039 Solvent Properties

Expt 039 -- Solvent Properties

Five solutes are tested in four solvents. On the basis of the nature of the solutes and solvents, generalizations about solution formation are drawn.

Background

Solutions form when the solvent and solute interact in such a way that the bonds between them make up in part for the bonds between solute or solvent molecules alone.
The formation of solutions is always favored to a zeroth degree by the increase in randomness that results when particles once strongly constrained to particular positions in a lattice are much less constrained and can move away from one another more freely. When ionic substances are to be dissolved, the ionic forces in the crystal must be somewhat balanced by polar interactions between the dissociated ions and solvent molecules.
Dielectric constant is a property of materials that measures their ability to increase the amount of electric charge that two adjacent parallel plates can hold without arcing.
In this experiment, qualitative observations regarding solution formation are made, and relationships between these observations and dielectric constant are noted.

Safety

Cyclohexane, ethanol, 2-butanol, iodine, and copper sulfate are toxic. Iodine causes burns and stains. Cyclohexane, ethanol, and 2-butanol are flammable. Wear goggles and apron. Wash spills immediately with large amounts of water and a sponge. Wash areas of skin that come in contact with these chemicals. Wash hands. Squeeze the sponge at the sink. Be especially cautious in handling iodine, which can irritate the skin and eyes. Avoid spark sources and flames in the laboratory while these solvents are in use. Know the location of the fire equipment; review use of that equipment before beginning work.

Procedure

The tests are performed in 6 - x 50-mm culture tubes. These tubes are supported in a 96-well plate.

Set 18 6- x 50-mm culture tubes(omit water+water and ethanol+ethanol) in a 96-well plate according to the following array:

Solute

Solvent

	Water	Ethanol	2-Butanol	Cyclohexane
Water
Ethanol
KCl
CuSO₄
I₂

The columns of this array involve using one solvent. Fill each tube in a column about 1/3rd full with the indicated solvent. Use a plastic transfer pipet. Insert the pipet stem into the tube and squeeze.
Across the first row, add 4 drops of water to each tube. Across the second row, add 4 drops 95% ethanol to each tube.
Across the third row, add 1-2 small crystals of KCl to each tube. Across the fourth row, add 1-2 small crystals of CuSO₄•5H₂O to each tube. Go to the hood. Find the I₂ crystals stored under the hood. Add 1-2 small crystals of I₂ to each tube in the fifth row.
Use flat toothpicks to stir the contents of each tube. Stir fairly vigorously using the toothpicks. For each tube, note and record any evidence for the formation of a solution (such as solution becomes colored; one phase seen; no liquid boundary interface).

!!!Click here to See Movie.
Pick up the tubes and move them around in the light over a dark surface to view any separation of colorless solvents. For example, view the cyclohexane mixtures with water and ethanol this way.
Use a plastic transfer pipet to withdraw the contents of the tubes and place them in appropriate disposal jars. Combine the water and ethanol solvents. Place the 2-butanol mixtures in a disposal jar specifically for that solvent. Place the cyclohexane mixtures in a disposal jar specifically for that solvent.
Wash the tubes that contained I₂ with 5% sodium thiosulfate. Wash the tubes with water. Wash the tubes with soapy water, and rinse with distilled water. Set the tubes with their open ends down on a paper towel to dry.

Questions

Potassium chloride and copper(II) sulfate are ionic solutes; iodine is held together by weak interactions. Account for the difference in solubility between these solutes in water and in cyclohexane.
Water is a polar liquid, while cyclohexane is nonpolar. Use your own words to summarize the meaning of the phrase "like dissolves like."
Acetamide, CH₃CONH₂, has a dielectric constant of 59. A solid at room temperature, acetamide melts at 82 ºC. Predict the outcome of adding some KCl to molten acetamide.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 039 Solvent Properties

Observe the slides in the movie carefully. Step through the slides and record data.

Solute
Solvent

Water Ethanol 2-Butanol Cyclohexane

Water

Ethanol

KCl

CuSO₄

I₂

Answer the questions.

Curriculum-

This activity is useful when solutions are first discussed. The concepts of solute, solvent, and "like dissolves like" come through.

Safety-

Cyclohexane, ethanol, 2-butanol, iodine, and copper sulfate are toxic. Iodine causes burns and stains. Cyclohexane, ethanol, and 2-butanol are flammable. Wear goggles and apron. Wash spills immediately with large amounts of water and a sponge. Wash areas of skin that come in contact with these chemicals. Wash hands. Squeeze the sponge at the sink. Be especially cautious in handling iodine, which can irritate the skin and eyes. Avoid spark sources and flames in the laboratory while these solvents are in use. Know the location of the fire equipment; review use of that equipment before beginning work.
Control the amounts put out for use. This is the best way to manage toxicity and fire hazards. Put the chemicals in containers from which small, appropriately-sized portions may be withdrawn.

Time-

Teacher Preparation: 10 minutes

Class Time: 40 minutes

Materials-

1.0 mL of 95% ethanol
1.0 mL of 2-butanol
1.0 mL of cyclohexane
0.10 g of KCl
0.10 g of CuSO₄•5H₂O
0.10 g of I₂
3 mL of 5% aqueous sodium thiosulfate(disposal)
96-well plate
20 6- x 50-mm culture tubes
toothpicks
plastic transfer pipets
3 disposal jars
hood
paper towels
water

Disposal-

Discard the contents of the water/ethanol disposal jar at the sink with large amounts of water. Keep the other disposed solutions separate. Place each solution into a shallow, flat dish under the hood. When the solvent has evaporated, wash each dish with 5% aqueous sodium thiosulfate, and discard the washing at the sink.

Answers-

Q1. Potassium chloride and copper(II) sulfate are ionic solutes; iodine is held together by weak interactions. Account for the difference in solubility between these solutes in water and in cyclohexane. A1. Water is a good solvent for KCl and CuSO₄, but a poor solvent for I₂, while cyclohexane is a poor solvent for KCl and CuSO₄, but a good solvent for I₂.
Q2. Water is a polar liquid, while cyclohexane is nonpolar. Use your own words to summarize the meaning of the phrase "like dissolves like." A2. Polar solvents like water are good solvents for polar and ionic materials but poor solvents for substances like I₂ or CH₄. Cyclohexane, a nonpolar solvent, is a good solvent for substances that have weak solute interactions.
Q3. Acetamide, CH₃CONH₂, has a dielectric constant of 59. A solid at room temperature, acetamide melts at 82 ºC. Predict the outcome of adding some KCl to molten acetamide. A3. Acetamide dissolves KCl, and the salt is dissociated in those solutions.

Literature Data-

Substance

Dielectric Constant

water

78.54

ethanol

24.30

1-butanol

17.8

2-butanol

15.8

cyclohexane

2.023

Reference-

Early versions of this experiment were developed by Terry Wortman, Hayes Center, NE. It was developed at an EESA workshop at Lincoln East HS, Lincoln, NE, in 1988. Significant enhancements appeared in an experiment by Jacqueline Simms, Jacksonville, FL, which appeared in Chem 13 News, February, 1992, p. 6. This experiment follows the Simms' procedure.

Key Words 1-

solvent, solute, solution, solubility, dielectric constant, force, interaction

Elements-

C H O I Cu S K Cl

Substance	Dielectric Constant
water	78.54
ethanol	24.30
1-butanol	17.8
2-butanol	15.8
cyclohexane	2.023