To determine the concentration of sodium hydroxide solution using the process of titration.
HOW DOES IT WORK?
The concentration of this standard solution Sodium hydroxide is determined with the formula:
c = m/MV
Dissolve approximately 0.2g of Oxalic acid in 50ml of distilled water. A burette is filled with NaOH(aq). And a beaker is used to transfer exactly 50 ml of Oxalic Acid (COOH)2∙H2O(aq) to the Erlenmeyer flask.
A few droplets of Phenolphthalein-solution is added to the Oxalic acid. The NaOH(aq) is titrated against (COOH)2∙H2O(aq) until the end point of the titration is reached. This happens when the solution discolours. The titration is repeated three times and the average volume of Sodium Hydroxide needed to neutralize the Oxalic acid solution, is determined.
The data obtained in the experiment is used to determine the concentration of the Oxalic acid (COOH)2∙H2O(aq).
It is important to reach a good end point, as an overly titrated solution would cause inaccuracies in your results and calculations.
- 2 x 100 ml beaker
- 1 x Funnel 50mm
- Burette 25ml acrylic
- Burette Base 160mm x 100mm
- Burette Stand and clamp
- Glass Stirring Rod
- 2 x 250ml Erlenmeyer flask
- Spatula (S/Steel) Chattaway 200mm
- 5g Oxalic Acid pre-prepared in vial (C2H2O4)
- 250ml Sodium Hydroxide (NaOH)
- 50ml Phenolphthalein (C20H14O4)
- Wash bottle 250ml
- 250ml Distilled water
- White tile
Part 1: Preparation
Time Allocation: 20 Min
- Put on your safety goggles and lab coat, for this experiment you should work in pairs.
- While one partner prepares the oxalic acid solution, the other should prepare the burette for titration. Each group member should do one titration!
- In a 250 mL Erlenmeyer flask, add the 0.20g of oxalic acid from the vial (this will be a very small amount already provided in exact quantity/ measure this amount out). Record this exact mass of oxalic acid used in the data table.
- Repeat this step in another Erlenmeyer flask for trial 2.
- Dissolve the oxalic acid in the flask with approximately 50mL of distilled water.
- Add 2-3 drops of phenolphthalein indicator to the flask.
- Rinse the burette thoroughly with tap water, then rinse it once with a small amount of distilled water in a wash bottle, draining the final rinses through the tip.
- Clamp the clean burette to the ring stand.
- Use 50 ml of NaOH solution in a 100 mL beaker.
- Position the burette so that the top is below eye level and ensure it is closed!
- Pour approximately 5 mL of the NaOH into the burette.
- Drain this solution through the tip to remove water and coat the inside of the burette with base solution.
- Fill the burette to slightly above the zero line with NaOH.
- With a waste beaker below the burette, drain some of the base through the tip to clear the burette of air.
- Stop between 0.0 and 2.0 ml.
- Remove the hanging drop by touching the tip to the inside of the waste beaker.
- Read the initial volume of the burette and record it in the data table.
Part 2: Titration
Time allocation: 25 min
- Place the flask with acid and phenolphthalein under the burette. The burette tip should be down about 1cm inside the mouth of the flask to avoid losing any of the base.
- Place a sheet of white paper under the flask to help highlight the pink indicator colour.
- Drip the base into the flask while swirling the flask to stir it, add the base quickly at first, but as the pink colour starts to last longer, slow the drip rate. (Note that it is better to take longer on this part than to need to start again!)
- When the whole flask flashes pink before turning clear again, add only one drop at a time and swirl the flask before adding more.
- Occasionally rinse down the splashes on the side of the flask using a little distilled water from a wash bottle (this water will not change your results).
- When the faintest pink colour persists for 30 seconds, stop and record the final volume in the burette.
- Repeat the titration for trial 2.
- Flush all chemicals down the sink and clean out the burette.
- Record all values in the observation table.
- Clean up your work area and wash your hands.
Draw a table to record your observations before and after , the table should have two columns labelled :
Volume of Oxalic Acid added to Sodium Hydroxide (ml)
Colour of the solution
- Wear safety goggles at all times.
- Avoid skin contact with oxalic acid and sodium hydroxide – in case of skin contact, rinse with cold water.
- Avoid eye contact with oxalic acid and sodium hydroxide – In case of contact with eyes, wash with cold water and get medical help.
- Sodium hydroxide is caustic and corrosive it causes severe skin irritation.