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Paper Chromatography: Separating and Identifying Metal Ions

Introduction This experiment involves a technique called paper chromatography, which will be used to separate and identify metal ions. In phase 1, you will explore the importance of added chloride to the success of separating metal ions using acetone/water mixtures. In phase 2 you will perform a statistical simulation designed to gain insight into the mechanism of how metal ions migrate on the chromatography paper. Then, in phase 3, you will be asked to design paper chromatography experiments to identify unknown metal ions. Goals: 1. To learn about paper chromatography and explore the importance of chloride in the migration of metal ions on chromatography paper using acetone/water mixtures. 2. To use a statistical simulation to think about how atomic scale chemical interactions can result in the migration of the metal ions on the paper. 3. To design an experiment to determine the identity of metal ions present in an unknown solution. Why are we still using analogical models? Consider the analogical model which used paperclips to represent the formation of slime from sodium borate and polyvinyl alcohol. This model had several intended purposes:

1) to provide practical language to describe the chemical phenomenon; Ex: We can describe polyvinyl alcohol as chains instead of polymers. We talk about linking chemicals together instead of sorting out the details of how they are bonding.

2) to describe what is occurring on a submicroscopic scale, too tiny for observation; Ex: By connecting white chains of paperclips together with single black paperclips, their movement is restricted to the point that they cannot flow down the funnel. The polyvinyl alcohol are chains which become a solid when reacted with sodium borate; that may be what is happening on the submicroscopic level.

3) to inform new, testable hypotheses about the reaction; Ex: Since there is a limit to how many black paperclips I can attach to the white paperclips, there

may be a limit to how much sodium borate can react with the polyvinyl alcohol. We can test this by adding twice as much sodium borate and observing the reaction.

4) to illustrate that models are not perfect, and understanding the ways that they don’t represent the target is also important.

Ex: The paperclip model doesn't show that most of the slime is made up of absorbed water. This is clearly a limitation but the model is still very useful in some ways. If absorbed water was important to model, then the model would need to be refined.

Throughout this semester, you have considered additional analogical models. Scientists use many types of models, including analogies, to help them understand problems and find solutions. It is an important skill that requires practice to be effective. In today’s lab, you will consider another analogical model to help you think about how metal ions can be separated using a technique called paper chromatography.

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What is paper chromatography? Have you ever watched a crime-scene investigation on TV where a forensics team used various clues like ransom notes to identify a suspect? Aside from their handwriting, the suspects can be identified by the chemical characteristics of the pen they use. Scientists can use a method known as chromatography to separate different components of a pen’s ink. This separation technique can be used to narrow down the possibilities for the type of pen used.

Paper chromatography is a specialized form of chromatography that is relatively fast and inexpensive yet powerful enough to separate a range of different chemicals. This type of chromatography uses a piece of paper and a solvent to separate the components of a mixture. The solvent bound on the paper is referred to as the stationary phase and the solvent that is free to flow by the paper is referred to as the mobile phase. Small drops of chemical samples (e.g. pen ink) are applied to the paper or “spotted.” Next, the bottom of the strip of paper is placed in a solvent. Through capillary action, the solvent moves up through the paper. The different chemicals spotted on the paper will be chemically attracted to the stationary phase, but they may also be chemically attracted to the mobile phase. Chemicals that have different levels of attraction to the stationary and mobile phases will travel different distances as a result. This causes mixtures of chemicals to separate into individual components on the paper. The chemical composition of the sample can be elucidated by comparing the results with paper chromatography results of known chemicals—similar to matching fingerprints.

Paper chromatography is particularly useful for identifying ions in aqueous (water-based) solutions. Atoms can readily gain or lose electrons. If electrons are removed or added to a neutral atom, a charged particle called an ion is formed. Positively and negatively charged ions are attracted to each other and form ionic compounds. The positively charged ion (called a cation) is often a metal and the negatively charged ion (called an anion) is often a nonmetal. Many of these ionic compounds will dissolve in water to form the individual ions of the compound. For instance, sodium chloride (NaCl) dissolves in water to form sodium ions (Na+) and chloride (Cl-) ions. Natural water sources contain many different species of metal ions including sodium (Na+), magnesium (Mg2+), calcium (Ca2+), and iron (Fe2+). They can also contain harmful metal ions such as lead (Pb2+).

