Question

You have successfully set up a simple distillation and start to heat up your solution. The liquid in the flask starts to boil slowly and then more rapidly. You look at the thermometer and write down in your notebook "The mixture started boiling at 24.5 °C" What is wrong with this scenario. Explain.

Answer 1

The recorded boiling point of 24.5 °C is incorrect for a water-salt solution during distillation, which should be over 100 °C. Possible errors include faulty equipment or misrecording of data. The student must check their setup and equipment accuracy.

Step-by-step explanation:

The scenario described is problematic because the boiling point of a pure solvent, like water, at atmospheric pressure is 100 °C. A mixture of table salt in water (a common solution in simple distillation practices) would have a boiling point higher than 100 °C due to the presence of the solute, which raises the boiling point. The recorded boiling point of 24.5 °C is significantly lower than what is expected, suggesting an error. There could be several reasons for this, including a malfunctioning thermometer, incorrect reading, misrecording of the data, or the use of a substance with a boiling point lower than water. Additionally, properly conducted distillation should result in the solution boiling steadily without rapidly increasing in temperature, since the added heat is used to facilitate the phase change from liquid to gas.

Moreover, boiling water in a sealed system with a vacuum can reduce the boiling point, but for educational laboratory setups, the pressure is usually close to atmospheric pressure, thus boiling below room temperature indicates a significant issue that must be addressed. Therefore, the student must reassess their setup, correct any procedural errors, and ensure the accuracy of their equipment.