Extremely acid < 4.5
Very strongly acid 4.5 - 5.0
Strongly acid 5.0 - 5.5
Moderately acid 5.5 - 6.0
Slightly acid 6.0 - 6.5
Neutral 6.5 - 7.3
Stlightly alkaline 7.3 - 7.8
Moderately alkaline 7.8 - 8.5
Strongly alkaline 8.5 - 9.0
Very Strongly alkaline > 9.0 "
Source: E.A. Fitzpatrick,