Apparatus list:
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25cm3 graduated Pipette – the pipette is used to measure 25 cm3 of the sodium hydroxide.
- Pipette filer – the pipette filer is used to draw liquid from the pipette.
- Conical flask – the conical flask is used to hold chemicals
- Clamp and stand – clamp and stand is used to hold the pipette while mixing the sodium hydroxide and the vinegar
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Filter funnel - the funnel is used to transfer liquids from one container to another without spilling.
- Lap coat – the lap coat is used to avoid harmful chemicals and dirt from the body
- Eye goggles – the eye goggles is used to avoid harmful chemicals from the eyes.
- Sodium hydroxide solution – the sodium hydroxide solution is used to mix with the vinegar to know how
- Beaker – the beaker is used to keep the sodium hydroxide solution.
- Ethanoic acid
- Samples of Standard vinegar
- Samples of Restaurant vinegar
- Samples of Take-away vinegar
Method:
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First the sodium hydroxide solution was used to wash the 25cm3 graduated pipette.
- The pipette filler was inserted the pipette with a gentle twisting motion for about ½ cm.
- The valve “A” was squeezed with the thumb and index finger of one hand. The other hand was used to squeeze the bulb.
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The pipette was placed into the 25cm3 of sodium hydroxide solution to pull the solution into the pipette. The “S” valve was squeezed until the solution reaches the meniscus.
- The “E” valve was squeezed to expel the solution into the conical flask. All the solution was flowed out of the pipette except for the last drop.
- For the last drop of the solution, the valve “S” was pressed to allow all the solution to flow out and the bulb was inflated to its normal size.
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3 to 4 drops of indicator was added into the 25cm3 of sodium hydroxide solution.
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The samples of vinegar were filled into the burette till it reached the meniscus of 0 to 1 cm3. The precise volume was recorded to the nearest 0.05cm3.
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The burette was placed on a clamp and stand as well as the 25 cm3 sodium hydroxide solution.
- The tap of the burette was opened to titrate with the sodium hydroxide solution while mixing it.
- As soon as the indicator turned to a colourless colour, the tap was closed. The remaining volume was recorded.
- The volume was repeated and recorded three times with each sample.
Results:
Standard:
Restaurant:
Take-away:
Analysis:
According to the table, the take-away units have bigger volume than the standard units which shows that more vinegar is added to the take-away to titrate. The volume used for restaurant is more than the standard but less than the take-away. The standard vinegar is more acidic than the take-away and the take-away is water down. On average 22.8 cm3 of standard vinegar required 25 cm3 of sodium hydroxide solution, 30.3 cm3 of restaurant vinegar required 25 cm3 of sodium hydroxide solution and 41.9 cm3 of take-away vinegar required 25 cm3 of sodium hydroxide solution.
Balancing equation:
Ethanol + oxygen Ethanoic acid + water
C2H5OH (aq) + O2 (g) CH3CO2H (aq) + H2O (l)
Ethanoic acid + Sodium hydroxide Sodium Acetate + Water
CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)
The equation is balanced and the ratio is 1:1, so the mole of CH3COOH and NaOH are equal to CH3COONa and H2O.
The structure of Ethanoic acid
Moles of NaOH = volume /10000 x concentration
= 25/1000 x0.1
= 2.5 x 10-3
The moles of vinegar are the same of NaOH because of 1:1 ratio, so the concentration of standard vinegar, restaurant vinegar and tale-away vinegar are:
Concentration of vinegar (standard) = moles x 1000 / volume
= 2.5 x10-3 x 1000 / 22.77
= 0.1098 moldm-3
Concentration of vinegar (restaurant) = moles x 1000 / volume
= 2.5 x10-3 x 1000 / 30.27
= 0.0826 moldm-3
Concentration of vinegar (take-away) = moles x 1000 / volume
= 2.5 x10-3 x 1000 / 41.87
= 0.0597 moldm-3
Calculation:
Amount of moles of NaOH used in standard vinegar = V x C = A
= 22.8 x 0.1 = 2.28
Amount of moles of NaOH used in restaurant vinegar = V x C = A
= 30.3 x 0.08 = 2.424
Amount of moles of NaOH used in take-away vinegar = V x C = A
= 41.9 x 0.06 = 2.514
Conclusion:
The concentration of the standard vinegar is 0.1098 moldm-3, the concentration of restaurant vinegar is 0.0826moldm-3 and the concentration of the take-away vinegar is 0.0597moldm-3. The standard vinegar is more concentrated than the restaurant and take-away which means the standard vinegar is more acidic than the take-away and restaurant vinegar so therefore the take-away and restaurant vinegar is water down. The reason why it is water down is because in restaurant, they use the vinegar as food favouring and preservative. Linking this to the aim and the background information, the titration method indicates the amount of concentration in vinegars.
Evaluation:
Overall, my accuracy in this experiment was accurate but it wasn’t perfectly accurate. While analysing the results, all the units of the experiment were close and the average volume was almost right and accurate except one or two of them. There are two types of error which can be occurred in this experiment:
- Procedure error
- Measurement error
- Procedure error
Procedure error can occur in the procedure of the experiment, the errors are mainly while transferring solution, the volume of the solution can decrease which would not be accurate for the final record. Another one is the reaction time for closing the tap when the colour become colourless, as few drops makes a big difference in the result. Furthermore, if there are air bubbles in the tip of the burette, the record will become inaccurate if there is an air bubbles stuck at the bottom of the tap, as this can cause inaccurate in readings of about 0.5cm3
How to improve it?
The only way to improve the procedure error is to make sure there are no air bubbles in the tip of the burette and to avoid transferring solution in many beakers or flasks. In addition, to make sure to close the tap in a way just to allow drops of the vinegar to go through.
- Measurement error
Measurement error can occur when people doesn’t take the readings from the bottom of the meniscus which create parallax error. Another error can occur while taking the reading from the burette as the reading should be rounded up to the nearest ±0.05 cm3 and the pipette should be ±0.06 cm3. This can be accurate most of the time in experiment but sometime it can’t be completely accurate.
How to improve it?
The best way to improve parallax error is to take the readings at the bottom of the meniscus and try to be more accurate rather than rounding up to the nearest numbers sometimes.
During titration, the pH of the alkaline solution will decrease as more acid is added. When the pH goes down to 7, the solution will be neutral. If more acid is added, the pH will continue to go down and the solution becomes acidic. Only a few drops of sodium hydroxide are needed to neutralise the reaction. Ethanoic acid is a weak acid which means it does not fully dissociate into ions in water. To make the results more accurate, the experiment should be carried out more than 3 times. Personally, I am quite satisfied with my results as I find it accurate.