Materials Included In Kit

Additional Materials Required

Prelab Preparation

10% Aqueous Solutions

10% CaCl₂: Dissolve 10 g of CaCl₂ in 90 mL of distilled or deionized water. Clearly label the solution.

10% MgCl₂: Dissolve 10 g of MgCl₂ in 90 mL of distilled or deionized water. Clearly label the solution.

Safety Precautions

The chemicals used in this lab are considered nonhazardous. Still, all standard laboratory safety procedures should be followed. Wear chemical splash goggles and chemical resistant gloves.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Leftover solids may be disposed of according to Flinn Safety Disposal Method #26a. Solutions may be disposed of accroding to Flinn Safety Disposal Method #26b.

Teacher Tips

• Point out to students that many of the products we purchase for personal use contain chemicals and those chemicals generally find their way into the environment very easily. For example, the chemicals used in road deicers leach into the ground and may affect plant growth such as observed in this lab experiment. Therefore, if greener chemicals can be used to accomplish an objective, in this case melting road/sidewalk ice, in a cost effective way, they should be used.
• This is a nice demonstration of a straightforward way of measuring ecotoxicity (and its relationship to toxicology) that need not be limited to ionic compounds. For example, the effects of other compounds such as alcohols on lettuce seed growth could be measured using the same protocol.
• Serial dilutions are commonly performed in analytical laboratories and hospital labs. This is a valuable technique to introduce students to, and one that is not often taught in introductory courses. This particular experiment is a nice way to introduce green chemistry, ecotoxicity, and introductory analytical chemistry in a single stroke.
• If time permits each lab group may set up trials for each compound. Or each lab group can be assigned a single compound for investigation and the lab groups can share data at the end of the data collection period.
• Set up another, subsequent experiment to run as a challenge in which students must determine the cut-off concentration at which the aqueous solutions deter germination and growth. Students can be left to determine how many new solutions must be prepared to make such as determination. For example, they may see that seeds grow in 3% solutions but not in 4% solutions and iteratively test until they settle on 3.5% as the cut-off. Also, they may find that the cut-off differs between the three compounds. This is a nice approach that challenges students’ experimental design skills and their ability to function in a guided-inquiry lab environment.
• Radish seeds can also be used for this experiment. You may want to have some students use radish seeds and others use lettuce seeds to see how that influences the results.

Sample Data

Data for NaCl, MgCl₂ and CaCl₂ appear in the top, middle and bottom rows, respectively.

Answers to Questions

1. Based on your data, do ionic compounds appear to be a green option for use as road deicers? Explain.

   Yes, ionic compounds appear to be a greener option for use as road deicers, at least when used in concentrations less than or equal to 1%. In these solutions, germination and significant growth occurred (against controls) in nearly all seeds, in all three compounds’ aqueous solutions with concentrations 1% or lower.
   
   However, no data were collected for solution concentrations in excess of 1%. Therefore it cannot be stated that road deicers, when used at such concentrations, are green or not green.

2. Based on the results of this experiment, would you feel comfortable using ecotoxicity data to estimate human toxicology data? That is, would you feel comfortable ingesting a chemical that did not prevent germination and growth in a vast majority of lettuce seeds? Explain.

   No. The data obtained in this experiment are not sufficient to draw conclusions about toxicity with respect to humans. We do not know whether these compounds will not harm humans, only that they do not prevent germination and growth of lettuce seeds when used in concentrations less than or equal to 1%.

References

Green Chemistry Laboratory Activities: Comparative Terrestrial Ecotoxicity of Road Salts and Common Alcohols. Travise A. Crocker, Irvin J. Levy and Timothy J. Swierzewski, Abstracts of the 240th ACS National Meeting, CHED 209 Boston, MA, August 2016.

Anastas, P.T.; Warner, J.C. Green Chemistry: Theory and Practice, Oxford University Press: New York, 1998.

Introduction

Road deicers are effective at preventing ice from forming and reducing accidents during winter months. Certain road deicers have unintended environmental impacts. Green chemistry promotes the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. This experiment introduces the idea that certain chemicals can be hazardous if allowed to leach into the environment. You will compare the ecotoxicity of three common ionic salts used as road deicers—sodium chloride, magnesium chloride and calcium chloride—by measuring germination rates and lengths of lettuce seeds in aqueous solutions of each alcohol.

