Determination of the concentration of ethanoic acid in vinegar by titration against standard sodium hydroxide solution Flashcards
Apparatus
- Safety glasses
- Funnel
- Conical flask
- Pipette
- Burette
- 250cm3 volumetric flask
- Retort stand
- Wash bottle of deionised water
- White tile
Materials
- 0.1M NaOH
- Vinegar
What is the first step (method)
The pipette, burette and conical flask were rinsed with deionised water to clean them.
What happens after the pipette, burette and conical flask were rinsed (2nd step)?
25cm3 of the vinegar were diluted to 250cm3 in the volumetric flask.
What was the dilution factor?
10
Why did the vinegar need to be diluted? (L.C)
Original vinegar would be too concentrated and would require an excessive amount of sodium hydroxide to react with it.
What happened after the vinegar was diluted in the volumetric flask?
The pipette was washed with some of the DILUTED vinegar.
Why was the pipette washed with diluted vinegar?
To prevent further dilution of the solution.
What happened after the pipette was washed?
25cm3 of the diluted vinegar were transferred to a clean dry conical flask observing the usual precautions.
Is acid usually placed in the conical flask?
No (but is in this experiment)
What was added to the conical flask after the diluted vinegar?
2-3 drops of phenolphthalein indicator
What colour is phenolphthalein in acid solution?
Colourless
What happened after the indicator was added?
The burette was washed with the sodium hydroxide solution.
Why was the burette washed with the sodium hydroxide solution?
To prevent a change in concentration.
Is the base usually placed in the burette?
No
Is the base placed in the burette in THIS experiment?
Yes
What is the base in this experiment?
NaOH solution
What happened after the burette was washed with the solution?
The burette was filled with the NaOH solution observing the usual precautions and was clamped vertically.
What happened after the burette was filled with NaOH solution and clamped vertically?
The conical was placed on a white tile and the titration was carried out observing the usual precautions until a colour change occurs.
What is the colour change that is seen?
Colourless to pink
What happened after the first titration is over?
The titration was repeated two more times more accurately.
When is the titration over?
When the solution changes to pink.
What was cleaned when the titration was done?
The burette was washed out thoroughly.
Why was the burette washed out thoroughly at the end?
To prevent the base from clogging up the tap.
What were the 3 results from the burette (NaOH)?
1 - 27.5 cm3 (ignore)
2 - 27.6 cm3
3 - 27.5 cm3
What was the average titre?
27.55cm3
What was the balanced equation?
CH3COOH + NaOH –> CH3COONa + H2O
Why was the base placed in the burette? (unusual)
As the colour change in this titration is easier to see accurately going from colourless to pink rather than the other way around.
What happens if in an exam question the base wasn’t placed in the burette (other way around)?
The colour change that indicates the end-point will be pink to colourless.
Why was the vinegar diluted? (L.C)
The vinegar was too concentrated and would require an excessive amount of sodium hydroxide to react with it.
Describe in detail the procedures involved in measuring a 25cm3 sample of the vinegar. (L.C)
- Use 25cm3 pipette
- Previously rinsed with deionised water
- And previously rinsed with vinegar
- (Pipette:) Read at eye level
Name a suitable indicator for this titration. What colour change is observed at the end point?(reversed in question) (L.C)
- Phenolphthalein
- From pink to colourless
Starting with a primary standard solution made from anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution? (L.C) (CORRECT ORDER IS NECESSARY)
1 - Anhydrous sodium carbonate titrated with a strong acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3).
2 - Acid titrated with sodium hydroxide (NaOH) solution
What is the equation for the titration? (L.C)
CH3COOH + NaOH –> CH3COONa + H2O
Describe the correct procedures for measuring exactly 25cm3 of vinegar and diluting it to exactly 250cm3 using deionised water. (L.C)
- Rinse pipette with water
- and then with vinegar
- Fill with pipette filler
- Deliver 25cm3 to 250cm3 volumetric flask
- Add deionised water until level of water near mark
Ethanoic acid is a carboxylic acid. Identify the carboxylic acid, which occurs in nettles and stinging ants. (L.C)
Methanoic acid / CH2O2
Name the piece of equipment that should be used to measure the ethanoic acid solution during the titration. (L.C)
Burette
State the procedure for washing and filling the burette in preparation for the titration. (L.C)
Washing - with deionised water, then solution
Filling - use of funnel
What compound in white wine is converted to ethanoic acid in vinegar? (L.C)
Ethanol
What type of chemical process converts this compound to ethanoic acid? (L.C)
Oxidation
Describe the procedure for accurately measuring the 50cm3 sample of vinegar and diluting it to 500cm3. (L.C)
- Pipette vinegar into volumetric flask and add deionised water
- When near mark, add dropwise
- Read bottom of meniscus
