Question

1) What causes the liquid to be drawn up the capillary tube during a micro boiling point determination?

2) What effect does an increase in atmospheric pressure have on the boiling point of a liquid? A decrease?

Answer 1

1. During micro boiling point determination, the tube is heated till the boiling point. So the vapor at the surface of the liquid enters the capillary tube. At this point, heating is stopped. So the vapor begins to cool. This creates a lower vapor pressure and hence a vacuum. Since the other end of the capillary is sealed, the liquid is drawn up the capillary tube.

2. At the boiling point, the vapor pressure of the liquid equals the atmospheric pressure. When the atmospheric pressure is increased, the boiling point, therefore increases.