Titration of 50.0mL of 0.130mol/L sulfurous acid with 0.14mol/L sodium hydroxide.
Approprite indicator for each equivalence point
The titration of sulfurous acid with sodium hydroxide involves two equivalence points. The appropriate indicators for each equivalence point are:
1. The first equivalence point occurs when all of the sulfurous acid (H2SO3) has reacted with sodium hydroxide (NaOH) to form sodium sulfite (Na2SO3) and water (H2O). At this point, the pH of the solution changes from acidic to neutral. A suitable indicator for this endpoint is phenolphthalein, which changes color from colorless to pink at a pH around 8.2-10.0.
2. The second equivalence point occurs when all of the sodium sulfite (Na2SO3) has reacted with sodium hydroxide (NaOH) to form sodium sulfate (Na2SO4) and water (H2O). At this point, the pH of the solution changes from neutral to slightly basic. A suitable indicator for this endpoint is methyl orange, which changes color from red to yellow at a pH around 3.1-4.4.
It is important to note that these indicator ranges are approximate and can vary depending on factors such as concentration and temperature. Therefore, it is recommended to perform a preliminary titration or consult a reference table to determine the specific indicator ranges for your experiment.