What factors affecting the rate of dissolving?

Answer 1

What factors affect the rate of dissolving

How quickly a substance dissolves in a solvent is unknown. A teaspoon of table sugar will dissolve rapidly in a hot drink. The same amount of sugar will take much more time to dissolve in a glass of ice water. Similarly, table salt dissolves rapidly in water at room temperature. Large pieces of salt, like those used in home water softeners, dissolve much more slowly, which makes this type of salt ideal for use over long periods. The rate of dissolving is affected by three main factors:

1. Stirring
2. Temperature
3. Particle Size

Stirring Stirring a solution increases the rate at which a solute dissolves in a solvent. For example, you may have tried to make a soft drink by dissolving flavor crystals in a pitcher of water. The flavor crystals are the solute and water is the solvent. If the package of flavor crystals is poured into the water, dissolving begins, but clumps of powder may remain. To speed up the process, you probably used a spoon to stir the water with the flavour crystals. This results in a more uniform arrangement of flavor crystals and water particles makes dissolving occur more quickly. You can actually see the flavor crystals being stirred until they dissolve in the water. The end result is a solution, as all parts of the soft drink mixture look the same.

Temperature Temperature affects the speed at which particles move. Particles move more rapidly at higher temperatures, as heat is transferred by the movement of the particles. Since the rate of dissolving depends on solute particles bumping into solvent particles, when the particles move more rapidly, more solvent and solute particles will bump into one another. In addition, the solvent particles at the edge of a piece of solute will more rapidly carry away the solute particles that they meet. This will quickly spread the solute particles throughout the solvent. With increasing temperature, most solutes dissolve more rapidly in most solvents. This explains, for example, why a teaspoon of sugar dissolves more quickly in a cup of hot tea then in a glass of iced tea.

Particle Size Particle size also affects the rate of dissolving. Large particles take longer to dissolve than smaller particles of the same substance. For example, sugar cubes dissolve more slowly than granular sugar, and rock salt dissolves more slowly than table salt. Solvent particles must bump into solute particles for dissolving to occur. Particles of a solvent will contact solute particles at the surface of a clump or crystal of solute particles. Therefore, large pieces of a solute must be broken apart to enable solvent particles to come in contact with solute particles.