1. You have a freshly prepared, degassed, buffered solution at pH 8.0 in a beake
ID: 482699 • Letter: 1
Question
1. You have a freshly prepared, degassed, buffered solution at pH 8.0 in a beaker. When you add a few drops of bromothymol blue indicator, the solution turns blue. You place a stir bar in this solution and stir vigorously. You come back 12 hours later and the solution is still blue.
2. You have a freshly prepared, degassed, unbuffered solution at pH 8.0. When you add a few drops of bromothymol blue indicator, the solution turns blue. You place a stir bar in this solution and stir vigorously. You come back 12 hours later and the solution is yellow in color.
Explain why color changed in solution 2. Provide chemical reaction to support the answer. Bromothymol blue indictator is yellow below pH 6.0 and blue above pH 7.6.
Explanation / Answer
1. The pH of the buffer does not change with time on stirring the buffered solution vigorously. Hence, there is no change in colour of the solution even after 12 hours. Infact, a buffered solution will resists any change in the pH upon the addition of an acid or a base.
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