Acid-Base Indicators: Spectroscopic Method of Determination of Ka

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| | |Acid-Base Indicators: Spectroscopic Method of Determination of Ka | |Sahib Kaur | | | | | |3/23/2012 |

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Introduction

The purpose of this lab experiment is to determine the Ka value for the indicator bromcresol green using spectroscopy. Bromocresol green is a weak organic acid; therefore, it doesn’t reacte to completion, rather it reacts to a dynamic equilibrium, the point at which the rate of reactants turning to products is equal to the rate of products changing back into reactants. An acid (in terms of the bromsted-lowry definition) is a substance that donates H+ ions in a reaction. In bromcresol green, the acidic proton is the that is attached to the SO3- group. The acid, in this lab will be represented by a HB and the conjugate base will be represented by B- . The Ka value for this reaction would be:

[H3O+][B-] / [HB]

In this lab, the concentration of [H30+] will be determined by adjusting to a known value by using a buffer solution of HOAc and it’s conjugate base OAc-. By adjusting the concentration of HOAc and it’s conjugate base in...
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