(b) In the 1850s, Michael Faraday prepared ruby-red

colloids of gold nanoparticles in water that are still stable

today. These brightly colored colloids look like solutions.

What experiment(s) could you do to determine whether a

given colored preparation is a solution or colloid?

Video transcript

All right. Hello everyone. So this question says that a certain colloid of nanoparticles in water appears as a colored solution to the naked eye. Which experiment below can be used to determine whether a given mixture is a solution or a colloid. Option. A says to shine a beam of light on the mixture and check for scattering of light. Option B says submersing the closed container with the mixture in water and determine its density relative to water. Option C says check for particles settling at the bottom of the container a few hours after preparation and option D says all of the above. So here to start off recall first and foremost, what a colloid actually is a colloid is a type of mixture in which we have particles of one substance suspended throughout another substance. Now, these particles are microscopically dispersed and they can be insoluble or soluble. And so with colloids comes a very specific phenomenon known as the tyndall effect and the Tindall effect is the effect of light scattering within a colloidal dispersion while showing no light in a true solution. So to check for light scattering, the outline of the light beam should be visible if it's a colloid and it should be invisible if it's a true solution. This means that option A is a valid answer, but let's go ahead and discuss the other two regardless because option D is all of the above which is not true. Now, here, option B is describing an experiment which tells us or can tell us about the density of the mixture relative to water. Now, the problem with this is that density does not necessarily tell us anything about the identity of the mixture because solutions and colloids can both be more or less dense than water. So experiment B is not going to tell us much. And option C is proposing that we check for particles at the bottom of a container a few hours after preparation. So here, option B is describing a solution separating or rather a mixture separating due to just gravity or the effect of gravity on separating a mixture. This is not going to tell us any information either because a suspension is the type of mixture that would be separated by gravity. A stable colloid should not separate by this lo so option C is not correct either. Meaning our answer is option A in the multiple choice in which we shine a beam of light on the mixture and check for scattering of light. And so with that being said, thank you so very much for watching. And I hope you found this helpful