Using Computer-Interfaced Sensors:
A Junior or Senior High School
Science and Engineering Teaching Module

Washington State University/National Science Foundation
Department of Chemical Engineering Institute

Allen Majors
Ritzville Junior High School
401 E. 6th Avenue
Ritzville, WA† 99169
509 - 659 - 0232

Summer, 1998

In cooperation with:

Dr. Bernie Van Wie
and
Dan M. Leatzow

Department of Chemical Engineering
Washington State University
Pullman, WA† 99164-2710

Module Outline

  1. Synopsis
  2. Introduction
  3. General Objectives
  4. Sensors
    1. Colorimeter
      1. Objectives and overview
      2. Glucose and the indicator reaction
      3. Principle of operation
      4. Teacher preparation
        1. Materials list
        2. Calibration notes
      5. Colorimetric assays
      6. Suggested variations
    2. Conductivity Probe
      1. Objectives and overview
      2. Ionic solutions
      3. Principle of operation
      4. Teacher preparation
        1. Materials list
        2. Calibration notes
      5. Conductivity assays
      6. Suggested variations
    3. Carbon Dioxide (gaseous) Sensor
      1. Objectives and overview
      2. Carbon Dioxide
      3. Principle of operation
      4. Teacher preparation
        1. Materials list
        2. Apparatus trial notes
      5. Carbon dioxide activities
      6. Suggested variations
  5. Appendices
    1. Reference Graphs
    2. Student Activity Sheets
    3. Hierarchy Charts
    4. Materials Sources
  6. References

Synopsis

This module shows how to assay aqueous sugar and salt solutions and gaseous carbon dioxide solutions using computer-interfaced sensors to collect data.† Software are used to instantaneously plot the data as the assays are run.† Students will establish reference graphs and subsequently interpolate and extrapolate from the reference plots.

Using common, household materials, students will design and build a system to gather optimal samples of exhaled studentsí breath, small animalsí breath, and air collected from a sealed terrarium for carbon dioxide assays.

Introduction

Sugar (glucose), salt (sodium chloride), and carbon dioxide are substances central to proper metabolic function in all life forms.† Junior high school students are quite familiar with all three substances, but are typically unaware regarding how basic assays to quantify respective substance solution concentrations may be completed.† Gravimetric (i.e., mass determination) activities for crystalline salt and sugar masses are completed easily enough with available balances, and volumetric activities for the same substances are as common as many cooking recipes.† Many junior high science classes include aqueous salt and sugar solutions as part of their laboratory exercises.† Solution concentration activities, though related to volumetric and gravimetric activities, are different from the latter two in at least two basic respects.† Solution activities, in essence, build upon an understanding of volume and mass, and determination of concentration involves proportional mathematical processing.

Employing computers to gather and process data frees students from the tedium of gathering data by "eye and hand" and precludes several sources of potential experimental error.† Calibration of an apparatus is quickly and accurately performed using associated software.† Extensive data are then easily collected and timing errors eliminated.† Students commonly reach invalid or unreasonable conclusions from misrecorded or misrepresented data.† Automated sensors, when properly calibrated, record data accurately and resultant autoscaled plots clearly represent data for student interpretation.

The laboratory apparatuses central to this module are marketed by Vernier Software of Portland, Oregon (U.S.A.).† Vernier sells many different sensors and probes additional to the three used in this module.† The sensors may be interfaced to selected Texas Instruments calculators using a Texas Instruments Calculator-Based Laboratory (CBL) interface or to a microcomputer using a Vernier Software Universal Laboratory Interface (ULI).† ULIís were utilized in this module.

Logger Pro is the software program that controls sensor selection and configuration as well as various data collection parameters.† This handy application allows standard data analysis such as function fitting, averaging, and integration, in addition to the ability to print tables and graphs directly from program windows.

A list of the specific Vernier Software products used for this module is as follows:

Vernier Software Instrumentation - interfaced to a computer workstation

Vernier Software computer software application

General Objectives

Sensors

Colorimeter

Colorimeter and Sugar Concentration Objectives and Overview.† Food coloring solutions and sugar solutions will be assayed using a colorimeter.† An appropriate indicator, Trinder reagent, will be employed to establish a color corresponding to a certain sugar concentration.† A reference relationship will be established from a computer graph.† Students will then determine the concentration of unknown samples by interpolating and extrapolating from a reference plot.

Glucose and the Indicator Reaction.† Glucose is a simple monosaccharide comprised of a six-carbon skeleton.† Aerobic respiration is essentially "burning" sugar by using oxygen to release the energy stored in the carbon-carbon bonds of the sugar molecule.† Blood serum glucose level monitoring is of critical importance in the diagnosis and treatment of certain metabolic disorders.† The most notable of these disorders is diabetes.

Glucose in solution is colorless.† Therefore, we can use glucose oxidase to catalyze a reaction in which aqueous glucose in the presence of oxygen yields gluconic acid and hydrogen peroxide.† In the second assay reaction, the hydrogen peroxide product from the first reaction combines with 4-aminoantipyrine in the presence of peroxidase to yield a roseĘ colored quinoneimine dye.† The dye product affords colorimetric assay.† The reagent kit used for this glucose indicator reaction series is commonly referred to as Trinder reagent after the scientist who first proposed the method.† The reactions described proceed as follows:

Colorimeter Principle of Operation.† A colorimeter is an instrument that can be used to determine the concentration of a solution by determining the amount of light that the solution absorbs.† Monochromatic light from an LED light source passes through a solution sample that is contained in a small cuvette.† Some of the light that strikes the solution is absorbed by the sample.† As a result, less light strikes the photodiode detector on the side of the sample opposite of the LED than strikes the cuvette on the same side on which the LED is positioned (See Figure 1, below).



Figure 1.† Colorimeter (lateral view).

