Buffer solution. Bottle containing a buffer solution for maintaining a constant alkalinity. At right is a piece of litmus paper which has turned blue after being dipped in the buffer, showing that it is alkaline. This buffer solution has been made by mixing a weak alkali with the salt that the alkali forms when it reacts with a strong acid. This mixture resists changes in its alkalin- ity (pH). If a strong alkaline is added, then it will react with the salt to form its own salt. If an acid is added it will react with the weak alkali; the lost alkali will be largely replaced as the salt dissociates. The solution loses its buffering abilities as the salt is depleted.
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