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.
Lo que aprenden los alumnos
La base científica de este experimento
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.
Equipo utilizado
- 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
Productos químicos y reactivos
- Sulphur powder — R:11-16 S:41
- Sucrose
Notas de seguridad
- Take care when using the burner and hot glassware.
- If the sulphur catches fire, cover the evaporating dish.
Preguntas para los alumnos
- 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?
Qué puedes esperar
<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>
Eliminación
Dispose of sulphur and sucrose in the solid wastes container.
Realiza este experimento en tu clase
Este experimento forma parte del « Mobile Lab » de ATP, un laboratorio autónomo que convierte un aula normal en un laboratorio de ciencias en pleno funcionamiento, con más de 200 experimentos de física, química, biología, robótica e ingeniería. « Gali », el tutor de IA integrado en ATP Connect, guía a los alumnos paso a paso y responde a sus preguntas en la mesa de trabajo.
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