When light is absorbed by a sample, the radiant power of the emitted light is diminished.† The transmittance (T) is the fraction of the emitted light that is not absorbed by the sample and that therefore passes through the sample.† The relationship between T and solution concentration is logarithmic.† Typically, light absorbance (A) is measured because, according to Beerís law, there is a direct relationship between absorbance and solution concentration (c).† Beerís law is at the foundation of analytical spectrophotometry and may be expressed as:

A = ebc

In Beerís law absorbance (A) is dimensionless, sample concentration (c) is usually moles per liter (M; molarity), and the sample pathlength (b) commonly centimeters.† Epsilon (e) refers to molar absorptivity, which is the amount of light that a substance characteristically absorbs at a certain wavelength of radiation.1

Colorimeter Activities Teacher Preparation.† The teacher should calibrate the colorimeter using a reference sample of desired concentration as per the instructions included with the apparatus.† Serial dilutions may then be prepared so that students may interpolate from their reference graphs.† One should be careful, especially when preparing solutions using food coloring, to avoid exceeding the linear range for the relationship between absorbance and solution concentration.† At certain relatively high solution concentrations, Beerís Law fails to describe the relationship accurately.

Materials list for colorimetry activities (per student or student workgroup):

The colorimeter was initially calibrated using blue food coloring solutions and glucose reference solutions.† The calibration was accomplished to determine the linear range of absorbance for the concentrations under consideration.

Food coloring solutions were prepared by using one drop of blue food coloring in 100 mL of solution.† Tap water served as the diluent.† This "concentration"Ē was then arbitrarily established as corresponding to a "1 M blue solution" (not to be confused with a true molarity concentration).† Serial dilutions were completed so that "0.75 M, 0.50 M, and 0.25 M solutions" were also prepared by adding the appropriate amounts of diluent to portions of the 1 M reference solution. Absorbance data were then gathered for the "0.0 M, 0.25 M, 0.5 M, 0.75 M, and 1 M solutions".† The plotted results were favorable in that when linear regression analysis was applied the value of the correlation coefficient was 0.9937 (See Appendix A, Figure A.1).† Higher concentrations were subsequently assayed in an attempt to reach the non-linear range of the Beers Law Plot/Function.† Concentrations of "1.5 and 2.0 M" were assayed and added to the original calibration line.† The results remained favorable, though the value of the correlation coefficient dropped to 0.9820 (See Appendix A, Figure A.2).† From these data it was concluded that "1 M" blue food coloring solution would provide a reliable upper limit for interpolation activities.

Glucose dilutions were prepared using a reference solution with a concentration of 1 g/dL.† The calibration samples were made using a thin stem pipette by mixing drops of the reference solution with drops of deionized water in the following ratios of glucose solution to deionized water:† 0:100, 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91, and 10:90.† These 11 samples were then mixed in respective cuvettes with Trinder reagent in a ratio of one part sample to nine parts Trinder reagent.† The reagent-sample mixtures were various intensities of roseĘ color.† Absorbance readings were taken at wavelengths of 470 nm (blue) and 565 nm (green).† Excellent agreement was obtained between the trends of the two plots.† The main difference was that the green results were "compressed" (i.e., the slope of the green wavelength data line is significantly lower than that of the blue wavelength line) in relation to the blue results.† In both cases the relationship was not linear beyond a concentration of a 5:95 ratio of reference solution to deionized water.† The linear fit for the ratio range from 0:100 to 5:95 was good (See Appendix A, Figure A.3).† At concentrations greater than a 5:95 ratio of reference solution to deionized water, a limiting reagent, most likely dissolved O2, constrains the reaction from proceeding further so that higher absorbance values are not obtained.

Colorimetric Student Assays.† The first colorimetry laboratory activity uses blue food coloring solution to facilitate a basic understanding of how the colorimeter works.† The relationship between solution concentration and absorbance for samples of known concentration values is used to determine the concentration of samples of unknown values employing both interpolation and extrapolation (See Appendix B, Student Laboratory Activity Sheet B.1).

The second colorimetry laboratory activity builds on the foundation established in the first activity by using Trinder reagent for glucose concentration in an assay that requires a two-step dilution for each sample.† Additionally, there is a question regarding an explanation of dilution procedure and another regarding discussion of results (See Appendix B, Student Laboratory Activity Sheet B.2).

Suggested Colorimetric Assay Variations.

Conductivity Probe

Conductivity Probe and Dissolved Ion Concentration Objectives and Overview. Various salt solutions will be assayed for dissolved ion concentration using a dissolved ion conductivity probe.† The teacher will provide reference concentration samples.† Students will use the reference samples to establish the relationship between concentration and conductivity. Students will then determine the concentration of unknown samples by interpolating and extrapolating data from the reference plot.† Comparisons will be made of table salt (NaCl) solutions against epsom salt (MgSO4∑7H2O) solutions and of epsom salt and sucrose mixed in the same solution.

Ionic Solutions.† Ionic crystals, of which table salt (NaCl) is a common example, maintain their structure by the attraction between the positively charged cations, such as Na+, and the negatively charged anions, such as Cl-.† When a salt crystal is placed in a solvent such as water, water molecules are able to "pull" anions and cations away from the crystal and into solution.† When the solute has been completely dissolved we may say that there are now sodium and chloride ions in solution.† Strictly speaking, it would be incorrect to say that there is sodium chloride in solution, for in fact, the sodium chloride crystal no longer exists.2

Water is able to dissolve many ionic compounds because of its polar nature.† Due to the relatively higher affinity of the oxygen atom than of the hydrogen atoms for the electrons that are shared among the three atoms, the bonds in a water molecule are polar covalent.† This results in the hydrogen atoms having a significant partial positive charge and the oxygen atom retaining a corresponding negative charge.† The negatively charged oxygen parts of water molecules therefore "attach" to the positively charged cations with sufficient strength so as to be able to "pull" the cations away from the ionic crystal. At this point, several water molecules have solvated the ion and the ion is now in solution.† The interaction between the hydrogen atoms of water and the anions of the salt crystal is essentially the same, though the charges are reversed (See Figure 2, below).

