Question 1

What is the capillary method for determining boiling point?

Accepted Answer

The capillary method involves placing an inverted capillary tube in a liquid sample and heating it gradually. As temperature increases, air in the capillary escapes and is replaced by the liquid's vapor. When vapor pressure exceeds atmospheric pressure, bubbles stream from the capillary. The boiling point is recorded when the liquid begins refilling the capillary after cooling, indicating vapor pressure has dropped to atmospheric pressure.

Question 2

Why does ethanol have a higher boiling point than acetone?

Accepted Answer

Ethanol has a higher boiling point due to hydrogen bonding between its molecules, which is a stronger intermolecular force than the dipole-dipole forces present in acetone. Hydrogen bonding allows ethanol molecules to hold onto each other more effectively, requiring more thermal energy to transition from liquid to gas phase. Although acetone has a slightly higher molecular weight, molecular structure and intermolecular forces have a greater impact on boiling point than mass alone.

Question 3

How does molecular structure affect boiling point?

Accepted Answer

Boiling point is directly related to molecular structure through the strength of intermolecular forces. Stronger intramolecular forces, such as hydrogen bonding, result in higher boiling points because molecules remain bonded in the liquid phase longer. Molecular weight has less impact than structure; for example, ethanol has a lower molecular mass than butane but a much higher boiling point due to hydrogen bonding, while butane relies on weaker van der Waals forces.

Question 4

What experimental errors can affect boiling point measurements?

Accepted Answer

Common experimental errors include heating the water bath too rapidly, which prevents accurate temperature equilibration, and poor alignment of the thermometer and sample. Rapid heating can cause temperature overshooting and inaccurate bubble observation. Misalignment prevents the thermometer from accurately reading the sample temperature. Careful temperature control and proper thermometer positioning are essential for obtaining boiling point values that match reported literature values.

Question 5

How do you know when the boiling point has been reached during the experiment?

Accepted Answer

The boiling point is identified by two key observations. First, when heating, record the temperature at which a rapid and continuous stream of bubbles emerges from the capillary tube. Second, when cooling, observe when the liquid begins to rise back into the capillary as bubble production decreases. The temperature at which liquid refills the capillary represents the boiling point, as this marks when vapor pressure equals atmospheric pressure.

Question 6

Why is thermometer alignment important in boiling point determination?

Accepted Answer

Proper thermometer alignment ensures the thermometer bulb is level with the liquid sample, allowing accurate temperature measurement of the boiling liquid. Misalignment causes the thermometer to read incorrect temperatures, leading to inaccurate boiling point values. Keeping the thermometer and sample close together and level prevents temperature gradients and ensures the thermometer responds to the actual temperature of the liquid being heated.

Question 7

What happens to vapor pressure inside the capillary as temperature increases?

Accepted Answer

As temperature increases, vapor pressure inside the capillary rises proportionally. Initially, air in the capillary escapes and is replaced by the liquid's vapor. When vapor pressure exceeds atmospheric pressure, vapor escapes in a continuous stream of bubbles. Upon cooling, vapor pressure decreases until it falls below atmospheric pressure, at which point the liquid is drawn back into the capillary, marking the boiling point temperature.

	טמפרטורת נקודת רתיחה (°C)
	Bubbles	נוזל בנימים
אצטון
אתנול

נקודות רתיחה

טבלה 1: נקודת רתיחה של אצטון ואתנול