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A 5E Lesson Plan on:
Solution Separation
Kelly Wiseman-Silva
Copernicus Project
July 2006

6th Content Standard: Solutions
Solutions are homogeneous mixtures of two or more substances. As a basis for under-standing this concept:
a. Students know the definitions of solute and solvent
solute into solvent (= major component)
homogeneous mixture = solution
b. Students know how to describe the dissolving process at the molecular level by using the concept of random motion molecular.
The kinetic molecular theory as applied to gases can be extended to explain how the solute and solvent particles are in constant random motion. The kinetic energy of this motion causes diffusion of the solute into the solvent, resulting in a homogeneous solution. When a solid is in contact with a liquid, at least some small degree of dissolution always occurs. The equilibrium concentration of solute in solvent will depend on the surface interactions between the molecules of solute and solvent. Equilibrium is reached when all competing processes are in balance. Those processes include the tendency for dissolved molecules to spread randomly in the solvent and the competing strength of the bonds and other forces among solute molecules, among solvent molecules, and between solute and solvent molecules. When salts dissolve in water, positive and negative ions are separated and surrounded by polar water molecules.
* keywords are highlighted

Material and Equipment
Engage Activity:
sand iron filings salt Styrofoam (small pieces)
500 mL beaker 250 mL beaker 4-100mL beakers water
magnet filter paper funnel

Explore Activity:
filter paper medicine cup water chromatography paper
Vis-à-vis markers (black, blue, brown, red, green, purple) black Sharpie

Engage
Prior to class, place equal volumes (approximately 50mL) of sand, Styrofoam, iron filings, and salt in individual 100mL beakers.

As the class begins, have students make suggestions with respect to the properties of the four substances found in the four 100mL beakers. Combine the sand, Styrofoam, iron filings, and salt in the 500mL beaker. Have students suggest ways in which to separate the mixture so that you might get each of the components separate again. After the students connect the component properties with methods of separations, carry out the separation with the help of the students. Utilize this activity to stress and model proper writing of procedure.

Explore
Prior to class, cut chromatography paper into 2-3 cm strips.

Break the students into working groups and have them work through the lab assignment entitled “When Is Green Not Green?” Do not direct the students to the answers. Let the students go through the procedure using their own terminology to explain and answer the questions posed.



Explain
The following day, after the class has done the extension activity at home, begin a class discussion. Start with a review of the engage activity. Then have the students discuss their results for the in-class exercise. The focus of the class discussion should be what their results and their interpretations of the results are.

Upon completion of the discussion, introduce the proper terminology for their explanations (guiding them to place the new vocabulary into their own scheme).

Elaborate
If this lesson is being used at the beginning of the year, during the “what is matter” stage of the course, then elaborate on the topics associated with mixtures – how physical properties can be utilized separate mixtures. Tie in the engage activity with that of the paper chromatography activity. Utilize the appropriate terminology for the elaboration section – introduce ideas of solute and solvent even of these topics will be later in the school year.

If the class is already studying the topics of solutions and solubility, bring in the ideas of attractions and how solubility (and therefore the ability to travel with the water front) is related to structure. Since water is polar, the dyes that traveled farthest are more polar than those that do not travel as far.

Evaluate
Have the students evaluate their results from the in-class activity. This is to be in the form of a lab report following the format below. They are to restate the procedure in their own words.

Title
Objective
Materials
Procedure
Data Table
Results (colors within each ink as well as relative solubilities for each color)
Experimental Design Limitations


Name: _________________________
When is Green not Green?
(adapted from Modern Chemistry, 2002)

What is paper chromatography?
Chromatography is a technique used to separate substances dissolved in a mixture. The Latin roots of the word are chromato, which means “color”, and graphy, which means “to write.” Paper is one medium used to separate the components of a solution.
Paper is made of cellulose fibers that are pressed together. As a solution passes over the fibers and through the pores, the paper acts as a filter and separates the mixture’s components. Particles of the same component group together, producing a colored band. Properties such as particle size, molecular mass, and charge of the different particles dissolved in the mixture affect the distance the components will travel on the paper. The components of the mixture that are the most easily dissolved in the solution and the least attracted to the paper will travel the farthest. Their band of color will be closest to the edge of the paper.

Ink Colors
In general, writing inks are of two types – water-soluble and oil based. Inks can be pure substances of mixtures. Most ballpoint pen inks are complex mixtures, containing pigments or dyes that can be separated by paper chromatography. Although there are thousands of different formulations for ink, the chemicals used to make them can be broadly classified into three categories: color, solvents, and resins.
An ink’s color is due to dyes or pigments, which account for 25% of the ink’s mass. Black inks can contain three or more colors; the number of colors depends on the manufacturer. Each ink formulation has a characteristic pattern that uniquely identifies it.
The pigments or dyes of the ink are dissolved or suspended in solvents, which comprise approximately 50% of the mass of the ink. Solvents are also responsible for the smooth flow of the ink over the roller ball in the tip of a ballpoint pen.
The remaining 25% of the ink’s mass is composed of resins. Resins control the creep, or flow of the ink after it is applied to the surface of the paper.

Objectives
• Demonstrate proficiency in qualitatively separating mixtures using paper chromatography.
• Explain how the inks are separated by paper chromatography.
• Observe the separation of a mixture by the method of paper chromatography.

Materials
12 cm filter paper water filter paper wick
pencil medicine cup black Sharpie
Vis-à-vis markers (black, blue, brown, red, green, purple)


Procedure: Prepare a chromatograph using water as the solvent
1. Record your observations in the appropriate data table when you are instructed to do so in the procedure.
2. Use a pencil to sketch a circle about the size of a quarter in the center of a piece of circular filter paper.
3. Write the following letters in a clock-wise fashion around the inner part of the circle:
a. B (for black)
b. BR (for brown)
c. BL (for blue)
d. G (for green)
e. R (for red)
f. P (for purple)
g. B SH (for black Sharpie)
4. Place a small dot of the ink on the line for the circle next to the letter corresponding to that color.
5. Use the pencil to poke a small hole in the center of the spotted filter paper. Insert a wick through the hole. A wick can be made from a strip of filter paper wick being rolled into a cylinder.
6. Fill the medicine cup two-thirds full of water.
7. Set the bottom of the wick in the water so that the filter paper rests on the top of the medicine cup.
8. When the water is 1 cm from the outside edge of the paper, remove the paper from the medicine cup, and allow the chromatograph to dry. Do NOT throw away chromatograph!
9. Record the color(s) of each pen’s chromatograph in the correct order on the data table.
10. Attach chromatograph to the lab report (in Results section).

Clean-Up and Disposal
The water may be poured down the sink. The cup is to be returned to the appropriate place as indicated by the teacher. Thoroughly wash your hands after completing the lab session and cleanup.

Data / Observations
Fill in the appropriate areas as you do the lab.
Observations
Black

Brown

Blue

Green

Red

Purple