Biology Core Practical 2

Biology Core Practical: How much Vitamin C does fruit juice contain? Purpose: The purpose of my experiment is to investigate the exact amount of Vitamin C content in fruit juice. In order to do this I will use liquids that contain Vitamin C, fruit juice, which is a strong reducing agent and use it to decolorize the dark blue DCPIP dye. Hypothesis: My Hypothesis is that the citrus fruit drinks such as orange or lemon will contain more Vitamin C than non citrus fruit drinks such as apple or blackcurrant. Null Hypothesis: My null hypothesis is that the citrus and non citrus fruit drinks both have the same amount of Vitamin C within each drink. What will I be measuring? I will be measuring the amount of fruit juice required to decolourise the DCPIP solution in cm3. I will also be working out the average of juice required to decolourise, and the Vitamin C content of the juice. Apparatus: During the experiment I will be using an array of items, these include: • • • • •

A range of fruit juices which is essential to the experiment as I need to measure the vitamin c content in each type of juice. Standard 1% vitamin c solution which I will be using as a baseline to compare with the Vitamin C content of each type of fruit juice. Measuring Pipette and burette which is essential in accurately measuring the fruit juice and the DCPIP solution. Standard Laboratory glassware and apparatus which is needed in order to have a place to contain the liquids used in the experiment. DCPIP which is a dark blue dye used to be decolorized by the vitamin c in order to measure the content of Vitamin C in the juice.

Independent Variable: The Independent variable in my experiment will have to be the different types of fruit juices that I will be testing in order to see if the fruit juice contains the amount of Vitamin C that it states to have in the label. Dependent Variable: The dependent variable in my experiment will have to be the amount of fruit juice needed to decolourize the DCPIP solution which will be different for each type of fruit juice. Control Variable: The control variable for this experiment will have to be the amount DCPIP that I use for each type of fruit juice as they need to be kept the same in order for the results to be more accurate and valid. Another control variable will have to be the colour of the fruit juice for example blackcurrant juice will be difficult as the colour of the juice is as dark as the colour of the DCPIP solution so noticing any changes will be difficult. Risk Assessment Hazard The DCPIP Solution staining skin or getting into peoples eyes.

Risk (1-5) 1 – Lowest, 5 – Highest 3

Glassware breaking.

2

Vitamin C or Fruit juices getting into peoples eyes.

3

Prevention Taken By wearing an Apron and goggles it will prevent the solution getting into peoples clothes or eyes. Carefully handle the equipment By wearing an Apron and goggles it will prevent the solution getting into peoples clothes or eyes.

Emergency Action/Control If the DCPIP stains your skin quickly wash it in cold water.

If the glassware breaks carefully put all of the pieces into the bin. If juice gets into your eyes quickly alert the teacher and they will tell you what to do next.

Method: 1. Use a 1 ml pipette and a pipette filler to prepare a test tube with 1 ml of blue DCPIP solution. Prepare a few in a batch. 2. Fill a 5 ml measuring pipette with the standard Vitamin C solution.

3. Slowly and gently add the Vitamin C solution into the DCPIP test tube drop by drop. Hold the dropper vertically. Make sure that the drop size is constant in order to make the results more accurate. 4. After adding one drop, do not shake the contents. 5. Stop dropping when the blue colour disappears. 6. The end result is taken when the dark blue solution suddenly becomes colourless. 7. Record the number of drops of Vitamin C solution in cm3 required to decolourise the DCPIP solution. 8. Repeat the experiment 3 times for each fruit juice. 9. Enter the results into an appropriate table 10. Repeat the experiment for other fruit juices. 11. Rinse the dropper/syringe with water and then a new fruit juice to reduce contamination and ensure accuracy.

Results: Juice tested

Volume of juice required to decolourise 1 cm3 of 0.1% DCPIP solution/cm3

Average of juice required /cm3

Vitamin C content of juice/mg cm–3

1% of Vitamin C

1ml

1ml

1ml

1ml

10mg

Apple Juice

4ml

2ml

3ml

3ml

1.14mg

Orange Juice

3ml

3ml

2ml

2.66ml

1.01mg

Volume of Juice required to decolourise 1cm3 of 0.01% DCPIP solution/cm3 4.5

Amount of Liquid (ml)

4 3.5 3 1% of Vitamin C

2.5

Apple Juice

2

Orange Juice

1.5 1 0.5 0 1

2 Experiments

3

Discussion: When reading my results my hypothesis of citrus based fruit drinks containing more vitamin c than non citrus based fruit drinks is inconclusive because although the apple juice that I have tested contained slightly more vitamin c than the orange juice it might be just that one particular brand of juice. The results maybe different for each brand of juice and also the freshly squeezed juices might have more Vitamin C than factory produced juice which have added additives in it. However by looking at my results you can see that I was wrong in hypothesis with the juices that I have used because the non citrus juice, apple, contained more Vitamin C than the citrus based fruit juice orange. I used a 1% concentration of Vitamin C in order for it to be a baseline on how much Vitamin C fruit juices are supposed to have, as you can see 1ml of the concentration contains more Vitamin C than 3ml of the apple juice that I used for the experiment. This may raise some question on the advertising used or the claims that the company makes about their fruit juice containing a lot of Vitamin C. Reliability and Validity: With every experiment even when special measure is taken there will always be a chance that the data recorded is anomalous and that is why whenever we got an anomalous result we decided to repeat the procedure. However people should take care to only note down accurate, reliable and valid data in order for the results to make sense. This is why we repeated the experiment two more time for each fruit juice to ensure that the data recorded was accurate, reliable and valid. We also made sure that there was only one independent variable in order to minimise confusion and to make sure that our results became more valid. The apparatus was washed with each use in order to minimise the chances of contamination and to make sure that our results were accurate, reliable and valid. By using measuring pipettes and measuring beakers we ensured that our results were accurate and valid. Errors: Like reliability and validity all experiments have a chance of encountering errors it is up to the group to ensure that this chance is as small as possible. Systematic errors have occurred during the experiment for example we may have measured the DCPIP solution inaccurately in order to fix this we made sure that our measuring pipette was accurate by making sure that it measured in millilitres. We also made sure that our measuring beakers where measuring the correct volume. We eliminated the inconsistency of results by using the same measuring droppers, beakers and other measuring equipment. However random errors may have occurred in our experiment but we tackled this problem by having everyone in the group become focused and careful this minimise the amount of errors that will happen within the experiment.

References: Salters-Nuffield Advanced Biology, Pearson Education Ltd 2008. © University of York Science Education Group. Activity 1.21