The science of separation of metal ions at the atomic scale. Paper chromatography works on the idea that there are two solvent phases, and that the metal ions can be separated by partitioning between the two phases. Both of the phases are composed of solvent. The stationary phase is where solvent (e.g. water) is tightly bound to the paper, which is composed primarily of cellulose. The other phase is the mobile phase composed of solvent (e.g. acetone) right next to the paper that can flow on the paper as the chromatogram is developed.

• Stationary phase: solvent bound to the paper surface • Mobile phase: solvent free to pass over the paper

Whatman is a leading brand of filter paper and is composed of 98-99% a-cellulose, whose structure is modeled below. Notice that there are many hydroxyl groups (-OH) in the cellulose. If the proton of a hydroxyl group dissociates, hydroxide (-O-) forms. Each hydroxide group has a negative charge (-1), which can attract a metal ion having a positive charge (e.g. Fe2+). One aspect of the experiment today will be to explore how adding chloride (which also has a negative charge) into the mobile aqueous phase may help increase the degree that metal ions can partition into the mobile phase, thus increasing metal ion mobility on the paper. The tug of war between the paper and solvent for the metal ion is what determines how far the metal ion travels up the paper.

Figure 1. A Model of a-cellulose.

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Quantitative measurement of metal ions migration. A strip of chromatography paper will be spotted with several known samples of metal ions and developed using a solvent mixture of acetone and water (with and without added HCl, as a source of Cl-). After measuring the distance that the solvent moves up the strip of paper (the solvent front distance), the paper is dried and then treated with several solutions that cause the samples to change colors to make it easier to visualize the results. The distance that the sample has moved can be measured and the Rf value (ratio of distance traveled by sample to distance traveled by solvent) for each sample can be determined. Rf values are usually expressed as decimals (e.g., 0.32) and are unit-less. Each type of ion will have a characteristic Rf value. Pre-lab Assignment: In your lab notebook, after reading the lab procedure, please prepare the following information and answer the questions. Remember, you will not be able to go into the lab if you have not completed the pre-lab assignment prior to the beginning of class.

1. Write 2-3 sentences introducing the lab.

2. Create a table of safety information including the chemicals used in the lab, the hazards associated with them, and any safety handling precautions.

3. Consider the following three chromatograms shown below. Each chromatogram was spotted with a copper ion solution. The first strip was removed from the solvent after 10 minutes and developed. The second was removed after 12 minutes and the third was removed after 14 minutes. 10 minutes: 12 minutes: 14 minutes:

Using a ruler, measure the distance (in centimeters) from the starting line to the solvent front on each of the strips shown here. Next, measure the distance from the starting line to the center of the spot. Divide the distance the spot traveled by the distance the solvent traveled. The decimal number you obtain is your Rf value for that spot. (a) Calculate the Rf values for each of the

copper ion samples on the chromatograms.

(b) Is the Rf value of a particular ion independent of time? (In other words, does it matter how long the spot travels?) Why or why not?

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4 Copyright Fall 2021, Mitchell Bruce and the ICN Team

Laboratory Guide On the following pages, you will find instructions for doing an experiment. In this experiment, you are asked to pair up with another student when doing lab work. If there are an odd number of participants in lab, one group

may be permitted to have three people. Your lab work will involve simultaneously being asked to individually make observations and record these in your own lab notebook, and working in partnership on certain activities which

may involve answering questions, discussing observations, analyzing results, or designing your own procedures in response to scientific questions.

