Since the number of fruit juice required decolorizing the blue CDPIP solution in decreased in the order: Red pepper >kiwifruit >lemon >orange. Therefore, Red pepper contain the largest concentration of vitamin C, the second is kiwifruit , the third one is lemon and the lest one which contain the least concentration of vitamin C is orange.
The reason for diluted the fruit juice is because the fruit juice are colored by the pigment in the fruit juice. It caused difficulty to observe the decolourization of the DCPIP solution. The diluted fruit juice could dilute the concentration of the fruit juice. It used to observe the accurate amount of vitamin C in different fruit juice clearly.
The limitation of the experiment is about the freshness of the fruit may different, it would affect the concentration of vitamin C in the fruit. Due to the different prolonged storage and the long shipping process would decrease the concentration of vitamin C in the fruit.
The first improvement to reduce the error in the experiment is to shark the DCPIP solution gently when dropping the diluted fruit juice drop by drop. After every drop of the diluted fruit juice, shark the DCPIP solution gently. it could observe the color change of the DCPIP solution more accurately.
Since orange contain the least concentration of vitamin C , it is not the richest sources of vitamin C. Therefore, “orange contain the richest sources of vitamin C” is the wrong common concept held by many people.