If my results are correct, then shops A and C are cheating on the vinegar, by watering it down, but shop B appears to have a stronger concentration of vinegar than the manufacturer, which is unlikely. In reality it is more likely that shop B was actually serving the correct concentration of vinegar, and that the experiment was incorrect. Overall shop A had the least amount of vinegar in. I think the burette method was a more accurate measurement than the pipette method, despite the anomalous results. This is because it is much easier to read off the measurement on the side, rather than from the side of a measuring cylinder.
Evaluation
The experiment went well apart from the anomalous results. I have enjoyed the practical and also writing up the experiment. I think it was a fair experiment because we always used the same amount of vinegar, sodium hydroxide and phenolphthalein. It may however have been an unfair test because it is possible that some of the acids may have been mixed up by accident, or, as the experiment was carried out over a period of two weeks, the concentration of the sodium hydroxide may have changed.
I am pleased with my results but realise that next time it would be beneficial to double check that no stupid mistakes have occurred, and to take make repetitions of the experiment to collect more results to create a fairer average.
The accuracy of the experiment can be questioned from our abilities of reading the marks on the burette, the pipette etc, but also on our abilities to judge the colour of the solution. Everyone sees colour slightly differently as it is subjective, and it would be unfair to take results from just one person so we swapped at intervals to get different opinions. Any anomalies could have been due to poor workmanship, or there may have a mix up with the vinegars because of the work being spread over two weeks.
Although we measured to 0.1 of a pH in the burette method, to improve the accuracy of the pH overall, it would have been better to use a pH probe. This probe can be connected to a handset used to calibrate the pH, and a data logger, which stores information. This data logger is connected up into a PC and can automatically create graphs of the pH levels you have collected. This would be a much more accurate way of collecting results.
Our results are not very accurate and are therefore unsuitable and unreliable to make any lasting conclusion. It would be beneficial for the experiment to be repeated using a data logger and a pH probe, to enable us to compare results and see how bad ours were.
Who’s cheating on the vinegar?
Aim
Our aim is to test three vinegars against the manufacturers’ to see who is diluting or ‘cheating’ on the vinegar.
Prediction
I think that there will be at least one out of the three vinegars that has been diluted, or in other words, at least one company will have been ‘cheating’ on the vinegar. This vinegar will take less alkali to make it neutral as the closer it is on the pH scale to neutral, the less alkali it needs to bring it back to neutral.
Below are the equations for the experiment that we are going to attempt..
Acid + Alkali = (Neutral) Salt + Water
Ethanoic acid + Sodium hydroxide = Sodium ethanoate + Water
Here is some background knowledge on weak/strong acids/alkalis and the particle theory.
Methods
Pipette Method
I will use a measuring cylinder to measure out 10ml of the manufacturers’ vinegar into a small beaker, and then I will add six drops of the indicator, which is called phenolphthalein. This won’t make any difference to the colour of the vinegar. Next I will wash the measuring cylinder well with water to make sure there is no vinegar left in it, and I will use it to measure out 20ml of the alkali, which is called sodium hydroxide.
Then I will use a dropping pipette to add a few drops of alkali to the vinegar, and swirl the beaker to help it to mix. I will repeat this process until the indicator changes and makes the vinegar turn pink. This is when I have added enough alkali to make all the vinegar neutral.
I will then measure how much alkali is left in the measuring cylinder. I will take this away from twenty to see how much alkali it took to make the vinegar neutral. I will replicate this experiment three times to check I have an accurate set of results. Then I will repeat the experiment with three other vinegars to see whether they all take the same amount of alkali to make them neutral. Each of these vinegars will also have three replicates to ensure accuracy.
Diagram of the pipette method
Titration Method
Alternatively, and I prefer this method, I will use titration. I will use a burette to measure each of the solutions and make them neutral. The vinegar and phenolphthalein will go in a beaker underneath the burette, and the alkali, or sodium hydroxide, will go into the burette. The burette holds 50ml of sodium hydroxide and I will put this much into it until it reads zero at the top. This will enable me to read off the amount that has been used very easily as it shows you on the side of the burette. I will still use 10ml of vinegar and 6 drops of phenolphthalein in the beaker under the burette.
Diagram of the titration
Diagram of the data logger
