- The temperature of a substance affects the rate at which it reacts with another. This is because the molecules have more kinetic energy making them react faster. Therefore each test-tube of orange juice must be cooled to the same temperature (probably room temperature) before they are tested for their ascorbic acid content, otherwise the results will be inaccurate.
- Using the same carton of orange juice should ensure that the Molar strength of each test solution is the same.
- If a stopwatch is used instead of a standard watch to time the 1 – 5 minutes in which the solutions are exposed to the water bath the results may be slightly more accurate.
- Use the same DCPIP each time.
- Use same water bath, to ensure temperature is the same each time.
My prediction is that the longer the Orange juice is heated for, at a set temperature the more Vitamin C/ Ascorbic Acid will be destroyed. Therefore the longer it is heated for, the more Orange juice there will have to be put into the DCPIP to turn it colourless.
- 1 water bath (set at 80°C)
- 1 glass pipette
- 1 pipette filler
- 5 x’s 2 mls of DCPIP
- 5 x’s 10 mls of Orange Juice
- 10 test-tubes
- 2 test-tube racks
- 1 stopwatch
- 1 thermometer
- Assemble equipment as shown in diagram.
- Measure orange solutions and DCPIP with glass pipette and pipette filler. (See equipment list for measurements).
- Pour 10mls of Orange juice in to five of the test tubes. Place them in one of the test tube racks.
- Pour 2mls of DCPIP into five of the test tubes and place them in a second test-tube rack.
- Place the five test tubes containing the source of Vitamin C into the water bath (set at 80°) and start the stopwatch.
- Remove one of the test tubes after 1 minute, another after 2, 3, 4 and 5.
- Label the solutions 1 – 5 (1 being one minute and 5 being five minutes.)
- Leave the orange solutions to cool down to room temperature.
- Fill the glass pipette up with solution one by using the pipette filler.
- Slowly add the orange juice to one of the test tubes containing DCPIP until it goes colourless.
- Record the volume of orange juice added in millilitres.
- Repeat this method 2 more times. Using the same equipment for multiple results.
The results in table 2 show that as the heating time is increased the more Orange Juice has to be added to the DCPIP to make it go colourless.
Graph to show the amounts of Orange Juice (heated at 80°C for 1 – 5 minutes) added to 2mls of DCPIP to turn it colourless.
Graph to show the average amounts of Orange Juice (heated at 80°C for 1 – 5 minutes) added to 2mls of DCPIP to turn it colourless. (Excluding results 2 and anomalies)
Orange = Anomalous result
Red = Anomalous set of results
Blue = Results to be used for averages
My conclusion is that firstly I was correct in my prediction that the longer the orange juice is heated for, the more Vitamin C is destroyed and therefore the more orange has to be added to the DCPIP to turn it colourless.
I had some anomalous results, set 2 was totally different to set 1 and 3 and some points didn’t fit the smooth curves. These anomalies can be explained in many ways:
If the investigation were carried out again I would take more than three sets of results because this would give me a more accurate average. I would make sure I used Orange juice from the same carton each time and that my DCPIP was not contaminated with any orange juice used by previous individuals. I would ensure that the solutions cooled down to the exact same temperature and that the volumes used of DCPIP and Orange Juice were recorded and measured accurately.
Concentrations of Ascorbic Acid
The results that I gained showed me how much Orange juice after being heated for 1-5 minutes was needed to turn 2mls of DCPIP colourless. However they didn’t tell me the concentration of the Ascorbic Acid content left after the heating process. If we refer to Graph 3 the concentration content in each solution can be gained.
To gain the concentration of a solution after being heated, multiply the amount of Orange juice added to the DCPIP to turn it colour less by 100. This has to be don e because the line of the graph does not continue as far down as e.g. 0.38.
Next read off 38 on the y-axis and follow along the x until you reach the line. Continue downwards along the y-axis and read off the value of the x.
Divide the value of x by 100 and this will give you the concentration of the Ascorbic Acid content in 1/1000M.
Divide the result by 1000 and this will give the concentration in Molar units.