Melting of sulphur
An example of a solid to liquid change of state, explained from the microscopic and thermodynamic point of view. The melting of sucrose is given alongside as an example of a change of chemical structure by heating, to point out the difference.
What students learn
The science behind this experiment
Matter takes form as solid, liquid and gas according to outer pressure and temperature. A well known example is water, which solidifies below 0 °C and vaporizes above 100 °C. What happens on heating a solid substance such as sulphur?
This experiment shows that a substance can exist not only in the usual three states – solid, liquid and gas – but also in different solid states. The existence of different solid states of a compound is called polymorphism; when an element is capable of existing in several distinct solid states, the phenomenon is called allotropy. The differences are usually only differences in physical properties and one particular form is always more stable than the others.
Equipment used
- Test tubes — 1473.60
- Test tube rack — 1680.06
- Test tube holder — 5423.30
- Spirit burner — 5514.10
- Tripod stand — 5533.10
- Triangle for crucibles — 5535.04
- Evaporating dish — 1920.25
- Spatula — 5460.34
Chemicals and reagents
- Sulphur powder — R:11-16 S:41
- Sucrose
Safety notes
- Take care when using the burner and hot glassware.
- If the sulphur catches fire, cover the evaporating dish.
Questions for students
- Record your observations, especially any colour changes.
- Record what is left in the evaporating dish. What are the differences between the sulphur you started with and the sulphur left in the dish?
- Note what happens. Why are there differences in behaviour between these two substances?
What to expect
<p>The sulphur melts to form a honey coloured liquid (if heated too strongly the liquid turns brown and viscous).</p><p>The sulphur left in the dish forms needlelike crystals and these are a darker yellow than the original sulphur. This form of sulphur is not stable at room temperature and slowly changes back.</p><p>The needlelike crystals are monoclinic sulphur and the more stable state is rhombic sulphur.</p><p>Sulphur underwent a change of state whereas sucrose decomposes changing its composition.</p><p>Repeating the experiment with sucrose at the end a dark brown solid is obtained – the sucrose melts to a pale brown.</p><p>Sucrose underwent a change in its chemical composition, decomposing because of the heat.</p>
Disposal
Dispose of sulphur and sucrose in the solid wastes container.
Run this experiment in your classroom
This experiment is part of the ATP Mobile Lab — a self-contained laboratory that turns an ordinary classroom into a working science lab, with over 200 experiments in physics, chemistry, biology, robotics and engineering. Gali, the AI tutor built into ATP Connect, guides students through each step and answers their questions at the bench.
See the Mobile LabTalk to our team