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Chapter 13: Problem 85

(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

Expert verified
(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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Most popular questions from this chapter

A solution contains 0.115 \(\mathrm{mol} \mathrm{H}_{2} \mathrm{O}\) and an unknown number of moles of sodium chloride. The vapor pressure of the solution at \(30^{\circ} \mathrm{C}\) is 25.7 torr. The vapor pressure of pure water at this temperature is 31.8 torr. Calculate the number of grams of sodium chloride in the solution. (Hint: Remember that sodium chloride is a strong electrolyte.)

Arrange the following aqueous solutions, each 10\(\%\) by mass in solute, in order of increasing boiling point: glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right),\) sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right),\) sodium nitrate (\textrm{NaNO} _ { 3 } ) .

List the following aqueous solutions in order of decreasing freezing point: 0.040 \(\mathrm{m}\) glycerin \(\left(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}\right), 0.020 \mathrm{m} \mathrm{KBr}\) 0.030 \(\mathrm{mphenol}\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\right)\)

Indicate whether each statement is true or false: (a) If you compare the solubility of a gas in water at two different temperatures, you find the gas is more soluble at the lower temperature. (b) The solubility of most ionic solids in water decreases as the temperature of the solution increases. (c) The solubility of most gases in water decreases as the temperature increases because water is breaking its hydrogen bonding to the gas molecules as the temperature is raised. (d) Some ionic solids become less soluble in water as the temperature is raised.

Calculate the number of moles of solute present in each of the following solutions: (a) 255 \(\mathrm{mL}\) of \(1.50 \mathrm{MNO}_{3}(a q),\) (b) 50.0 \(\mathrm{mg}\) of an aqueous solution that is 1.50 \(\mathrm{m} \mathrm{NaCl}_{1}\) (c) 75.0 g of an aqueous solution that is 1.50\(\%\) sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) by mass.
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