Figure 2: Salt Crystal (NaCl) Solvation by Polar Covalent Water.

Conductivity Probe Principle of Operation. A conductivity probe measures the ability of a solution to conduct an electric current between two electrodes.† In an ionic solution, current flows by charge transporting ions that move to oppositely charged electrodes in a conductivity probe (See Figure 3, below).† Increasing the ion concentration of a solution will therefore result in a proportional increase in conductivity, as more current is able to flow.† Electrolyte solutions cannot be measured reliably using direct current due to changes in electrolyte concentrations and the accumulation of electrolysis products at the electrodes.† Buildup of electrolysis products on or near electrodes changes the resistance of a solution.† For these reasons, it is efficacious to use alternating current in conductivity analyses.3

Figure 3. Conductivity Probe: Cations are reduced at the cathode, anions are oxidized at the anode.

Conductivity Probe Activities Teacher Preparation.† As per the instructions included with the apparatus, the teacher should perform a two-point conductivity probe calibration the using reference samples of appropriate concentrations. Serial dilutions may then be prepared so that students may interpolate from their reference graphs.† One should be careful to avoid exceeding the linear range for the relationship between conductivity and solution concentration.† At certain relatively high solution concentrations, ion-ion interactions preclude linearity.

Materials list for solution conductivity (per student or student workgroup):

The initial calibration line was completed by collecting ion concentration data for NaCl solutions of 0.0 g/L, 2.5 g/L, 5.0 g/L, 7.5 g/L, and 10 g/L concentrations.† Each of these solutions was prepared individually (i.e., serial dilution was not used to prepare lower concentrations from a higher, standard concentration).† The results are included in the appendix (See Appendix A, Figure A.4).† From a relative perspective the results were favorable.† Applying linear regression analysis a correlation coefficient of 0.9953 was obtained.† In absolute terms the results were somewhat unexpected.† The measured NaCl concentration values for the 2.5 g/L, 5.0 g/L, and the 7.5 g/L samples as determined by the conductivity probe were approximately 0.5 g/L higher than what was expected based on a linear interpolation between the reference and 10 g/L solutions.† Instead of using a two-point calibration, one could use a best fit line that included several data points to minimize experimental error.

It was decided to repeat the above series but to prepare the solutions this time by making serial dilutions of the reference concentration.† The reference concentration would serve as the "high point" on the reference line.† The results obtained were not significantly different than those obtained previously.† The data are again linear, and the middle three values repeat at unexpectedly elevated levels (See Appendix A, Figure A.5).

A third calibration series was completed which was similar to the first two, but this time tap water, rather than nanopure water, was used as the solvent.† This series more closely approximates the actual assays that might be performed in the typical classroom setting.† The data obtained from this third series agreed closely with the data from the other two.† The function was again linear and the middle values were similar as well (See Appendix A, Figure A.6).

From these data one may conclude that there is no significant difference insofar as obtaining linear data when carefully preparing samples by weighing out the amount of salt necessary for each different concentration, by making serial dilutions to complete the concentration series, or by "substituting" tap water for de-ionized water.

A comparison of dissolved ion concentration was also completed to compare laboratory grade "nanopure" water, "generic" distilled water obtained from a local grocery store, and tap water.† The results were favorable in that there was no appreciable difference in the ion concentrations when comparing the "nanopure" water with the distilled water purchased from the store.† Tap water was found to have slightly less than 200 mg/L of dissolved ions.† These results are presented in the appendix (See Appendix A, Figure A.7).† This is a positive finding in light of the absence of multiple filtration, reverse osmosis systems in nearly all classroom laboratory settings.† Distilled water from a local store should serve just as well.

A second salt calibration series was completed using hydrated magnesium sulfate (MgSO4∑7H20) or "epsom salt".† Concentrations of 0.0 g/L, 2.5 g/L, 5.0 g/L, 7.5 g/L, and 10.0 g/L were evaluated.† The† results were again linear (See Appendix A, Figure A.8).

Solution Conductivity Student Assays Students will begin investigating solution conductivity by establishing a reference plot for the relationship between conductivity and solution concentration for a table salt solution.† They will subsequently use the reference plot to interpolate and extrapolate the concentration of unknown samples (See Appendix B, Student Laboratory Activity Sheet B.3).† In a second activity students will investigate the relationship between conductivity and solution concentration for another ionic compound, magnesium sulfate (MgSO4∑7H2O).† They will extend their understanding of this relationship to discuss the conductivity results of a salt and sugar solution (See Appendix B, Student Laboratory Activity Sheet B.4).

Suggested Conductivity Assay Variations.

†Carbon Dioxide Sensor

Carbon Dioxide Sensor and Gaseous Concentration Objectives and Overview.† The CO2 sensor emphasis will be on designing and testing systems to contain and assay gaseous samples.† Studentsí breath, air from an insect enclosure, and air from a sealed terrarium will be measured for CO2 concentration.† These will be direct measurements.† Plotting and data analysis will be done by gathering data over time from the plantsí and animalsí respective sealed environments and by evaluating diluted breath.† Students will engineer/design and build systems to enable collection of gaseous CO2 samples.† Breath analysis will focus on qualitative data.† Comparisons of the results of the various completed designs will be made.

Carbon Dioxide Information.† Carbon dioxide is a "waste" product of aerobic respiration.† When metabolic systems release the energy in carbohydrates or when organic compounds are otherwise combusted, water and carbon dioxide are the material products.† In higher animals, carbon dioxide in aqueous solution is exchanged for oxygen in the lungs and leaves the body as a gas.

