Answers to Concept Checks

12.1

The two solvents    must    be  immiscible  and must    have    different   polarity    or  acid–base   properties

that    allow   a   compound    of  interest    to  dissolve    more    easily  in  one than    the other.

It  is  better  to  do  three   washes  with    10  mL  than    to  do  one with    30  mL; more    of  the compound    of

interest    would   be  extracted   with    multiple    sequential  extractions than    one large   one.

Acid    dissolves   better  in  aqueous base    because it  will    dissociate  to  form    the conjugate   base    and,

being   more    highly  charged,    will    become  more    soluble.    Note    that    like    dissolves   like    applies to

polarity;   acids   and bases   dissolve    more    easily  in  solutions   with    the opposite    acid–base

characteristics.

12.2
Distillation takes advantage of differences in boiling points in order to separate solutions of
miscible liquids.
A solution of ether and methylene chloride, which have very close boiling points, can be
separated by using fractional distillation.
Vacuum distillation would be the best technique to separate two chemicals with such high
boiling points because the decreased ambient pressure will allow them to boil at a lower
temperature.

12.3
Each of these methods separates compounds using charge and polarity.

Type    of  Column

Chromatography

Method  for Separating  Sample

Ion-exchange Column is  given   a   charge, which   attracts    molecules   with    the opposite    charge

Size-exclusion Small    pores   are used;   smaller molecules   are trapped,    while   larger  molecules   pass    through the

column

Affinity Specific   receptors   or  antibodies  can trap    the target  in  the column; the target  must    then    be  washed