Formations of Solutions
Objectives:
• 1.Explain the process by which solutions form.
• 2.Give the definition of solubility and explain
how it is affected by variousfactors.
KeyTerms:
• Solvation, hydration, solubility
Solutions
• Solutions are homogenous (looks the same) mixtures of
substances in a single state.
– Solutions can exist in any phase
– The particles in a solution are very small - atoms, ions,molecules
– Particles in a solution are evenly distributed –
• one part of the solution has the same molecular make-up as another
– Solutions do not separate under normal conditions
• Common solution types:
– alloy - solution consisting of 2 or more metals
– aqueous - any solution containing water
– hydrate - solution where water is the solvent
Solvation
• Solvation is the term given to the interaction
between solvent and solute.
– If the solvent is water the reaction is called hydration water is the most common polar solvent
• solute - substance dissolved in a solution
• solvent - substance that does the dissolving
• soluble - substance that is capable of dissolving
– Remember that “like dissolves like”… polar and ionic solutes
dissolve in polar solvents and non-polar solutes in non-polar
solvents
• insoluble - substance that does not dissolve
• miscible – soluble in any amount
Solubility
• Solubility is the amount of solute that can dissolve in a solution at given
conditions.
– expressed in grams of solute per 100grams of solvent.
– A solvent containing its maximum amount of solute is said to be saturated
with solute
• any amount less is unsaturated
• holding more solute (past saturation point) is supersaturated
– Created by cooling a saturated solution
– substances that can mix in any proportions are said to be miscible
• example: alcohol and water
• solvent is substance with the greater amount
• Substances that don't mix in any proportion are said
to be immiscible
– example: oil & water
Factors Affecting Solubility Temperature
• Temperature
– Solubility of a gas is decreased with an increase in
temperature
• due to an increase in the kinetic energy of the molecules
vapor pressure of the gas rises
– Solubility of a solid is usually increased with an
increase in temperature by increasing the KE of the
solution
• exception:
– Exothermic rxns (reactions releasing heat) - increasing
temperature decreases solubility
– an increase temperature has no effect on solubility when there is
no temperature change for the solution (boiling)
Factors Affecting Solubility - Pressure
• Pressure
– Solubility of a gas is increased with and increase in
pressure (Henry's Law)
• S1/P1 = S2/P2
• Solubility of a gas is directly proportional to the pressure exerted above it
– Solubility of a solid is usually unaffected by pressure
Factors Affecting Solubility – Solute
Size
• Surface area
– The greater the surface area the greater the rate
of dissolving
– Breaking the solute into smaller pieces increases
the surface area
Greater Surface Area
Factors Affecting Solubility – Stirring
• Stirring - increases the rate of dissolving by
bringing solvent in contact with solute