Benzoic Acid Synthesis Lab Report

Unit 4 Assessment 2-Benzoic Acid Synthesis
Synthesis and Investigation of Benzoic Acid
Our aims:
Create benzoic acid using benzaldehyde and hydrogen peroxide.
Then remove some impurities from the benzoic acid crystals.
Apparatus:
Titration
Pipette (25 cm3)
Burette (50 cm3)
Retort stand
Clamp
Conical flask (250 cm3)
Volumetric flask (250 cm3) and stopper
White tile
Beakers (250 cm3)
Dropping pipette
Filter funnel
Deionised water
Phenolphthalein indicator
Volumetric flask
Melting point experiment apparatus
Melting point apparatus
Capillaries
Thermometer
Bunsen burner
Recrystallization
Filter paper
Buchner funnel
Conical flask
Specular
Benzaldehyde + hydrogen peroxide
Heat mat
Beaker
Conical flask
Indicator
Oven
Litmus paper
TLC Experiment apparatus
Plate
UV lamp
Beaker
Pipette
Scissors
Watch glass

Method:

To start the experiment we added hydrogen peroxide (H2O2) to benzaldehyde (C7H6O) in a 1:1 ratio to form benzoic acid (C7H6OOH). We did this by heating the solution on a heat mantle and stirring with a thermometer, when the solution went clear and cool we added concentrated hydrochloric acid to it until the blue litmus paper went red.
When the benzoic acid is solidifies, we filtered it off using a Buchner funnel and leave it to dry in the oven over night. The day after benzoic acid crystals are placed into a container, after this we took the melting point of three samples of the crude benzoic acid crystals. We then took the melting point of the crystals by using a melting point apparatus, we then found the average temperature for the crude crystals.
When the crystals dried we roughly took 1.00g of the product and water to the crystals. We then heated the mixture using a heat mat, after it had cooled and cleared we filtered the solution again using a Buchner funnel, and then we left it in the oven overnight again to dry the crystals again.
The following day we took the purified crystals to check for the melting point using a melting point apparatus, we took 3 results to find an average melting point, we then wanted to check for the purity of the crystals so we out a small amount a side for a titration.
First of all we started with a balanced equation for the reaction, followed by placing the purified crystals into a volumetric flask and then dissolving them in sodium hydroxide (NaOH) we placed a few drops of indicator into the sodium hydroxide and filled a burette with benzoic acid, we started the titration and recorded the results from the experiment to work out the crystals purity. We then repeated the experiment two more times to find the mean average titre.
Results:
Crude Benzoic Acid
Crystals Mass
Empty Vial
21.655g

Vial with Crystals
23.053g

Crystal’s weighs
1.398g

Melting Point
First Melting Point
119 oC

Second Melting Point
119 oC

Third Melting Point
119 oC

Average Melting Point
119 oC

Yield Percentage = (Actual Yield/Theoretical Yield) x 100
Yield Percentage = (0.76g/3.053g) x 100
Yield Percentage = 24.89%

Pure Benzoic Acid
Crystals Mass
Empty Vial
21.535g

Vial with Crystals
22.353g

Crystal’s weighs
0.818g

Melting Point
First Melting Point
121 oC

Second Melting Point
120 oC

Third Melting Point
121 oC

Average Melting Point
121 oC

Recovery = (Mass of Purified benzoic/Mass of Crude Benzoic) x 100
Recovery = (0.818/1) x 100
Recovery = 81.8%

When comparing the average melting point of crude benzoic acid and pure benzoic acid, it is clear that the pure benzoic has a higher melting point. This increase in the melting point for the benzoic acid is most likely the result of the successful recrystallization, this process removed some impurities from the crude benzoic acid, therefore increase the acids melting point (impurities decrease the melting point). However the pure benzoic acid still contained some impurities as the melting points was not 123oC (benzoic acid actual melting point).
TLC
When doing the Thin Layer Chromatography experiment we took a picture at the end of the experiment showing the results, the images shows two dots; one located in the middle of the bottom white line, the other is located in the middle of the plate. This dot located nearest to the bottom line shows that the solvent contains impurities, whilst the dot in the located in the centre of the plate is the benzoic acid.

