Dissolving

Many solids have naturally occurring geometrical shapes called rystals. Crystals are solids that have regular faces and edges. Crystals can have different types of shapes, some of which are shown below:

When a solid is mixed into a liquid and disappears, the solid is said to have dissolved. Some common examples of dissolving are stirring sugar crystals into your coffee, or dissolving salt crystals into a saucepan of water. 

A solution is the end product of mixing a solution into a solid. 

The process of dissolving a solid into a liquid can be explained by considering the particles involved. 

The solute (solid) particles are initially in a fixed arrangement (lattice) with the solvent (liquid) particles moving about freely. 

Attractive forces between the solvent particles and the outer solute particles pull those solute particles free of the lattice and allow them to mix among the solvent particles. 

Dissolving and melting are different!

A solid may not dissolve in a liquid (e.g. chalk in water). The substance is said to be insoluble. 

Some substatnces dissolve very readily and others more slowly. Solubility describes how much a solid will disoolve in a liquid. 

The solubility of a substance depends on the nature of the solute particles, the nature of the solvent particles, and the temperature of the solvent. 

The solubility of a substance is the number of grams of solute that will dissolve in 100 grams of the solvent at a certain temperature. 

When no more solute will dissolve, a solution is saturated. 

As temperature increases, more solute will dissolve. The solubility of a substance at different temperatures can be plotted on a solubility curve. 

The number of grams of solute (e.g. sugar) that will dissolve in 100 grams of solvent (e.g. water) is plotted against the temperature of the solvent. 

A dilute solution is one which has a low concentration of solute. 

A concentrated solution has a high concentration of solute.