Describe the colour changes when sulphur (melting point \(113^{\circ} \mathrm{C}\), boiling point \(445^{\circ} \mathrm{C}\) ) is heated from \(25^{\circ} \mathrm{C}\) to \(500^{\circ} \mathrm{C}\) ? It turns from a yellow solid to a (a) Yellow liquid and then it boils (b) Straw colour liquid which turns dark reddish brown and then it boils (c) Dark reddish brown liquid and then boils (d) Reddish brown solid and then into reddish brow liquid and then boils.

Understanding the melting point of sulphur is fundamental when examining its physical properties. Sulphur, a non-metallic element known for its bright yellow crystals, starts its transformation from solid to liquid at approximately 113 degrees Celsius. At the melting point, the crystalline structure of solid sulphur breaks down, allowing the molecules to move more freely, converting into a liquid form. This stage is crucial for chemical reactions and industrial processes involving sulphur. Despite the change in state, sulphur maintains its distinctive yellow hue as a liquid, indicating that the melting process does not alter its color.

In practical applications, like the vulcanization of rubber, knowledge of sulphur's melting point allows for precise control over manufacturing processes. For students observing this transition in a laboratory, it's important to monitor temperature closely to recognize the exact moment of change from solid to liquid sulphur.

As we dig deeper into the thermal properties of sulphur, the boiling point emerges as a key characteristic. Sulphur's boiling point is recorded at around 445 degrees Celsius. It's at this temperature that liquid sulphur becomes energetic enough for its molecules to completely overcome intermolecular forces, transitioning into a gaseous state. During a controlled heating experiment, observing sulphur's transformation from dark reddish-brown liquid to vapor is a clear indication that the boiling point has been reached.

Educationally, it exemplifies how phase transitions are influenced by temperature. In industry, understanding the boiling point is relevant for processes like the Claus process in petroleum refining, where gaseous sulphur compounds are converted back into elemental sulphur.

The color changes of sulphur upon heating provide a fascinating window into how temperature affects the properties of elements. Initially a bright yellow solid at room temperature, sulphur undergoes notable transformations as it is heated. After melting into a liquid at 113 degrees Celsius, it retains its yellow color. As heating continues, it transitions into a straw color, before finally turning dark reddish brown just before boiling.

These color changes are more than just visually intriguing; they also indicate alterations in the physical structure of sulphur. It’s a visual confirmation of the phase changes and the presence of different allotropes at varying temperatures. These dynamic changes can aid in a better understanding of chemical reactions and are particularly significant in educational demonstrations.

Sulphur exists in numerous allotropes, displaying distinct physical forms and chemical properties. Allotropes are different structural modifications of an element; with sulphur, these include rhombic and monoclinic sulphur – two crystalline forms that are stable at different temperature ranges. The polymeric sulphur that forms when liquid sulphur is rapidly cooled is called plastic sulphur, a unique variety with rubber-like properties.

Students examining sulphur should understand that these allotropes are a result of the element's ability to form rings and chains with varying lengths and complexities. The transition from yellow to reddish brown liquid upon heating reflects changes in allotropy, influenced by temperature. This property is not only important for academic studies but also plays a critical role in industries where sulphur is a key ingredient.