Analyse the samples by titration and to decide which of the samples, if any have been watered down.

Prediction

        My prediction is ‘The higher the concentration of vinegar the less vinegar needed to neutralize the solution of vinegar and sodium hydroxide’ because if the vinegar has a low concentration then it contains a smaller number of moles per litre. So therefore more of the vinegar would be needed to neutralize the sodium hydroxide. If the vinegar was of a higher concentration less of it would be needed to neutralize the sodium hydroxide.

Equipment List

Burette

Pipette

Pipette filler

Conical flask

Beakers x2

Funnel

Clamp stand

White tile

Phenolphthalein indicator

Sodium hydroxide

Vinegar samples: manufacturers, sample 1,2,3

Diagram of Equipment

Risk Assessment

        I decided to make the experiment safe by wearing goggles at all times and not sitting down while doing the experiment. Also I tried not to spill and liquid or get any on my clothes and skin.

Step by Step Procedure

        This is what I did:

1. I will get all equipment out that is on the equipment list.
2. I will label and fill two beakers with the reacting solutions.
3. I will pour a little of the vinegar into the burette to rinse it. Then pour away the solution.
4. I will fill the burette with vinegar and then let the solution out until the meniscus is on the zero line.
5. Then using a pipette filler I will rinse out the pipette using the sodium hydroxide and then pour it away. Then fill the pipette to way past the line.
6. Carefully let the solution out until the meniscus is on the line.
7. I will then run the solution into a conical flask.
8. I will add 7 drops of indicator and the solution will turn purple and put it on the white tile that is on the clamp stand.
9. Run the solution from the burette into the conical flask a bit at a time, swirling the flask all the time.
10. Stop when the indicator has changed the solution from purple to clear and note the reading on the burette.
11. Empty and rinse the conical flask and then refill and zero the burette.
12. Using the pipette filler, refill the pipette and let the solution out until the meniscus is on the line.
13. Repeat steps 5, 6 and 7.
14. Repeat step 8 but stop about 1cm before the previously recorded volume. Then add the vinegar drop by drop until the solution goes clear.
15. Record the volume added in a table.
16. Do at least three readings within 0.1 cm  of each other for each sample.  

Scientific Knowledge

        Equation for the reaction:

Acid + Alkali → Salt + Water

Sodium Hydroxide + Ethanoic Acid → Sodium Ethanoate + Water

NaOH + CH3COOH → CH3COONa + H2O

1 Mole + 1 Mole → 1 Mole + 1 Mole

I know that it takes 1 mole of NaOH to neutralize 1 mole of CH3COOH and then you get 1 mole of CH3COONa and 1 mole of H20

amount of moles = concentration x volume

a = cv

  = 0.1 x 25/1000

  = 0.0025 moles of NaOH

 0.0025 moles of sodium hydroxide and Ethanoic acid are needed each time.

The less concentrated the vinegar the smaller the number of moles it will contain per litre so it will therefore take more of the solution to neutralize the solution.

Test Runs

My test runs were to show me how the equipment was set up and how the experiment worked and what I had to do in the experiment.

Recording Results

        I recorded my results in a table but also in a graph. I will take an average of each set of results.

The reaction that takes place is the neutralization of sodium hydroxide and ethanoic acid.

           Acid + Alkali = Salt + Water

CH3COOH + NaOH = CH3COONa + H2O

      1 mole + 1 mole = 1 mole + 1 mole

Conclusion

       

Here are my calculations to find out the concentration and 1/concentration of each of the samples of vinegar. The calculation is: concentration = amount in moles/volume x 1000.

The first graph I plotted was average volume of vinegar against the concentration of vinegar. In this graph I have found that the points join up as  a curve the graph shows me that the higher the concentration of vinegar the less vinegar needed to neutralize the solution of vinegar and sodium hydroxide. This matches up with my original prediction that ‘The higher the concentration of vinegar the less vinegar needed to neutralize the solution of vinegar and sodium hydroxide.’ As the volume halves the concentration doubles, for example on my graph the volume is 26 cm  and the concentration is 0.10 moles and when the volume is 13cm  ,the concentration is 0.20 moles.

On the second graph I plotted the axis was volume of vinegar against 1/concentration of vinegar. In this graph I have found that all the points join up to become a straight line. I have found that sample 1, 2 and 3 have been watered down because the concentration for those three samples is lower than the concentration of the manufacturers sample.

Evaluation

In my experiment I have completed it fairly, the equipment I used to make it fair was the same volume pipette and burette. This is because they have a line on them and the meniscus of the liquid is on the line so I will be using the same volume of liquid every time. On my first graph the first three points are joined up by more of a straight line than the curve that joins the 3rd and 4th points up. To make this more of a smooth curve I could have missed a point out of it to make it smooth. I have enough results to support my conclusion because every result I took was within 0.1 cm  of each other. To further my experiment I could react all of the samples with magnesium and then the less concentrated vinegars will react slower.