Harry Pearce 9U
Titration of Lemonade
Aim: To compare the acidity levels of flat and fizzy lemonade
Hypothesis: The fizzy lemonade should be more acidic because it has more carbon dioxide in
it than the flat. This is because carbon dioxide reacts with water and turning it into carbonic acid.
Apparatus and Materials
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Flat lemonade
Fizzy lemonade
Phenolphthalein
NaOH
Beaker x 2
Measuring beaker
Safety goggles (safety)
Lab coat (safety)
Method:
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First put on your safety equipment
Assemble the materials as listed
Take two beakers and using measuring beaker add 5mL of flat lemonade to the first one and
5mL of fizzy lemonade to the second one
Then add two drops of Phenolphthalein to each beaker
Take the first beaker and add one drop at a time of NaOH recording the number of drops
added until the sample turns purple
It is important to record the exact number of drops to these are the results
Then repeat this process on second beaker
Independent variable:
The amount of gas in the lemonade
Dependent variable:
The amount of NaOH required causing a colour change
Controlled variables:
The volume of lemonade, the formula of the lemonade, and
the NaOH and its concentration.
Diagram:
When the purple colour shows the
experiment is finished.
Results:
Lemonade Samples
Test 1
Test 2
Amount of NaOH drops till
liquid turns purple
Amount of NaOH drops till
liquid turns purple
Fizzy
21
20
Flat
13
15
Discussion:
We tested the samples twice and the results were similar in both cases. The fizzy sample required 20
drops and 21 drops of NaOH to neutralize the acid. The flat lemonade sample only took 15 drops and
13 drops of NaOH solution in the replicate tests. The fizzy sample required 1½ times more NaOH
than the flat sample. The reason for the difference is because the fizzy sample is more acidic and
requires more NaOH solution to become neutral. Phenolphthalein is an indicator that changes
colour at pH 7 which is neutral indicating the change from acid to base. Carbonic acid is formed
when atmospheric CO2 is dissolved in water, and is present in the fizzy sample of lemonade.
The Chemical Reaction can be explained via the following:
1) Gas dissolution
2) Carbonic acid formation
3) Carbonic acid equilibrium
Evaluation:
The amount of data collected was a good and reliable and showed that there was more acid in fizzy
lemonade sample. This is because these samples needed more of the NaOH to be neutralized than
the flat sample. The reason why the fizzy lemonade sample is more acidic can be explained by the
presence of carbon dioxide mixing with the water and creating carbonic acid. The presence of gas
bubbles indicates that there is a reaction with the water and carbon dioxide. So the acid formation is
actively taking place. In the flat lemonade sample all the gas present as dissolved gas has been
released into the atmosphere.
Both samples show a base line of acidity which is due to the formulation of the lemonade sample
and likely to be citric acid from the lemon.
The strengths in our experimental design is that we repeated the experiment and that we used
brand of commercially available lemonade which is likely to have a constant formulation.
Other investigations that would expand this experiment further is by comparing different
lemonades or different soft drinks, like Coke and Coke Zero to see if the sugar difference changes
the acidic level. The temperature of the liquid could be experimented with and the age of the liquid.
Conclusion:
This experiment demonstrated the relative acidity levels between flat and fizzy lemonade samples.
In a repeated experiment comparing flat and fizzy lemonade samples it can be concluded that fizzy
lemonade is 1 ½ times more acidic than the flat lemonade samples.