PART 5-Acids and bases Reference: Chapter 15, 16.1-16 4 in textbook
PART 5 – Acids and Bases Reference: Cha p , ter 15, 16.1 —16.4 in textbook 1
Bronsted-LoWey Definition Acid Compound that can increase the hydrogen ion(Ht) concentration when dissolved in water e.g. HCI(ag)+ H2O()H3O+(ag)+ Cl(aq) e.g. HCN(aq)+ H20 ()>H3O+(aq)+ CN(aq) Base Compound that can increase the hydroxide ion(OH-) concentration when dissolved in water g NaoH(aq)> Na(ag)+ OH (ag) e.g. NH3(aq)+ H2o()NH4(aq)+ OH(aq)
Brønsted-Lowe y Definition z Acid Compound that can increase the hydrogen ion (H +) concentration when dissolved in water concentration when dissolved in water. ¾ e.g. HCl (aq) + H 2O (l) Æ H 3 O + (aq) + Cl- (aq), ¾ e g HCN (aq) + H2O (l) Æ H O + (aq) + CN- ¾ e.g. HCN (aq ) + H2O (l) Æ H (aq ) 3 O (aq ) + CN (aq ) z Base Compound that can increase the hydroxide ion (OH-) concentration when dissolved in water. ¾ e.g. NaOH (aq) Æ Na + (aq) + OH-(aq) ¾ e.g. NH 3 (aq) + H 2O (l) Æ NH 4 + (aq) + OH- (aq) 2
Strong and Weak Acid(Base) Strong acid(base) Strong acid completely dissociated into h+& anions in water (e.g.HC,HN○3,H2SO4,HBr,H,HC|O4…) Strong base: completely dissociated into OH& cations in water (all IA, IIA cations hydroxide, e.g. NaOH, Ba(OH)2,.) Weak acid(base) Weak acid: partially dissociated, majority as molecules e.g. HF, HCIO, HCN, H2s, HCOoH (formic acid), CH3COOH (acetic acid), HCO3, H2o, Weak base: partially dissociated, majority as molecules e.g. NH3, (CH3)NH2,(CH3)3N, C6H5NH2(aniline), HCO3, H2O,... 3
Strong () and Weak Acid (Base) z Strong acid (base) Strong acid: completely dissociated into H+ & anions in water (e g HCl HNO3 H2SO4 HBr HI HClO4 (e.g. HCl, HNO ) 3, H2SO4, HBr, HI, HClO4, …) Strong base: completely dissociated into OH- & cations in water (all IA, IIA cations’ hydroxide, e.g. NaOH, Ba(OH)2, …) z Weak acid (base) Weak acid (base) Weak acid: partially dissociated, majority as molecules ¾ e.g. HF, HClO, HCN H,S HCOOH (f i id) CH COOH ( ti 2S, HCOOH (formic acid), CH3COOH (acetic acid), HCO3-, H2O, … Weak base: partially dissociated majority as molecules Weak base: partially dissociated, majority as molecules ¾ e.g. NH3, (CH3)NH2, (CH3)3N, C6H5NH2 (aniline), HCO3-, H2O, … 3
Conjugate Acid-Base Pair Acd:HA+H2O→H2O++A Base:B+H2O→HB++OH HA and A, or HB* and B, are called conjugate acid ba ase paIr. Q: Write the conjugate acid/base of species in the previous slide? Weak acid: HF HCIO. HCN. HaS HCOOH. CHaCOOH HCO3, Fe(H2O)6 Weak base: NH3, (CH3)NH2,(CH3)2NH, (CH3)3N, C6HSNH2 (aniline), HCO3, Fe(H2O)5(OH) How about strong acids? Strong base? H,o? 4
Conj gu ate Acid-Base Pair z Acid: HA + H2O Æ H3O+ + ABase: B + H2O Æ HB+ + OH- HA and A- or HB+ HA and A , or HB and B are called conjugate acid and B, are called conjugate acidbase pair. Q: Write the conjugate acid/base of species in the previous slide? previous slide? ¾ Weak acid: HF, HClO, HCN, H2S, HCOOH, CH3COOH, HCO3- Fe(H2O)6 HCO 2+ 3 , Fe(H2O)6 ¾ Weak base: NH3, (CH3)NH2, (CH3)2NH, (CH3)3N, C6H5NH2 (aniline), HCO3-, Fe(H2O)5(OH)+ ¾ How about strong acids? Strong base? H2O? 4
Poly-protic acid Define: contain more than one mole ionizable hydronium ions e.g. H2SO4, H2CO3, H3PO4, H2C2O Is it a strong acid or weak acid? For strong acid, each step is fully dissociation For weak acid, each step is partial dissociation Identify the conjugate acid-base pairs of each dissociation equation 5
Poly-protic acid z Define contain more than one mole Define: contain more than one mole ionizable hydronium ions. e.g. H2SO4, H2CO3, H3PO4, H2C2O4 ¾ Is it a strong acid or weak acid? Is it a strong acid or weak acid? ¾ For strong acid, each step is fully dissociation. ¾ For weak acid, each step is partial dissociation. Identify the conjugate acid-base pairs of each dissociation equation dissociation equation. 5
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 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 z pOH = - log [OH-] pH + pOH = ( log [H+]) + ( log [OH- pH + pOH = (- log [H ]) = pK = 14 +]) + (- log [OH-]) = pKw = 14 10
