled as "C{Ca(OH) 2 } = 0.15 M " 1. RECOGNITION: What type of species? 2.
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This note was uploaded on 04/17/2011 for the course CHEM 1040 taught by Professor Prokiacpak during the Spring '08 term at University of Guelph.

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Lecture Notes Week 03 - WEEK 3 ACIDS & BASES IN AQUEOUS...

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