(Chemists have Solutions!) Unit 4: Solutions (Chemists have Solutions!)

Definitions Solution: Homogenous mixture of two or more substances in a single phase Solvent: is the component of a solution that exists in the greatest quantity. Solute: is the component of a solution that exists in the smaller quantity. Saturated Solution: A solvent is said to be saturated with a solute, when no more solute will dissolve into it. Unsaturated Solution: is one in which more solute can be dissolved

Definitions Soluble: a solute is soluble in a solvent if the solute and the solvent mix to form a homogenous mixture. Insoluble: a solute is said to be insoluble in a solvent if less than 0.1 moles of the solute will dissolve in a liter of solution Solubility: is the maximum amount of a given solute that dissolves in a given solvent at a given temperature. I.e., when measuring the solubility of a system it must be for a saturated solution.

Units of Solubility Solubility is the maximum concentration of a solute in a solvent for a given temperature. Units of solubility are: Grams(solute)/liter of solution Moles(solute)/liter of solution (M, molarity)

Determining Solubility Must prepare a saturated solution Use an xs amount of solute (goal is to have some un-dissolved solute separate from the solution) Mix thoroughly and let sit over night at a constant temperature Pipette a known amount of the saturated solution (25.00 ml) into a pre-weighed weigh boat Evaporate solution to dryness (remove solvent) Determine the weight of the solute Calculate solubility in grams/liter (convert to mol/L if required

Properties of Solutions Conductivity: is a measure of how well a solution conducts electricity. ( for a solution to conduct electricity, it must contained charged particles, I.e., IONS) pH: the pH of a solution is a measure of how much H+ ions are in solution, the lower the pH the more H+ ions there are present , the Higher the pH the less H+ ions there are. Neutral water has a pH of 7.0 ( at 25 C.)

Dissolving Vs. Dissociating Dissociating is when an Ionic compound breaks down into its ions in solution Dissolving is when a covalent compound is absorbed by the solution, however it keeps its same chemical composition.

The Theory of Solubility Polar solvents will dissociate ionic compounds and dissolve polar covalent compounds Non-polar solvents will dissolve only non-polar covalent compounds.

What is Polarity? A compound is said to be polar if it processes a net permanent dipole moment that do not cancel each other out. Permanent dipole moments occur in covalent molecules where bonds exists between atoms with different electron-negativity. A Net permanent dipole occurs when all the dipoles in a molecule do not cancel each other out.

Molecular Shapes and Polarity

Importance of Polarity Polarity effects the solubility of a solute in a given solution Polarity effects the phase a pure compound will likely be in Polarity effects the shape of large molecules such as proteins

Intermolecular Forces Vs. Intramolecular Forces Intramolecular forces: are the forces internal to the molecule. They are responsible for holding the atoms in the molecule together. Intermolecular Forces: are the forces between molecules Dipole/Dipole interactions (polarity) Hydrogen bonding London forces