Question

A weak triprotic acid, H3Z has the following Kg values K9.7 x 107 Pta : 601 Write the NIE associatedwith each Ka value H22 K5.3 x 10-9 8.23 = 1.4 x 104 Ka Pkg= 3.85 a. H30 H32 tHz0 + M30 H22 H22 H20 2- H2t1120 + b. Of the four weak acid species: H,Z, H,Z", HZ^, Z"; which two could be used to prepare a buffer of pH 3.55? Explain. c. A buffer is made by pouring 250.0 mL of 1.688 M Na,HZ into 350.0 mL of 1.455 M Z,Cit. Calculate the pH of this buffer solution. d. Calculate the pH if the original buffer solution is diluted to 1200 mLs.

Answer 1

Augwer: @ is correct. 6 Butter is a mixture of weak conjugate and I Base and vice versa so Solution ① H2Z /H22- CB = confregate base and CB H22-123- and CB mores of Na2H2 = voleme (L) x molority = 0.250 L xl-688 m. = 0.422 mel moles of 23 = 0.350LX 1.455m. = 0. Sog mo) Now for H2²- ² ut + 23- Kaz= 5.3x10-9 Plaz a log (Kan) = -log 15.3x10-9) - 8.276 PH- Praz & log [ Zz] [Na2H2] = 8.276+ log o.sog = 8.36 answal 1.422

wwn volume of solution = 250.omit 350.0mL = 600.0mL PM = 8.36 ie. Cht] a 10-ply = 10 -8:36 = 4.36X10ng for dilution mui= M2 U2 1a initial 22final [Mt = m = 4.36x109 m; v1 = 600.0mL [ht] = M2² , & U2 = 1200.00mL i. m2 = 4.36x10-9m x 600.0mL 1200.comL = 2.18 x 10-am pH = -log (m2] = log (2.18810-9m) = 8.66 (consenal so final ph= 8.66