EXP 16

• A standard sol'n or titrant is the sol'n with known concentration to a high degree of accuracy
• Standard acid solutions are usually prepared from hydrochloric acid, although nitric, sulfuric, and oxalic acids are occasionally used.
• sulfuric and oxalic acids have the advantage of being non-volatile in case the solution to which they have been added in excess must be boiled before completing the titration.
• Standard alkali solutions are usually prepared from sodium hydroxide, although potassium hydroxide and barium hydroxide are occasionally used.
• However, these solutions absorb carbon dioxide from air, thereby changing rapidly in concentration.
• herefore, all alkali solutions should be re-standardized frequently
• In any case, the choice of solution depends upon the nature of the substance to be titrated and upon the substances present.