Experiment: Determining the Strength of NaOH Solution with Standard HCl
Objective:
To determine the strength of an approximate N/10 NaOH solution using standard decinormal HCl solution.
Apparatus:
- Burette
- Pipette
- Funnel
- Conical flask
- Stand with clamp
- Wash bottle
Chemicals:
- Phenolphthalein indicator
- N/10 HCl solution
- NaOH solution
Theory:
This experiment involves titration between a strong acid (HCl) and a strong base (NaOH). The reaction can be represented as:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
At the equivalence point, neutral salt (NaCl) is formed, and the pH of the solution is around 4-10, making phenolphthalein a suitable indicator.
Procedure:
- Wash all apparatus with water.
- Rinse the burette with distilled water, then with HCl.
- Fill the burette with HCl up to the zero mark without leaving any gaps.
- Clean the pipette with distilled water and the given NaOH solution.
- Pipette 10ml of NaOH solution into a conical flask and add 1-2 drops of phenolphthalein until the solution turns pink.
- Slowly add HCl from the burette into the flask, swirling continuously, until the solution turns colorless. Note the burette reading.
- Repeat the titration until you get two consecutive readings.
Observation Table:
| S.No. | Volume of NaOH (ml) | Burette Reading Initial | Burette Reading Final | Volume of HCl (ml) | Concurrent Reading |
|---|---|---|---|---|---|
| 1 | 10 | 0 | 9 | 9 | |
| 2 | 10 | 9 | 17 | 8 | 8 |
| 3 | 10 | 17 | 25 | 8 |
Calculation:
Normality of HCl (Na) = 0.1
Volume of HCl (Va) = 8ml
Volume of NaOH (Vb) = 10ml
Using the equation: NaVa = NbVb
0.1 × 8 = Nb × 10
Nb = 0.08
The normality of NaOH (Nb) is 0.08N.
Result:
The strength of the NaOH solution, determined using standard HCl solution, is found to be 0.08N.
Conclusion:
The strength of a base can be accurately determined using a primary standard solution of acid.
Precautions:
- Thoroughly wash apparatus.
- Remove air bubbles from the burette nozzle.
- Use the lower meniscus of the solution from the burette.
- Do not rinse the conical flask.
- Avoid using excess indicator.