Exercise: Determination of a Melting Point

A. Describe your results for the melting point of acetamide. Were your results consistent? What was the range of values?

B. The published melting point of acetamide is 81°C, calculate the percent error between your experimental values and the published (theoretical) value. Show your work.

C. Describe what occurs to the particles of a substance when the substance melts. Explain why this occurs.

D. When performing this experiment, when is the acetamide in a condensed phase? Explain your answer.
E. Based on your observations of acetamide when it reformed a solid after melting, does acetamide form a crystalline or amorphous solid? Explain the difference between these two terms as part of your answer.

F. Give some examples of how it might be useful to know the melting or boiling points of a substance. Think in terms of both scientific and commercial/industrial settings.

G. Describe any possible sources of error for this exercise.

Exercise: Temperature and Phase Changes

Questions
A. Using the temperature data recorded in Data Table 2, create a heating curve.

• Plot time (minutes) on the x-axis (horizontal axis) and temperature (°C) on the y-axis (vertical axis). Connect the plotted points with a line.

• Label the heating curve to show each phase of matter (solid, solid + liquid, liquid, liquid + gas).

• Label the melting point and boiling point on the heating curve.

Note: An example heating curve is given in Figure 6 of the Background.

B. Are there parts of the curve with positive slopes and parts that are flat (slope of zero)? What states of matter are present when the slope of the heating curve is positive and what states of matter are present when the slope is zero or close to zero?

C. Describe the key characteristics for the three states of matter.

D. Define the melting point. What was the observed melting point of water?

E. Define boiling point. What was the observed boiling point of water?

F. What happens to heat energy when it is not increasing the temperature of the substance in the beaker? Use your heating curve to explain your answer.

G. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not.

H. The published melting point of H2O is 0°C, and the published boiling point is 100°C. Why may you have found different values?

Use the following information to determine if the intermolecular forces of isopropyl alcohol are greater or weaker than the intermolecular forces of water. Explain your answer. The melting point of isopropyl alcohol (rubbing alcohol, C3H8O) is about -90°C and the boiling point is about 82°C.