Is Salt Melting When It Dissolves in Water?

• Alan Goodwin ^[1]
  1. [1] Manchester Metropolitan University

     Manchester Metropolitan University

     Reino Unido

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 79, Nº 3, 2002, pág. 393
• Idioma: inglés
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• Resumen

  • This paper explores the terms melting and dissolving as applied to a variety of pure substances and mixtures, including water, salt solutions, and alloys. Even though the two terms are usually strongly differentiated in elementary science teaching, it is concluded that the two processes are essentially the same as soon as the ideas are extended to systems containing more than one component. By definition, the extension to two components has already been done when solutions are considered. Both melting and dissolving involve transition between the solid and liquid states and are controlled by analogous thermodynamic and kinetic principles. It is suggested that very strong differentiation between the terms is unnecessary and potentially damaging. In elementary science learning, signaling that "salt melting into water is a totally wrong concept" may erect a barrier to subsequent chemistry learning.

    There are many parallels to this dilemma in making strong differentiation between classifications throughout the learning and teaching of chemistry. Other examples include solute and solvent, and physical and chemical changes. Seeking an appropriate balance between certainty and flexibility seems to be important for current learning in chemistry and, at the same time, facilitating more sophisticated learning in the future. A feature of this paper is the continuing development of the author's understanding of melting and dissolving, a process that is clearly not yet complete.