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Solubility - what is it?
Solubility - what is it?
The solubility of a substance is the maximum amount of that substance that will dissolve in a litre of solvent; substances we are concerned with are ionic compounds
The solubility of a substance is the maximum amount of that substance that will dissolve in a litre of solvent; substances we are concerned with are ionic compounds
Solubility is measured in molL⁻¹ or g L⁻¹
Solubility is measured in molL⁻¹ or g L⁻¹
Like solvents dissolve like solvents, polar solutes will dissolve in polar sovents
Like solvents dissolve like solvents, polar solutes will dissolve in polar sovents
To dissolve the forces of attraction holding the solute together must be overcome and the force of attraction between the solvent and solute must be greater than that holding the solute together. In the solution of AgCl the force of attraction between the positive end of the water molecule (H+) and the negative Cl-, and the force of attraction between the negative end of the water molecule (O with its 2 non bonding pairs of electrons) and the positive Ag+ ion must be stronger than that between the Ag+ and the Cl-
To dissolve the forces of attraction holding the solute together must be overcome and the force of attraction between the solvent and solute must be greater than that holding the solute together. In the solution of AgCl the force of attraction between the positive end of the water molecule (H+) and the negative Cl-, and the force of attraction between the negative end of the water molecule (O with its 2 non bonding pairs of electrons) and the positive Ag+ ion must be stronger than that between the Ag+ and the Cl-
Soluble substances are where 10g or more will dissolve in 1 litre of solvent; insoluble substances are where <0.001g will dissolve in 1 litre of solvent
Soluble substances are where 10g or more will dissolve in 1 litre of solvent; insoluble substances are where <0.001g will dissolve in 1 litre of solvent
Sparingly soluble refers to substances that dissolve a little, somewhere between these values
Sparingly soluble refers to substances that dissolve a little, somewhere between these values
A saturated solution is one where no more solid can be dissolved in a given volume at that temperature
A saturated solution is one where no more solid can be dissolved in a given volume at that temperature
A saturated solution of a sparingly soluble solid, like the one shown above is in equilibrium, and an equilibrium constant expression can be written
A saturated solution of a sparingly soluble solid, like the one shown above is in equilibrium, and an equilibrium constant expression can be written
RECAP ON EQUILIBRIUM AND INTRODUCTION TO SOLUBILiTY EXPRESSION
RECAP ON EQUILIBRIUM AND INTRODUCTION TO SOLUBILiTY EXPRESSION
The solubility product
The solubility product
solubility calculations
solubility calculations
Using solubility to find out the solubility product of an ionic compound
Using solubility to find out the solubility product of an ionic compound
Using Ks to find the solubility of an ionic compound
Using Ks to find the solubility of an ionic compound
Solubility and a common ion
Solubility and a common ion
(see further down this post for where this is covered with other factors affecting solubility)
If a solution of KCl was added to AgCl then the common ion is Cl⁻ . This would have an effect on solubility and is called the common ion effect. According to Le Chatelier and equilibrium principles when more of the same ion is added then equilibrium will shift to favour the reaction that will remove this ion.
If a solution of KCl was added to AgCl then the common ion is Cl⁻ . This would have an effect on solubility and is called the common ion effect. According to Le Chatelier and equilibrium principles when more of the same ion is added then equilibrium will shift to favour the reaction that will remove this ion.
This is because for a saturated solution, Ks has to stay constant, at a given temperature.
This is because for a saturated solution, Ks has to stay constant, at a given temperature.
Ks = [Ag⁺] [Cl⁻], and if [Cl⁻] is increased for Ks to remain constant for this saturated solution [Ag⁺] must decrease, meaning less AgCl dissolves in a solution already containing chloride ions.
Ks = [Ag⁺] [Cl⁻], and if [Cl⁻] is increased for Ks to remain constant for this saturated solution [Ag⁺] must decrease, meaning less AgCl dissolves in a solution already containing chloride ions.
The common ion could be H⁺ or OH⁺ and if the solute contains an ion that can produce a weak acid or base then the pH of the solution will affect solubility
The common ion could be H⁺ or OH⁺ and if the solute contains an ion that can produce a weak acid or base then the pH of the solution will affect solubility
Common ion and solubility calculation
Common ion and solubility calculation
Predicting precipitates
Predicting precipitates
To predict whether a precipitate will occur for a given reaction the ionic product (IP), sometimes given as Q, is used. The IP is the product of the concentration the 2 relevant ions raised to the number of moles (coefficient) in the balanced chemical equation. Unlike Ks, IP can apply to all solutions at any concentration.
To predict whether a precipitate will occur for a given reaction the ionic product (IP), sometimes given as Q, is used. The IP is the product of the concentration the 2 relevant ions raised to the number of moles (coefficient) in the balanced chemical equation. Unlike Ks, IP can apply to all solutions at any concentration.
Remember Ks is only applicable to saturated solutions.
Remember Ks is only applicable to saturated solutions.
For example if we wanted to predict whether a precipitate of Lead hydroxide would form when Lead nitrate was added to sodium hydroxide, IP = [Pb²⁺] [OH⁻]² IP would then be compared to Ks for Pb(OH)₂ to predict whether a precipitate would form.
For example if we wanted to predict whether a precipitate of Lead hydroxide would form when Lead nitrate was added to sodium hydroxide, IP = [Pb²⁺] [OH⁻]² IP would then be compared to Ks for Pb(OH)₂ to predict whether a precipitate would form.
Calculating IP to predict precipitates
Calculating IP to predict precipitates
Other factors affecting solubility
Other factors affecting solubility
There are two other key factors to consider that affect solubility:
There are two other key factors to consider that affect solubility:
1) Formation of complex ions
1) Formation of complex ions
2) Effects of pH
2) Effects of pH
Solubility CALCULATIONS WALK THROUGH
Solubility CALCULATIONS WALK THROUGH
Solubility calculations 2
Solubility calculations 2
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