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Chemistry (Tara) > Determination of the concentration of ethanoic acid in vinegar by titration against standard sodium hydroxide solution > Flashcards

Determination of the concentration of ethanoic acid in vinegar by titration against standard sodium hydroxide solution Flashcards

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1
Q

Apparatus

A
  • Safety glasses
  • Funnel
  • Conical flask
  • Pipette
  • Burette
  • 250cm3 volumetric flask
  • Retort stand
  • Wash bottle of deionised water
  • White tile
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2
Q

Materials

A
  • 0.1M NaOH

- Vinegar

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3
Q

What is the first step (method)

A

The pipette, burette and conical flask were rinsed with deionised water to clean them.

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4
Q

What happens after the pipette, burette and conical flask were rinsed (2nd step)?

A

25cm3 of the vinegar were diluted to 250cm3 in the volumetric flask.

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5
Q

What was the dilution factor?

A

10

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6
Q

Why did the vinegar need to be diluted? (L.C)

A

Original vinegar would be too concentrated and would require an excessive amount of sodium hydroxide to react with it.

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7
Q

What happened after the vinegar was diluted in the volumetric flask?

A

The pipette was washed with some of the DILUTED vinegar.

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8
Q

Why was the pipette washed with diluted vinegar?

A

To prevent further dilution of the solution.

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9
Q

What happened after the pipette was washed?

A

25cm3 of the diluted vinegar were transferred to a clean dry conical flask observing the usual precautions.

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10
Q

Is acid usually placed in the conical flask?

A

No (but is in this experiment)

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11
Q

What was added to the conical flask after the diluted vinegar?

A

2-3 drops of phenolphthalein indicator

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12
Q

What colour is phenolphthalein in acid solution?

A

Colourless

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13
Q

What happened after the indicator was added?

A

The burette was washed with the sodium hydroxide solution.

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14
Q

Why was the burette washed with the sodium hydroxide solution?

A

To prevent a change in concentration.

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15
Q

Is the base usually placed in the burette?

A

No

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16
Q

Is the base placed in the burette in THIS experiment?

A

Yes

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17
Q

What is the base in this experiment?

A

NaOH solution

18
Q

What happened after the burette was washed with the solution?

A

The burette was filled with the NaOH solution observing the usual precautions and was clamped vertically.

19
Q

What happened after the burette was filled with NaOH solution and clamped vertically?

A

The conical was placed on a white tile and the titration was carried out observing the usual precautions until a colour change occurs.

20
Q

What is the colour change that is seen?

A

Colourless to pink

21
Q

What happened after the first titration is over?

A

The titration was repeated two more times more accurately.

22
Q

When is the titration over?

A

When the solution changes to pink.

23
Q

What was cleaned when the titration was done?

A

The burette was washed out thoroughly.

24
Q

Why was the burette washed out thoroughly at the end?

A

To prevent the base from clogging up the tap.

25
Q

What were the 3 results from the burette (NaOH)?

A

1 - 27.5 cm3 (ignore)
2 - 27.6 cm3
3 - 27.5 cm3

26
Q

What was the average titre?

A

27.55cm3

27
Q

What was the balanced equation?

A

CH3COOH + NaOH –> CH3COONa + H2O

28
Q

Why was the base placed in the burette? (unusual)

A

As the colour change in this titration is easier to see accurately going from colourless to pink rather than the other way around.

29
Q

What happens if in an exam question the base wasn’t placed in the burette (other way around)?

A

The colour change that indicates the end-point will be pink to colourless.

30
Q

Why was the vinegar diluted? (L.C)

A

The vinegar was too concentrated and would require an excessive amount of sodium hydroxide to react with it.

31
Q

Describe in detail the procedures involved in measuring a 25cm3 sample of the vinegar. (L.C)

A
  • Use 25cm3 pipette
  • Previously rinsed with deionised water
  • And previously rinsed with vinegar
  • (Pipette:) Read at eye level
32
Q

Name a suitable indicator for this titration. What colour change is observed at the end point?(reversed in question) (L.C)

A
  • Phenolphthalein

- From pink to colourless

33
Q

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)

A

1 - Anhydrous sodium carbonate titrated with a strong acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3).
2 - Acid titrated with sodium hydroxide (NaOH) solution

34
Q

What is the equation for the titration? (L.C)

A

CH3COOH + NaOH –> CH3COONa + H2O

35
Q

Describe the correct procedures for measuring exactly 25cm3 of vinegar and diluting it to exactly 250cm3 using deionised water. (L.C)

A
  • 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
36
Q

Ethanoic acid is a carboxylic acid. Identify the carboxylic acid, which occurs in nettles and stinging ants. (L.C)

A

Methanoic acid / CH2O2

37
Q

Name the piece of equipment that should be used to measure the ethanoic acid solution during the titration. (L.C)

A

Burette

38
Q

State the procedure for washing and filling the burette in preparation for the titration. (L.C)

A

Washing - with deionised water, then solution

Filling - use of funnel

39
Q

What compound in white wine is converted to ethanoic acid in vinegar? (L.C)

A

Ethanol

40
Q

What type of chemical process converts this compound to ethanoic acid? (L.C)

A

Oxidation

41
Q

Describe the procedure for accurately measuring the 50cm3 sample of vinegar and diluting it to 500cm3. (L.C)

A
  • Pipette vinegar into volumetric flask and add deionised water
  • When near mark, add dropwise
  • Read bottom of meniscus

Chemistry (Tara) (50 decks)

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