n(HCl) = 45mL * 0.1mol/L = 0.0045mol
n[Ba(OH)2] = 5mol * 0.5mol/L = 0.0025mol
Ba(OH)2 ------ 2HCl
1 2
=0.00225mol 0.0045mol
反应后,溶液中剩余的Ba(OH)2 的物质的量 = 0.0025mol - 0.00225mol = 0.00025mol
n(OH-) = 0.00025mol*2 = 0.0005mol
c(OH-) = 0.0005mol/ 500mL = 0.001mol/L
则:c(H+) = 10^(-14) / 0.001 = 10^(-11)
pH = -lg[c(H+)] = -lg [ 10^(-11) ] = 11