The following activity will prepare your students to better understand color as a complex mixture. It will also engage students to better understand water as a universal substance.
Step 1: Establishing a Context for Color Studies
Ask students to identify different categories of colors in the room. For example, ask students to divide themselves into groups according to the color of the shirt they are wearing. Notice different hues of the same color in each group. Present the following problem to your class: You are going to the prom and your dress is a color called "To Die for Blue." It is not quite royal blue, and not quite purple. If you are a male, your prom date wants your tie and cummerbund to match her dress. Brainstorm what the biggest problem in resolving this issue might be. (There are many different versions of the same color; variations in color are the result of different recipes and chemical compositions of mixtures.)
Step 2: Identifying Hydrogen Bonding as an Important Principle Governing the Behavior of Water
Demonstrate one of the unique properties of water that make it a universal substance useful for a variety of different things. Using a metallic spoon, coat the spoon with a layer of water from your breath, by hold the clean spoon closely to your mouth and exhaling deeply about three times until you see a layer of "steam" on its surface. Use a clean paper towel, napkin, or cloth to remove excess oil from the skin on your nose (the oil from your skin can prevent this "trick" from working). Hang the spoon off the tip of your nose. Hand each group a metallic spoon and ask each pair of students to try to repeat this activity. After about two minutes, ask them to identify reasons why the spoon "sticks" to your face. (Possible responses might include gravity, that there is excess oil that acts like glue, and that condensation acts like glue.) Assure students that this "trick" is not really a trick at all.
Say to students, "Water has special 'properties' that enable it to do some rather fascinating things. One of the properties of water that makes it a relatively strong substance is hydrogen bonding. Hydrogen bonding is the name used to explain the force of attraction between hydrogen, oxygen, nitrogen, and fluorine."
Step 1: Exploring the Properties of Water's Chemical Composition and Structure
Ask students what the chemical composition of water is. (The chemical composition of water is H2O: two hydrogen atoms are connected to one oxygen atom to form the water molecule.)
Log onto the "Water" Web site at www.sirius.com/~johnkyrk/H2O.html. Point out to students that one of the ways water is represented so that most people can understand what it looks like is to use models to represent the atoms. In general, red spheres are used to represent hydrogen, while white spheres are used to represent oxygen. Instruct students to start navigating the site. Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to raise their hands when they can identify the amount of space between the oxygen and hydrogen atom. (The amount of space between atoms is called the bond angle. In the water molecule, the bond angle between atoms is ~104.5º. It is important to note that this bond angle represents more than a right angle, which is 90º, and less than 180º, which is a line. This difference is due to the repulsion of electrons found on the outer shell of the atom.)
Allow students an additional three to five minutes to navigate the site. Provide students with a FOCUS FOR MEDIA INTERACTION, by asking them to record at least three special characteristics/properties of water that they discover when viewing the Web site. Tell students to record their answers on their Water Analysis Sheet. CHECK for comprehension by asking student volunteers to identify some of the properties of water described thus far. (There are many properties of water. Some of those properties explored on this site are chemical composition, molecular structure/bond angle, polarity, hydrogen bonding, and crystal structure.)
Step 2: Exploring Other Properties of Water Bonding and Polarity
Provide the class with a FOCUS FOR MEDIA INTERACTION by asking students to predict what will happen as the two water molecules try to approach each other. Record their hypothesis on their Water Analysis Sheet. Inform students that we will explore another Web site that addresses the effects of bonding patterns and polarity on the behavior of water. Log onto the Water Modules site at http://cwis.nyu.edu/pages/mathmol/modules/water/water_concepts.html. Observe what happens as two water molecules approach each other. (The bond distance, which started at 3.33 units, fluctuates, but the two molecules never touch.)
Provide students with a FOCUS FOR MEDIA INTERACTION, by asking students to investigate the differences between liquid and solid water. Students should click on the site's "movies" to investigate these differences. Record comparisons on the Water Analysis Sheet.
