Video Transcript
Which of the following substances
or phenomena is an example of a solid foam, a gas dispersed through a solid? (A) Whipped cream, (B) smoke, (C)
air, (D) marshmallow, or (E) glass.
To start, let’s discuss the phase
composition of each of the possible answer choices, starting with (A) whipped
cream. Whipped cream is made from heavy
whipping cream, which is made up of a mixture of water, lipids, and soluble
components. When whipping cream is stirred or
whisked for enough time, it begins to entrap air inside. And once enough air is incorporated
into the liquid, you end up with whipped cream, a gas dispersed through a
liquid. But the question is asking for a
gas dispersed through a solid dispersion medium. So we can correctly eliminate
answer choice (A).
Answer choice (B), smoke, is formed
when organic material, such as wood, is incompletely burned. This leads to solid particles being
pushed up and dispersed through air. And since smoke is an example of a
solid dispersed in a gas, air, we can correctly eliminate answer choice (B).
Answer choice (C), air, is a
complex mixture of a number of different gases. It’s made up of 78 percent
nitrogen, 20.9 percent oxygen, 0.9 percent argon, 0.03 percent carbon dioxide, and
0.17 percent of other gases. But since all the components in air
are in the gas phase, we know that answer choice (C) cannot be the correct
answer.
Marshmallows are made up almost
entirely of sugar. And similarly to whipped cream, air
has been incorporated into the sugar to give it its fluffy texture. And because a marshmallow is made
up of air, which is a gas, dispersed through sugar, which is a solid, we can
confidently choose answer choice (D) as the correct answer.
To further confirm answer choice
(D), let’s take a look at answer choice (E) glass. Glass is primarily made up of sand,
soda ash, and limestone. When heated to over 1700 degrees
Celsius, the combination of these three solids creates what we know as glass. And since glass is a mixture of
solid materials, we can finally say that answer choice (E) is not the correct
answer.
