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patino_chm2046_chapter16

0 ml 0001 l 0100 mol hno 2 000400 mol hno 2 1 ml 1l

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Unformatted text preview: [Bz-], because half of At [HBz], initial moles of HBz has been converted to Bz− initial Therefore, [H3O+] = Ka = 6.3 x 10-5 pH = 4.20 = pKa of the acid A 40.0 mL sample of 0.100 M HNO2 is titrated with 0.200 M KOH. Calculate the pH after adding 5.00 mL KOH Write an equation for the rxn of KOH with HNO2. Determine the mol of acidbefore & mol of added KOH Make a stoichiometry table and determine the moles of HNO2 in excess and moles NO2− made HNO2 + OH− → NO2− + H2O 40.0 mL × 0.001 L 0.100 mol HNO 2 × = 0.00400 mol HNO 2 1 mL 1L 0.001 L 0.200 mol KOH 5.00 mL × × = 0.00100 mol KOH 1 mL 1L HNO2 mols before 0.00400 mols added -0.00100 mol reacted mols after NO2- OH− 0 ≈0 - 0.00100 +0.0010 -0.00100 0 0.00300 0.00100 ≈0 44 A 40.0 mL sample of 0.100 M HNO2 is titrated with 0.200 M KOH. Calculate the pH after adding 5.00 mL KOH. HNO2 + H2O ⇄ NO2− + H3O+ ( ) pK a = − log K a = − log 4.6 × 10 −4 = 3.15 Ka = 4.6 x 10-4 Write an equation for the reaction of HNO2 with H2O Determine Ka and pKa for HNO2 Use the HendersonHasselbalch eqn to determine the pH NO 2 − pH = pK a + log HNO 2 0.00100 pH = 3.15 + log = 2.67 0.00300 HNO2 NO2- OH− 0 ≈0 mols Before 0.00400 mols added 0.00100 mols After 0.00300 0.00100 ≈ 0 45 Titra tio n C urve s : Ac e tic a c id titra te d with Na O H T itra p H = 8 .7 Weak acid titrated with a strong Weak base base Strong acid (HCl) titrated with Strong acid (HCl) titrated with Strong a strong base (KOH) a strong base (KOH) Same for HCl + NaOH, and Same for HCl + NaOH, and HNO3 + KOH or NaOH HNO3 + KOH or NaOH Weak diprotic acid (H2C2O4) titrated with a (H titrated strong base (NaOH) strong Figure 18.7 Figure Weak base (NH3) Weak base (NH3 ) ttitrated with a strong itrated with a strong acid (HCl) or HNO3 acid (HCl) or HNO3 pH indicators pH An acid-base titration requires an acid-base indicator to determine the equivalence point. indicator This is usually an organic compound that is a weak acid or weak base (similar to dyes of flowers). (similar The aci...
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