As you go through the experimental guide, you will notice there are questions that are deliberately indicated in the guide (i.e., “Q:”). For example:

Q: What is happening to the solvent level on the paper over time? You are required to respond to these questions in your lab notebook. Our expectation is that you write

enough to give an indication of what you were thinking about. You do not have to write down the question AND answer, but you must address the answer, for example: “we found that the solvent level was creeping up the

chromatography paper…,” Part of the purpose of making entries into a notebook is to allow you to remember later what you were

thinking at this part of the lab, which can be very useful when writing your lab report. It is also evidence for your lab instructor of your thinking process. Please note that you are not required to provide any particular question and answer in your lab report. However, you may find that some of the answers would be useful to include in your report. Goggles are required at all times in the lab. There are no exceptions. Gloves and aprons are available. If you have questions about safety, please do not hesitate to ask your laboratory instructor. This lab has portions of the procedure that must be completed under the hood.

Materials: chemicals, equipment, and supplies:

Chemical samples Chemicals

0.25 M Copper (II) nitrate for the Cu2+ ion solution Acetone

0.25 M Nickel (II) nitrate for the Ni2+ ion solution 3 M HCl (in aqueous ethanol)

0.25 M Iron (III) nitrate for the Fe3+ ion solution 8M Ammonium hydroxide (NH4OH)

0.25 M Cobalt (II) nitrate for the Co2+ ion solution 1 % Dimethylglyoxime (DMG in Ethanol)

“Unknowns” consisting of one or more of the above solutions

Ethanol

Water

Equipment and Supplies:

Chromatography filter paper, paper towels, pencil, ruler*, capillary tube**, beaker, 2 pint bottles

with corks, sample cups, disposable pipettes, markers.

*a ruler is in your lab drawer **capillary tubes are tiny glass tubes that will be in the front of the room.

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Phase 1 Making observations: Chromatography in the presence and absence of chloride The following activities should be completed in the lab. 1. You are to test two different chromatography conditions. Prepare the following two solutions and

place them in two labelled glass pint bottles with cork stoppers. The glass bottles will become the chromatography “chambers”.

a. Acetone Solution: use a graduated cylinder to measure 30 mL of acetone. Pour the solution into a glass pint bottle, labeling the bottle "Acetone". Place the cork stopper on the bottle until this chamber is needed.

b. Acetone/HCl Solution: use a graduated cylinder to measure 18 mL of acetone and 12 mL of 3 M HCl (in aqueous ethanol) solution into a beaker. Pour the solution into a glass pint bottle, labeling the bottle "Acetone/ HCl Solution". Place the cork stopper on the bottle until this chamber is needed.

2. Obtain two 8-inch (20 cm) strips of chromatography paper. Please note that

when handling chromatography paper, it is easy to contaminate it with the solutions and chemicals present in the laboratory. Always keep chromatography paper on a clean paper towel and hold the strips at the sides with your gloved fingertips.

a. Prepare two chromatography papers labelled identically; one will be “developed” in the acetone chamber and the other will be “developed” in the acetone/HCl chamber. Use a PENCIL to draw a straight line across each paper 1.0 inch (2.54 cm) above the bottom edge. Draw small X’s on the line on each paper. The x's will be the target for your metal ions.

b. Select 2-3 metals ions to test. Please note: that it can be very difficult to spot the chromatography paper with 4 ions, so we recommend that 2 or 3 is a good number to try. You will need to share your results with other groups in order to obtain results pertaining to the four metal ions. Your lab instructor will help organize this for the lab class]. Appropriately label the x’s with the metal ions you have selected: Cu, Ni, Fe, or Co. Remember, prepare two chromatography strips that are labeled exactly the same.

3. Spotting the chromatography strips. Obtain 3 sample cups (one for each metal ion being tested) and label them on the outside ring using a marker. To the cup, add 3-5 drops of the corresponding metal ion solution. These sample cups will be used for the remaining steps. If a sample cup becomes contaminated, a new cup may be prepared. To apply the samples, place the end of a clean capillary tube in the ion solution. Then, hold the tube perpendicular to the strip, and gently touch the tip of the tube to the center of the marked X on the paper. Allow the solution to form a very small single spot that is about 1-2 mm in diameter (if the spot is any larger, you will get poor resolution). Allow the spot to dry. Use the same capillary tube to apply a spot of the same metal ion to the 2nd chromatography paper. Repeat the spotting procedure with each sample of metal ion that you have chosen. Please make sure to use a clean separate capillary tube for each metal ion. To keep track of each capillary tube, rest the tube in the appropriate labeled sample cup when not in use.