Carbon dioxide is also involved in regulating blood pH.† Carbon dioxide is moderately soluble in water, and in aqueous solution reacts to a limited degree with water to yield H2CO3 (carbonic acid).† Carbonic acid is a weak diprotic acid, but its conjugate base, HCO3-, serves as a buffer to acidic protons.4

Atmospheric carbon dioxide levels have been under intense scrutiny for several years.† Some of the radiation from the sun that strikes the surface of the earth is reradiated back into the atmosphere as infrared radiation (IR).† Carbon dioxide in the atmosphere absorbs some of the reflected IR producing a warming effect.† Elevated atmospheric CO2 levels have been attributed to burning fossil fuels and deforestation of tropical areas.† From 1880 to 1980 atmospheric CO2 rose from 272 ppm to 339 ppm.2† The current level is over 360 ppm.† Human activity releases approximately 25,000,000,000 metric tons of carbon dioxide per year.5† Exhaled human breath has a carbon dioxide concentration of approximately 50,000 ppm.

Carbon Dioxide Sensor Principle of Operation. The carbon dioxide gas sensor measures CO2 by monitoring the amount of IR that is absorbed by carbon dioxide molecules.† A safely housed, hot metal filament serves as an IR source.† The sensor consists of a short, hollow tube with the metal filament mounted on one end and an IR detector on the other end that measures how much IR is absorbed by the sample (see Figure 4, below).† The detector measures in a narrow bandwidth centered at 4260 nanometers.† The cylindrical sensor housing is vented by eight small holes to allow sample introduction and subsequent sensor purging after data have been collected.† The upper limit of the operating range of the Vernier Software CO2 gas sensor is 5000 ppm.

Figure 4 - Carbon Dioxide Gas Sensor.

Carbon Dioxide Activities Teacher Preparation.† The materials needed for this assay are as varied as the designs one may wish to test.† Typically, students and teachers are constrained because needed materials are expensive and not easily procured.† If one desires to used forced air, a (high school) laboratory with such an amenity, a small compressor, a blow dryer, or a small fan might be accommodated to serve the purpose.† Tygon tubing, rubber hose, or even garden hose may be adaptable to a desired application.†

Materials list for CO2 gas concentration (per student or student workgroup):

The CO2 gas sensor obtains direct ppm concentration data.† Equipment and materials limitations precluded this teacher from running a standard calibration plot.† A reference line would require obtaining pure nitrogen (or some other inert gas) as a zero value standard and mixing or obtaining a sample of known CO2 concentration.† Overcoming the challenges presented by this situation are considered beyond the value of the results one would obtain for the application under consideration.† Typical science budget, equipment, and logistic limitations further compel this conclusion.

Documentation included with the sensor states that the CO2 level of outside air typically ranges around 400 ppm.† Samples taken in Pullman somewhat agreed with this statement.† Values of 316 ppm and 321 ppm were obtained.† Values obtained in the laboratory ("room air") typically ranged from 600 ppm to 635 ppm as the sensor was resting on the bench in the room with no open windows.† Without reference samples of known CO2 concentration, one could "calibrate" the sensor at 400 ppm for ambient levels or simply use as a reference level whatever current "live reading" one were to obtain.

Samples of experimentersí breath quickly and obviously exceeded the operating range (0 ppm - 5000 ppm) of the sensor.† The sensor documentation stated that exhaled breath commonly exceeds 50,000 ppm of CO2.† To overcome the problem presented by the 5000 ppm upper limit of the CO2 sensor with regard to human breath samples, it was decided to dilute breath samples accordingly by means of an apparatus fashioned in the laboratory.† Various design considerations were discussed and a few designs tested.† A major challenge to some of the designs was to deliver the sample consistently.† One of the designs tested used a "blow-by" apparatus to dilute the breath sample in order to achieve numbers within the sensor range (See Figure 5, page 19).† 50 cc breath samples were introduced into the flowing air stream by hand-depressing the attached syringe.† This "blow-by" apparatus was not considered successful because of the nonrepeatability of the results.† It was concluded that variations in the sample entry times were at least party the cause of the nonrepeatability.† Curve integration yielded no further insight in resolving the problem, as widely varying areas were obtained.† There is acute variation in peak heights.† For example, peak heights varied from three highs of over 2,500 ppm to some approximating merely 500 ppm† (See Appendix A, Figure A.9).

A variation of the "blow by" apparatus proved fairly successful.† Here a small, aquarium-type air pump was used to introduce each breath sample from a syringe.† The repeatability of this approach was favorable (See Appendix A, Figure A.10).† It is speculated that the pump provided a more consistent sample introduction rate than what could be accomplished with by-hand depression of the syringe.† The flow rate of the forced air line was approximately 1.4 L/min and that delivered by the small pump approximately 0.7 L/min.† These numbers were arrived at by a water displacement measurement.† To do this, a large flask was filled with water, immersed in a bucket of water, and inverted.† Then, the time for the water in the flask to be displaced by air delivered via a tube was recorded.

The pump-modified "blow by" design was used to assay samples from holding oneís breath for increasing time periods.† Samples were run from a normal breathing frequency breath and then compared on the same graph with samples from having held oneís breath for 15, 30, and 45 seconds (See Appendix A, Figure A.11).

Another design, and one that produced positive results, involved injecting a diluted breath sample into a sealed flask inside of which was the CO2 sensor (See Figure 6, Page 20).† In this design, time was allowed (approximately 6 minutes) for the gas to diffuse so that a uniform CO2 level was achieved throughout the flask.† After the initial plot curve had leveled such that an equilibrium CO2 level existed throughout the flask, the data were then collected.† A representative plot showing equilibrium establishment is included in the appendix (See Appendix A, Figure A.12) as well as a graph summarizing five trials run from equal portions of the same large sample employing this approach (See Appendix A, Figure A.13).

Figure 5 - Tubing Assembly for "blow-by" CO2 Gas Analysis

In "resetting" the CO2 sensor, a significant decay time from high, sample ppm readings back down to room levels was noted.† The sensor took almost two minutes to settle back to ambient levels.† The design of the sensor is such that diffusion of gases in and out of the space immediately surrounding the actual sensor is somewhat occluded.† It was found that fanning the sensor or waving it in the air could significantly reduce this decay time.† Nearly immediate decay times were obtained using forced air to purge the sensor housing.