Log onto the Visionlearning site at www.visionlearning.com/library/science/chemistry-1/CHE1.7-bonding.htm. Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to record and define the following terms: bond, ionic bond, covalent bond, polar covalent bond and polar non-covalent bond on a sheet of paper to be maintained in their notebook. Ask students to use the Web site to determine the definitions for the terms, provide molecular examples of compounds that exhibit each type of bonding, and observe what happens as atoms form these types of bonds.
BOND A bond is formed when atoms interact with each other; they interact with each other in order to accommodate their valence shell of electrons. Most atoms are filled/stable when they have 8 electrons in their valence shell. This concept was discovered/proposed by Gilbert Lewis in the early 20th century.
Step 3: Exploring the Properties of Liquid Surface Tension
IONIC BONDS are formed by the transfer of electrons in order to fill the valence shell. Ionic bonds form between metals and non-metals. Ionic compounds dissolve easily in water and other polar solvents. In solution, ionic compounds easily conduct electricity. Ionic compounds tend to form crystalline solids with high melting temperatures. An example of an ionic bond is NaCl.
COVALENT BONDS are formed by the sharing of electrons in order to fill valence shell. Covalent bonding occurs because the atoms in the compound have a similar tendency for electrons (generally to gain electrons). Covalent bonding commonly occurs when two non-metals bond together. Covalent compounds exist as true molecules. An example of a covalent bond is H2O.
NON-POLAR AND POLAR COVALENT BONDING There are two sub-types of covalent bonds. The H2 molecule is a good example of the first type of covalent bond, the non-polar bond. Because both atoms in the H2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are equally shared by the two atoms, and a non-polar covalent bond is formed. Whenever two atoms of the same element bond together, a non-polar bond is formed. A polar bond is formed when electrons are unequally shared between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other does (yet not enough to pull the electrons away completely and form an ion). A good example of a polar covalent bond is the hydrogen-oxygen bond in the water molecule.
You will now be examining additional properties of water, including polarity, hydrogen bonding, surface tension, and capillary rise.
INSERT Science for You, Episode #14: "Why Do Insects Walk on Water?" into your VCR.
Provide students with a FOCUS FOR MEDIA INTERACTION by asking students to define surface tension.
PLAY tape when you see a man in a pool of water; you will hear him say, "Why can bugs walk on water and I can't?" PAUSE tape when you see a close up of a dropper tip with water over a glass of water, and you hear the narrator say, "Surface tension is holding it in the glass."
CHECK for comprehension. (Surface tension is the force of a liquid that causes it to be attracted to itself).
RESUME tape. STOP tape when you see a glass of water filled to almost overflowing. You will hear narrator say, "Water behaves as if it has a skin holding it together and in a way it does." FAST FORWARD the tape until you see a pair of hands filling two glasses in a tank of water. The narrator will say, "...seal between two glasses so water won't fall out." MUTE TV. PLAY tape. Provide a FOCUS FOR MEDIA INTERACTION by asking students to describe why the water didn't fall out of the glasses when the coins were deposited between the two glasses. PAUSE tape when you see scientist stack glasses on top of each other with water inside of them.
CHECK for comprehension. (Surface tension creates an attraction between water molecules that is not easily compromised, not even by the coins.)
FAST FORWARD tape, until you see the image of a space shuttle with a world globe in the background. Provide a FOCUS FOR MEDIA INTERACTION by asking students to write down three attributes of surface tension. PLAY tape. PAUSE tape when you see two drops of water on separate strips merge into one large sphere; you will hear music in the background.
Ask students to hold up their Water Analysis Sheet. You should see the first three questions filled in. Ask class, "How many of you were able to identify at least three properties? How many students were able to identify at least two properties?"