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4. Running the experiments:

a. Insert one of the spotted chromatography strips into each bottle so that the bottom of the strip just touches the liquid. Make sure you do not submerge the spots! If this happens, you will need to re-spot a new paper. The strip should not touch the sides of the bottle and the top part of the paper should extend out of the top of the bottle. Hold the top of the paper while you carefully insert the cork, making sure that the metal ion spots are above the solvent. Secure the strip by inserting the cork. Repeat this procedure using the other strip in a second chamber, so they both can be developed at the same time.

b . As the strips are developing, answer the following questions:

Q: What is happening to the solvent level on the paper over time?

Q: What is happening to the marked spot you placed on the paper? What colors are the spots you observe?

c. Allow the solvent to move approximately 10 cm up the strip (just to the shoulder of the bottle). Do not allow the solvent front to come near the cork in the top of the bottle. Remove the cork and carefully pull out the paper. Immediately draw a straight line at the highest point of the solvent front with a PENCIL. It’s important to do this fast because the solvent will evaporate off the paper quickly! Let your sample dry for a few minutes in open air. Mark the center of any spots that you observe once you take the paper out of the bottle. Some of the spots may not be visible yet.

Health Warning: the next two steps (on the next page) must be performed under the hood. Exposure to ammonia at low concentrations may rapidly produce skin or eye irritation. Higher concentrations of ammonia may cause severe injury and burns. Dimethylglyoxime (DMG) is toxic. Spray it in the hood and away from yourself.

d. Under the hood, move each chromatogram back and forth above an open bottle of concentrated ammonia (NH4OH) solution. You will see the vapors of the ammonia gas reacting with the HCl on the paper to form a white gas of ammonium chloride (NH4Cl). If a spot develops, lightly mark the center of the spot with a pencil.

e. Under the hood, lay the chromatograms on a paper towel and spray each with a mist of 1% Dimethylglyoxime (DMG in ethanol) solution. Again, lightly mark the center of any new spots observed, and record their colors, if any. If you still do not see a spot (in particular, for nickel) you may repeat the developing process: wave the strip over the concentrated ammonia solution again and spray with DMG.

Keep the chromatograms in the hood until the DMG has dried on them! Once the strips are dry, they can be taken into the breakout room to be analyzed. Don’t empty out the pint bottles full of solvent. They will come in handy later! This is the end of Phase 1.

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Phase 2: Understanding Chromatography The following activities should be completed in the breakout room. Work together to complete the following activities. In Part 1 you will analyze your results. In Part 2, you will explore a simulation of chromatography. Throughout this process we would like you to think about how paper chromatography works at the molecular level. 1. Part 1 of Phase 2. Data analysis of your own results

a. In your lab notebook, draw sketches to illustrate the shapes of spots and label the colors that appeared in your chromatogram. You will need to provide a picture of each of your chromatograms for your laboratory report. b. Next, using your chromatograms, compute the Rf values for each of your known ions by measuring the distance the center of the spot moved from the starting line and dividing it by the distance the solvent moved from the starting line. If determining where the center of the spot is located is difficult visually, you can estimate a value by measuring the distance from the bottom of the spot to the starting line and the distance from the top of the spot to the starting line. The average of these two distances will give you an estimate of the center of the spot. You can create a table like the one below in your laboratory notebook to organize and record these results.

MetalsIons

ExperimentalConditions

DistanceSpotMoves(cm)

DistanceSolventMoves(cm)

Rf value

Color

Ni2+ Acetone/Water Ni2+ Acetone/Water/HCl

c. Compare your Rf values with other groups: Find a couple of other groups that used other metal ions and record their Rf values (remember to get the names of these students for your lab report). Your lab instructor can help the class organize and share this data. Remember, that changing the experimental conditions can influence Rf values, so if you analyze other group's data, focus on looking for trends in the Rf values rather than absolute values. You can organize this information by creating another table like the one you made to analyze your own results:

d. Claims about added chloride: Did the presence or absence of chloride influence the results? Try to imagine the chemistry on the atomic scale that could be responsible for your experimental results. We recommend that you try drawing your two cases: presence and absence of Cl- and provide a drawing to explain your experimental results:

Please make a drawing in your lab notebook, so that a copy of your drawing can

be collected by your TA at the end of lab.

