1The pH scale
The pH scale runs from 0 to 14. Below 7 is acidic, 7 is neutral and above 7 is alkaline.
pHacidicalkaline
Lesson 14.2 notes
The pH scale
Universal indicator and pH meters, how acidic or alkaline, diluting, and pH in everyday life and in your body.
2Universal indicator
Universal indicator is a mixture of indicators. Its colour shows the pH: red to yellow for acids, green for neutral, blue to purple for alkalis.
universal indicator
3How acidic?
The lower the pH, the more acidic: pH 1 is strongly acidic, pH 6 only weakly. The higher the pH, the more alkaline.
strongly acidicweakly acidic
4pH meters
A pH meter measures the pH and shows it as a number, so it is more precise than an indicator colour.
pH meter
5Diluting
Adding water to an acid makes it less acidic: its pH rises towards 7. However much water you add, it never goes past 7.
dilute
6pH all around
Lemon juice is about pH 2, milk about 6.5, soap about 10 and oven cleaner about 13.
7pH in your body
Your stomach is strongly acidic, about pH 2, which helps kill microbes. Saliva is close to neutral and the small intestine is slightly alkaline.
Explore: pH lab
Test everyday substances with universal indicator and a pH meter, then add water and watch the pH.
Common mistake: A bigger pH number does not mean more acidic
It is easy to think a bigger number means more acid. It is the other way round: pH 1 is much more acidic than pH 5.
Remember
- pH below 7: acidic. pH 7: neutral. pH above 7: alkaline.
- The further below 7, the more acidic. The further above 7, the more alkaline.
- Universal indicator shows the pH by its colour. A pH meter gives a more precise number.
Going further at GCSE