The Dissolving Process

Hydration is the process in which ions are surrounded by water molecules. Dissociation is the separation of individual ions from an ionic compound as it dissolves in water.

Writing Dissociation Equations

Write a chemical equation for the dissociation of Na2SO4

Na2SO4(s) → Na(aq) + SO4(aq)

Balance the the number of ions on both sides and thus balance the charge.

Na2SO4(s) → 2Na(aq) + SO4(aq)

The Dissolving of Molecular Compounds

Miscible means that substances can mixed together and they dissolve forming a solution.

Immiscible means that substances cannot mix to form a solution.

Water and Oil Do Not Mix

Hydrocarbons do not mix with water, due to fact they are nonpolar and water is polar.

The water molecules are attracted to one another much, more greatly than the nonpolar long carbon chain of hydrocarbons, due to their polarity. When they are mixed water intermolecularly bond with one another and the hydrocarbon chains group together due to their London Dispersion Forces.

The hydrocarbon floats on top of the water because it is less dense.

Like Dissolves Like

The General Rule for what dissolves what is “Like Dissolves Like”.

Meaning polar substances dissolve polar substances and non polar dissolves nonpolar.

Many substances can be washed away with just water due to the fact they are polar.

But if you are painting with an oil based paint you will need a nonpolar solvent to get the paint off, such as varsol or if desperate gasoline.

Surfactants

A surfactant is a compound that can reduce the surface tension of a solvent.  They have both a hydrophobic (“water fearing”) end and a hydrophilic (“water liking”) end.

They can used to encourage oil and water to mix.  This is accomplished by breaking down the hydrogen bonding at the surface of the water. Which allows a polar substance like water to mix with a nonpolar liquid like oil.

Summary

For a substance to dissolve, solute-solvent attractions must overcome the attractions within both solute and solvent

Ionic compounds dissociate as they dissolve, releasing their ions into solution.

The symbol (aq) after a chemical formula means that the dissolved entity is surrounded by a sphere of water molecules

Solutes dissolve in solvents of similar properties (“Like Dissolves Like”).  Ionic and polar covalent compounds are soluble in polar solvents.  Nonpolar covalent compounds are soluble in nonpolar solvents.

Miscible liquids mix to form a solution.  Immiscible liquids do not mix.

Surfactants are compounds that reduce the surface tension of a solvent.  Surfactant ions have a hydrophilic end that is attracted to water and hydrophobic end that is repelled by water.