Carbon Dioxide Student Assays. The student activities using the carbon dioxide probe have two central emphases.† One focus will be on designing and building an apparatus which will consistently dilute human breath samples (approximately 50,000 ppm CO2) so that repeatable results are obtained within the sensorís range (5,000 ppm CO2 upper limit) (See Appendix B, Student Laboratory Activity Sheet B.5).† A second activity will entail using small plants and animals in sealed containers and plotting respective changes in carbon dioxide levels (See Appendix B, Student Laboratory Activity Sheet B.6).

Figure 6.† Flask Assembly for CO2 Equilibrium Assays.

Suggested Carbon Dioxide Sensor Assay Variations.

Appendices

A. Reference Graphs

Note:† As per convention, data plots are presented with the independent variable as the abscissa and the dependent variable as the ordinate, and data tables are presented with the X axis values to the left of the Y axis values.

A.1†† Blue food coloring:† Absorbance versus concentration (1M maximum)
A.2†† Blue food coloring:† Absorbance versus concentration (2M maximum)
A.3†† Calibration data of glucose concentration by Trinder reagent
A.4†† NaCl solution conductivity:† discrete solutions
A.5†† NaCl solution conductivity:† serial dilutions
A.6†† NaCl solution conductivity:† tap water solvent
A.7†† Comparison of dissolved salts for three water sources
A.8†† Magnesium sulfate solution calibration plot
A.9†† CO2 blow by apparatus:† sample injection by hand
A.10 CO2 blow by apparatus:† sample injection by pump
A.11 CO2 levels for incremental periods of held breath
A.12 Representative plot for CO2 equilibrium establishment in a sealed flask
A.13 CO2 equilibrium data summary

B. Student Activity Sheets

B.1††† Colorimeter Lab A (blue food coloring)
B.2††† Colorimeter Lab B (glucose levels)
B.3††† Ion conductivity: sodium chloride
B.4††† Solution conductivity:† magnesium sulfate and sucrose
B.5††† CO2 test design activity
B.6††† CO2 level assay of small organisms

C. Hierarchy Charts

C.1†† Task analysis for colorimetry data plots
C.2†† Task analysis for solution conductivity data plots
C.3†† Task analysis for CO2 assays

D. Materials Sources

Figure A.1.† Blue Food Coloring:† Absorbance versus Concentration (1 M maximum).

Figure A.2.† Blue Food Coloring:† Absorbance versus Concentration (2 M maximum).

Figure A.3.† Calibration Data of Glucose Concentration by Trinder Reagent.† Note:† "pph" refers to parts per hundred.

Figure A.4. NaCl Solution Conductivity: Discrete solutions

Figure A.5.† NaCl Solution Conductivity:† Serial dilutions.

Figure A.6.† NaCl Solution Conductivity:† Tap water solvent

Figure A.7.† A Comparison of Dissolved Salts for Three Water Sources.

Figure A.8.† Magnesium Sulfate Calibration Plot.

Figure A.9.† CO2 Blow-By Apparatus:† Sample injection by hand.

Figure A.10.† CO2 Blow-By Apparatus:† Sample injection by pump.

Figure A.11.† CO2 Levels for Incremental Periods of Held Breath (from left to right:† regular breathing rate, held for 15 seconds, held for 30 seconds, held for 45 seconds).

Figure A.12.† Representative Plot for CO2 Equilibrium Establishment in a Sealed Flask.

Figure A.13.† CO2 †Equilibrium Data Summary.

 

Colorimetry Lab A Name: date: period:

Page 1 of 2: Blue food coloring.25 pts. scale, 28 pts. max. possible.† The point value for each question is in parentheses beside the question number.

We can use the color of a solution to determine the concentration of an unknown sample.† We will pass a beam of light through a sample and determine how much of the original, emitted light was absorbed by the sample.† The instrument that performs this test is called a colorimeter.† The more concentrated the sample, the more light will be absorbed.† Note that when light strikes an object (in this case the object is a solution), some of the light is absorbed by the object and some is reflected, or transmitted, away from the object.† When you collect your data it is the absorbance that will be needed for this activity.† What we "see" as an object with our eyes is the color of light that is transmitted.† In this regard the colorimeter works differently than our eyes.† The colorimeter is able to determine the light that has been absorbed, or that is "missing", whereas we see what remains of the full spectrum of light after some has been absorbed.† The blue solutions in this activity are therefore absorbing all of the light that strikes them except for the blue.† They appear blue to our eyes because they do not absorb blue.

A Simplified
Colorimeter
Diagram
(side view)

Tips:

keep cuvettes clean - scratch and smudge free
handle cuvettes only by the ribbed sides
record ABSORPTION (not transmission)
be careful around the computer and with the colorimeter, but donít waste time - others may be waiting to use the equipment
all samples to be tested must be capped!† (the lids simply snap on and off)
clean up any mess/spills.
leave the cuvettes thoroughly rinsed and drying upside-down when you are done with them.

