pH is a fundamental property of any water soluble chemical (although acid-base reactions do not necessarily require water) and the concept of "acidness" is generally known by the public. 'Acid Test' attempts to gently increase the knowledge of acids without being too technical for our visitors.

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Click to enlarge
   Description of the Experiment   

The visitor is presented with 6 different household substances mounted on the turntable contained inside the glass case (there is also a buffer and a cleaning solution that are used in the operation of the exhibit), and a computer touch screen. The household substances are bathroom cleaner, oven cleaner, drain cleaner, Cola drink, vinegar, stomach anti-acid medicine.

When the visitor touches the computer screen to begin the interaction they can make one of 3 choices.

  1. To find out about pH (two simple pages of basic information).
  2. To test the samples.
  3. To find out about the maker of the exhibit.

If the visitor selects (2) some information about the sample is provided and some simple questions are asked.
Then the electrode is lifted clear of the storage buffer, the turntable rotates, the electrode is washed in the cleaning solution and then lifted again and the correct sample is brought to the electrode, which takes the pH reading.

This reading can be taken from the meter in the case or from the computer screen which also gives some information about the result and suggests other samples to try.

   Duration   

If all samples are tested the interaction takes about 5-6 minutes.

   Conclusion   

pH varies from low (acidic) for things like Coca-Cola and vinegar (which have a similar pH, often surprising to the visitor) to high for drain and oven cleaner.

   Detailed Conclusion   

Acids usually have the following properties: They do not conduct electricity when pure, but do conduct when dissolved in water. Acids in water undergo characteristic reactions with metals and metal compounds. In water they change the colour of some "indicators" (substances which have characteristic colours at different pH levels). Acids which dissolve easily in water are called strong acids, others are weak acids. Those that dissolve easily produce more hydrogen ions for a given concentration of acid. The concentration of hydrogen ions is quantity on which pH is based (pH = -log[H+]) i.e. negative log hydrogen ion concentration.