Experiments to Provide Evidence in a Prosecution Case with the Pervis Vinegar Company on Unknown Toxins
The aim of this experiment is to preform tests on two samples of vinegar, one that is commercially safe and the other not (from the Pervis Company) to determine the unknown toxin contained in the Pervis Vinegar.
Materials:* Numerous Beakers/Conical Flasks* Phenolphthalein Indicator* Burette* Numerous Test Tubes* Sticky Tape* Test Tube Rack* Sodium Hydroxide (NaOH)* Calculator* Sample of Commercially Safe Vinegar* 2 Surgical Swabs (large cotton bud)* Sample of Pervis Vinegar (Toxic)* 2 Agar Gel Plates* Universal Indicator* Incubator Oven* Incubator* Bunsen Burner* Water* 2 Small Syringes* Potassium Chromate Solution* Hydrochloric Acid
MethodsTo fully determine and identify the unknown toxin present in the Pervis vinegar sample, four tests were needed. A molarity test was completed, a sample of the vinegar was then allowed to grow on an agar plate to ascertain whether bacteria were present and a pH test would also be done. The final test was a precipitant test to discover if the heavy metal Lead was present in the Pervis sample. A titration experiment was now set up using Sodium Hydroxide solution as the alkali in the burette with a molarity 0.01177 and 25ML of Pervis vinegar was placed in the beaker underneath the burette. Approximately four drops of Phenolphthalein indicator where added to the Pervis vinegar and then the measured amounts of NaOH were slowly added to the vinegar. The burette needed to be refilled several times and the average amount of NaOH solution needed to neutralise the Pervis vinegar was 181.5 ML. That same experiment was then tried using commercially safe vinegar in the beaker below the burette. Four drops of Phenolphthalein indicator were again placed in the vinegar and then measured amounts of NaOH were released from the burette into the beaker. This was completed three tines with the average NaOH needed to neutralise the safe vinegar approximately 154.5 ML. These amounts for the NaOH added were then recorded for later analysis. The pH test was now done with both samples of vinegar. Two test tubes were placed in a test tube holder and 14ML of each sample of vinegar poured into one of the test tubes. About two drops of Universal Indicator were placed in the test tubes and the reaction colourers were recorded for later use.
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The next experiment was to place a small amount of each sample of vinegar into their own Agar plate to see if any bacteria growth in the Pervis sample. Two syringes surgical swags, Agar plates, and a roll of sticky tape were collected. The surgical swabs were unwrapped from their sealed sterile packages and now both syringes were full of the two samples of vinegar. Each surgical swab had injected on it, a reasonable amount of vinegar from the syringe and this occurred with both samples. One surgical swab was then spread across the surface of one of the Agar plates in a ‘zig zag’ fashion. This also occurred with the other sample although it was placed in a separate Agar plate. Both plates had their lids sealed with sticky tape to ensure no potential pathogens or other organisms were released. Both plates were then placed in an incubator for 5 days at approximately 37ºC. The final experiment was to ascertain whether the Pervis vinegar had any Lead in its sample. To find this out a precipitant test for Lead was used which needed water, HCl, Potassium Chromate Solution and a Bunsen burner. A small amount of each sample was put in a test tube and then a few drops of HCl were added. 20MLS of water was then added to each test tube and then both test tubes were boiled under a Bunsen burner. Then 10MLS of Potassium Chromate solution were added to each sample and at that point the Pervis sample reacted with a yellow precipitant while the other sample only be came yellow coloured.
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ResultsThe table below shows the average NaOH needed to neutralise both samples and what their molarity was after calculating it with a calculator.
Vinegar TypeAverage NaOH NeededApproximate MolarityPervis 181.5 ML0.08545 MCommercially Safe154.5 ML0.07273 MLooking at the graph above you can see that there isn’t a huge difference in the Molarity between the two samples, only 0.01 Mole.
As for the bacterial samples, after analysing both of the plates after 5 days it is clear that bacteria or fungi are not the toxins responsible in the Pervis Vinegar. Neither sample plate had the slightest sight from the naked eye that there was any growth on them.
The results from the pH tests with the Universal indicator concluded that both samples were of pH 4 or lower however the Pervis sample was a deeper red.
The lead precipitant test concluded that there was a substantial amount of Lead in the Pervis sample for it to come up in the precipitant test. This test however is only a qualitative test not a quantitative test so the amount of Lead was impossible to ascertain and only presence is recorded. The commercial safe vinegar sample resulted as negative for this test.
ConclusionIt is quite clear that after running the molarity, pH, pathogenic organism and Lead precipitant tests on both samples that Lead was the heavy metal toxin in the Pervis vinegar. The difference in Molarity in both samples could have lead to a deeper investigations in that area but it was later found out that these results had a major error in them and should have been the same. This could have been because the NaOH solution Molarity standard was recorded several years ago. Our titration experiments didn’t froculate and go cloudy like other groups, which could have been from a contamination in the Sodium Hydroxide. Concerning the error with the Molarity, it could have been an observational error with the reading from the naked eye or it could have been a dilution error.
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