Video Transcript
Fill in the banks. Methyl orange is a useful
indicator, particularly for titrations against acids. It is blank in strongly acidic
solutions and blank in basic solutions.
An indicator is a weak acid or base
that undergoes a color change over a specific pH range. Indicators are often used during
acid–base titrations. As the acid and base react, the pH
will slowly increase. But as we draw near the equivalence
point, the point at which the acid and base have completely neutralized one another,
the pH will change drastically. If an appropriate indicator was
used, then a color change should be observed during this drastic change in pH. The indicator’s color change
signifies the end point of the titration.
There are many indicators that can
be used, and each indicator changes color over a different pH range. This question specifically asked us
about the indicator methyl orange. This figure shows us the color of
methyl orange at a variety of pH values. We can see that at very low pH
values, methyl orange is red. As we increase the pH from
approximately three to approximately four, methyl orange changes from red to
orange. And at any pH greater than pH five,
methyl orange is yellow.
The question specifically asked us
about methyl orange in strongly acidic solutions and basic solutions. To determine the color of methyl
orange under these conditions, we need to recognize that a pH of seven represents a
solution that is neutral. As the pH decreases, the solution
becomes increasingly more acidic. And as the pH increases, the
solution becomes increasingly more basic. We can see then that methyl orange
will be red in strongly acidic solutions and yellow in basic solutions. So we should fill in the first
blank with the word “red” and the second blank with the word “yellow.”
