Phenolphthalein changes color when the pH rises over 07.00, and methyl orange changes color at a pH of 3.4. As a result, methyl orange is used when titrating a strong acid with a weak base, while phenolphthalein best option than methyl orange when titrating a weak acid with a strong base.
The pH of the equivalence point for an acid-base titration determines which indicator to use. The indicator that changes color at or near the point of equivalence should be selected. The titration curve will be steep at this point, and you will get a good endpoint.
Phenolphthalein is a synthetic indicator that is colorless in an acidic medium and pink in basic conditions. Methyl orange is also a synthetic indicator that shows various colors in acid, base, and neutral substances. As the pH of the solution increases, it changes color from red to orange to yellow.
Both phenolphthalein and methyl orange are acid-base indicators that are chosen based on the neutralization reaction that occurs. A phenolphthalein indicator is used to do a strong acid-strong base titration because it changes color over a pH range of 8.3 to 10.
Methyl orange is a pH indicator that ranges from 3.1 and 4.4. Since its pH range does not include the pH equivalence point (~8) for the reaction, it is not a good indicator for the neutralization reaction between a weak acid and a strong base (eg. Oxalic acid vs. sodium hydroxide).
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