  1. Obtain a small sample of blue known concentration.† We will call this sample 1 molar (1M).
  2. Fill a cuvette to within about 1 cm from the top with water.† This is your "blank".† Fill a second cuvette to the same level with 1M known solution.
  3. 3.(2 pts.)† Make sure that the colorimeter is set to "red".† Use the colorimeter to run the "blank" (water only) sample, and then run your known, 1 M, blue sample. The % concentration for the water blank will be zero, for the 1 M known it will be 100%.† Fill both the "blank" and 1 M cuvettes to within about one-half of a centimeter from their respective tops.† Record the results below and also print out your graph.
    __________ absorption water __________ absorption 1 M
  4. (1 pt.)† Obtain a sample of blue unknown #1.† Use the colorimeter to determine its absorption.
    __________ absorption blue unknown #1
  5. (2 pts.)† Next, use your graph and a ruler to determine the molar concentration of unknown #1.† Enter the answer below.† On your graph, show the lines you used to determine the concentration.
    __________ concentration of blue unknown #1
  6. (8 pts.)† Repeat step 3 for blue unknowns #2 and #3.† Note:† for blue unknown #3 you may need to alter (extend) your graph.† Enter your results below. On your graph, show the lines you used to determine the concentrations.
    __________ absorption blue unknown #2† †††††††††† __________ concentration of blue unknown #2
    __________ absorption blue unknown #3† †††††††††† __________ concentration of blue unknown #3
  7. (4 pts.)† Now use your understanding of the relationship between absorption and solution concentration to prepare a 0.25 M solution.† Show the sample to the teacher after you have successfully mixed a 0.25 M solution so that the teacher can check the absorption with you.† Record the absorption results below. On your graph, show the lines you used to determine the concentration.
    __________ absorption value for a 0.25 M sample
  8. (9 pts.)† Turn in your graph.† It should include:
    1. your original "reference" line from the water blank and the 1 molar known
    2. the lines you used to determine the molar concentrations of unknowns 1-3
    3. the line you used to plot the absorption value and concentration of your 0.25 M sample
  9. (2 pts.)† The solutions for this activity were blue.† Why do we not set the colorimeter to use blue light?† In other words, why would red light, which we used, be preferred over blue light?
Colorimetry Lab B Name: date: period:

Page 1 of 2:† Glucose levels. 25 pts. scale, 28 pts. max. possible.† († ) denotes points per question.

In this activity we will extend the (blue) solution colorimeter activity we recently completed.† The goal of this lab is to use a special indicator, Trinder reagent, that turns a pale reddish color in the presence of the sugar glucose to determine the concentration of sugar in unknown solutions.† As before, the more concentrated the solution, the more light will be absorbed (and correspondingly less transmitted).† In this case the more sugar that is dissolved in the solution, the higher will be the absorbance.

Tips:

keep cuvettes clean - scratch and smudge free
handle cuvettes only by the ribbed sides
record ABSORPTION (not transmission)
be careful around the computer and with the colorimeter, but donít waste time - others may be waiting to use the equipment
all samples to be tested must be capped!† (the lids simply snap on and off)
clean up any mess/spills.
leave the cuvettes thoroughly rinsed and drying upside-down when you are done with them.

  1. Obtain a sample of known concentration.† This sample was prepared by dissolving 1 gram of sugar in 1 liter of water.† We will therefore call the concentration of this solution 1 g/L.
  2. (3) Use a pipette and your graduated cylinder to prepare 100 mL of a solution that is half the strength/concentration of the original 1 g/L known.† Label this solution 0.5 g/L.† Clearly explain below how you diluted/mixed some of the 1 g / L known to obtain 100 mL of 0.5 g/L solution.
  3. Obtain a cuvette.† Use a thin stem pipette to place 6 drops of tap water in one of the cuvettes.† Add 54 drops of Trinder reagent to the 6 drops of water.† Cap the cuvette and invert 2-3 times to mix the water and the Trinder reagent.† Since this sample has no sugar, this is your "blank" sample.
  4. Obtain another cuvette.† Use a thin stem pipette to place 6 drops of your 0.5 g/L solution in the (second) cuvette.† Then place 54 drops of Trinder reagent into this same cuvette.† Cap your solution and invert it 2-3 times to mix the solution well.† The solution should now appear a pale pinkish-red.
  5. (2) Make sure that the colorimeter is set to "blue".† Use the colorimeter to run your blank and 0.5 g/L known.† The % concentration for the "blank" will be zero; for the 0.5 g/L sample it will be 100%.† Record the results below and print out your graph.
    __________ absorption of "blank"†††††††††††††††††††††††††††††††††††††††† __________ absorption of 0.5 g / L
  6. (3) Obtain a sample of glucose unknown #1.† Use a thin stem pipette to place 6 drops of unknown #1 solution in a cuvette.† Then place 54 drops of Trinder reagent into this same cuvette.† Cap your solution and invert it 2-3 times to mix the solution well.† The solution should now appear a pale pinkish-red.† Use the colorimeter and your graph from step 5 above to determine the concentration of glucose in unknown #1.† Record your results below:
    __________ absorption of unknown #1†††††††††††††††††††††††††††††††† __________ g/L of unknown #1
  7. (3) Repeat step six above, but this time use unkown #2.
    __________ absorption of unknown #2†††††††††††††††††††††††††††††††† __________ g/L of unknown #2
  8. (5)† Now use your understanding of the relationship between absorption and solution concentration to clearly explain below how to prepare a 0.4 g/L glucose solution.† On your graph, show the lines you used to determine what the concentration of this solution should be.† Record the anticipated concentration of the 0.4 g/L solution below:
    __________ absorption of 0.4 g/L glucose solution††††††††††††††††††††††††††† Explain below:
  9. (3) Suppose you had to make a presentation to your city council about water quality data and issues.† During the course of your presentation some of the council members question you on the validity of the analytic assay you used (i.e., the colorimeter) because they donít understand the principles behind why these tests are sound.† How would you go about explaining the test and convincing them of the validity of your tests and hence your data?† Keep in mind that these are not technically trained persons.
  10. (9)† Turn in your graph.† It should include:
    1. your original "reference" line from the Trinder reagent blank and the 0.5 g/L known
    2. the lines you used to determine the molar concentrations of unknowns 1 & 2
    3. the line you used to determine the absorption value of your 0.4 g/L sample
Name: date: period:

Page 1 of 3:† Ion Conductivity (sodium chloride).† 20 pts. Scale, 23 pts max.†††††††† Respond to written questions with complete sentences.† († ) denotes points per question.

