Name _________________________
Melting Points of Common Substances
A solid substance melts when it absorbs enough energy for its particles to overcome the
attractive forces that lock them together. The particles then can slide around and about each other
randomly, giving the substance fluid properties. Nearly all pure substances have distinct melting
points that are determined by the strengths of attractions between their particles. The greater the
attractive forces, the more energy is needed to overcome them.
Molecular compounds have melting points considerably lower than those of ionic compounds,
which contain electrostatic attractions between their ions. Among molecular compounds,
differences in melting points depend on the degree of intermolecular forces that occur. These
forces include dipole-dipole forces, dispersion forces and hydrogen bonding.
In this assignment, you will determine the melting points of four molecular substances by
researching them on the Web. You will also compare the structural formulas of the substances
and determine what factors might account for the similarities and differences in the melting
points that you find. The four substances you will be working with are below…
S
S
S
S
S
S
S
S
Sulfur-8
And lastly, Sucrose, which has a formula of C12 H22 O11 (and P.S. – sucrose is POLAR)
Name(s) ____________________________
Melting Point Lab – one per group!!
Observations, Data, and Analysis and Conclusions
Data Table 1
Substance
Melting Point (oC)
Molar Mass
benzoic acid (C7H6O2)
Naphthalene (C10H8)
Sucrose (C12 H22 O11)
Sulfur (S8)
In the table below, put the substances above in order, from lowest melting point to highest
melting point. Also write the polarity of each substance on the appropriate line.
Data Table 2
Substance
Melting Point (oC)
Polarity
Analysis and Conclusions:
1. Look at the melting points of the two non-polar substances, and compare them to the melting
points of the two polar substances. Explain why the difference in melting points occurs between
the two groups. Explain your answer THOROUGHLY.
2. Now, compare the melting points of the two non-polar substances. What factor could account
for this difference in melting points between the two non-polar substances? Then, compare the
melting points of the two polar substances. What factor could account for this difference in
melting points between the two polar substances? Explain your answer THOROUGHLY.