الكيمياء

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.

المادة، والمخاليط، والمحاليل
melting; allotropes; sulphur

ما يتعلمه الطلاب

الجانب العلمي وراء هذه التجربة

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.

المعدات المستخدمة

  • 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

المواد الكيميائية والمواد الكاشفة

  • Sulphur powder — R:11-16 S:41
  • Sucrose

ملاحظات السلامة

  • Take care when using the burner and hot glassware.
  • If the sulphur catches fire, cover the evaporating dish.

أسئلة للطلاب

  • 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?

ما يمكن توقعه

<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>

التخلص

Dispose of sulphur and sucrose in the solid wastes container.

قم بإجراء هذه التجربة في فصلك الدراسي

تُعد هذه التجربة جزءًا من برنامج «مختبر العلوم المتنقل» (ATP) Mobile Lab — وهو مختبر متكامل يحول الفصل الدراسي العادي إلى مختبر علوم فعال، ويضم أكثر من 200 تجربة في مجالات الفيزياء والكيمياء والبيولوجيا والروبوتات والهندسة. ويقوم « Gali » — وهو المعلم الذكي المدمج في موقع ATP Connect — بتوجيه الطلاب خلال كل خطوة والإجابة على أسئلتهم أثناء إجراء التجارب.

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