Acids, alkalis and bases are used all the time in daily life. You have probably seen this image on bottles. It means that the substance inside is corrosive and will try to dissolve what it comes into contact with – like a metal bar – or a hand!
However, not all acids, bases and alkalis are quite so dangerous! Have a look at the scale on the right.
The line represents the pH scale. A pH of 7 is neutral. Absolutely pure water has a pH of 7. Acids have a pH of 0–6.5 and alkalis from 7.5–14.
You will be shown a number of different substances. Drag the slider on the pH scale to indicate the approximate pH value for each substance.
The key to an acid, base or alkali's strength is what happens to it in solution (when dissolved in water) when it dissociates into ions.