Video Transcript
Which of the following diagrams shows a beaker containing a solution?
When working in a chemistry lab, at times it may be necessary to be able to determine various properties of mixtures. In this example, you’ve come across three different glasses that display different properties when a beam of light is shined through them. In the first example (A), we can see that no light is observed within the glass. In answer choice (C), we observe that the beam of light has the same intensity both inside and out of the glass. And answer choice (B) is somewhere in the middle of the two other choices because we see that the beam of light is less intense as it passes through the glass.
In order to determine which of the diagrams shows a beaker containing a solution, we can use what is known as the Tyndall effect. The Tyndall effect describes the scattering of light that occurs when it passes through a colloid or fine suspension. The way in which the Tyndall effect is observed has to do with the particle size of a mixture, and the three types of mixtures that we’ll be talking about are solutions, colloids, and suspensions.
Let’s start by describing a solution. A solution is a homogeneous mixture where the particle sizes are between 0.01 and one nanometer. These particles are so small that we can’t even see them with a standard light microscope. Because the particles in the solution are so small, we don’t observe any scattering when light passes through it. And when no scattering is observed when light passes through this type of mixture, that means no light is observed.
The next type of mixture we’ll discuss is a colloid. Colloids are heterogeneous mixtures with particle sizes that range from one to 1000 nanometers, and these particles are large enough that they can be observed with a light microscope. Some of these particles are large enough that when short wavelengths of light collide with them, the light will scatter. This scattering causes some visibility of the light beam as it passes through.
And the final type of mixture is a suspension. Suspensions are heterogeneous mixtures where the particle sizes are greater than 1000 nanometers. These particles are large enough that they can be seen without a microscope. Because of the large particle size, more scattering is observed when a beam of light is passed through. And the more scattering there is, the more visible the light beam becomes.
At this point, we should have sufficient information to be able to answer the question. Which of the following diagrams shows a beaker containing a solution? We know that solutions have a small particle size, and because of that, there’s no observable scattering. And because answer choice (A) shows no observable scattering, we can choose this as the correct answer. We can also be confident that answer choices (B) and (C) are incorrect due to the fact that there’s some observable scattering as the light beam passes through both mixtures.
