Chapter 18 Laboratory: Colloids and Suspensions 321SBSTITUTIU oNS ANd modIfICATIoNS- You may substitute any clear glass container of
similar size for the 250 mL beaker(s). It saves time to
use multiple containers, because you can make up
samples and test the Tyndall Effect in one container
while waiting for earlier samples to separate by gravity
in other containers. - You may substitute a sheet of thin cardboard or plastic
cling-wrap for the watch glass; anything that covers
the beaker will do. - You may substitute any color of laser pointer for the
red laser pointer, but be aware that green, blue, and
white laser pointers are typically higher power and
more hazardous to use. - You may substitute tobacco (cigar, cigarette, or pipe)
smoke for the smoke produced by the incense or
joss stick.
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LABORATORY 18 .1:
oBSERvE SomE pRopERTIES of CoLLoIdS ANd SUSpENSIoNS
In this laboratory session, we’ll use gravitational
separation and the Tyndall Effect to test
various samples to determine whether they are
solutions, colloids, or suspensions.
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ eye dropper or Beral pipette£ beaker, 250 mL (1 or more)£ watch glass£ stirring rod£ matches or lighter£ laser pointer, red£ incense or joss stick (1)£ table salt (~1/4 teaspoon)£ club soda (~200 mL)£ homogenized milk (~20 drops)£ vegetable oil (~20 drops)£ starch water (~200 mL)£ talcum powder (~1/4 teaspoon)POCEDURER
1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing.
- Light the incense or joss stick and blow it out. When
it starts to produce smoke, place the 250 mL beaker
inverted over the incense and allow the beaker to fill with
smoke. Use the watch glass to cover the beaker. - Direct the beam from the laser pointer into the beaker
and note whether the Tyndall Effect is evident. Allow the
beaker to sit undisturbed for at least a minute or two,
and then note whether the smoke/air sample separates
on standing. Based on your observations, decide
whether the smoke/air sample is a solution, colloid,
or mixture. Record your observations by circling the
appropriate items on line A of Table 18-3. - Rinse the beaker thoroughly. Add about a quarter
teaspoon of table salt to about 200 mL of water in
the beaker and stir until the salt dissolves. Repeat the
procedures in step 3 and record your observations on
line B of Table 18-3. - Rinse the beaker thoroughly. Add about 200 mL of club
soda to the beaker. Repeat the procedures in step 3 and
record your observations on line C of Table 18-3. - Rinse the beaker thoroughly. Add about 200 mL of water
to the beaker and then about 20 drops of homogenized
milk. Stir until the contents of the beaker are thoroughly
mixed. Repeat the procedures in step 3 and record your
observations on line D of Table 18-3. - Rinse the beaker thoroughly. Add about 200 mL of water
to the beaker and then about 20 drops of vegetable
oil. Stir until the contents of the beaker are thoroughly
mixed. Repeat the procedures in step 3 and record your
observations on line E of Table 18-3. - Rinse the beaker thoroughly. Add about 200 mL of
starch water to the beaker. Repeat the procedures in
step 3 and record your observations on Line F of
Table 18-3. - Rinse the beaker thoroughly. Add about a quarter
teaspoon of talcum powder to about 200 mL of water in
the beaker and stir until the contents of the beaker are
thoroughly mixed. Repeat the procedures in step 3 and
record your observations on line G of Table 18-3.