Concepts

• Green chemistry
• Ecotoxicity
• Serial dilutions
• Aqueous solution chemistry

Background

Much of what makes this world modern is the result of the application of chemistry and chemical reactions. Oil and gasoline, prescription drugs, plastics, solvents, and fertilizers, to name a few, are all products of chemistry. Over time, many of the processes used to create these products were found to have unintended consequences and be quite harmful, whether to workers, the consumers or to the environment. In response to these pressing issues, green chemistry was developed as an approach to creating safer chemical products and processes from the initial design stage. The principles of green chemistry provide a framework for scientists to use when designing new materials, products, processes and systems. The principles focus on sustainable design criteria and provide tools for innovative solutions to environmental challenges. These principles are as follows.

Prevention
It is better to prevent waste than to treat or clean up waste after it has been created.

Atom Economy
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product, leaving few or no atoms behind.

Less Hazardous Chemical Syntheses
Synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

Designing Safer Chemicals
Chemical products should be designed to be fully effective while minimizing or eliminating their toxicity.

Safer Solvents and Auxiliaries
Minimize the use of auxiliary substances (e.g., solvents, separation agents) wherever possible and make them innocuous when used.

Design for Energy Efficiency
Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.

Use of Renewable Feedstocks
Renewable raw material or feedstock should be used whenever technically and economically possible.

Reduce Derivatives
Unnecessary derivatization (use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate additional waste.

Catalysis
Catalytic reagents are superior to stoichiometric reagents.

Design for Degradation
Chemical products should be designed so that at the end of their function they break down into innocuous products that do not persist in the environment.

Real-Time Analysis for Pollution Prevention
Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.

Inherently Safer Chemistry for Accident Prevention
Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions and fires.

Experiment Overview

In this lab you will assess the toxicities of aqueous solutions of three potential road deicers—sodium chloride, calcium chloride and magnesium chloride—by examining the effect these substances have on germination of lettuce seeds. The procedure introduces toxicity measurements, while using standard equipment and common techniques such as serial dilution and volumetric measurement. The experiment involves setting up Petri dishes with wetted filter paper on which the seeds are placed. Data including germination percentage and average root length are collected and correlated to salt identity and concentration.

Materials

Safety Precautions

The chemical used in this lab are considered nonhazardous. Still, all standard laboratory safety procedures should be followed. Wear chemical splash goggles and chemical resistant gloves.

Procedure

Preparing Lettuce Seeds for Germination

1. Using a permanent marker, label a test tube with the deicer assigned by your teacher (e.g., 10% CaCl₂).
2. Fill the test tube with 10 mL of the stock (10%) solution.
3. Use the permanent marker to label 5 additional test tubes:
   • 1%
   • 0.1%
   • 0.01%
   • 0.001%
   • 0.0001%
4. Using a pipette, add 9 mL of distilled water to test tubes 2 to 6.
5. Remove 1 mL of your stock solution from test tube 1.
6. Using serial dilution, complete 1/10 dilutions from tubes 2 to 6. In other words, to make the 1% solution mix 1 mL of 10% solution with 9 mL of water. To make the 0.1% solution mix 1 mL of 1% solution with 9 mL of water and so on.
7. Label 7 Petri dishes as follows: 10%, 1%, 0.1%, 0.01 %, 0.001%, 0.0001% and “control.”
8. Place a filter paper into the bottom of each Petri dish.
9. Put 5 mL of each test tube solution into its associated (labeled) Petri dish.
10. Add approximately 40 lettuce seeds to each of the Petri dishes.
11. Stack and place Petri dishes into a single zipper-lock bag and seal to retain moisture.
12. Place in a well-lit location, but out of direct sunlight.
13. Allow seeds to germinate over 5 to 7 days. Be sure to check on the germinating seeds daily if possible.
14. Construct a data table to record your observations.
15. Record your observations daily in the data table.
16. After germination is complete, use the Figure 1 as a model to measure growth of the seed (length indicated in the figure).
    {14088_Procedure_Figure_1}
17. Record results in a data table.

1. Count the number of seeds germinated in each Petri dish and record in the data table. Note: Use forceps; be careful not to break roots! If part of a root breaks, ignore that root in the following step.
2. Measure the length of root of all germinated seeds with unbroken roots. Record the data. Measuring protocol: Before measuring, dry all the seeds by patting them with a Kimwipe^® to remove as much moisture as possible. For each sprout, measure the root length (not the shoot or seed itself) to the nearest mm (see Figure 1). Measure when the root is straight. (If the root is curved, try to measure it as you roll it along a ruler.) Calculate the average length (mean) for each plate of seeds. Do not include seeds that did not germinate or seeds with broken roots when calculating average.
3. Dispose filter papers and seedlings in the waste container provided by your instructor.

Student Worksheet PDF

14088_Student1.pdf