Acid–base titration

A/L Chemistry · G.C.E. Advanced Level · Grades 12–13

Aim

To find the concentration of a sodium hydroxide solution by titrating it against 0.100 mol dm⁻³ hydrochloric acid.

Apparatus

• Burette, pipette (25.00 cm³) and conical flask
• Standard 0.100 mol dm⁻³ HCl and NaOH solution
• Phenolphthalein indicator and a white tile

Method

1. Rinse and fill the burette with HCl and note the initial reading.
2. Pipette 25.00 cm³ of NaOH into the flask and add 2–3 drops of phenolphthalein (pink).
3. Add acid while swirling; add drop by drop near the end.
4. When the pink just disappears (end point) read the burette: the titre.
5. Repeat until 3 titres agree within 0.10 cm³ (concordant).

Conclusion

At the end point n(HCl) = n(NaOH), so c(NaOH) = 0.100 × titre ÷ 25.00 mol dm⁻³.