pH Levels in Different Citrus Fruits
Aim: To determine which citrus fruit has the highest acidity.
Hypothesis: When the pH levels in the citrus fruits are tested, the lime will have the highest acidity.
Equipment & Materials:
Variables:
Dependent Variable:
Independent Variable:
Controlled Variables:
Method:
Risk Assessment:
Hypothesis: When the pH levels in the citrus fruits are tested, the lime will have the highest acidity.
Equipment & Materials:
- Newly-picked ripe orange
- Newly-picked ripe lime
- Newly-picked ripe grapefruit
- Knife
- 3 small bowls (labelled 'Orange', 'Lime' and 'Grapefruit')
- Dropper
- Chopping board
- 9 pH test strips
- pH scale
Variables:
Dependent Variable:
- The pH levels of the citrus fruits(orange, lime and grapefruit)
Independent Variable:
- Different citrus fruits(orange, lime and grapefruit)
Controlled Variables:
- pH Test Strips from the same packet
- Age of citrus fruits
- Juice from the same fruit
Method:
- Place orange on chopping board and slice in half with knife. Squeeze a portion of juice into relevant bowl.
- Wash knife.
- Repeat step 1 and 2 for the lime and grapefruit.
- Lay out 3 pH Test Strips, one in front of each bowl.
- Squeeze the rubber top of dropper and dip the tip into the orange juice. Release and wait for dropper to fill.
- Carefully dispense a few drops of orange juice onto the pH test strip in front of the bowl.
- Squeeze leftover orange juice into the sink and clean dropper.
- Repeat steps 5 to 7 for the lime and grapefruit juice.
- Observe and note the colour in each of the pH test strips. Match the colours to the pH scale to determine the acidity level for each citrus fruit and record results.
- Repeat steps 4 to 9 twice to ensure accuracy of results.
Risk Assessment:
Potential Risk Measure to reduce risk
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Diagram
Results
In the first attempt, the orange’s pH was 5, the lime was 2 and the grapefruit was 5. For both later attempts, the results were the same.
Discussion
Reliability
The results are accurate, as the experiment was conducted with the variables kept in mind; the pH levels of the citrus fruits as the dependent variable, different citrus fruits as the independent variable as well as making sure the experiment was a controlled one- using pH Test Strips from the same packet and newly-picked ripe citrus fruits, thus proving their reliability.
Validity
The results of the experiment are valid, proven through repetition of the experiment to ensure accuracy of results and the use of newly-picked ripe citrus fruits as age of fruits affects their acid levels. As each repetition of the experiment produces more replications of the results, comparison between the replications determines the validity of the results.
Limitations/Errors
The limitations/errors of the experiment include:
- Human error: During cleaning the dropper, water may have been accidentally left in the dropper, and thus when squeezing the dropper again to obtain juice, water may have been deposited into the bowl
- External influences: When drying, the pH strips may have picked up excess juice that was not cleaned up or the experimenter’s hand may have accidentally touched the strips whilst having wet juice from handling the dropper
- Instrumental limitations: The pH test strips used have a pH range of 1-14. The test strips have low sensitivity as they don’t change colour sharply at one particular level, as seen with the grapefruit’s results and the orange’s results, making it difficult to determine which fruit has the higher acidity, even though researched data states that they are almost 1 pH level apart. The accuracy of the observed results is therefore limited
Successes
The experiment succeeded by centring it around the dependent variable, the independent variable and the controlled variables. This ensured the experimenter knew what to observe, what to deliberately change in the experiment and what to keep the same to make the experiment fair and consistent -which meant that the results would be accurate.
Improvements
Improvements that could be made to the experiment include:
- Using bigger bowls rather than small bowls; this will help prevent the fruit leaking juice onto the table when squeezed
- Laying out cling wrap underneath the test strips before dispensing juice; this will make cleaning up the excess juice from the strips easier for the next repeat
- Instead of laying out the test strips in front of the bowls and using a dropper to dispense juice onto them, the pH test strips should be dipped into the bowls as this will prevent the strips from picking up any excess juice that may have not been cleaned up properly from the previous attempt of the experiment and is a more convenient method than using a dropper
Conclusion
Although the experiment determined that the lime contained the highest acidity -proving the hypothesis to be correct-, it was not possible to determine from the results collected if the grapefruit or the orange has the higher acidity. pH test strips with a higher sensitivity and a narrower pH range of colour change are therefore required to determine whether the grapefruit or the orange has the higher acidity.