The ability of a solution to conduct an electric current is known as conductivity.† We can measure the conductivity of some solutions to determine the concentration of the solutions because certain atoms, when in solution, are ionized and are able to carry charge (transport electrons).† In this activity you will use distilled water and prepared standard solutions to determine the concentration of some "unknown" solutions.† Also, you will prepare two solutions of desired concentrations.† Tip:† It is essential that you keep the test electrode "clean".† This means that you must do a distilled water rinse before all trials to ensure that water on the electrode from another sample does not contaminate the sample you are testing.

Conductivity Probe

  1. 1.†††† Fill a small container with distilled water to a depth of approximately three cm.† Distilled water has been purified by evaporation.† Fill a second container in a similar manner with "standard" salt solution.† Label each container appropriately to avoid confusion.† Salt water and distilled water look the same.
  2. (2)† Determine the solution concentration of distilled water and of a prepared standard solution by immersing the electrode in each of the samples for approximately 10 seconds.† Do a distilled water rinse on the electrode before collecting each number.† The software will show the concentration of each sample in mg/L.† Record your results below and print out your graph.
    __________ mg/L for distilled H2O __________ mg/L for standard solution
  3. (3)† Now determine the concentration of the three unknown solutions in a manner similar to steps 1 and 2.† Remember to rinse the electrode with distilled water before each trial.† Each result is in mg/L.
    __________ unknown #1 __________ unknown #2 __________ unknown #3
  4. (2)† Use the standard solution, distilled water, pipettes, and a graduated cylinder to prepare 100 mL of solution with a concentration of 3 g/L in a small, clean jar (remember, 1000 mg = 1 g).† Show your "successfull" solution to the teacher as you take your reading.† Record the actual results below.
    __________ mg/L (concentration of prepared solution A)
  5. (4)† Show your math and clearly explain the process of how you used distilled H2O and standard solution to prepare a 3000 mg/L solution for question #4.
    _________ mL of distilled H2O††__________ mL standard solution
  6. (2)† Use the standard solution, distilled water, pipettes, and a graduated cylinder to prepare 100 mL of a solution with an 8 g/L concentration in a clean jar (remember, 1000 mg = 1 g).† Show your "successfull" solution to the teacher as you take your reading.† Record the actual results below.
    __________ mg/L (concentration of prepared solution B)
  7. (4) Show your math and clearly explain the process of how you used distilled H2O and standard solution to prepare 100 mL of an 8000 mg/L concentration solution for question #6.
    _________ mL of distilled H2O __________ mL standard solution
  8. (6) In your own words, explain how we can use reference samples of known concentration to make a graph and then use the graph to determine the concentrations of unknown samples.† Attach your graph from question 2 and turn it in with this sheet.
Name: date: period:

Page 1 of 2.† Solution Conductivity: Magnesium sulfate and sucrose.20 pts. Scale, 23 pts max.† († ) denotes points per question.

In this activity you will increase your understanding of salt solutions by testing epsom salt solutions. You will also test solutions prepared as a mixture of both salt and sugar. Tip:† It is essential that you keep the test electrode "clean".† This means that you must do a distilled water rinse before all trials to ensure that water on the electrode from another sample does not contaminate the sample you are testing.† Also, you will need your completed NaCl salt solution laboratory paper to answer some of the questions included in this activity.

  1. (1) Obtain approximately 100 mL of epsom salt standard solution.† This solution was prepared by mixing 10 g of epsom salt in 1 L of water and therefore has a concentration of 10 g/L.† Use the conductivity probe to verify its concentration and record your results below.† Note that the software will display the concentration as mg/L (remember that 1000 mg = 1 g).
    ______________________ g/L (concentration of epsom salt reference solution)
  2. (3) Prepare a NaCl solution by dissolving 1 gram of NaCl in 100 ml of water. †Does this solution have more, less, or the same mass of salt per volume of water as the epsom salt standard solution?† Explain your answer.
  3. (1) Use the conductivity probe to determine the concentration of the NaCl solution using the sofware settings for the epsom salt solution.† Record your results below.
    ______________________ g/L (NaCl solution concentration)
  4. (3) Compare your numbers from steps 1 (concentration of epsom salt solution) and 3 (10g/L NaCl solution).† If you had to choose between 10 g of epsom salt or 10 g of table salt to prepare a solution with the most conductivity, which salt would you use, and why?
  5. (1) Prepare a sugar solution by dissolving 1 g of table sugar (sucrose) in 100 mL of water.† Use the conductivity probe and find out what the probe "thinks" the concentration of the sugar solution is.† Remember that the probe works because some atoms in some solutions are able to carry charge (transport electrons).
    _____________________ g/L (as "seen" by the conductivity probe)
  6. (2)What can you say about the ability of table sugar in a solution to conduct an electric current?
  7. (2) Obtain a sample of unknown crystal mixture #1.† This unknown is a mixture of espom salt and sugar.† Weigh out one gram of the unknown and mix it in 100 mL of water.† Use the conductivity probe to† determine the salt concentration of the prepared solution and record your results below:
    ____________________ g/L epsom salt for unknown #1
  8. (2)Use subtraction to calculate the sugar concentration in unknown #1 solution.
    ____________________ g/L sugar for unknown #1
  9. (4) Repeat steps 7 and 8 using unknown #2
    ____________________ g/L epsom salt for unknown #2
    ____________________ g/L sugar for unknown #2
  10. (2) Compare your number for question 3 with that of several classmates.† Speculate on why you think the numbers/results vary as they do (Why are they different?):
  11. (2) Speculate how your results would likely be affected if you didnít rinse the electrode between tests.† Include reasoning to support your speculation.
Name: date: period:

Page 1 of 2.† Carbon Dioxide (CO2) Test Design Activity: 25 pts. Scale, 27 pts max.† Respond to written questions with complete sentences.† For this activity you will work with one partner.† You will only need to turn in one set of papers for your group.† († ) denotes points per question.