Create this table in your laboratory notebook

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2. Part 2 of Phase 2. The movement of metal ions. a. Metal chlorides and an example of jumping frogs: when you apply positively charged metal ions to paper, they form a chemical interaction with negatively charged hydroxyl groups, which are on the surface of the paper. The explanation of why chloride enhances the rate of flow during a paper chromatography experiment involves recognizing that metal chlorides are more soluble than the metal ions. Thus, as the equation below suggests, the presence of chloride may shift the partitioning of the metal ions into the mobile phase.

n Cl- Mn+(on surface of paper) MCln(soluble in solution)

As a non-chemical example using frogs: imagine a line of frogs like this:

If you wait a minute, perhaps one of the frogs would leap forward like this:

However, if you provide a stimulus (like prodding each frog), the situation after a minute might look like this:

The prodding provides a stimulus to help move some of the frogs forward. The presence of chlorides acts that way, because it enhances moving some of the metal ions into the mobile phase, where they can move forward on the paper.

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a. A statistical "thought" experiment. Let's imagine that instead of just frogs we have a mixture of 128 frogs (F) and 128 snails (S) lined up at the bottom of the “paper” (see below).

Solvent Front

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS (128 Frogs) (128 Snails)

Now imagine that the paper is placed in solvent, which “prods” the frogs and snails to start moving up the paper. We can represent the solvent moving up the paper by writing the words “solvent front” in the next compartment up the paper (as shown below). Let's also assume that 75% of the frogs move along with the solvent while 25% stay behind, and 25% of the snails move along while 75% stay behind. The situation would then look like this: 96 frogs move to the second compartment with 32 staying behind, and 32 snails move to the second compartment with 96 staying behind.

Solvent Front

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS (96 Frogs) (32 Snails)

Solvent SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS

(32 Frogs) (96 Snails)

Finally, if we repeat the simulation three more times, the final result will look like this:

The resulting distribution shows that the major "spot" of frogs would be located 80% of the length of the solvent front and a major “spot” of snails would be located 20% of the length of the solvent front. This would result in Rf values of about 0.8 for the frogs and 0.2 for the snails. You can also see how the number of frogs and snails distribute differently along the length of the paper: 0|7|26|54|41 vs. 41|54|26|7|0.

Solvent Front

FFFFFFFFF FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF (41 Frogs) (0 Snails)

Solvent FFFFFFFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSS (54 Frogs) (7 Snails)

Solvent FFFFFFFFFFFFFFFFFFFFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSS (26 Frogs) (26 Snails)

Solvent SSSSSSSSSSSSSSSSSSSSSS FFFFFFFF SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS (7 Frogs) (54 Snails)

Solvent SSSSSSSSS SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS (0 Frogs) (41 Snails)

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We refer to each row as a theoretical plate. This is a concept used to explain chromatography. You can see that the separation we obtain will depend on how many theoretical plates there are as well as the metal ion partition efficiency. Both of these will influence the shape of the spot as it moves up the paper, ranging from being very coherent (sharp) to very diffuse (blurry). There are other variables that are important in the separation, including experimental conditions (like the solvent and temperature) as well as additives in solution (like the chloride).

b. A statistical simulation experiment using the glass beads provided. You will notice that the Table used in the above examples has the same shape as the utility trays we have provided in lab. In this analogy, the trays represent the paper, the beads represent metal ions and the sponge is used to show movement of the solvent front up the tray. Your first task is to “run” a short chromatography simulation by placing 32 glass beads in the bottom compartment and the sponge in the left bottom compartment. Now, move the sponge up by one level, and move 50% of the beads up to the next compartment. Repeat the process: first move the solvent front up to the next compartment, next move up 50% of the beads from the top most compartment to the next level and move up 50% of the beads from each of the levels below in a step wise fashion. Then advance the solvent front to the next compartment and repeat the procedure until there are some beads in the top level.

