Biopharm 8 Solubility

Write the equilibrium equation for a saturated mixture

[D]solid ⇌ [D]soln

Explain the relative rates of dissolution and precipitation in two phase mixtures

Explain the processes that occur in solutions and suspensions at equilibrium

Solubility is NOT a

Process

Solubility definition

The dissolved concentration of a solute in equilibrium with excess undissolved solute; [Dsolid] ⇋ [Dsolution]

Dissolved definition

Solute molecules in solution phase

Undissolved definition

Solid particles

What is a solubility value?

A solution concentration (mg/mL, mM, etc.)

What does it mean to be “saturated” with dissolved drug molecules?

The solution phase concentration where the solvent cannot dissolve any more of the solid

What is an example of a saturated mixture?

A suspension

“Mixture of a solid in a liquid” definition

A solid material and liquid material put into the same container and stirred or otherwise agitated to disperse the two materials uniformly throughout the container

2 types of solid-liquid mixtures in pharmacy

Solution and suspension

What is Ibuprofen surrounded by in a solid?

Other Ibuprofen molecules

What are two processes that begin immediately upon mixing a solid and a liquid?

Molecules from the particles dissolve into the liquid phase; molecules from the solution phase precipitate onto solid particles

When is dissolution much faster than precipitation?

At the beginning of mixing

What happens to the dissolved concentration over time?

Increases with time BUT quickly at first, then slower over time

Dissolution and precipitation continue, and dissolved concentration continues to increase UNTIL (1)

The solid particles all completely dissolve, leaving only the liquid phase; the mixture is a solution

Dissolution and precipitation continue, and dissolved concentration continues to increase UNTIL (2)

The dissolved concentration reaches the solubility limit for the mixture; the mixture is a suspension

What can happen what the dissolved concentration reaches the solubility limit for the mixture?

The mixture is a suspension; dissolution and precipitation continue at equal rates so dissolved concentration remains constant, and excess particles remain in liquid

In a solution, all solute molecules are ______ and ______

Separated from each other and surrounded by water molecules

In a solution, when there are the same number of solute and water molecules diffusing in every direction and the solute concentration is homogenous throughout the mixture

The system is at equilibrium

In a solution, at equilibrium there is no dissolution or precipitation because

There are no particles