Planning and Designing Chemistry Lab – To determine whether green limes have a higher level of acidity than yellow limes using titration
Ms. Lawrence wanted to know if her green limes, had a higher level of acidity than the yellow limes.
Yellow limes have a higher level of acidity than green limes.
To determine whether green limes have a higher level of acidity than yellow limes using titration
Apparatus and Materials
Sodium hydroxide solution (0.1mol dm3), burette, burette stand conical flask, beaker, pipette filler, filter funnel, pipette, phenolphthalein indicator, yellow and green limes.
- In a beaker squeeze 10 yellow limes, and in another beaker squeeze the green limes.
- Use a pipette to transfer 10cm3 of yellow lime solution to a conical flask
- Add 2 drops of phenolphthalein to the flask
- Set up burette on stand appropriately.
- Use the funnel to fill the burette with sodium hydroxide (NaOH)
- Perform the titration and record all readings
- Repeat procedure for a total of three readings
- Record all readings and tabulate results
- Repeat steps 2-8 with the green limes
- Controlled: The volume of lime juice and the amount of indicator used.
- Manipulated: the types of limes
- Responding: pH reading
Treatment of results
If the lime juice from yellow limes gave the lower pH reading, then the lime juice of yellow limes is more acidic and the hypothesis is correct
Interpretation of results:
Lime juice contains citric acid which is a weak acid and thus contains free hydrogen ions when dissolved in water. A higher level of acidity means a higher concentration of hydrogen ions present in the aqueous solution.
pH is related to hydrogen ion concentration via the formula pH = -log[H+]
This means the higher the hydrogen ion concentration, the lower the pH value
Sources of errors / Assumptions / Limitations:
Passing the end point thus using too much of the carbonate, thus altering the results.
there are no other substances besides citric acid present that would affect the acidity of the lime.