Vinegar

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 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