26、(15分)
(1)从图中可知,60mL
Ba(OH)2溶液恰好中和10mL混酸。(1分)则:
[H+]×10 = (0.025×2)×60,解得:[H+]
= 0.3
(2分)
设[H2SO4]为C1,[HCl]为C2,从图中可知,20mL Ba(OH)2恰好跟H2SO4完全反应,则:0.025×20 = C1×10,解得C1 = 0.05
,C2 = 0.3-0.05×2 = 0.2
。(4分)
(2)A点:因为20mL Ba(OH)2正好将混酸中H2SO4中和完全,所以混酸中只有HCl。(1分)则[H+] = 
(2分),pH = -lg6.7
10-2 = 1.17。(1分)B点:混酸中的HCl被加入的(40-20)mL Ba(OH)2溶液中和了一部分,(1分)
则[H+]
= 
(2分), pH = -lg2
10-2 = 1.7。(1分)