Reagent solutions
Standard 0.10 mol dm-3 sodium hydroxide. If this is not available, dissolve 1.00 g of sodium hydroxide in about 100 cm3 of pure water. Wash carefully to a 250 cm3 graduated flask and make up to the graduation mark. Homogenise the solution. Standardise by titration with 0.10 mol dm-3 dhydrochloric acid, itself standardised against solid potassium hydrogencarbonate.
Phenolphthalein indicator. Weigh out 0.20 g of phenolphthalein and dissolve in about 50 cm3 of methanol. Transfer solution to a 100 cm3 graduated flask, make up to the graduation mark with methanol and homogenise the solution.
Procedure
Take one orange flavoured Hubba Bubba® bubble gum piece, unwrap it and place onto a wood block.
With the rolling pin, roll the bubble gum into a very thin strip approximately 160 x 30 x 0.5 mm.
Cut the thin strip into small pieces about the size of long grain of rice.
Weigh out 1.00 g of orange flavour Hubba Bubba® bubble gum bits.
Add to 100 cm3 of pure water contained in a 250 cm3 conical flask. Add a magnetic follower and stopper.
Stir vigorously for 30 min, making sure bubble gum bits do not lump together.
Add 0.50 cm3 of phenolphthalein indicator and titrate with 0.1 mol dm-3sodium hydroxide contained in a 10 cm3 burette. The end point is pink.
Repeat twice more and average the three results. Average titration = V cm3.
Calculations
Use the following to calculate the percentage by mass of citric acid monohydrate in the Hubba Bubba® bubble gum:
Each cubic centimetre of 0.10 mol dm-3 sodium hydroxide is equivalent to 7.00 mg of citric acid monohydrate.
% by mass citric acid monohydrate = 0.70V
Note: a correction factor is necessary if the sodium hydroxide solution is not exactly 0.10 mol dm-3.
Expression of results
Give the mass of citric acid monohydrate in Hubba Bubba® bubble gum in percentage by mass (mass of citric acid monohydrate in 100 g of bubble gum). The manufacturer’s allowed range is 1.9–2.1 percentage by mass.
Precision
The precision of the analysis is determined by the burette readings. An inexperienced student might read a burette to a precision of ± 0.05 cm3. More experienced students might read to a ± 0.02 cm3.
The graph
The graph below shows the results obtained by students in other European countries (accurate at time of going to press). If your students are interested in finding out the latest status, they can view the most up-to-date results onlinew5.
If your students want to add their own results to the graph, email Luca Szalay (luca@chem.elte.hu). You will get a username and password to be able to use this function of the StandardBase database. Then you can register your students, which will allow them to upload their numbers on the graph.