In this investigation I am going to find out the concentration of ethanoic acid in vinegar. The concentration of acid is different in the product made by different manufactures
Concentration of Vinegar
Introduction
In this investigation I am going to find out the concentration of ethanoic acid in vinegar. The concentration of acid is different in the product made by different manufactures. I will react the acid in the vinegar solution of sodium hydroxide of known concentration in a titration experiment.
Equipment
* Plastic beaker
* Glass beaker
* Pipette
* Funnel
* Phenolphthalein
* Vinegar
Method:
* Rinse the pipette with the diluted solution of vinegar.
* Rinse the conical flask with distilled water Pipette 25cm³ of diluted vinegar solution to the conical flask and add 4-5 drops of the indicator.
* Rinse the burette with the solution of Sodium Hydroxide and be sure to get rid of any air bubbles in the tip of the burette.
* Using the filter funnel, carefully fill the burette with the solution of Sodium Hydroxide.
* Record the initial burette reading in a results table.
* Set up the burette and the conical flask in the corresponding places for the titration.
* Make sure there are no bubbles in the burette before using it.
* Slowly and carefully run Sodium Hydroxide solution from the burette into the conical flask with swirling.
* Do this until the solution changes from colourless to light pink. This is the end-point.
* Record your final burette reading also to the nearest 0.05 cm³.
* Repeat this procedure until 2 concordant results are obtained making sure you rinses the conical flask between every titration.
Accuracy
All burette readings must be recorded to the nearest 0.05 cm³ (1 drop). Consecutive titrations should be concordant. This means that they are either identical or within 0.10 cm³ of each other. The titration must be repeated until this is achieved. Burette readings must be recorded to 2 decimal places. Results table for a titration: Burette Rough 1st Accurate 2nd Accurate Final (cm³) Initial (cm³) Titre (cm³) Titre: final burette reading - initial burette reading
We know that NaOH is in a one to one reaction with the Ethanoic acid:
NaOH + CH3COOH › CH3COONa + H2O
Safety
For safety, these rules should be followed: Wear safety goggles at all times. Make sure there is good ventilation as some solutions have strong smells. Sodium Hydroxide is corrosive and Hydrochloric Acid is irritants so wash your hands thoroughly if there is any contact with the chemicals.
* Thermometers contain mercury which is poisonous so be careful not to break it.
* Handle all glassware with ...
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We know that NaOH is in a one to one reaction with the Ethanoic acid:
NaOH + CH3COOH › CH3COONa + H2O
Safety
For safety, these rules should be followed: Wear safety goggles at all times. Make sure there is good ventilation as some solutions have strong smells. Sodium Hydroxide is corrosive and Hydrochloric Acid is irritants so wash your hands thoroughly if there is any contact with the chemicals.
* Thermometers contain mercury which is poisonous so be careful not to break it.
* Handle all glassware with care as they may be hot after a reaction takes place.
Risk Assessment
Sodium Hydroxide in its pure form is very corrosive and can cause severe burns. In its diluted form it is less harmful, but still an irritant. It can also cause severe permanent eye damage.
Pipette - always hold the pipette vertically close to the open end and not the tip.
If broken, do not touch, use parker and brush to pack into the broken glass container. If stabbed, seek medical advice.
Glass ware
If broken, do not touch, use parker and brush to pack into the broken glass container. If stabbed, rinse under running water and plaster. Seek medical advice.
Fair Test
To make sure that the test is fair I will measure the amounts of each liquid very carefully. Each time I start a new test, I will have washed and dried the beaker out as not to leave any of the liquids from the last experiment in. Instead of measuring the amount from a certain temperature, I will take the start temperature and then one at the end. The difference will then be taken. I will use a different measuring cylinder for each liquid, and the water will be taken from the tap. The Hydrochloric acid and the Sodium Hydroxide will be taken from a bottle. This should give time for the different liquids to mix together and hopefully neutralise. There are many things in the experiment that could be considered not fair but that is why we are doing the experiment, to see how the different amounts of each liquid react. In each of the experiments the total amount of liquid in the mixtures will be 100ml. One of the experiments does not contain water, but otherwise, the lowest amount in any one is 24.1ml and the highest 24.1ml. Having 50ml of liquid in each mixture will keep the experiment fair.
