Extended Essays 2021

Discussion: At the absorbance of 515nm, as expected, and hypothesised by application of Beers law, the

calibration curve in Figure #4 , showed a linear trend between light absorbance value (Au) and

the concentration of methyl salicylate (%) in the ferric chloride solutions. In reference to the

background research, due to ferric chloride’s characteristic reaction to phenols, the concentration

of methyl salicylate in a ferric chloride solution is directly proportional to the intensity of the

purple colour of the solution. Quantitatively, the absorbance value measured by the UV spectrophotometer also increases 17 . As the trend in Figure #4 produced data which supports this

theory, the ferric chloride calibration curve was then validified and able to be used to determine

the percentage concentration of methyl salicylate in the synthesized solutions.

Using the equation calculated from the standard calibration curve [ = 0.0317 + 0.7914] the

percent concentration of methyl salicylate in the synthesised solutions from varying reflux

duration were calculated ( example calculation #1 ) and recorded into table #4 . The data was then

graphed in Figure #5, which produced a linear relationship between the duration of reflux and

the percentage concentration of synthesised methyl salicylate. This trend is supported by the 2

value of the best fit line. As generated by graphical software, the data produces the near perfect

2 of 0.99 (out of 1), showing that the variance of the data points range extremely close to the

trendline and show high chance of the relationship continuing as the duration of reflux and

percentage concentration increase. The range of the percentage concentration increased from

21% for one hour, to 33% for five hours . This indicates that the esterification requires a much

greater duration of reflux to synthesize higher concentrations of methyl salicylate. Using the

trendline equation of Figure #5 [ = 4.040 + 14.838] , it can be theoretically determined that

for a synthesized solution of methyl salicylate to be 100% (under the same conditions as this

experiment), the duration of reflux must be 21 hours. This, however, would be unrealistic to

expect as it would be expected that approaching much higher concentrations would result in a

slowing of the rate due to reduced molecular collisions and at some point, an equilibrium would

be reached with the reverse reaction. However, we can still make the general assumption that

greater hours of reflux would be required to increase the yield of the product. Hence, in terms of

industrial processes, the results from this experiment can be used to understand that to better

balance cost and efficiency, a higher-powered reflux system (higher voltage) would be more

effective in producing methyl salicylate in a shorter time.

17 (Sajin Kattuvilakam Abbas, 2014)

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