This activity is likely quite different from any other you have done.† Working with gaseous samples, as opposed to mixing wet solutions or weighing crystals, presents a unique set of challenges.† You cannot leave an open sample container on the table for even a short time without losing part or all of the sample.† To overcome this problem we will approach this activity by using sealed containers and designing systems in which the gas samples we wish to analyze are isolated from the surrounding air.

The CO2 sensor with which we will work has a range of detection of 0 - 5000 ppm (parts per million).† A CO2 concentration of 5 ppm means that 5 out of every 1,000,000 molecules of air are CO2 or that 5/1,000,000ths of the air is CO2.† Human exhaled breath typically has a CO2 concentration of 50,000 ppm, well beyond the upper limit of our sensor.† To analyze breath we must therefore mix the breath with room air to dilute (decrease) the CO2 concentration of the gas mixture that the sensor will analyze.† You will need to consider a variety of possible designs which could be used to mix breath samples with room air.† Three primary considerations should be kept in mind when planning, building, and testing your design:

      1. The breath sample must be diluted enough to reduce the CO2 to well under 5000 ppm.
      2. The samples must be kept contained at all times.
      3. Your design should be able to produce repeatable results.
  1. (1) Record the CO2 level in the room:† _________________ ppm
  2. (3) On the computer screen, tell the software to begin plotting ppm data by clicking on the "collect" button.† Hold the sensor approximately 3 inches from your mouth and gently blow on the vent holes.† In the space below sketch the plot and explain what has happened (i.e., why the graphical† results appear as they are).
    CO2 level
    (ppm)
    ††††
  3. (4)† Within your group discuss various possible designs that might fulfill the three primary considerations listed on the previous page.† On separate sheets of paper sketch and label two of your designs (one design sketched and labeled on each separate sheet of paper).† Keep in mind equipment and time limitations.† You are not expected to purchase any extra materials for this project, but to use only commonly available supplies as one might already have around the house, garage, or shop.† On further discussion with your partner, decide on a design which you will build and test together.† Include your two sketched and labeled designs when you turn in this paper.
  4. (15) Build and test your "best" design.† The data should not exceed 5000 ppm and should produce repeatable results.† You will be required to keep laboratory notes of your testing that will serve as a record of your work and to turn in your laboratory notes.† In your laboratory notes include:
    1. results
    2. comments regarding any design changes you made
    3. dates of work/progress
    4. notes on what seems to be working and what needs improvement
    5. printed out graphs of your trial runs
  5. (2) When working on a project of this nature, what is the benefit of working with a partner?
  6. (2) Why is it of critical importance to discuss often your work with your partner?
Name: date: period:

Carbon Dioxide (CO2) Level Assay of Small Organisms:† 25 pts. Scale, 27 pts max.† Respond to written questions with complete sentences.† For this activity you will work with one partner.† You will only need to turn in one set of papers for your group.† († ) denotes points per question.

In this activity you will use the understanding of handling gaseous samples that you gained in the last activity to collect data on living organisms.† In this activity it should not be necessary to dilute/mix any samples, but you will still need to keep your samples isolated from room air.† Your group will use either 4-5 crickets or a marigold in a sealed container to determine changes in CO2 levels in a sealed (isolated) environment.† Your main challenge will be to use readily available materials (you are not expected to purchase any materials) to adapt a container of your choice to contain organisms and enable data collection by the CO2 sensor.

  1. With your partner, decide on which organism you wish to test.† If there are other organisms readily available (worms, beetles, "pillbugs", violets, sprouting seeds), you may, with teacher approval, use them.
  2. (4) Decide on a container that you will use to hold the organism(s) that you will be using.† Keep in mind that it should easily hold the organism(s) and, if you are working with animals, be large enough to allow the animals to survive for at least two days.† Also, keep in mind that the container must be readily sealable, but also allow for the attachment of the CO2 sensor.† Transparent containers are not absolutely necessary, but are preferred so that the organisms may be observed during data gathering.† In the space below, sketch and label your design plan:
  3. (23) Build and test your "best" design.† The data should not exceed 5000 ppm.† You will be required to keep laboratory notes of your testing that will serve as a record of your work and to turn in your laboratory notes.† In your laboratory notes include:
    1. results (data table from computer)
    2. comments regarding any design changes you made
    3. dates of work/progress
    4. comments regarding what worked well and what needed improvement
    5. printed out graphs of your data run
    6. your conclusion:† What do your data show?† Why did you get the results that you did?

Figure C.1.† Hierarchical Task Analysis for Colorimeter Data Plots.

Figure C.2.† Hierarchical Task Analysis for Conductivity Data Plots.

Figure C.3.† Hierarchical Task Analysis for CO2 Data Plots.

Materials Sources

HardwareVernier Software
8565 S. W. Beaverton-Hillsdale Hwy.
Portland, OR† 97225-2429
(503) 297-5317

Glucose (Trinder) reagent† (note:† both of these companies graciously donated reagent for student use)

Reagents Applications, Inc.
8225 Mercury Court
San Diego, CA† 92111
(800) 438-6100
(619) 569-8009

Sigma Diagnostics
P.O. Box 14508
St. Louis, MO† 63178
(800) 325-0250

References

  1.        Harris, D. C.† Quantitative Chemical Analysis, 4th Edition.† New York:† W. H. Freeman and Company, 1995, 837 pp.
  2. Smoot, R. C., R. G. Smith & J. Price.† Chemistry.† New York:† Glencoe, 1995, 910 pp.
  3. Levine, I. N.† Physical Chemistry, 4th Edition.† New York:† McGraw-Hill, 1995, 901 pp.
  4. Petrucci, R. H.† General Chemistry, 5th Edition.† New York:† Macmillan, 1989, 1042 pp.
  5. †† Swerdlow, J. L.† "Physical World."† National Geographic.† 193(5), p. 47.