Solution Formation

Introduction

A number of polar and nonpolar liquids and solids are mixed in order to study their solubilities and miscibilities and the factors involved in the solution formation process.

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1. Using a wooden splint or microspatula, place one very small crystal of iodine into each of the 4 disposable centrifuge tubes. Use a Beral pipet to fill the first tube to within 1 cm of the top with water. Close the lid securely and shake vigorously. Use a 96-well plate as a test tube rack. Set the tube in a well and allow it to stand.
2. Repeat this procedure using, in order, ethanol, toluene, and 1,1,1-trichloroethane in each of the other 3 tubes. Some may have to be shaken more than once. Record evidence of solubility and color of solution.
3. Calibrate 4 Beral pipets to use for mixing experiments. Cut the stems from 4 Beral pipets to leave 4 cm of tube attached to the bulb. Cut each at an angle. Use a ball point pen and a ruler to make 3 marks 1 cm apart on each bulb.measured from the closed end of the bulb. Label these bulbs 1 through 4 and place them a test tube rack (24-well plate).
4. In the following experiments, the objective is to fill the calibrated Beral bulbs so that, when inverted and held stem up, the liquid levels are at a calibration mark. For most of the liquids, use a Beral pipet with a long, pulled tip to fill the calibrated Beral pipets.
5. Glycerol is quite viscous and must be filled directly. Fill bulb number 1 to the first mark directly from the beaker labeled glycerol. It may take a little bit of trial and error to get it to the first mark when pipet is held stem up.
6. Fill bulb number 2 to the first mark with ethanol, bulb number 3 with ethylene glycol, and bulb number 4 with water using the pulled Beral pipet supplied with each solution and inserting the long thin stem into your pipet until the thin stem is in the bulb of your pipet.
7. Add to each bulb enough toluene to come to the second mark. Grasp each bulb by the end of the stem tightly and shake vigorously, keeping the open end of the stem up. Then return the bulb to the rack and allow 1 to 2 minutes to settle. Record evidence of miscibility (no layering) or immiscibility (layering).
8. To each bulb just prepared that had more than one layer, add ethanol to bring the total liquid volume to the third calibration mark. Shake. Allow to settle. Record number of layers and relative height of boundary to total mixture.

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Results of mixing toluene and...

Results of mixing toluene + ethanol +...

Questions

1. Do you think toluene and 1,1,1-trichloroethane would be miscible? (Try it.)
2. Methanol is a compound like ethanol, but more toxic. It is sold at gasoline stations as a gasoline additive for special situations. These situations occur when the gasoline does not contain alcohol, i.e., is not gasohol. What chemical role does ethanol play when added to wet gasoline?
   

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Safety

• Toluene, heptane, and ethanol are toxic and flammable. Ethylene glycol is toxic by ingestion and inhalation. Iodine causes burns and stains.
• Dispensing bottles of liquids should be kept in the fume hood for the duration of the laboratory session. All liquids are used in 1 mL quantities because of the toxicity and flammability. Review the location of fire extinguishers; check that the extinguishers are fully charged.
• Store the main containers for the solvents in a solvent cupboard in a different room; do not permit student access to the cupboard.
• Shaking of mixtures is to be performed only in Beral pipet devices.
• Iodine must be handled with a wood splint or microspatula so that the recommended quantity of two tiny crystals is used in each case.
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1. Toluene and 1,1,1-trichloroethane are expected to be miscible.
2. Methanol brings the water and gasoline together in a ternary (3 component) solution.

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When one substance dissolves in another, particles of the solute must be distributed throughout the solvent. In a sense, solute particles in solution occupy places that are normally taken by solvent molecules. In a liquid, molecules are packed together very closely and interact strongly with one another. The ease with which a solute molecule may replace a solvent molecules depends on:

1. The relative forces of attraction of solvent molecules towards one another.
2. The relative forces of attraction of solute molecules for one another.
3. The strength of the solute-solvent molecule interactions.

Substances that exhibit similar intermolecular attractive forces tend to be soluble in one another. This is stated simply as "like dissolves like."

