Chemical Principles of Sample Preparation

Solution

• homogenous mixture

• solute, solvent

Concentration

• weight/volume

• Molarity

• Formailty

• Normality

Concentration (mg/mg)

• Weight/Weight

• Molality

• Percent composition

Physical solutions

• exist in the body

• most solvation/dissolution

• solvent molecules separate lattice of solids

• reversible

Chemical solutions

• form new prodcuts

• derivatization

Ionic bonding

• complete transfer of electrons

• Ions are attracted to each other by charge

• Not a true bond

Covalent

• electrons are shared between atoms

• true bond-fixed distances and directions

  • nonpolar covalent bond- electrons are equally shared

  • Polar covalent bond- electrons are unequally shared

London Dispersion Forces

• weakest

• effective only when molecules are in close proximity

• instant/induced dipole

Chemical Equilibrium

• derived from the law of mass action

• rate of the forward reaction is equal to the rate of the reverse reaction

Dissolution

• chemical composition

• dipole moments

Nonpolar chemical families

• experience primarily London dispersion forces

• Saturated hydrocarbons

Polar chemical families

• ionic compounds

• molecules capable of hydrogen bonding

• water

Dipole Moment

polarity of a molecule is the sum of all molecular forces

Moderately Polar

• Molecules are comprised of polar covalent bonds with heteroatoms

  • dispersion forces

• Soluble in non-polar and polar solvents

  • where most chemistry happens

Lattice Energy

energy required to separate a mole of an ionic compound

Electron Affinity

Negative of the energy released when an electron is added to an atom

• increases from left to right across the periodic table

Ionization Energy

Energy required to remove an electron from an atom

Solvation

• Solvent interacts with a solute to form an ion surrounded by solvent molecules

  • energy is needed to break the interactions between ions

  • energy is released by the interaction of ions with solvent molecules

• Energy of solvation is higher than lattice energy

Solubility

Energy of solvation must be higher than the lattice energy to dissolve a solid

Factors Affecting Solubility

• Time

  • more time is generally better

• Surface Area

• Temperature

• Common Ions

  • Le Chatelier’s Principle

• Salt Effect

Purpose of Extraction

• extract compounds from matrix

• separates from impurities

• based on molecular characteristics

Acid-Base extraction

• liquid-liquid extraction

• two solvents that are immiscible with conflicting polarities

• based on compounds affinity and solubility for one solvent over the other

Partition Coefficient

ratio of concentration of analyte in the organic layer to the concentration in aqueous layer

Bronstead-Lowry Theory

• Acids are proton donrs

• bases are proton acceptors