Question

A titration involves adding a reactant of known quantity to a solution of an another reactant while monitoring the equilibrium concentrations. This allows one to determine the concentration of the second reactant. A pH titration curve specifically monitors the pH as a function of the titrant.

When conducting calculations involving a titration, the first step is to write the balanced chemical equation. Then, use the stoichiometric ratios developed from this equation to determine how many moles of each reagent are reacting.

100. mL of 0.200 M HCl is titrated with 0.250 M NaOH.

Part A

What is the pH of the solution after 50.0 mL of base has been added?

Express the pH numerically.

Part B

What is the pH of the solution at the equivalence point?

Express the pH numerically.

Answer 1

write balanced equation first

HCl + NaOH ----> NaCl + H2O

from the equation it is clear that one mole of NaOH required one mole of HCl

no of moles of HCl = Molarity x volume in liters

= 0.2 x 0.1

= 0.0200 moles of HCl

50 mL of 0.25 M base was added that means

no of moles of NaOH added = 0.25 x 0.05 L

= 0.0125 moles

after addition 0.0125 moles of HCl was nuetralised from the 0.0200 moles of HCl

remaining molea of HCl = 0.0200 - 0.0125

= 0.0075 moles of HCl remaining, total volume become a 100 + 50 = 150 mL

concentration of HCl = 0.0075 / 0.15

= 0.05 M

since it is stronh acid concentrationof HCl = con centration of H+

pH = -log[H+]

pH = - log [0.05]

= 1.30

it is a strong acid and strong base titration

at equilent point means all the acid will get nuetralise with base

so pH = 7