Ochem Lab Final VT questions with
correct answers
boiling point - correct answer ✔✔ Endothermic. Temperature at which the liquid's vapor
pressure equals the system's applied pressure. It is less affected by impurities than melting
points are.
Attractive forces weakest to strongest - correct answer ✔✔ induced dipole, dipole dipole,
hydrogen, ionic
Melting point - correct answer ✔✔ an endothermic process, highly sensitive to impurities that
will lower the melting point and widen its range. Used in identification by mixing with 10% of a
known solid with unknown solid
intensive properties - correct answer ✔✔ do not depend on the amount of matter present
extensive properties - correct answer ✔✔ depend on the amount of matter that is present
good recrystallization solvent - correct answer ✔✔ be inert, low bp, inexpensive and be
nontoxic
Recrystallization - correct answer ✔✔ impure solute is dumped in a recrystallization solvent,
while its boiling. It is then filtered and cooled. As the temperature decreases, the solute
becomes less soluble and the solution becomes saturated. It is then vacuum filtered, and the
crystals can be washed with cold solvent.
, refractive index - correct answer ✔✔ a measure of the light-bending ability of a medium.
Wavelength and temperature affect it. It is measured by the movement through air over the
movement in liquid.
Liquid Chromatography - correct answer ✔✔ components of a mixture are separated by
partitioning between a mobile liquid phase and a solid absorbent
Thin Layer Chromatography (TLC) - correct answer ✔✔ a competition between a compound's
attraction to a highly polar solid phase (silica, alumina, cellulose) and a solvent traveling over
the solid phase
TLC is used to - correct answer ✔✔ estimate purity, id a compound by comparing to a standard,
and test the completeness of a reaction.
Less polar substances on a TLC plate - correct answer ✔✔ advance further
More polar substances on a TLC plate - correct answer ✔✔ stay closer to the bottom
Rf value on a TLC plate - correct answer ✔✔ Distance travelled by substance / distance travelled
by solvent
Tailing on a TLC plate results from - correct answer ✔✔ application of too much compound on
the spotting line, and a compound slowly decomposing on the plate
Ethyl acetate - correct answer ✔✔ the polar component of the solvent,
Hexane - correct answer ✔✔ the nonpolar component of the TLC solvent from lab
Henderson-Hasselbalch equation - correct answer ✔✔ pKa = pH + log [HA]/[A-]
correct answers
boiling point - correct answer ✔✔ Endothermic. Temperature at which the liquid's vapor
pressure equals the system's applied pressure. It is less affected by impurities than melting
points are.
Attractive forces weakest to strongest - correct answer ✔✔ induced dipole, dipole dipole,
hydrogen, ionic
Melting point - correct answer ✔✔ an endothermic process, highly sensitive to impurities that
will lower the melting point and widen its range. Used in identification by mixing with 10% of a
known solid with unknown solid
intensive properties - correct answer ✔✔ do not depend on the amount of matter present
extensive properties - correct answer ✔✔ depend on the amount of matter that is present
good recrystallization solvent - correct answer ✔✔ be inert, low bp, inexpensive and be
nontoxic
Recrystallization - correct answer ✔✔ impure solute is dumped in a recrystallization solvent,
while its boiling. It is then filtered and cooled. As the temperature decreases, the solute
becomes less soluble and the solution becomes saturated. It is then vacuum filtered, and the
crystals can be washed with cold solvent.
, refractive index - correct answer ✔✔ a measure of the light-bending ability of a medium.
Wavelength and temperature affect it. It is measured by the movement through air over the
movement in liquid.
Liquid Chromatography - correct answer ✔✔ components of a mixture are separated by
partitioning between a mobile liquid phase and a solid absorbent
Thin Layer Chromatography (TLC) - correct answer ✔✔ a competition between a compound's
attraction to a highly polar solid phase (silica, alumina, cellulose) and a solvent traveling over
the solid phase
TLC is used to - correct answer ✔✔ estimate purity, id a compound by comparing to a standard,
and test the completeness of a reaction.
Less polar substances on a TLC plate - correct answer ✔✔ advance further
More polar substances on a TLC plate - correct answer ✔✔ stay closer to the bottom
Rf value on a TLC plate - correct answer ✔✔ Distance travelled by substance / distance travelled
by solvent
Tailing on a TLC plate results from - correct answer ✔✔ application of too much compound on
the spotting line, and a compound slowly decomposing on the plate
Ethyl acetate - correct answer ✔✔ the polar component of the solvent,
Hexane - correct answer ✔✔ the nonpolar component of the TLC solvent from lab
Henderson-Hasselbalch equation - correct answer ✔✔ pKa = pH + log [HA]/[A-]
