Illustrated Guide to Home Chemistry Experiments

326 DIY Science: Illustrated Guide to Home Chemistry Experiments

SBSTITUTIU oNS ANd modIfICATIoNS

• You may substitute any glass container of similar size
  for the beaker.


• You may use any form of polystyrene, including
  Styrofoam or the polystyrene foam used in insulated
  drinking cups and foam packing peanuts.

LABORATORY 18 .3:

pREpARE A GELLEd SoL

A sol is a solid phase dispersed in a liquid

continuous phase. Ordinarily a sol is a liquid,

but it can be converted to a semi-solid gel by

adding a gelling agent. In some cases, the solid

phase itself may also serve as the gelling agent.

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ balance and weighing boat

£ beaker, 250 mL

£ graduated cylinder, 100 mL

£ stirring rod

£ matches or lighter

£ watch or other timing instrument

£ gasoline (100 mL)

£ rigid polystyrene foam (35 g)

In this lab, we’ll prepare a flammable gelled sol that comprises
ordinary gasoline as the liquid continuous phase with polystyrene
plastic serving as both the dispersed solid phase and the gelling
agent. This gelled sol is a slightly modified version of the material
the military calls Super Napalm B. (Actual Super Napalm B uses
low-octane gasoline rather than standard gasoline, and includes
a small percentage of benzene, which we’ll leave out because it’s
difficult to obtain.)

POCEDURER
1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing. Verify that
there are no open flames or other potential ignition
sources nearby, and make sure that you have a fire
extinguisher handy.

2. Use the graduated cylinder to measure 50.0 mL of
   gasoline and transfer it to the 250 mL beaker.


3. Weigh 15.0 g of polystyrene. The density of polystyrene
   foam (Styrofoam or similar) is so low that you need a
   large weighing boat to contain a reasonable mass. I used
   a 1-quart plastic kitchen container that comfortably held
   15 g of rigid Styrofoam packing material broken into
   small chunks.


4. Add a small (thumb-size) chunk of polystyrene to the
   beaker and observe the reaction. The foam fizzes and
   appears to dissolve in the gasoline, leaving a small
   amount of undissolved residue. In fact, what appears
   to be undissolved residue is the first appearance of the
   gelled sol.


5. Continue adding the first 15 g of polystyrene in small
   chunks, using the stirring rod to press the polystyrene
   down into the liquid. Note that the gelled sol continues
   to grow in volume. After you’ve added the first 15 g, the
   beaker appears to contain mostly gelled sol, but with a
   significant amount of liquid gasoline remaining.


6. Weigh out another 15 g of polystyrene, and continue
   adding it in small chunks to the beaker, with stirring.
   When you’ve added a total of 30 g of polystyrene, the
   sol appears to have “soaked up” nearly all of the liquid
   gasoline, as shown in Figure 18-3.

FIGURE 18-3: The gelled sol forms