Sucrose water-solid interactions

We now leave pure materials and the limited but important changes they can undergo and examine mixtures. We shall consider only homogeneous mixtures, or solutions, in which the composition is uniform however small the sample. The component in smaller abundance is called the solute and that in larger abimdance is the solvent. These terms, however, are normally but not invariably reserved for solids dissolved in Kquids one liquid mixed with another is normally called simply a mixture of the two liquids. In this chapter we consider mainly nonelectrolyte solutions, where the solute is not present as ions. Examples are sucrose dissolved in water, sulfur dissolved in carbon disulfide, and a mixture of ethanol and water. Although we also consider some of the special problems of electrolyte solutions, in which the solute consists of ions that interact strongly with one another, we defer a full study until Chapter 5. The measures of concentration commonly encoimtered in physical chemistry are reviewed in Further information 3.2. 

For solids that dissolve without molecular interactions with their solvents, we can make tolerable estimates of the solubility from the extrapolated liquid-phase vapor-pressure curve. Many common solids, such as NaCl and sucrose, do interact with water as a solvent, thus producing much greater solubility than we would estimate this way. 

Species (atoms, molecules, and ions) that are not chemically bonded to each other may interact with one another through intermolecular forces. The strength of intermolecular forces dictates the inherent properties of solids, liquids, and gases. Compounds with very strong intermolecular forces are normally solids at room temperature, whereas compounds with intermediate intermolecular forces are liquids, and those with extremely weak intermolecular forces are gases. The strength of these intermolecular forces explains why a solid such as sucrose melts at 185 °C, whereas ice water melts at 0 °C and molecular nitrogen boils at -196 °C. 

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