If there are more than four students who were not been able to identify at least two properties, RESUME NORMAL VOLUME, REWIND tape to the image of the world globe, and PLAY tape again. CHECK for comprehension. (Surface tension causes a force of attraction between the molecules of liquids; it also causes liquids to form a type of skin and it determines the shape liquids will take.)
FAST FORWARD tape to the point at which you see a water fountain running; you will hear music in the background. Provide a FOCUS FOR MEDIA INTERACTION by asking students to observe for other examples of water's attraction to itself. PLAY tape. PAUSE tape when you see three "streams" of water converge into two. The narrator will say, "Streams come together because of surface tension." CHECK for student comprehension, asking students to raise their hands when they can explain why the streams of water came together. (The force of attraction between the water streams drew them together like a magnet.)
Provide a FOCUS FOR MEDIA INTERACTION by asking students to watch the video clip and determine how else they might test the surface tension of liquids using the criteria established thus far. RESUME tape. STOP tape when you see the scientist blow a large bubble. You will hear the scientist say, "A bubble is nothing but surface tension." (Rather than test surface tension by the relative height of a drop, test the attraction of the liquid for itself. Test for attraction by duplicating the experiment as demonstrated in the video. For each liquid, use a toothpick to drag the drop the furthest distance possible on the sheet of wax paper. The drop that travels the furthest without breaking apart has the greatest intermolecular attraction, a correlate to surface tension.)
Ask students to add a drop of food coloring to each drop of liquid and mix it on the wax paper. If the dye mixes with the liquid, it is probably similar to water in its properties. Remove the masking tape label covers to reveal what each liquid is. Record which liquids mix and assume that those liquids are like water. (Water, acetone, vinegar, and alcohol should mix with the food coloring. Oil, glycerin, and syrup will not mix.)
Step 4: Reviewing the Concepts of Mixtures
Ask students to identify ways of knowing whether a substance is pure or a mixture. (A substance is pure if it cannot be broken down to form simpler substances. A substance is a mixture if it can be broken down into simpler substances. The major means of separating the parts of most mixtures would be physical processes, in comparison to the chemical processes required to separate the parts of a pure substance.)
Ask students to identify examples of common mixtures and pure substances. Record their responses on the board/large instructional writing space. (See chart below for possible responses.)
|| Pure Substances
(dye, sugar, and water)
(several oils and perfume)
(penny: copper-coated zinc)
Explain to students that when a mixture is uniform (particle size, type/phase) and when its components cannot be clearly distinguished, it may be called a solution, a homogeneous mixture. A solution has two parts: 1) solute and 2) solvent. Ask students to record the definition of these terms on a separate sheet of paper to be maintained in their notebook. (A solute is the substance available in the smallest quantity in a mixture. The solvent is the substance that is available in the greatest amount. The solute is the substance that is being dissolved, while the solvent is the substance that does the dissolving.)
Step 5: Establish Color as a Complex Solution
Remind students of the Introductory Activity that considered the differences in colors even though they were technically all the same.
INSERT the video Art's Place into your VCR. CUE tape to appropriate starting place. You will see a painter's palette and hear music in the background. Provide students with a FOCUS FOR MEDIA INTERACTION, by asking them to record in their notebook the definition of primary colors and examples of primary colors.
PLAY tape. PAUSE tape when you see three color patches on the screen with the word "Primary" written beneath it. Allow students enough time to record the meaning and examples of primary colors. (Prior learning experiences should cause most students to identify red, yellow and blue as primary colors. Primary colors would represent those colors that are pure and can not be made by combining any other colors.)
RESUME play. PAUSE tape when narrator asks what red and blue will make. (Purple.) You will see a purple splash on the screen. Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to brainstorm what orange, green, and purple might be considered in comparison to their individual "primary" counterparts. (In terms of art terminology, these color mixes are considered secondary because they are made from two of the primary colors. Secondary colors would then represent a type of mixture or a solution rather than a pure substance.) STOP the tape.
