Lesson+Plan

· 28 July 2010 · Atchinson and Harrison || · Chemistry: Grade 10-12 · Arps 274 · Introduction to Beer’s Law ||
 * · Tammy Beilke, Stacey Hauser, and Ashton Shetler

__Standards Addressed__ Students develop scientific habits of mind as they use the processes of scientific inquiry to ask valid questions and to gather and analyze information. They understand how to develop hypotheses and make predictions. They are able to reflect on scientific practices as they develop plans of action to create and evaluate a variety of conclusions. Students are also able to demonstrate the ability to communicate their findings to others.
 * Scientific Inquiry**


 * Benchmark A:** Participate in and apply the processes of scientific investigation to create models and to design, conduct, evaluate and communicate the results of these investigations.


 * Patterns, Functions, and Algebra**
 * Students relate the various representations of a relationship such as relating a table to a graph. They understand how to describe the relationship between the graph of a line and its equation, including being able to explain the meaning of slope as a constant rate of change and y-intercept in real-world problems. **

Data Analysis and Probability Students create a scatterplot for a set of bivariate data, sketch the line of best fit, and interpret the slope of the line of best fit.Students will make conjectures about possible relationship in a scatterplot and approximate line of best fit.

Creativity and Innovation Students demonstrate creative thinking, construct knowledge, and develop innovative products and processes using technology. Students use models and simulations to explore complex systems and issues. Students identify trends and forecast possibilities.

__Student Objectives__ Students will be able to use a spectrometer to obtain data; they will be able to represent this data graphically through use of graphing paper, TI-graphing calculator, and SMARTBoard technology. Students will be able to use and apply Beer's Law in order to determine the concentration of food dye in a glass of Kool-Aid.

__Pu____rpose and Rationale for Lesson__ To integrate science, mathematics, and technology while showing real-world applications of spectroscopy.

__Opening (~10 minutes)__ Food safety is an important part of the food industry. Scientists are always performing studies to determine what kinds of food additives are safe for people to consume, and part of that involves determining how much of the additive is present in the food.
 * What kind of food additives can you think of that you consume every day?
 * What kinds of foods have food coloring in them?

Food scientists must have very accurate ways to measure the concentration of food additives. Too little additive, and it may not produce the effect they desire (preserving freshness, giving the right color, etc.). Too much additive, and it may have toxic effects on the body. This lesson will investigate one technique that scientists might use for measuring how much of a particular substance is present in their sample. In this case, we are going to measure how much food coloring is in a particular Kool-aid. First, we need to learn about the methods by which we can measure the food coloring concentration.

Virtual Manipulative: Present the virtual manipulative to the class, and ask the following questions to prompt discussion about the relationship between concentration of a solution and the amount of light that is absorbed.
 * What is this video representing?
 * What is the darker color representing? What change does it indicate?
 * What is happening to the light particles that seemingly disappear?
 * What happens to the light passing through the solution as the solution is more concentrated?
 * Why does less light pass through a more concentrated solution?

Finish by having the students write down a hypothesis which states relationship they have determined between the concentration of a solution and the absorption of light through the solution.

__Body of the Lesson (~40 minutes)__ · //Materials// Spectrometer Kool-Aid Graphing Paper Stock solution of Food Dye- Yellow, Red, Blue Computer w/ Internet Access Cuvettes Lab Instructions

· //Arrangements// Tables will be arranged to maximize group efficiency. For a class of 24, there should be six groups of four students. There will be six groups of six to accommodate the 36 students. Each table group will have their own spectrometer to use throughout the lab instruction. Groups will be given one color dye to test; each group has a partner-group containing the same test dye. These groups will be situated near each other to minimize movement throughout the testing phase.

· //Discussion Questions (~ 5 minutes)// Questions will be asked while students work in groups to ensure they are both on the right track and thinking about their solutions conceptually. Questions to be asked are among the following: -Should the graph of absorbance versus concentration go through the origin? In other words, should the absorbance read 0 when the concentration is 0? -Is is possible to have a negative absorbance? Why or why not? -Do you think that the slope of the graph should be negative or positive?

· //Safety// Students should wear safety goggles while handling any chemicals and glassware. The chemicals that are being used in this lab may be disposed down the drain with water.

Prior Lessons/Prior Knowledge Required In previous lessons, we would have introduced the properties of light, such that student would be aware of the wave like properties. Students would have learned about the electromagnetic spectrum, which gives an overall picture of the nature of light at different wavelengths. An important feature of light that would be studied is how light is absorbed by different molecules, and how that affects the way we can detect the absorbance. Discussions about color, and the wavelengths of light that are associated with particular colors, will also have been conducted. Students will be also introduced to the relationship between Absorbance and % Transmission, where transmission tells how much of the incident light reaches the detector as a ratio: % Transmission = I/Io x 100%, where I = the intensity of the light that reaches the detector, and Io = the intensity of the incident light The amount of light that gets absorbed is related to the transmission: Absorbance = -log(T), where T is the transmission.

Content Notes for This Lesson Beer's law shows the relationship between the concentration of a solution relates to its absorption. A = ebc where A = Absorbance, e = extinction coefficient, and c = concentration of analyte {Change the font on the e to be an epsilon - using SYmbol - this stupid wiki didn't work}

By making a calibration curve using data from samples with known concentrations, the absorption of an unknown sample can be determined. Four concentrations should be used to give an accurate line. The best fit line should be linear and drawn through the origin, since the blank is set at a reading of zero. The equation of the best fit line is then found using m=rise/run.

