Which fruit juice (Orange, Apple, Peach, Pineapple, and Apricot) has the highest concentration of ascorbic acid?

RAW RESULTS:

Volume of DCPIP used to neutralize each juice:

TABLE ANALYSIS:

The table above shows the amount of DCPIP used to neutralize the juices. According to the chart, pineapple juice required most DCPIP to neutralize and apple juice needed the least amount of DCPIP to neutralize.

In order to find the concentration of ascorbic acid in each juice, we use the neutralizing reaction below;

ACID + BASE  SALT + WATER

In this case, acid is fruit juice and base is DCPIP. When acid and base react, the reactants are salt and water. The reaction in this experiment was 1:1. Therefore, to calculate the concentration of ascorbic acid in the juices, I use the formula below:

.

Calculated concentration of Ascorbic Acid (mol

):

The table above shows the concentration of ascorbic acid of each fruit juice calculated from the volume of DCPIP, concentration of DCPIP and volume of ascorbic acid. It can be seen that they all have different concentrations of ascorbic acid however, they are very close to each other.

An example of the procedure of calculating the concentration of ascorbic acid is below:

Recorded values Apple Juice and DCPIP:

Concentration of Ascorbic Acid =

TRIAL 1

Concentration of Ascorbic Acid =

 = 0.027 ±1.19% mol

TRIAL 2

Concentration of Ascorbic Acid =

 = 0.02 ±1.44% mol

TRIAL 3

Concentration of Ascorbic Acid =

 = 0.02 ±1.44% mol

Average: 

 = 0.029±4.07% mol

The example calculations above show how the concentration of ascorbic acid of a juice can be found. Uncertainties should be taken into consideration because of the meniscus; we may not see 0.05 mL of difference.

CONCLUSION:

The task of this experiment was to find the concentration of ascorbic acid in different fruit juices by using an indicator called DCPIP in a titration reaction. Adding DCPIP (base) to juice (acid) made the fruit juice change color. By looking at the volume of DCPIP used to change the color (neutralize) the acid, the concentration of ascorbic acid in 5 different types of fruit juices. The results show that the acid contents were quite similar to each other’s but still had differences.

According to my calculations, orange juice had the highest concentration of ascorbic acid (0.146 mol

) and peach juice had the lowest concentration of ascorbic acid (0.027 mol

). In between, pineapple juice had the highest concentration of ascorbic acid after orange juice (0.052 mol

apple juice was next (0.029 mol

) and apricot juice (0.028 mol

 

The smaller the volume of fruit juice needed to decolorize DCPIP solution, the higher is the ascorbic acid/vitamin C content in the fruit juice. Therefore. orange juice has the highest concentration of ascorbic acid/vitamin C content.

Evaluation:

Limitations:

This experiment was not done in a professional laboratory therefore there has been some limitations. First of all, the juices were kept in an open place therefore the concentration of ascorbic acid might have been oxidized in the air and therefore I might have recorded lower results as it should’ve been.  Secondly, when fruit juice is dropped into test tube containing DCPIP solution, a suspension formed and its color slowly changes to black. The presence of the suspension in DCPIP solution makes it harder to determine whether DCPIP solution has been completely decolorizes. Another limitation would be that we considered there would only be ascorbic acid in the juices however, there might be other chemicals or different types of acid that has contributed to the neutralization process as well.

Improvements:

Since we did not work at a professional lab, there was no way to avoid oxidation of the ascorbic acid to the air. The only way to avoid that would working a little bit faster so there is less oxidation. In addition, using a colorimeter might help to determine completely colorization. This would help me by having results that are more accurate.