|
Suggested follow-up (discussion)
|
|
(Possible answers in italics, but other answers might also
apply.)
This activity models the concept of the molten lead collecting
the gold or other precious metal atoms in the molten rock during
the fire assay method of analyzing rocks for gold content. What
might be similar in the two processes? (The gelatinous
aluminum hydroxide precipitate is distributed throughout the
solution, then starts falling toward the bottom as the particles
get larger. The lead is also distributed throughout the melted
rock sample, and as bigger particles accumulate it starts to fall
through the melted rock.) What might be different? (The
water is less viscous than the melted rock; the lead is much more
dense than the aluminum hydroxide precipitate.)
Think about possible reasons the clay particles might be
caught by the gelatinous aluminum hydroxide precipitate. What
might be the reasons gold might be caught by the lead? (The
clay particles might be physically trapped by the gelatinous
aluminum hydroxide precipitate. The clay particles might be
attracted to the aluminum hydroxide precipitate because of slight
electrical charges on different parts of the particles. The gold
might be attracted to the lead because they are both metals; or
it might be forced out of the melted rock because it is still a
metal, not in a compound with the other elements in the melt.)
Extensions
- Water treatment plants use several flocculants, usually
including the aluminum sulfate. A field trip to a water
treatment plant would expand understanding of the uses of
flocculants.
- The chemistry of attractions of one molecule to another
involves the structure of each of the molecules. Partial
charges on one part of the molecule may attract
oppositely charged parts of another molecule such as is
found in hydrogen bonding. Study the locations of partial
charges on the aluminum hydroxide molecule and on clay
particles. For the gold and lead atoms, partial charges
are not a factor because these elements occur here as
atoms not combined into molecules with other elements.
Study the properties of gold and lead atoms to see if
they might be attracted because they are similar in
electronic structure.
|
|
Suggested follow-up (discussion)
|
|
