The Effect of Temperature on the Vitamin C Content of Lemon Juice

Conclusion and Evaluation

Conclusion

In my experiment I investigated the effect of changing temperature on the Vitamin C content of lemon juice by looking at the number of drops of lemon juice required to turn DCPIP colourless. The number of drops of lemon juice required to turn the DCPIP colourless indicates Vitamin C content as vitamin C is a reducing agent. DCPIP is blue in its oxidised form¹, so with the addition of vitamin C (or in this case lemon juice which contains Vitamin C) the DCPIP is reduced, forming a colourless substance. Therefore the higher the concentration of vitamin C, a smaller volume of vitamin C is needed to decolourise the DCPIP solution. 

From my results I can infer that changing the temperature had a significant effect on the Vitamin C content of the lemon juice. There was a positive trend between the variables showing that as temperature of the lemon juice increased the number of number of drops of lemon juice required to turn DCPIP colourless increased. This shows that as the temperature of the lemon juice increased its vitamin C content decreased, as more lemon juice is needed to be added to the DCPIP to cause it to decolourise. The mean amount of lemon juice drops required to turn the DCPIP colourless at 20°C was 2.8, while at 60°C it was 16,  this shows a marked increase in the number of drops of lemon juice required to turn the DCPIP colourless indicating a large decrease in the vitamin C content of lemon juice as the temperature increases.

Ascorbic acid, or Vitamin C, is a naturally occurring compound, its structure is illustrated in the diagram on the left. At high temperatures ascorbic acid is broken down by higher temperatures, by affecting the carbon molecules. Heat breaks down the carbon atom bonds, when these then break up they reduce the stability of the molecular chains². This causes the ascorbic acid to lose its reducing agent ability so it can no longer successfully reduce the DCPIP solution.

My data has a reasonably small systematic error meaning that my results were mostly accurate. We managed to do five trials which meant that my results were quite reliable, and the relatively small error bars mean that my recorded values were close to the mean and therefore precise. I had one major outlier during the fourth 60°C which only required 10 drops of lemon juice while the result from the other trials was between 16-20 drops. This result would have greatly lowered my mean, if I ignore the value from the fourth trial the mean for 60°C increases to 17.5 instead of 16 so my results are not as accurate. The consistency of my other results means I can assume that this outlier was due to systematic errors. My results are reflected by these other experiments such as the one a found online which directly measured the concentration of vitamin C in different fruit juices at varying temperatures. Their results are shown in the table below.

The findings were very similar to my own, as the temperature increases the vitamin C content also decreases. “It can be seen from analytical results that the lower the temperature the better the concentration of Vitamin C in fruit juice.”³ Therefore I can conclude that my findings and my explanation is correct as it is confirmed by an outside source.  

Evaluation:

Sources

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