The aim of the experiment is to check whether pH of the chosen fizzy drink is basic, neutral or acidic. To find the answer the titration method will be used. The chosen fizzy drink will be Sprite due to its transparency (it is easy to see when the color changes during the experiment).
Sprite will probably have acidic pH (smaller than 7) as one of ingredients is citric acid. However as it is drink used by people pH cannot be to small as it would be harmful to the human organism. As I checked pH of Sprite should oscillate somewhere around 2.75.
“A titration is a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration flask. A buret is used to deliver the second reactant to the flask and an indicator or pH Meter is used to detect the endpoint of the reaction.
A typical titration begins with a beaker or Erlenmeyer flask containing a precise volume of the reactant and a small amount of indicator, placed underneath a burette containing the reagent. By controlling the amount of reagent added to the reactant, it is possible to detect the point at which the indicator changes colour. As long as the indicator has been chosen correctly, this should also be the point where the reactant and reagent neutralise each other, and, by reading the scale on the burette, the volume of reagent can be measured.
As the concentration of the reagent is known, the number of moles of reagent can be calculated (since concentration = moles / volume). Then, from the chemical equation involving the two substances, the number of moles present in the reactant can be found. Finally, by dividing the number of moles of reactant by its volume, the concentration is calculated.”
In this case phenolphthalein is the indicator as it stays transparent in the acidic or neutral environment and changes its color into pink in the acidic environment.
– NaOH – 5g
– Sprite – 125 ml
– Distillated water 250ml
– Erlenmeyer flask
– volume of NaOH
– type of fizzy drink
– volume of the fizzy drink
1. Prepare all needed apparatus and substances
2. Weight 5g of solid NaOH and put it into beaker
3. Fill the beaker with 250 ml of distilled water to make 0.5 mol NaOH solution
4. Fill the burette with NaOH solution and write down to what level the burette is filled so you can later know how many of the solution was needed to neutralize fizzy drink
5. Measure 25 ml of Sprite in the cylinder
6. Put 25 ml of Sprite into the flask
7. Add to it 4 drops of phenolphthalein
8. Put the flask under the burette
9. Slowly pour the NaOH solution into the flask with Sprite
10. When the color of Sprite is pink stop the titration (it is important to be precise)
11. Write down how many NaOH solution was needed to neutralize your fizzy drink
12. Repeat steps 4-11 five times to get some more reliable results
13. After you finished your experiment neutralize NaOH solution that you still have and then clean the equipment you used during the experiment.
!!! – Work areas should be arranged so that a person does not need to travel through a high-hazard area while attempting to exit the laboratory during an emergency.
!!! – Eyewashes and showers must be accessible to all chemical laboratories.
!!! – Do not consume food and drink in the laboratory.
!!! – Wear your googles and gloves to protect your eyes and skin
!!! – Move in the labolatory carefully
!!! – Keep the labolatory clean in order to prevent any accidents
!!! – Pay particular attention to the protection of eyes and skin because NaOH can couse damage to your.
!!! – Confine long hair while working in a labolatory.
!!! – Do not panic if you have done something in a wrong way, just report your teacher and do what he/she has said
!!! – Flush away all accidentally spilled substances with water and report your teacher
!!! – Neutralize the remaining substances and remove them from equipment
!!! – Wear your gown while working in lab
number of the test
Initial quantity of NaOH solution in burette (in ml)
Final quantity of NaOH solution in burette(in ml)
Quantity of NaOH solution used to neutralize fizzy drink(in ml)
Table 1. data collected during the experiment
Data Processing and Presentation
In order to find the pH of Sprite at first the average quantity of NaOH solution used to neutralize the fizzy drink has to be calculated:
In order to make some other calculations ml has to be changed to dm3
1 dm3 = 1000 ml
5.18/1000 = 0.00518 dm3
Next the number of moles of NaOH solution used in the experiment has to be determined from the formula
n is number of moles
C is molar concentration
V is volume in dm3
Next the number of H+ ions in the solution has to be determined using the following formula:
[H+] is the molar concentration
n is number of moles of H+ ions
V is the volume of the solution
As number of moles of OH- ions in the solution is equal to the number of moles of H+ ions, nH+ = nOH- = 0.00259mol
By knowing this pH of Sprite can be calculated by using the formula below:
pH = -log[H+]
pH = -log0.1036
pH = 0.98464
The result obtained in the experiment differs a lot from the reality (pH is approximately 2.75). Even not knowing the proper value of pH of Sprite it is rather obvious that the result is wrong as no substance drank by human can have such a little pH. This would destroy our organism and therefore could not be sold as a fizzy drink. The percentage error equals:
This is a huge difference and it can be explained by a number of reasons:
1. we did not catch the exact moment of neutralization but the moment, when the mixture was already basic so, this difference in time can be crucial
2. little differences in measurements during the experiment could also be the cause of mistake
3. the time when the color of phenolphthalein did not disappear could be measured wrong and that can be another cause of mistake
Summing up these sources of mistake could not change the result in such a great extend – 279%. Although the results of the experiment were imprecise, the aim was partially achieved. Sprite was proved to have acidic pH.
The experiment could be done on some greater amounts of Sprite so that the results would be more precise. Although 5 tests were made, maybe some more should be done to make the data collected during the experiment more reliable. Besides that it is hard to find some other ways to make the experiment better or more reliable as the titration method is quite precise and the results should not differ much from the reality.
– “Chemistry for the IB Diploma (standard and higher level)” by Geoff Neuss
– “Chemistry” (second edition) by John Green and Sandru Damji
– www.en.wikipedia.org entry: titration