Vinegar: Sodium Hydroxide and Measuring Cylinder
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
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