Vinegar
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Whos 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 Ðo salt + water
Hydrochloric acid + Sodium Hydroxide Ðo Sodium chloride + water
Vinegar is a weak acid and therefore it only partially ionises in solution.
CH3COOH ЯÐo CH3COO- + H+
An alkali such as Sodium Hydroxide has a formula NaOH. If the alkali is strong then it ionises fully in solution.
NaOH ЯÐo 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