Lab final Flashcards
What determines the melting point?
the strength of intermolecular forces between molecules-H-bonds, dipole-dipole interactions, and van der Waals interactions
Hydrogen bonding
Hydrogen bonding
the non-covalent interactions between H a either N, O, or F
it is stronger than van der Waals forces, but weaker than covalent bonds
dipole moment
difference in charge/distance
dipole-dipole interactions
the attraction between two permanent dipoles (ex. HCl)
van der Waals interactions
any attraction between permanent or induced dipoles-usually over short distances, they are weak and temporary
How is melting point affected?
-Pure compounds typically melt over a narrow range
-Small impurities can cause the compound to melt over a relatively wide temperature range
-Too much sample, will also give a misleading result.
What is recrystallization?
What is recrystallization?
The process in which a crystalline material (solute) dissolves in a hot solvent and then returns to a solid again by crystallization in a cooled solvent.
-impurities typically will not crystallize if the process is conducted carefully
What three factors affect crystal formation?
- concentration of solute
- What solvent is used
- The temperature of the solvent
Like dissolves
Like
Most solvents have a BP under
100 c
Most solvents need to be volatile to
Evaporate quickly
Most solvents should have a maximum and minimum solubility
Hot- max and cold-min
Ex. of high polarity solvents
Methanol and ethanol
Ex of low polarity solvents=diethyl ether and ethyl acetate
Diethyle ether and ethyl acetate
