Quick answer: A titration finds an unknown concentration by measuring the exact volume of one solution that reacts with a known volume of another. This Chemistry 9-10 lab on titration gives the aim, the equipment, the safety points, a step-by-step method, sample results and 8 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
A bottle of sodium hydroxide solution has lost its label. This lab uses a titration against hydrochloric acid of known concentration to find out how concentrated the alkali is, using good technique and several concordant titres.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE C4 RP
Aim
To find the concentration of a sodium hydroxide solution by titrating it with hydrochloric acid of known concentration.
Equipment
- 50 cm³ burette, stand and funnel
- 25.0 cm³ pipette and pipette filler
- 250 cm³ conical flask, white tile, wash bottle
- 0.100 mol/dm³ hydrochloric acid
- Sodium hydroxide solution of unknown concentration
- Phenolphthalein indicator with a dropper
Safety
Wear safety goggles. Sodium hydroxide is corrosive: wash any splash on skin or eyes with plenty of water. Never pipette by mouth. Remove the funnel from the burette before reading it, because drips change the reading.
Method
- Rinse the burette with a little acid, fill it above zero and run acid through the tip until there is no air bubble and the level is at or below 0.00 cm³.
- Rinse the pipette with sodium hydroxide, then pipette 25.0 cm³ into the conical flask and add three drops of phenolphthalein.
- Record the starting reading and run in acid while swirling until the pink just disappears (rough titration).
- Repeat with fresh alkali, adding acid drop by drop within 2 cm³ of the rough value.
- Repeat until two or three titres are concordant.
Results
| Run | Start (cm³) | Final (cm³) | Titre (cm³) |
|---|---|---|---|
| Rough | 0.00 | 20.80 | 20.80 |
| 1 | 0.00 | 20.10 | 20.10 |
| 2 | 20.10 | 40.15 | 20.05 |
| 3 | 0.10 | 20.10 | 20.00 |
Analysis questions
Question 1 Select the concordant titres
State which titres should be used in the mean and why.Question 2 Mean titre
Calculate the mean titre.Question 3 Moles of acid
Calculate the moles of HCl in the mean titre.Question 4 Concentration of NaOH
NaOH + HCl → NaCl + H₂O. Calculate the concentration of the sodium hydroxide in mol/dm³.Question 5 Concentration in g/dm³
Convert the answer to g/dm³ (Ar: Na = 23, O = 16, H = 1).Question 6 Uncertainty
Each burette reading has an uncertainty of ±0.05 cm³. Calculate the percentage uncertainty in the mean titre.Question 7 Why swirl and go slowly
Explain why the acid is added drop by drop near the end point.Question 8 Improving the lab
Suggest two improvements to reduce error.
