| pH = –log[H3O+] | aqueous solution has no effect on litmus | aqueous solution turns blue litmus red and has a lower pH than H2O | ||||
acid | CH3OH not acidic | H2O | NH4+ weak acid |  weak acid | H3O+ | HCl strong acid |
| conjugate base | CH3O– strong base | OH– | NH3 weak base |  weak base | H2O | Cl– not basic |
| aqueous solution turns red litmus blue and has a higher pH than H2O | aqueous solution no effect on litmus | |||||
- Aqueous solutions of acids have pH lower than that of water (due to the H3O+ produced by reaction of the acid with water).
- Aqueous solutions of bases have pH higher than that of water (due to H3O+ in water being consumed by OH– produced by the reaction of the base with water).
- If one member of a conjugate pair is strong, the other member does not react with water to change its pH.
- Both members of weak acid-base conjugate pairs react with water to change its pH.