The molarity of an aqueous solution of sodium hydroxide, NaOH, is determined by titration against a 0.102 M hydrochloric acid, HCl, solution HCINaOH-NaClH20 If 30.1 mL of the base are required to neutralize 21.7 mL of hydrochloric acid, what is the molarity of the sodium hydroxide solution? Molarity Solution 1. HCl + NaOH -------> NaCl + H2O In the above reaction equation; HCl and NaOH reacts in 1:1 ratio. 21.7 mL of 0.102 M HCl So, moles of HCl = 0.102 M x 0.0217 L = 0.0022134 moles Hence, the moles of NaOH will also be equal to 0.0022134 moles Volume of NaOH = 30.1 mL = 0.0301 L [NaOH] = 0.0022134 mol / 0.0301 L = 0.074 M 2. HBr + Ba(OH)2 -------> BaBr2 + 2H2O In the above reaction equation; HBr and Ba(OH)2 reacts in 2:1 ratio. 28.0 mL of 0.0471 M Ba(OH)2 So, moles of Ba(OH)2 = 0.0471 M x 0.028 L = 0.0013188 moles Hence, the moles of HBr = (0.0013188 x 2) moles = 0.0026376 moles Volume of HBr = 16.9 mL = 0.0169 L [HBr] = 0.0026376 mol / 0.0169 L = 0.156 M 3. pOH = 6.10 pH = 14 – pOH = 14 – 6.10 = 7.90 pOH = 6.10 Or, - log [OH-] = 6.10 Or,[OH-] = 10 -6.10 = 7.94 x 10^-7 pH = 7.90 Or, - log [H3O+] = 7.90 Or,[H3O+] = 10 -7.90 = 1.26 x 10^-8 4. pH = 7.20 pOH = 14 – pH = 14 – 7.20 = 6.80 pOH = 6.80 Or, - log [OH-] = 6.80 Or,[OH-] = 10 -6.80 = 1.58 x 10^-7 pH = 7.90 Or, - log [H3O+] = 7.20 Or,[H3O+] = 10 -7.20 = 6.31 x 10^-8 .