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(a) Do colloids made only of gases exist? Why or why not? (b) In the 1850 s, 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?

Short Answer

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(a) Colloids made only of gases do not exist because gases naturally mix together uniformly to form a uniform solution rather than a mixture with a dispersed phase. (b) To differentiate between a colored colloid and a solution, perform experiments such as observing the Tyndall Effect by shining a light, filtering the substance to check for residue, and allowing the substance to sediment or using a centrifuge to check for particle settling.

Step by step solution

01

(a) Existence of Gas Colloids

Colloids, as you may recall, are a mixture where one substance is dispersed evenly throughout another. However, it is important to note that colloids made only of gases do not exist. This is because gases, unlike liquids or solids, have the tendency to mix together evenly and form a homogeneous solution—even when they are of different types. This behavior of gases prevents the formation of gas-gas colloids. In summary, colloids made only of gases do not exist because gases naturally mix together uniformly to form a uniform solution rather than a mixture with a dispersed phase.
02

(b) Identifying a Colloid Vs. a Solution

To differentiate between a colored colloid and a solution, you can perform the following experiments: 1.
03

Tyndall Effect

Shine a light through the substance, preferably a directed beam such as a laser pointer. If the substance is a colloid, you will see the path of the light through the substance due to the scattering of light by its large particles (the Tyndall Effect). In a solution, the light will not scatter and you will not be able to observe the path of the light through the substance. 2.
04

Filtration

Pass the substance through a filter, such as filter paper or a membrane with small enough pores to trap colloidal particles. A colloid will leave some residue on or within the filter because the colloidal particles are larger and will be trapped in the filter. A solution will pass through the filter without leaving any residue since the particles in solution are much smaller and do not get trapped in the filter. 3.
05

Sedimentation and Centrifugation

Allow the substance to sit undisturbed for some time, or use a centrifuge to speed up the process. If the substance is a colloid, you may observe sedimentation or the settling of particles at the bottom over time. On the other hand, a solution will remain homogeneously mixed and not show any signs of particle settling. By performing these experiments, you can effectively determine if the given colored preparation is a colloid or a solution.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tyndall Effect
The Tyndall Effect is a simple yet fascinating phenomenon associated with colloids. It refers to the scattering of light as it passes through a colloidal mixture. Imagine shining a flashlight through fog. You observe the beam illuminating the air, highlighting the path through which it travels. This is due to the light being scattered by larger particles in the colloid. The same effect can be seen when you shine a laser pointer through a colloid. If the light path is visible, it confirms the presence of a colloid, as solutions do not scatter light in the same way. This makes the Tyndall Effect a practical experiment for distinguishing between solutions and colloids.
  • Light is scattered by particles in a colloid.
  • Can be demonstrated with laser pointers or flashlights.
  • Helps in identifying colloids from solutions.
Sedimentation
Sedimentation involves the settling down of particles in a colloidal mixture over time. It's like watching sand settle at the bottom of a glass of water. In colloids, the dispersed particles are larger than those found in solutions. This size allows them to eventually settle due to the force of gravity. By observing a colloid, you might notice layers forming or particles gathering at the bottom over time, known as sediment. This property can be helpful to determine the stability of a colloid and differentiate it from a solution.
  • Particles settle over time due to gravity.
  • Indicates particle size larger than solutions.
  • Useful for identifying colloids from homogeneous mixtures.
Centrifugation
Centrifugation is a technique used to speed up the process of sedimentation. This method involves spinning the colloid rapidly in a centrifuge, which applies a force greater than gravity. The force propels larger particles to move quickly to the bottom. This process efficiently separates the dispersed phase from the dispersing medium of a colloid. In a laboratory setting, centrifugation is an essential tool for separating and purifying colloidal particles. It provides a clear visual way to distinguish between a colloidal suspension and a true solution. Solutions do not separate under the same conditions due to their much smaller and uniformly distributed particles.
  • Uses centrifugal force to speed up sedimentation.
  • Separates larger particles in colloids from the medium.
  • Effective for laboratory analysis and purification.
Filtration Techniques in Chemistry
Filtration is a common laboratory process to separate solids from liquids or gases. In the context of colloids, filtration can help differentiate them from true solutions. Colloidal particles are larger, and when passed through a filter with appropriately sized pores, they are trapped. Contrast this with a solution that passes through the filter without leaving any residue, as its particles are too small to be caught. Different types of filters can be used depending on the specific requirements, from simple filter paper to advanced membranes. Filtration serves as a versatile technique in various fields, including chemistry, to clean, purify, or analyze colloidal dispersions.
  • Traps larger colloidal particles but allows solutions to pass through.
  • Utilizes different filter types for various applications.
  • Essential for separating, cleaning, and analyzing colloids.

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Most popular questions from this chapter

The density of toluene \(\left(\mathrm{C}_{7} \mathrm{H}_{8}\right)\) is \(0.867 \mathrm{g} / \mathrm{mL},\) and the density of thiophene \(\left(\mathrm{C}_{4} \mathrm{H}_{4} \mathrm{S}\right)\) is 1.065 \(\mathrm{g} / \mathrm{mL}\) . A solution is made by dissolving 8.10 \(\mathrm{g}\) of thiophene in 250.0 \(\mathrm{mL}\) of toluene.(a) Calculate the molefraction of thiophene in the solution. (b) Calculate the molality of thiophene in the solution. (c) Assuming that the volumes of the solute and solvent are additive, what is the molarity of thiophene in the solution?

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