The test would be preformed again until it is accurate and so making this experiment a very fair test. I think that these are important factors because it can be detrimental to how accurate and reliable the results were on the whole and it could leave me with anomalous results that have no reason behind their appearance.
The amount of alkali should be used to neutralise vinegar that has not been diluted. However, we can see that for some of the other vinegar, the amount of alkali is less, which shows that it has been diluted. Having obtained the rough titre from this experiment we can be more accurate.
I will keep the alkali I use the same by always using Sodium Hydroxide, NaOH. I will keep the concentration of NaOH the same by ensuring I use a 1M solution each time. I will always keep the acid the same by always using Ethanoic acid, CH3COOH. Although the concentration will vary, the amount will always stay the same.
Results
Burette readings for the Vinegar solution
Rough titration
Run 2
Run 3
Run 4
Run 5
Run 6
Run 7
Burette readings at the end/cm³
24.00
24.20
24.00
24.10
24.00
25.00
25.10
Burette readings at the start/cm³
0.00 cm³
0.00cm³
0.00 cm³
0.00cm³
0.00cm³
.00cm³
.00cm³
Volume/cm³ of diluted vinegar added to 25.00cm³ of sodium hydroxide solution
24.00
24.20
24.00
24.10
24.00
25.00
25.10
Prediction
I predict that if any of the solutions have been diluted, the amount of alkali needed to neutralise them will be less. If they have not been diluted the amount of alkali used will be the same as for the first solution.
Conclusion / Evaluation
To ensure my experiment was a fair I had to cover a few things. I made sure the factors which needed to be constant were constant such as the volume of vinegar was measured accurately, the amount of indicator was added drop by drop, the concentration of sodium hydroxide was all ready supplied, I made sure any human errors such as not switching the tap off in time was switched of to the best of my ability and if the tap was not switched off and it overdosed the vinegar.
During my experiment I used a number of techniques to try and ensure the results I obtained were as reliable and accurate as possible. Despite this it is very likely that qualitative and quantitative errors have had an effect on the accuracy of my results.
Quantitative Errors are due to the limitations of the equipment that I have used, and therefore if I know the accuracy of my equipment I can work out the maximum percentage effect quantitative error could have had on my results. To do this I will measure the maximum percentage error of each piece of equipment and add them together to form a total maximum percentage error. Since I performed two different techniques I will need a maximum percentage error for each one.
Qualitative errors also may well have had an effect on the accuracy of my results; however they cannot be calculated so I cannot be sure how much of an effect they would have had. There are many possible qualitative errors that may have occurred. Firstly during my distillation of Ethanoic acid it is very likely that, as it was dangerous to evaporate to dryness some of the Ethanoic acid was left in the round-bottomed flask. Also some may well have been left behind in the condenser or evaporated for example when a conical flask was left uncovered. All these would of lead to lower values for the concentrations of Ethanoic acid being obtained.
During other procedures qualitative errors could have affected my results. For example whilst performing my titration it was difficult to get the end point of my titration exactly right especially as the vinegars were coloured, and so occasionally more NaOH may have been added then was necessary. Also as I read the levels of the NaOH from the meniscus lines on the burette with my eyes these readings could be affected by human error and therefore may well be inaccurate. As well as this in experiments acid is generally added from the burette, so there could have been acidic impurities left in it that could have neutralised some of the NaOH and decreased its concentration. This also could have occurred for any other glassware used in my experiment especially my round bottomed flask which I didn't change between experiments, and so ethanoic acid could have remained in it from previous distillations.
Naz Mariwan
Science Coursework - Unit 1