Introduction
DrDAQ is used here as a pH meter with the addition of a pH probe to measure the pH level over the entire pH scale of a range of common drinks.
Recently dentists have begun warning about the dangers of drinking acidic drinks. Teenagers, they suggest, who drink large amounts of fizzy ‘pop’ drinks suffer from tooth erosion whereby the enamel covering of the tooth is dissolved by the acid in the drink. Athletes are also at risk from drinking sports drinks.
The recommended ‘safe’ level for the pH of drinks is 5.5, anything below this can promote tooth erosion.
This experiment looks at the relative pH values of different drinks and can be used to determine whether a particular drink is ‘safe’ according to the above criteria. It can also be used as a good introduction to further studies into tooth decay and enamel stripping.
It is suitable for ages 14+ and requires some knowledge of the pH measurement.
Equipment required
A selection of common drinks - we used:
- Orange juice
- Apple juice
- Black coffee
- Black tea
- Lemon tea
- Original Coke
- Pepsi
- Cherry Coke
- Ribena
- Lemon squash
- Milk
Experiment setup
- Fill all cups with an equal amount of liquid which will cover the pH probe tip.
- Mark the cups so that they can be identified later.
- Plug the pH probe into DrDAQ and run PicoLog software.
- Optionally, you can calibrate the pH probe using buffer solutions.
- It is important to allow all the drinks to stabilise at room temperature since pH readings vary with temperature.
Diagram showing the experiment set up
Carrying out the experiment
Here is a table showing the pH of some common substances for reference.
| Substance | pH |
|---|
| Hydrochloric acid | 0 |
| Stomach acid | 2 |
| Vinegar | 3 |
| Tomatoes | 4 |
| Pure water | 7 |
| Blood | 7.5 |
| Household cleaners | 11 |
| Oven cleaners | 14 |
Before starting the experiment, make a table listing drinks that you will test and indicate what you expect the pH of each drink to be.
Create your table as shown below:
| Liquid | Expected pH | Recorded pH |
|---|
| Orange juice | | |
| Apple juice | | |
| Black coffee | | |
| Black tea | | |
Gently agitate the pH probe in each liquid for a minute or two while the pH reading settles then record the reading in the table and move onto the next liquid.
NOTE: Take care to thoroughly clean the pH probe in a large container of water between each liquid to reduce cross-contamination of the liquids.
When you have tested all your available drinks, plot the results on a bar graph with each bar showing the expected value and recorded value for each liquid.
Questions and discussion of results
The formula for pH is: pH = –log[H+]
Q1. With respect to the results you have obtained, can you make any predictions about the likely pH values of the foods and drinks we consume ?
Q2. Find the pH of a solution whose [H+] is 9.5E-8 M
Q3. Calculate the [H+] of a solution with a pH of 5.45
Further study
- How does the pH reading of a liquid vary with temperature? (possibly heat a buffer solution)
- If you did not do so, investigate how you would calibrate the pH probe.
