Who’s been cheating on the vinegar?
Aim:
To investigate if the vinegars have been diluted by working out their concentrations.
Scientific Background:
Vinegar is an acid and there fore can be neutralised by an alkali.
Acid + Alkali à salt + water
Hydrochloric acid + Sodium Hydroxide à Sodium chloride + water
Vinegar is a weak acid and therefore it only partially ionises in solution.
CH3COOH ßà CH3COO- + H+
An alkali such as Sodium Hydroxide has a formula NaOH. If the alkali is strong then it ionises fully in solution.
NaOH ßà Na+ + OH-
When the acid H+ reacts with the alkali OH- the solution neutralises.
Prediction:
If the acid has been diluted there will be less H+ ions present in the volume used. Therefore to cancel the alkali more acid will be required. This is on the assumption that the alkali volume and concentration stay constant.
Method:
· Measure 10cm3 of 0.1m alkali into a measuring cylinder then place the solution into a 75cm3 conical flask.
· Then add 2-3 drops of indicator to the alkali (it will go purple in colour)
· Measure out 50 cm3 of the vinegar into a measuring cylinder and then place into a glass beaker.
· Then using a dropper add the vinegar drop wise to the alkali until 1-drop changes the solution to colourless.
· Replace the vinegar back into the measuring cylinder and record the volume of vinegar used.
· Repeat this process twice more, recording results.
· Then repeat the whole procedure for each different concentration of vinegar.
Preliminary Work:
Aim:- To find out which concentration of alkali will give accurate, measurable values.
Concentration(M) Volume of acid(cm3)
0.1m 21.45cm3
0.5m 78.9cm3
0.75m 100+cm3
1.0m 100+cm3
2.0m 100+cm3
We decided from the results that the best measurable concentration of alkali would be the 0.1m concentrations.
Investigation:
Test 1 Test 2 Test 3 Average
Manufacturers’ 10.27cm3 10.3cm3 9.73cm3 10.11cm3
Shop 1 10.3cm3 9.5cm3 10.25cm3 10.11cm3
Shop 2 18.4cm3 17.9cm3 18.4cm3 18.23cm3
Shop 3 40.1cm3 38.45cm3 35.7cm3 38.08cm3
Analysis:
These results show that the vinegar from Shop 2 and Shop 3 have been significantly diluted with water or some other substance. The results obtained from shop1 show that its is very similar in concentration to the manufacturers’. Two of the results show that it is less concentrated than the manufacturers’, but one shows that it is more concentrated, this is impossible so its is most likely due to human error and not taking the readings properly.
Concentrations:
Manufacturers’= 1¸10.11 = 0.0989119683
Shop1 = 1¸10.11 = 0.0989119683
Shop2 = 1¸18.23 = 0.054854635
Shop3 = 1¸38.08 = 0.026260504
These results show an obvious difference in the concentration with the manufacturers’ being the most concentrated and shop 3’s being the least concentrated.
Evaluation:
The results from this experiment can be considered reasonably accurate we took the results quite accurately.
Each subsequent trial will use one gram more. 2.Put baking soda into reaction vessel. 3.Measure 40 mL vinegar. 4.Completely fill 1000 mL graduated cylinder with water.
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It mainly exists as H2C2O4.2H2O, which is known as oxalic acid dihydrate. The 2H2O attached to the oxalic acid means that for every one molecule of Oxalic acid there is, there will be 2 molecules of water. This makes it predictable and allows for the standardization of NaOH. The reaction between NaOH and Oxalic acid dihydrate is as follows:
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