Tips for the Teacher

Language of Chemistry
Major Factors in the Dissolving Process

Language of Chemistry

Vocabulary

precipitate

solid formed in solution by a reaction.

solubility

amount of a substance that dissolves in a given quantity of solvent (for example water) at a given temperature.

solubility-product constant (Ksp)

equilibrium constant for the dissolving of\par a slightly soluble (or nearly insoluble) ionic compound.

tincture

an alcohol solution, as in “tincture of iodine.”

Major Factors in the Dissolving Process

DH_solute + DH_solvent + DH_mixing = DH_solution

If DH in "A" is GREATER than DH in "B," then

• DH_solution is Endothermic
• Solution gets colder as it forms
• Heating will cause more solid to dissolve
• Energy needed to break old attractive forces > Energy released by formation of new forces

If H in "A is LESS than DH in "B," then

• DH_solution is Exothermic
• Solution gets warmer as it forms
• Heating will decrease the amount of solid dissolved
• Energy needed to break old attractive forces < Energy released by formation of new forces

There is a tendency for entropy to increase when solutions form.

IF DS is positive, solution is favored.
IF DS is large enough, it can overcome DH effects and substance will go into solution.

These conditions for dissolving can also be represented by the following charts.

(page 11,12,13)

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