Amphoteric Substance Define(loosely) can react as either an acid or base under different circumstances Normally it is a poly-protic weak acid or base EXample NaHCO3 HCl NaCl H2CO3 NaHCO3 NaoH> Na2CO3+ H2O Na2HPO4, NaH2PO HO Fe(H2O)2+,A(H2O)3+,N(H2O)5(OH) However, even a strong acid may behave as a base, when it encounters with a stronger acid 6
Amphoteric Substance z Define (loosely): can react as either an acid or base under different circumstances z Normall y py it is a pol y - protic weak acid or base z Example: NaHCO 3 + HCl Æ NaCl + H NaCl + H 2CO 3 NaHCO 3 + NaOH Æ Na 2CO 3 + H 2 O Na 2HPO 4, NaH 2PO 4 H 2 O Fe(H 2O)2+, Al(H 2O)3+, Ni(H 2O) 5(OH) + z However even a However, even a “strong acid strong acid ” may behave as a may behave as a base, when it encounters with a stronger acid. 6
Lewis Acid Base Theory Lewis Acid (electron pair acceptor) Has an empty orbital and can accept an e pair e.g. BF3, H Lewis Base(electron pair donor) Has an e-pair and can donate(to a Lewis acid) e.g. NH3, Cl- Comprises the Bronsted-Lowey definition A Bronsted-Lowey acid/base is a Lewis acid/base; A Lewis acid/base may not be a Bronsted-Lowey acid/base
Lewis Acid & Base Theory z Lewis Acid ( p p) electron pair acce ptor ) Has an empty orbital and can accept an e- pair e.g. BF 3, H + , z Lewis Base (electron pair donor) Lewis Base (electron pair donor) Has an e- pair and can donate (to a Lewis Acid) e.g. NH 3, Cl-, z Comprises the Brønsted Comprises the Brønsted -Lowey definition Lowey definition A Brønsted-Lowey acid/base is a Lewis acid/base; A Lewis acid/base may not be a Brønsted-Lowey acid/base 7
Lewis Acid Base Theory B Lewis acid Lewis base Two electron covalent bond Electron-pair acceptor, Electron-pair Lewis Acid/Base Vacant orbital · EXamples Cao So Caso H++OH→HOH Lewis calcium base acid sulphate Proton transfer to alcohols H H HN计+BF→HN:BR∧ Br H Lewis id Base Acid Conjugate Conjugate 8
Lewis Acid & Base Theory z Examples 8
lon Product for Water, K ●H2O+H2O←H2O++OH K=[H3QO]*[OH]=1.0×1014@259 An equilibrium constant, used in all aqueous solution (i.e. acid, base, salt, or their mixture Calculate [H3o*] and [OH] TH3o]>1.0X 10-7>[oH(acidic solution [H3o*=1.0X 10-=[OH](neutral solution) [H3o]<1.0 X 10-< [OH] (basic solution)
Ion Product for Water, Kw H O+H O ↔ H O + + OH - z H 2 O + H 2 O ↔ H 3 O + OH z K w = [H 3 O +] * [OH -] = 1.0 x 10-14 (@ 25 oC) An equilibrium constant, used in all aqueous solution, (i e acid base salt or their mixture) (i.e. acid, base, salt, or their mixture). z Calculate [H 3 O +] and [OH -]: [H 3 O +] > 1.0 x 10-7 > [OH-] (acidic solution) 7 [H 3 O +] = 1.0 x 10-7 = [OH-] (neutral solution) [ H 3 O + ] < 1. 0 x 1 0-7 < [O H- [ ] (basic soluti o n ) 3 O ] 00 [O ] (bas c so u o ) 9
pH value Define: pl H=-log [f Deduction pKW=-log[1014=14 In water or neutral solution, pH=-log [10-7=7 In acidic solution, pH <7 In basic solution, pH>7 pOH=-log [oH-1 pH pOH=(-log [Hf]+(log [OH)=pKw=14 10
pH value Define pH log [H+ z Define: pH = - log [H ] + z Deduction: pKw = - log [10-14] = 14 In water or neutral solution, pH = - log [10-7] = 7 In acidic solution pH < 7 In acidic solution, pH < 7 In basic solution, pH > 7 z pOH = - log [OH-] pH + pOH = ( log [H+]) + ( log [OH- pH + pOH = (- log [H ]) = pK = 14 +]) + (- log [OH-]) = pKw = 14 10