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Investigation to find out if vinegar from chip shops is watered down

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Introduction

Investigation to find out if vinegar from chip shops is watered down Planning and prediction To find out if samples of vinegar have been watered down I'm going to use the titration method. First I'll test vinegar that hasn't been watered down. I'll do this by adding (triturating) a solution of known concentration to the vinegar solution to determine its concentration. The solution I'll be adding from a burette into the vinegar will be an alkaline, as seen as the vinegar is an acid. An indicator (phenolphthalein) will show when the solutions reach neutralisation because it will turn them magenta in colour. The reaction that I'm using is [H + OH H O] neutralisation By doing this you will be able to see how much alkaline it needed to neutralise the solution, therefore how much hydrogen ions was present in the vinegar. Then I will do the same test on watered down vinegars and then I will be able to compare these results to it. For the alkaline I will use sodium hydroxide with the concentration of 0.5m. I have decided to use sodium hydroxide with the concentration of 0.5m by doing some preliminary work and I have picked this one because ...read more.

Middle

I have done preliminary work so I have already used the equipment so I know how to use them properly. I have chosen the correct equipment for the job they need to do so everything should work and go as planned. Apparatus & chemicals Burette, Sodium hydroxide, 4 conical flasks, 3 types of colourless vinegars Beaker, from different shops, Pipette, Original colourless vinegar that hasn't Pipette filler, been watered down, Burette stand, Phenolphthalein indicator, White tile, Funnel, Fair Test 1. Use same volume of vinegar. 2. Use same concentration of sodium hydroxide of 0.5m for the alkaline to neutralise the vinegars. 3. Use clean equipment as not to affect the chemicals that I'm using. 4. Use the same equipment. 5. Use the same method. 6. The only variable will be the vinegar type, everything else stays the same. 7. Compare all the results to the original vinegar type. Obtaining evidence During titration the colour change can be rapid to counter this I have used a weak concentration of sodium hydroxide, which is why I used a concentration of 0.1 mol rather than 0.5 mol. ...read more.

Conclusion

In titration it is impossible for someone to judge the solution during the end point of the indicator to be the exact same colour every time with just the naked eye. This is another limitation in the procedure. During titration the colour change can be rapid to counter this I have used a weak concentration of sodium hydroxide, which is why I have used a concentration of 0.1 mol rather than 0.5 mol. The experiment can be improved by using a computer, camera or keep another neutralised solution to compare the colours with. If the computer could hold the colour of the first titration then one could do the second titration while looking at the computer screen, so all the titrations would be stopped at exactly the same colour. This would totally reduce the human error when it comes to the colour change of the indicator, making the results more fair, accurate. Another way I could have improved the experiment was if I was to use a larger quantity of vinegar for the titration and, as a whole would reduce the percentage error. I feel that I collected enough evidence to make me confidence about my conclusion, but next time I could test more vinegar from different shops to give me a bigger range and variety. ...read more.

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