Ask students to log onto Chromatography of Mr. Sketch Pen Colors site at http://science.csustan.edu/tutorial/color. Provide students with a FOCUS FOR MEDIA INTERACTION, asking them to identify what colors are required to make white and what colors are required to make black. Record their responses on a separate sheet of paper to be maintained in their notebook. Instruct students not to scroll down before recording their answers. Traverse the room to CHECK for student comprehension. (All students should record red, green, and blue as primary colors that make white, as well as cyan, magenta, and yellow that make black. These two triads represent the difference between additive and subtractive color production.)
Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to examine the Web site and identify careers in which color mixing is an important skill. (Expertise in color mixing is important for painting, theater lighting, and marketing displays.)
Step 6: Establishing a Context for Understanding Color Composition
Distribute a pack of water-soluble markers to student groups. Ask each group to separate those markers that are probably color mixtures and those that are most likely not mixtures. Ask students to choose one color from those that are probably a mixture and hypothesize what colors were used to engineer that color for the dye manufacturer. (Brown, black, purple, turquoise/light blue, and orange are among the standard colors found in most packages of markers that are most likely mixtures. Pink, yellow, red, and blue are most likely not mixtures for most dyes.)
Log onto the ChemConnections Web site at http://mc2.cchem.berkeley.edu/Java/RGB/example1.html. Provide students with a FOCUS FOR MEDIA INTERACTION by asking students to try to duplicate the color composition of their selected color choice. Students should record their Red-Green-Blue compositions on their Color Analysis Sheet. (Responses will vary; brown may be achieved using 0.29 (29%) red, 0.14 (14%) green and 0.10 (10%) blue.)
Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to also record the composition of black and white by moving the sliders until the color window shows black and white. Record their observations on their Color Analysis Sheet.
CHECK for comprehension. (Black is 0.00 on each; white is achieved using 1.00 on each.)
Step 1: Using Polarity Principles to Separate Dyes
Say to the class, "When substances are dissolved by other substances, this usually means that they have similar characteristics; usually their polarities are the same. Because oil and water do not mix, we can assume that oil and water have different polar properties." Ask students what the statement "water soluble markers might mean." (In a water-soluble marker, the dyes found in the marker will most likely be dissolved in water. This would suggest then that the molecules found in the dye are polar, like water.)
Explain to students that we are going to test the polarities of different substances by seeing how well they separate the components of the water-soluble dyes found in markers. We know that these dyes are polar because they can be dissolved by water, so we can test the polarity of liquids that look like water and may behave like water by seeing how well they dissolve and separate dyes.
Distribute supplies for this activity to each pair of students (chromatography paper strips, four test tubes, water-soluble markers, and solvents). Say to students, "We will be using several of the ideas discussed in this lesson to separate the components of various colors, using a technique called chromatography. The word chromatography comes from two ancient roots: 'chroma,' which means color, and 'graph,' which means writing."
Inform students that chromatography is a technique used by scientists to separate the components of mixtures using principles of polarity, surface tension, and capillary rise. The liquid travels up the surface of the paper as it is absorbed. This is why water travels up into a straw even when it is not siphoned or sucked. Different colors have different polarities and will travel along with the water if its polarity is close to that of water. This means that the more polar a dye molecule is, the further it will travel up the surface of the paper.
Provide a FOCUS FOR MEDIA INTERACTION by asking students to revisit the Chromatography of Mr. Sketch Markers Web site (http://science.csustan.edu/tutorial/color) to better understand this technique. Scroll down the page to the heading "Chromatographic Separation of Black Ink." Duplicate the start point of the experiment by placing a pencil dot on the paper strips about 1-2 cm above the bottom of the strip. Use one of the hypothesized mixture markers to place an ink dot sample directly on the starting point indicated by the pencil dot. Get a small amount of each of the polar solvents as demonstrated by the "wax paper" experiment. (Those substances that have properties similar to water should have been identified.) Add the first solvent (water) to the test tube so that the level of the liquid in the test tube will be beneath the level of the sample spot to be tested. Gently stand the paper strip in the test tube. Allow the liquid to travel up the surface of the strip until the colors travel with the liquid. (The liquid in the test tube is called the solvent because it dissolves the sample and is available in a relatively large amount. The solvent is part of what is known as the mobile phase in chromatographic terms, because it is actually moving.)
