Question

Benzene-1,2,3-tricarboxylic acid (C₆H₃ (CO₂H) ₃) is a three-protic, water-soluble carboxylic acid with the following pK_a values: pK_a1 = 2.86, pk_a2 = 4.30 and pk_a3 = 6.28. What will be the pH of a 0.075 M solution of this treprotic carboxylic acid?

Answer 1

pkai -2• $6 -1°јка, =) а, а löpka, О-оо138 4 = а, - «Нұ(сон, ана (он), coe+ ht I 0.075M Х E c.o1S-X х 14, - [C6H3(CO2H)2(00] € [«Нҳ сон), О»oo138 X X О•o7S-X

x² = 0.00138 %0.075 -0.00138% 2²+0.001384 0.000103550 -0.00138 + (0.00138)2-40)6-0.0001035) 2(1) -0.00138 So. 0.0004.16 2 -0.00138 +0.02039 0.01901 2 2 ga 0.009505 M conudered only the "Ponitive" value for X

x = fH;CCOMB 2003 = 0.0095057 ka, = 10 lopka ·4·3 10 = 5.012X105 4H3(CO2H) 2002 CH3CCOLH) (600), + H+ 0.009505 m the ty ty C 2 9 E 0.009505-3 yy Kaz 0.009505-9 Neglect y in the denominator because y is very dmall. S. 0124185 - y 0.009505 y?= 0.009505 * 5.012 x105 y2 = 47.64x 108 =) Y = √47:64x104 [Mtbc = y = 6.9x104 = x+y= 0.009505 +6.97164 -0.016195 Total [HHE PH logCutie E-log 0.010195 M 1.99 pH ~ 2
We can neglect the contribution of third dissociation towards H+ concentration.