Popular LabKit · Recipe
0.1 N Sodium Hydroxide: Preparation and Standardisation
How to prepare 0.1 N (0.1 M) NaOH and standardise it with potassium hydrogen phthalate (KHP) – quantities, method, formula, a worked example and a calculator for your factor.
Preparation: 0.1 N (0.1 M) sodium hydroxide, 1000 mL
| Component | Amount |
|---|---|
| Sodium hydroxide pellets, NaOH | 4.2 g (4.0 g theoretical) |
| Carbon dioxide-free purified water | to 1000 mL |
For sodium hydroxide, 0.1 N and 0.1 M are the same (n-factor 1). The extra 0.2 g allows for the moisture and carbonate that NaOH pellets always carry; the exact strength is found by standardisation.
Preparation
- Boil purified water for 5 minutes and cool it with the vessel covered, to remove dissolved CO₂.
- Weigh about 4.2 g NaOH quickly (it absorbs moisture) and dissolve in about 800 mL of the CO₂-free water. It warms up; let it cool.
- Make up to 1000 mL and mix. Store in a tightly closed polyethylene bottle, ideally with a soda-lime guard tube.
Standardisation with potassium hydrogen phthalate (KHP)
- Dry KHP at 120 °C for 2 hours and cool in a desiccator.
- Weigh accurately about 0.5 g KHP into a conical flask and dissolve in 75 mL of CO₂-free water.
- Add 2 drops of phenolphthalein solution.
- Titrate with the NaOH solution to the first permanent faint pink colour.
- Repeat twice more and use the mean factor.
1 mL of 0.1 M NaOH ≡ 0.02042 g KHP
Factor = actual molarity ÷ 0.1
Worked example
0.5112 g KHP needed 24.85 mL. Molarity = 0.5112 ÷ 204.22 ÷ 0.02485 = 0.1007 M, factor 1.0073.
Calculate your factor (pre-filled) →
Recipes are calculated with the Popular LabKit buffer model (ionic strength and temperature corrected) and checked against published buffer tables. For a pharmacopoeial test, follow the reagent or buffer recipe in your monograph. Always confirm pH with a calibrated pH meter.
Frequently asked questions
How often should 0.1 N NaOH be standardised?
Before use if it is kept for more than a few days, and at least weekly. NaOH absorbs CO₂ from air, which lowers its strength.
What factor range is acceptable?
Most laboratories accept a factor between 0.98 and 1.02 for routine work; pharmacopoeias allow the strength to differ from the nominal value but require it to be determined precisely. Follow your SOP.
Can I standardise NaOH with standard HCl?
Yes, against an already standardised acid – use the “Against a standard solution” tab of the factor calculator. A primary standard such as KHP is preferred.