Ken Gadd and Luca Szalay introduce a procedure used in industry – and adapted for school students – to measure the citric acid level in chewing gum.
How many people do you know who chew gum? Why do they? You could try a straw poll, but the most likely answer will be for the flavour. Chewing gum consists of a water-insoluble gum base and water-soluble ingredients such as flavourings and sweeteners. When you chew it, the flavourings and sweeteners are released, dissolved and swallowed (hopefully the gum stays in the mouth). Once the flavour has been extracted, the gum is discarded. Unfortunately it sticks strongly to hard surfaces such as concrete and is very hard to remove.
There’s plenty of evidence for this if you look at the pavements you walk on. But back to flavouring....
A common ingredient in chewing gum and other confectionary is citric acid. It gives that sharp, refreshing citrus taste that ‘attacks’ the tongue. The packaging will tell you how much citric acid is in the chewing gum. It’s the role of an analytical chemist in the quality control laboratory to check it out. The method below is based on the standard procedure used by a company that manufactures various flavours of chewing gum and bubble gum (a type of chewing gum). It has been adapted for use in schools and colleges so that your students can mimic authentic workplace practice.
Here are some questions that could be used to get students thinking:
The StandardBase project has produced 72 standard analytical procedures, used in industry and adapted for use by students in schools and colleges, accessible via the Internet. For more information about the project, see ‘StandardBase: a Leonardo da Vinci pilot project for practical education and training in chemistry’ in this issue of Science in School.
|Analytical instruments used||Volumetric glassware|
|Sample specification||Orange flavoured Hubba Bubba® bubble gum|
Most confectionary shops and supermarkets
|Component to be determined||citric acid|
|Field(s)||food and beverages|
Before they start the practical, teachers may want their students to understand the chemistry of the analysis. To check they have an appropriate knowledge, students might try the interactive test on the StandardBase websitew1. To help their work, students can also download a file about titrationw2.
The aim of this analytical procedure is to determine the citric acid content in Hubba Bubba® bubble gum. This bubble gum is available in the UK and most parts of Europe. It is manufactured by Wrigleyw3 in Plymouth, UK. The method described here is based on an analytical procedure used by Wrigley in their Plymouth laboratories.
The determination is based on an acid/base reaction between the citric acid in the bubble gum and standard sodium hydroxide. The citric acid content of the bubble gum can be calculated from titration results.
Use the following to calculate the percentage by mass of citric acid monohydrate in the Hubba Bubba® bubble gum:
Note: a correction factor is necessary if the sodium hydroxide solution is not exactly 0.10 mol dm-3.
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.
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 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 online.
If your students want to add their own results to the graph, email Luca Szalay (firstname.lastname@example.org). 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.