A **scatter plot** is a graph consisting of isolated points that shows the general relationship between two sets of data. The scatter plot is used to determine if the relationship is positive (having positive slope), negative (having negative slope), or no relationship exists (i.e. the points are random). The purpose of the graph is to visually display relationships which may not be apparent from data tables. Experimental errors which are always present might obscure the relationships. A **line of best fit** is used to average out these errors.

//How to create a Line of Best Fit// Using a graphing calculator or Excel is the best option, but an estimated line can be found without using these technologies. 1. Plot all data points 2. Draw a straight line through the middle of all the points. Approximately half of the data points should fall on one side of the line and the other half on the other side of the line. 3. Calculate the slope of the line. 4. Write the equation of the line.

· //Student Activities// Students will adapt the procedure outlined below in order to determine the concentration of food dye in a glass of Kool-Aid. After the students have completed their scatterplot with line of best fit, they will discuss with other groups using their colors to develop the best equation of a line. Students will then have one representative of each color group draw and label their plot and give the equation of the best fit line.

Once all of the equations are given (one for each yellow, red, and blue) students will use the information to find the concentration of food dye in their unknown Kool-aid solution.

Procedure for the Students to Follow:
 * Using the stock solution of your given food coloring, make a total of four solutions, using the technique of serial dilution. The total volume of your solutions should be 10 mL. Calculate the concentration of your diluted solutions.
 * Measure the absorbance of each of the four solutions.
 * Make a plot of the absorbance vs. concentration, and determine the equation of your best fit line.
 * Finally, find the concentration of food dye in your unknown Kool-aid solution using the absorbance and the plot you just made.

Accommodations: This lesson/lab exercise should be accessible to SpED and ELL students. The work is done in groups.

Extensions for G&T: For G&T students, have students determine the concentration of multiple colors within the same solution. They would need to make multiple calibration plots (one for each color) and measure the absorbance at the wavelength corresponding to that particular color.

· //Assessment// Types of assessments included in this lesson plan are mostly informal, formative assessments. Pre-assessment of the students’ knowledge is covered in the opening of this lesson. The teacher(s) will walk around and have discussions among the groups in order to get a feel for how well students are learning the material. Furthermore, the teacher(s) is responsible for looking at the plotted points of the data collected using the spectrometer. Graphs should be linear with a positive slope and eventually level off. In the walk-around, teachers should be listening to their students and their explanations of any phenomena they notice; this will provide questions for the teacher to ask to the whole class during the closing of the lesson. The post-assessment will be in the form of a homework assignment. This assignment will include a new set of data points; the students’ role is to analyze the data to come up with a solution. The set-up will be much like the lab used in this lesson, but the data will already be provided to them. Teachers will evaluate the students’ solutions to see if there are still misconceptions or a clear lack of understanding.

· //Potential Pitfalls// In order to successfully learn and understand this lesson, students must have prior knowledge in graphing and analyzing data. Most of the knowledge needed will be discussed during the opening of the lesson plan to ensure that students are on the same page. A common misconception about the Kool-Aid flavors is that each flavor contains only a single color dye. This, however, is not accurate since Kool-Aid consists of multiple food-dye colors, even cherry! Students will be able to reverse this misconception and gain new knowledge through the lab instructions. A potential difficulty for students in the graphing activity may be that the points may not accurately reflect a straight line; instead, a line of best fit (or regression line) must be graphed to correspond with the collected data. Students may have difficulties using and reading the results of the spectrometer; the aid of the teacher(s) will help to minimize this possibly troublesome area

//Prior Knowledge// In order to successfully graph the data and find a line of best fit students must know how to graph data on a coordinate plane. They must also know how what slope is and how to find slope of a line. Finally students must know how to find an equation of a line using either slope-intercept or point-slope forms of a line.

· //Accommodations// This lesson accommodates students of a variety of learning styles and exceptionalities. Students who are audio-learners will be accommodated through the both class and group discussions. By working in groups, students of all education levels will be able to aid each other’s progress through discussions and working together on a single goal. Students who enjoy working on their own will have the chance to do-so with the final homework assignment that is to be completed independently. For the visual learners, the virtual manipulative will provide an interactive view of what happens when light is absorbed. The lab activities will help kinesthetic learners as they will have to work with all materials physically throughout the lab activity.

· //Homework// A handout will be given with questions to review about how to apply Beer's law.

1. Explain how the three factors below affect absorption.
 * Extinction coefficient
 * Path length
 * Concentration of the analyte

2. Given that the extinction coefficient for a particular compound is 0.922 cm-1 M-1, what is the concentration of the analyte if the absorption is 0.461 at 350 nm?

3. Suppose your teacher wants you to find the concentration of a copper (II) sulfate solution. She tells you that you have the following items available to you to use: copper (II) sulfate solid, distilled water, volumetric flasks of various sizes, balance, cuvettes, spectrophotometer, graphing paper, and any common glassware that is available in the lab. Design an experiment that will allow you to determine the concentration of the unknown copper (II) sulfate solution. Be as specific as possible, but you do not have to do actual calculations.

__Clean up__ Leave at least 5-10 minutes for sufficient clean up. All cuvettes should be rinsed and returned, and the spectrophotometers should be checked to be sure that no cuvettes have been left inside them.

__Closure (~ 5 minutes)__ Review the relationship between light absorbed and the concentration of the solution. Relate how this technique is used in industry to measure a particular analyte in solution to establish that it is within the proper working range. Tomorrow we will continue learning about the relationship between light absorbed ans the concentration of the solution when we discover Beer's Law.

__Evaluation of the Lesson__ TBD