题中似乎漏字,估计为体积相等.
为了简便起见,不妨假设二者体积均为500 mL (0.5L); 反应后体积为1L
HCl:0.2*0.5 = 0.1 mol
Ba(OH)2:0.05*0.5 = 0.025 mol
2HCl + Ba(OH)2 = BaCl2 + 2H2O
2 1
x 0.025
x = 0.05 mol,即0.05molHCl反应,剩余0.1 - 0.05 = 0.05molHCl
[H+] = 0.05/1 = 0.05 mol/L
pH = 1.30