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.
Cosa imparano gli studenti
La scienza alla base di questo esperimento
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.
Attrezzatura utilizzata
- Provette — 1473,60
- Portaprovette — 1680.06
- Portaprovette — 5423.30
- Bruciatore ad alcool — 5514.10
- Tripod stand — 5533.10
- Triangle for crucibles — 5535.04
- Evaporating dish — 1920.25
- Spatola — 5460.34
Sostanze chimiche e reagenti
- Sulphur powder — R:11-16 S:41
- Sucrose
Note sulla sicurezza
- Prestare attenzione durante l'uso del bruciatore e degli oggetti in vetro caldi.
- If the sulphur catches fire, cover the evaporating dish.
Domande per gli studenti
- 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?
Cosa aspettarsi
<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>
Smaltimento
Dispose of sulphur and sucrose in the solid wastes container.
Prova a fare questo esperimento in classe
Questo esperimento fa parte dell’ATP “ Mobile Lab ” — un laboratorio autonomo che trasforma una normale aula in un vero e proprio laboratorio scientifico, con oltre 200 esperimenti di fisica, chimica, biologia, robotica e ingegneria. “ Gali ”, il tutor basato sull’intelligenza artificiale integrato in ATP Connect, guida gli studenti in ogni fase e risponde alle loro domande direttamente al banco di lavoro.
Vedi il Mobile LabContatta il nostro team