Once the liquid continues to travel above the level of the separated colors, the experiment is complete. Repeat the activity using a different solvent (vinegar, alcohol, and dilute alcohol). Sketch diagrams of experiment results on the Color Analysis Sheet similar to those included on the Chromatography Web site. Compare chromatograms to expected hypothesis. Write an explanation of the results on the Color Analysis Sheet.
Step 2: Exploring Fabric as a Medium for Art
Duplicate the experiment using fabric instead of paper. Distribute a small fabric square to each student. Instruct students to write their name on the square, using one of the markers that are "proven" mixtures; indicate to students that they should write their name on the bottom portion of the square in block-style text. Add one of the "proven" solvents to the small beaker or cup so that the level of the liquid is slightly below that of the text. Stand the fabric in the small beaker so that the solvent travels up the surface of the fabric. After a few minutes, remove the fabric square and observe the pattern. Invite students to use other available materials to create different patterns. (Students may use rubber bands or folding techniques to influence patterns. Additionally, students may use different colored markers for each letter to create different color patterns.)
LANGUAGE ARTS AND WORKPLACE ESSENTIAL SKILLS
Read the article "One Artist's Journey" by Beverly Nelson, available online at http://unite.ukans.edu/explorer/explorer-db/browse/static/Natural^Science/browse/f57.html. Once on the site, choose "Crazy Colors," and download the file, available as PDF or HQX.
Contact a local or regional theater, and arrange for an interview with a lighting designer. Ask questions regarding color scheme and set design.
Gather pictures or swatches of various textiles that were created using a tie-dye technique and that clearly demonstrate an ethnic/cultural motif (e.g., Native-American, American Southwestern, African, and Hippie.)
The Hippie Movement was a social revolution among American youth in the 1960s. One of the symbols associated with the movement was tie-dye fashion. Gather samples of 1960s memorabilia and art, and research the forces behind the "hippie" movement.
Consider the differences in media used to separate color mixtures by completing the culminating activity using different types of paper (construction paper, paper towel, filter paper, bonded paper, or newspaper).
Explore water as a prism (a tool used to separate the components of light). Water will separate white light, and generate a continuous spectrum of visible light commonly referred to as a rainbow. Put a small amount of water in a beaker. Place the beaker on the surface of an overhead projector. Turn out the lights in the classroom and turn on the power to the overhead projector. Project the effects of the light on the water onto a blank white screen. An NTTI lesson called "Somewhere Over the Rainbow" examining this phenomena is available online at www.thirteen.org/wnetschool/ntti.
Gather botanical samples from various colored plants and/or flowers. Extract the dyes found in these samples by grinding small pieces of the plant leaves in a mortar and pestle with a small amount of water and alcohol (standard rubbing alcohol, a 70% aqueous solution of isopropyl alcohol in water, will work). Place a sample dot of plant extract on a strip of filter paper, using the same techniques explored in this lesson. Rather than using water as your solvent, experiment with solvents that contain dilute hydrochloric acid, acetone, and alcohol mixed. You can experiment with the actual concentrations of your solvent to find a solvent that works best for your plant samples.
Forensic investigators used chromatography to explore the tragedy behind the World Trade Center bombing in 1993. Interview a forensic scientist. Ask him/her how chromatography may be used to solve crime-related mysteries.
- Visit a local art museum, and view a watercolor exhibit. Investigate the different types of canvas used to display the artwork.
- Explore the effects of pollution on the population of insects in your area. Research the environmental benefits of insects.