Sponge (solvent front)

start with 32 glass beads

Draw a sketch in your lab notebook to show the number of beads in each level at the end of the “experiment”. Hint: At the end of the simulation, you should have at least 2 beads in each compartment.

Q: What is the Rf value for this simulation? [For this exercise, you can assume that the compartment with the most beads would be the center of your spot.]

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Fill out the analog to target worksheet (see page 12) before proceeding to phase 3.

Post lab question: Please note that there is a post lab question that is part of the lab report (see rubric). Your group may want to use the glass beads and tray to answer this question before leaving lab:

In the simulation, you started with 32 beads, with a 50% efficiency of moving from compartment to compartment. If you ran a similar experiment starting with 3.2 moles of metal ions, how many metal ions would you have in each bin after "running" the simulation?"

Sponge (solvent front)

start with 3.2 moles of metal ions

This is the end of Phase 2.

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Analog and Target Worksheet (page 12) Name: _____________________________ Fill out the worksheet individually as you perform the analogy activity. Work together to discuss similarities and differences. Each student must include a scanned copy of this sheet with their lab report. Make sure your scan is entirely legible. Please label the components in your drawings.

Analog and Target Comparison

The glass beads compared to metal ions.

The horizontal compartments of the plastic tray compared to small segments of the stationary and mobile phases of the paper

The action of moving the glass beads from one compartment to another compared to the chemical interactions resulting in partitioning of metal ions across the stationary and mobile phases as the solvent flows over the paper.

The position of the most glass beads compared to the metal ion spot that develops at the end of the paper chromatography experiment

Similarities: What characteristics does the analog share with the target?

Differences: How does the analog not accurately represent the target? (This question asks you to think about familiar objects and compare them to an unfamiliar concept.)

Differences: What features of the target are missing from the analog? (This question asks you to think about the molecules that you can’t see and compare them to familiar objects.)

Draw a representation of the following at the molecular level:

The paper and metal ions in the presence of solvent and chloride ions during a chromatography experiment. Label the stationary and mobile phases.

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Phase 3: Designing experiments

Plan your experiments in the breakout room before proceeding to lab to complete them. Please use the worksheet on the next page to summarize your lab group’s experiment and findings. Before going into lab, have your lab instructor check your experimental design and initial it. This worksheet is to be submitted as part of your lab report. Make sure that when scanned, it is entirely legible! Using the analogical model to make predictions: Q: If you applied a sample of nickel ions and iron ions together on the same spot on the chromatography paper and developed them, will they eventually separate on the paper? Use the analogical model to justify your answer. What do you think causes the separation at the molecular level over time? The experiment: Design an experiment that will allow you to identify metal ions in an unknown solution. You will select one of the unknown solutions provided. This unknown solution will contain a mixture of more than one of the metal ions that you already tested in Phase 1. For example, it might have cobalt and nickel ions in the same solution. Use the Designing Experiments worksheet (page 14) to summarize the process as a group. Make sure to take careful notes in your own laboratory notebook about your experiment. Hint: you may need to run additional known samples and mixtures and/or to include the data from Phase 1 in your analysis. Consider performing multiple trials because chromatography results can sometimes vary. What other evidence, in addition to Rf values, can you use to build a stronger case? Scientific Questions:

• (1) What differences did you find in the Rf values of the metal ions you investigated? • (2) Why does shape of the metal ion spots change as they move up the paper? • (3) What is the chemical origin for different Rf values? • (4) What metal ions are in your unknown solution?

