Advanced Chemistry Notes
Solution Notes
Solutions
Solutions – homogeneous mixtures of
two or more substances
• Made up of:
– Solvent – substance that does the dissolving
– Solute – substance being dissolved
• Examples of Solutions
– Kool-Aide: water – solvent, sugar – solute
– Pop: water – solvent, carbon dioxide – solute
Solutions
Types of Solutions
• Liquid – Solid solution
– Ex: salt water
• Liquid – Liquid solution
– Ex: hydrochloric acid and water
• Miscible – when two liquids mix
• Immiscible – when two liquids will not mix
• Liquid – Gas solution
– Ex: oxygen and water
Solutions
Other types of Solutions
• Solid – Solid solutions
– Brass alloys
• Solid - Liquid solutions
– Gold dissolves Mercury
• Solid – gas solutions
– Palladium dissolves hydrogen
• Gas – Gas solution
– air: O2, N2, Ar
Creating Solutions
The dissolving process consists of three steps
• Dissociation
• Solvation
• Diffusion
The Dissolving Process
The Dissolving Process (Ex: sugar and water)
1. Dissociation
• Attractive forces between solute molecules
must be overcome.
• Water pulls sugar apart molecule by
molecule
The Dissolving Process
2. Solvation
•
Positive ends of solvent molecule attach to
negative ends of solute molecule and vise
versa.
Water molecules surround and interact with
sugar molecules.
Water molecules remove sugar molecules
from the crystal
•
•
–
Dispersion and dipole forces are at work here
Solvation
The Dissolving Process
The Dissolving Process
• When the
solvent is
water the
solvation
process is
called
hydration.
The Dissolving Process
3. Diffusion
•
•
Random molecular movement spreads solute
through out the solution
Sugar molecules are evenly dispersed
throughout the water
Factors Influencing Dissolving
• Factors that influence that rate at which a
substance dissolves
– Temperature
– Stirring
– Large surface area of solute exposed to
solvent
• How does this relate to putting sugar in
your coffee?
Solvent Selectivity
What will and will not dissolve?
• G R of T  Like dissolves Like
• Polar substances dissolves other polar
substances
– Polar – ionic and polar covalently bonded
compounds have dipoles
• H2O and HCl
Solvent Selectivity
• Non-polar substances dissolve other nonpolar substances
– Non-polar compounds lack dipoles
• CO2 and N2
• Oil and Soap
• Exceptions to the rule
– Chalk (CaCO3) does not dissolve in water –Why?
Both are polar.
• Water has to be able to overcome chalks (CaCO3)
intermolecular attractive forces to dissolve it – it can’t
• Chalk (CaCO3) is to tightly bonded intermolecularly
Solubility
• How much solute can a substance hold?
• Unsaturated solution – the solvent could
dissolve more solute under standard
conditions
Solubility
• Saturated solution – when solvent can
hold no more solute at a given
temperature.
– When solution is saturated some of the solute
remains at the bottom of the glass.
Dissolving and precipitating occur at equal
rates. This is called Dynamic Equilibrium.
– H2O(l) + NaCl(s) == Na+(aq) + Cl-(aq)
Solubility
• Supersaturated – solution holds more
solute than it would at standard conditions
Solubility
Temperature and Solubility
• When temperature is increased solubility also
increases
• Consider the endothermic reaction below (solid
dissolved in liquid)
KClO3(s) + H2O(l) + heat == K+(aq) + ClO3-(aq)
– Heat acts as a reactant (needs heat to dissolve)
• Adding heat increases solubility  makes more
solution
Solubility
Solubility
Temperature and Solubility
• When temperature is increased solubility
decreases
• Consider the exothermic reaction below (liquid
dissolves a gas)
CO2(g) + H2O(l) == Heat + CO2(aq)
– Heat acts as a product (gives off heat)
• Adding heat decreases solubility
– What holds more carbonation – warm or cold pop?
Solubility
Pressure and Solubility
• Effects of pressure on the solubility of liquids
and solids are minimal.
• Effects of pressure on the solubility of gases are
drastic.
– Henry’s Law – the solubility of gases increases with
the partial pressure of gases above the solution.
• EX: Pop – when you open a can of pop the result is the
carbon dioxide escaping from the solution because the partial
pressure of the gases above the pop decreases.
Solubility and Pressure
Solutions
Summary
• Components of a solution
• The dissolving process
– Factors affecting dissolving Process
• Solvent Selectivity
• Solubility
– Unsaturated / saturated /supersaturated
– Temperature / Pressure