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Chemistry Cwk Concentrations: Who's cheating on the vinegar?

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Who's cheating on the Vinegar? I will be investigating the concentrations of ethanoic acid in 6 different samples of diluted vinegar using the process of titration. I will use the following apparatus and chemicals: * Burette * Clamp stand * 6-12 Conical flasks * Measuring Cylinder * White Tile * Goggles * Lab Coat * Funnel * 6 different concentrations of ethanoic acid solution (vinegar) * Sodium Hydroxide * Phenolphthalein Firstly, I will set up the burette and the clamp stand and fill the burette with Sodium Hydroxide to the zero mark. I will then measure out 20cm� of one of the ethanoic acid solutions, using a measuring cylinder, and place the vinegar into a conical flask. Next, I will add three drops of phenolphthalein indicator to the vinegar solution and position the flask under the burette. Gradually, I will release small quantities of the Sodium Hydroxide into the solution until the liquid turns a pale but distinct pink, indicating that the solution has been neutralised. ...read more.


the number of moles of sodium hydroxide can be calculated using the formula (the volume being the amount of sodium hydroxide used to neutralise the solutions). Moles of NaOH (sodium hydroxide) = titre/1000 x 0.1 As the ratio of ethanoic acid and sodium hydroxide is 1:1 in the chemical reaction, there will be an equal number of moles of both chemicals for the vinegar to be neutralised. From this knowledge, the concentration of the vinegar can be calculated by rearranging the formula. Concentration = (Moles x 1000)/volume The volume used of each vinegar solution was 20cm�, and the moles are already known as they are equal to the moles of NaOH. Concentration of vinegar solution = (Moles NaOH x 1000)/20 Concentration of ethanoic acid in solution Vinegar A 0.18225M/dm� Vinegar B 0.092M/dm� Vinegar C 0.068625M/dm� Vinegar D 0.04625M/dm� Vinegar E 0.02325M/dm� Vinegar F 0.01175M/dm� The vinegar with the highest concentration of ethanoic acid (the factory vinegar) was vinegar A. This is because it required a greater volume of sodium hydroxide to neutralise the solution, therefore there was a greater volume of ethanoic acid within 20cm� of that solution compared to the other vinegars. ...read more.


As you manipulate the primary data further, the multiple processes may degrade the level of precision, turning a small difference into a larger one. The true concentrations of the solutions are unknown so the accuracy of my results can not be judged. There is also not an independent variable to compare my results to and judge accuracy in that way. However, the strategy used is a recognised method to find the concentration of an acid solution, so the concentrations calculated are probably very close to the true concentrations, if the experiment was successful. The two tests for vinegars A, B and C produced a considerable difference between the two tests. Vinegars D, E and F all have either identical or very close results for their first and second tests, which leads to believe that either one or both of the tests from the first three vinegars are incorrect and are anomalies. The different results could have been because I released too much sodium hydroxide into the solutions, turning them alkali, or too little in hesitation of going over and running that test. ...read more.

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Response to the question

The author asks “Who’s cheating on the vinegar?” but fails to explain what they mean by this, and thus to answer their own question, my suggestion would be to use a boring but simple coursework title such as “Which of ...

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Response to the question

The author asks “Who’s cheating on the vinegar?” but fails to explain what they mean by this, and thus to answer their own question, my suggestion would be to use a boring but simple coursework title such as “Which of samples A to F is the most concentrated?”. However, as a piece of coursework it does explain how to conduct the experiment mentioned, and manipulates results accurately.

Level of analysis

The author clearly explains the purpose of the experiment, and calculates the concentrations of the acids by using various formulae, however they could go into a lot more depth than they do. In the tables produced they fail to give the units of the measurements, making them less useful than they would otherwise be. The formulae given are correct for their experiment (or so I assume, though as there are no units on the tables, they might not be) but could be given in their more general forms and then turned into the ones required for the experiment. This would make their coursework easier to understand because the equations would be better derived. The author also mentions that ethanoic acid reacts with sodium hydroxide in a one to one ratio, which is true and a useful and important point. To improve their coursework the author could have given the equation for the reaction to show how they knew the ratio was one to one. The author talks about how they would improve their results, but does not mention using a more accurate measuring cylinder, or doing more repeats. The author could also have drawn a graph of their results, and could have created a test solution with a known concentration of ethanoic acid to check the accuracy of their results.

Quality of writing

The author uses spelling, grammar and punctuation correctly, and uses scientific language to improve his work. Their communication is good and makes their piece easy to understand.

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Reviewed by E13 13/02/2012

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