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• Toluene and 1,1,1-trichloroethane are relatively nonpolar solvents. Iodine crystals are composed of nonpolar molecules. Water, ethanol, ethylene glycol, and glycerol contain polar hydroxy groups. Of these four, the ethanol molecules are the least polar, each having a hydrocarbon-like portion attached to a hydroxyl group.
• Nonpolar iodine dissolves readily in both nonpolar solvents, toluene and 1,1,1-trichloroethane.
• Water is very polar and the magnitude of the attractive forces between water molecules is much greater than the forces of attraction between water and iodine. Thus iodine is not very soluble in water. However, iodine is soluble in ethanol, a less polar solvent. Here, the iodine-ethanol forces of attraction are great enough to overcome the iodine-iodine forces for attraction, and a solution forms.
• Toluene and ethanol, and toluene and 1,1,1-trichloroethane form miscible combinations. When combined with either water, glycerol or ethylene glycol, toluene is immiscible.
• Adding ethanol did increase the miscibility of toluene with ethylene glycol, but not with the other substances tried.
• Solution formation appears to be strongly dependent upon the nature of the interacting substances. These data support the notion that like dissolves like.

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• Iodine (I₂) is a nonpolar covalent solid. Using the "like dissolves like" general rule, we will attempt to dissolve iodine in several liquids to determine if they are polar or nonpolar.
• Toluene is a relatively nonpolar liquid. We will try to dissolve it in four other liquids to determine if they are polar or nonpolar.

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• Heptane, toluene, and ethanol are flammable materials so keep at least 10 ft (3 m) from any source of ignition. If a good, efficient, operating fume hood is available, pour the material into a shallow pan and allow the material to evaporate inside the hood.
• Glycerol and ethylene glycol can be dissolved in 10 volumes of water and then poured down the drain with plenty of water.
• Iodine should be added to a 5 % solution of sodium thiosulfate. Add sufficient 3 M sulfuric acid to make the solution acid. Check with indicator paper. Allow several hours to pass for reduction to occur. Then neutralize this mixture with sodium bicarbonate. Dispose of the neutralized material down the drain with large quantities of water.
  

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Heptane, ethanol, and cyclohexane are toxic and flammable. Ethylene glycol is toxic by ingestion and inhalation. Iodine causes burns and stains.

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• ethanol
• ethylene glycol
• toluene (can substitute heptane)
• 1,1,1-trichloroethane
• 1 Beral pipet for each of the above, pulled so there is at least 5 cm of thin stem on each pipet.
• glycerol
• iodine crystals (very small)
• 4 Beral pipets
• 5 disposable centrifuge tubes with caps
• 1 ruler marked in mm
• 1 wooden splint (or microspatula)
• 1 96-well plate
• 1 test tube rack

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Iodine dissolves in all but water. Indicating water is quite polar and the others are nonpolar (or at least have a nonpolar region). Colors are:

• Ethanol --> yellow (to red brown depending on size of crystal)
• toluene --> violet
• 1,1,1-trichloroethane --> Red-violet
• Water --> clear (may turn slightly yellow upon prolonged standing)

Toluene dissolves in ethanol but not in the other three. Addition of ethanol with the ethylene glycol and toluene results in almost complete solubility with either no discernable layer or a layer about 19/20 of the height of the liquid. In the other two, the ethanol will dissolve in the more polar liquid, leaving the toluene on top. The ratio of layers is 2/3 of the liquid. Since ethanol, toluene, and ethylene glycol were almost totally miscible, it must be the next most polar liquid, with glycerol next and the most polar of all, water.

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• Dispensing bottles of liquids should be kept in the fume hood for the duration of the laboratory session. All liquids are used in 1 mL quantities because of the toxicity and flammability. Review the location of fire extinguishers; check that the extinguishers are fully charged.
• Store the main containers for the solvents in a solvent cupboard in a different room; permit no student access to the cupboard.
• Shaking of mixtures is to be performed only in Beral pipet devices.
• Iodine must be handled with a wood splint or microspatula so that the recommended quantity of two tiny crystals is used in each case.

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The microscale version of this lesson was developed by:

Daniel E. Miller
Crofton Community Schools
Crofton, NE 68730

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