Hello Chemistry 20. This is a short example video in the acid base unit. This is predicting the pH of a solution using indicators. Example number one. If an unidentified solution was tested with different indicators and the below results were obtained, what would be the approximate pH range of the solution? Pause the video and attempt this example.
Below we can see a variety of indicators that were used in the unknown solution. and the color that the solution turned while using that indicator. For example, when using phenol red, the unknown solution turned yellow.
While using methyl orange, the unknown solution also turned yellow. To complete this question, we need to first write a pH scale, which goes from 0 to 14. Zero. being the most acidic and 14 being the most basic.
We then have to list the indicator range below on the pH scale. Our first indicator was phenol red which was yellow when put into the solution. Using the Chemistry 20 data booklet when phenol red is yellow it is in a pH range from zero to 6.6.
Our next indicator was methyl orange which also appeared yellow in the unknown solution. Methyl orange is yellow in a pH range from 4.4 to 14.0. Our next indicator was phenolphthalein which appeared colorless in the unknown solution.
Phenolphthalein is colorless from a pH range of 0.0 to 8.2. And finally, our last indicator was methyl red, which appeared as red. Methyl red is red in a pH range from 0.0 to 4.8.
Now, we have to find a pH range on the scale that includes all indicators and we want the narrowest pH value as possible and that will be 4.4 which occurs from the methyl orange to 4.8 which occurs at the methyl red. In this region we have all pH indicators. As a result the pH range of the unknown solution is 4.4 to 4.8