Titration
Results
Titre 1
11.4cm3
Titre 2
11.4cm3
Titre 3
12.0cm3
Titre 4
12.0cm3

Average Titre
11.7cm3

Benzoic acid + Sodium hydroxide Sodium benzoate + Water
C6H5COOH + NaOH  C6H5COONa + H2O 1 : 1
I used 11.7cm3 of 0.02M (NaOH)
Converted into moles (0.02/1000 x 11.7) = 2.34x10-4 moles
Since the ratio between benzoic acid and sodium hydroxide is a one to one.
The number of moles C6H5COOH is 2.34x10-4 moles.
2.34x10-4 was used in 10cm3
Concentration = (2.34x10-4/10) x 1000 = 0.0234
Purity = (0.0234/0.025) x 100 = 93.6%

The titration results showed that the titration were accurate and somewhat concordant. With the results from the titration we could work out the concentration, and then use the concentration value to work out the purity of the benzoic acid. The benzoic acid purity came out at 93.6%, a high value for the purity showing that the recrystallization was very effective in removing impurities.

Conclusion:
When doing this experiment I made a batch of crude benzoic acid, this batch was meant to be used for a titration, recrystallization, six melting points and a TLC experiment. When I started the experiment I believed that I would have enough crystals to complete all experiment with some crystals left over, however once the titration came about I realised that I did not have enough benzoic acid, therefore instead of using a 250cm3 volumetric flask I had to use a 100cm3 flask
instead.
The yield percentage was 24.89 % showing that a fourth of the product was lost in the creation of the pure benzoic acid, this product was most likely lost due to various conditions that could not have be altered; such as the amount of crystals that couldn 't be collected from the filter paper in the recrystallization experiment.
The purity of the crystals was 93.6%, a very high value for the purity of benzoic. This high purity value would explain for the high melting points found from the pure benzoic acid, as the melting point was 121oC, only 2oC off the correct value of 123oC. However I believe that if I had recrystallization more than once, I would have achieved a higher purity, but I would also have received a lower yield percentage.

M2)
When making the product there were factors that affected the purity of the crystals, these factors would have most likely increased the purity of the crystals.
Using a 99.9% purity solvent.
Recrystallization more than once would have increased the purities of the product by removing impurities.
Cooling the crystals within the recrystallization process slower, as to allow more crystals to form.

M3)
The burette measures volume of liquids accurately, it is designed for titration work, also gives accurate results with small % error.
TLC plates are used to separate mixtures into their components, TLC plates are suitable for use with simple mixtures this makes them fine for our purpose.
Melting point apparatus measures melting points in °C, this is well suited for our task if used with care, designed for our purpose.

D2) D3)
Error Calculations

Burette Titre
±0.1cm3

Pipette
25cm3 ±0.06cm3

Volumetric Flask
100cm3 ±0.4cm

Balance
±0.0005g

Total Error

0.5605%
The thermometer had a 200 0C scale. Therefore for the error calculation the minimal reading of the thermometer was taken 10C, it was then halved as to find the smallest value. The smallest value that can be measured on the thermometer value (0.5 oC) is then divide by the average melting point, and then timed by a hundred.
Hence 10C /2 = 0.50C
Error % (0.5/119) x 100 =± 0.4201680672268908 =±0.4201 (3 s.p)

Although the TLC had many benefits towards it, the accuracy of it isn 't exactly great compared to doing a titration, which is more accurate. The TLC is used because it is a lot quicker and a lot cheaper than doing a titration, both procedures have their benefits but one will give you the more accurate readings, for example you can do a titration and repeat it to get calculate and average, you can 't exactly do this with TLC due to the fact that you may place the starting sample in different areas which would result in inaccurate results, which is why the titration will give you the more accurate results. As well as getting an average you can compare it to other peoples results which with the TLC you can 't do. The Thin layer chromatography is started by placing a dot of sample on a specific area of the users choosing, but if other people look at it after the procedure they may have a different perception of where the dot is. TCL is accurate, it is a simple and quick and also inexpensive procedure. TLC is good enough for our purpose. you need to do the TLC experiment is a UV lamp, a solvent.

Bibliography
Jim Clark. (2007). THIN LAYER CHROMATOGRAPHY. Available: http://www.chemguide.co.uk/analysis/chromatography/thinlayer.html. Last accessed 1st Mar 2014.