Clean-up: PLACE ALL EXCESS and USED CHEMICALS IN THE PROPERLY MARKED WASTE CONTAINERS. Wash pint bottles and capillary tubes and return them to the front of the room. Finally, wash and wipe down the lab bench where you were working. If you have completed your sketches of the chromatograms, place them in your drawer in a beaker. Reflections & post-lab discussion (to be completed at the end of the laboratory session) 1. Team up with another group. Take turns discussing the evidence and reasoning you are using to make claims about which metal ions are in your unknown solution. When the other team presents their reasons to you, try to play devil’s advocate. Are there alternative explanations? Have they convinced you? 2. In a group, discuss how the analogical model can be used to explain the results of paper chromatography at the molecular level to someone unfamiliar with the chemistry in this lab.

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Names: Experiment #: Signatures: Section:

Designing Experiments Worksheet

Please use this sheet to summarize your lab group’s experiment and findings. Before going into lab, have your lab instructor check and initial it. This worksheet is to be scanned and submitted as part of your lab report. Make sure that it is entirely legible! Scientific Question: What metal ions are in your unknown solution?

Please describe your proposed experiment. (Check in with your lab instructor before performing experiments) Instructor’s initials:________

(attach extra pages if needed)

After you perform the experiment, please summarize the success or failure of your experiment and any claims you think you will be able to make in your lab report.

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Your answer to a post lab question is to be included in your lab report in a separate section called Post Lab question. It is worth 5 pts.

Rubric for laboratory reports (see lab report template) (due next lab meeting) Introduction: (5 pts)

Goal: To provide a short introduction.

Content: The title of your report, the date that the lab work was done, your partners, if any, and a couple overview sentences about what the lab experiment was about.

Post Lab Question: (5 pts)

Includetheanswertothispostlabquestion,rightaftertheintroduction:Inthesimulation,youstartedwith32beads,witha50%efficiencyofmovingfromcompartmenttocompartment.Ifyouranasimilarexperimentstartingwith3.2molesofmetalions,howmanymetalionswouldyouhaveineachbinafter"running"thesimulation?

Data, Results, Evidence: Scientific data that supports the claim. Submission of the Analog to Target and Designing Experiments Worksheets is required. (25 pts total)

Goal: To describe what you did and what data was collected and observed

Downloaded Procedure: Reference the laboratory procedure that was downloaded and the date it was accessed (e.g. Paper Chromatography, InterChemNet, accessed: 10/25/2016). Any changes in procedures should be noted.

Analogy: The Analog and Target Worksheet should be included.

Student Developed Procedure: The Designing Experiments Worksheet should be included. If insufficient details are present on the worksheet, provide further details in your lab report.

Data, Results, and Evidence: Carefully organize and present the data you collected. Observations can be important data to use in your analysis. Since patterns are often critical to understanding data, present data in Tables as well as Figures. Present your observations of qualitative data (e.g., color changes during developing). Use a table to present the Rf values calculated for your known and unknown metal ions. Provide a carefully labeled diagram of your chromatograms.

Analysis of Evidence (Reasoning): Scientific explanations. (30 pts total)

Goal: To provide the logic to evaluate your data and observations

Discussion: Explain why the evidence you presented supports your claim. This will include a discussion of the Analog to Target and Designing Experiments worksheets.

Hints for writing this lab report: Are any patterns evident? Discuss the phenomena at both the submicroscopic (molecular) level & macroscopic (visible to your eyes) level. Use the analogical model to further develop your explanations of results and underlying chemical concepts in your discussion.

Claim(s): Statement(s), derived from evidence, using scientific reasoning. (15 pts total)

Goal: To describe what claims or conclusions you can make from the data. For example, what claims can you make about the identity of the metal ions in the unknown solution?

Claims: Clearly state what claims or conclusions you can make. The logic of your claims builds from the evidence and reasoning presented in your previous sections. What reasoning can you provide to make meaning of the experiments you conducted (along with outside references). A good claim will include a short summary of the major pieces of evidence and analysis. Please write your claims clearly in order for them to be assessed reasonably.

Hints for writing this lab report: Think about your experimental procedure and how it allows you to understand how to analyze an unknown solution.

Other items to incorporate into your laboratory report: 1. The Analog and Target Worksheet (legible scan). 2. The Designing Experiments Worksheet (legible scan).