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1 AP Chemistry Lab Brockport High School NY USA Determination of the K a of Weak Acids Mr Keefer Introduction Acids and bases are important classes of chemical compounds. They control the pH of biological systems and participate in many industrial reactions. In addition, they act to exacerbate many unwanted reactions, resulting in substantial financial loses to consumers. An understanding of acids and bases is therefore paramount to understanding chemistry. Weak acids are those that dissociate partially according to the following: HA ⇌ H + + A - The acid dissociation constant K a is an expression for the amount of dissociation. It can be found by K a = [H + ][A - ]/[HA] Thus, if you know the original concentration of the weak acid and can determine the [H + ], then K a can be determined. The [H + ] can be ascertained with the use of a pH meter which works on the principal of a voltage difference between the inside of the probe and the solution. Materials
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