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Hydrogels Make Happy Plants

Grades: 10 Biology
Author: Nancy Q. Miller
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC-1161732.


This is a series of activities that allow the students the opportunity to investigate hydrogels. These polymers have the ability to absorb (swell) and release water under certain conditions. First the students will read about hydrogels (Hydrogel: Preparation, characterization, and applications: A review) and develop a working knowledge of the materials. Then, they will go on a Hydrogel Scavenger hunt allowing the teacher the ability to assess their understanding AND demonstrating to the students how prevalent and important these materials are in the world. Then the students will be involved in an investigation where they study different soils with regard to their water retention abilities. This study will include soil that has hydrogel beads mixed in. The addition of the hydrogel beads allows more water to be retained creating a more steady water supply and will then require less watering. Finally, the students will create different formulations of hydrogels using Sodium Alginate. During this part of the investigation, they will first examine bead production in different salts (Lithium Chloride, Potassium Chloride, Magnesium Chloride and they will have already tested Calcium Chloride.) The groups will then select a particular salt and will create the “best” hydrogel beads to be added to their “New and Improved “soil. In this part of the investigation, the students will vary concentrations of the selected salt and determine which bead would have the highest water retention ability and therefore would work most effectively in potting soil.


What should students know as a result of this lesson?

  • Students will be able to identify characteristics of hydrogels.
  • Students will be able to identify 5 common uses for hydrogels.
  • Students will be able to be able to predict a hydrogel’s ability to hold and retain water based on the concentrations of the salts in the interaction.
  • Students will be able to revise a chemical formulation to create a material with desired characteristics.

What should the students be able to do as a result of this lesson?

  • Students will be able to apply their knowledge of hydrogels to complete a Hydrogel Hunt identifying and describing the characteristics of each.
  • Students will be able to make observations while investigating known hydrogels and then formulate hydrogels of their own meeting a given set of criteria.
  • Students will be able to connect the hydrogel behaviors to the effectiveness of their "New and Improved" potting soil.


  • Soda bottle cut in half (1/group)
  • Potting soil with sand (enough for each group)
  • Potting soil (enough for each group)
  • Potting soil with hydrogels (enough for each group)
  • Sodium Alginate (1% solution, enough for each group )
  • 3Lithium Chloride (3% stock solution)
  • Potassium Chloride (3% stock solution)
  • Magnesium Chloride (3% stock solution)
  • Calcium Chloride (3% stock solution)
  • Electronic balance



Students will gather background information when completing Hydrogel Basics

Using that preliminary information, they will complete the Hydrogel Hunt

Assessment for this Engagement will be the final poster created from the hydrogel hunt utilizing both the background information and information gained from further independent research.


Students will complete 2 different investigations. The first is somewhat teacher directed because the procedures are clearly outlined. (Worksheet #3 Hydrated Hydrogels Make Happy Plants) The students will be asked to measure rate of water flow through the soil. They will be told that one of the soil samples had a hydrogel and they will be asked to determine which sample had the hydrogel using their data to support their selection. Additionally, at the end of the investigation the students will be asked to analyze their lab experience and identify any potential experimental errors, assess the importance of the error and revise their protocol for the next investigation.

The second investigation has two parts. (Worksheet #4 What Bead is Best) First, the students will carry out tests using Sodium Alginate and 3 different molecules in solution. (Calcium Chloride was used in the previous investigation so there is no need to test it again here.) They will test the 3 materials and compare them to each other and the Calcium Chloride. This simple test will allow the students to see that only certain materials will form beads and others will not.

In the second half of the investigation, the students will select one of the 4 solutions to use to make beads with Sodium Alginate. Now, they will alter the concentrations of the solutions to determine if the concentration of the solution alters the water retention abilities of the beads created.


Students will present their findings as a group and individually. The group presentation will be in an oral fashion and the individual will be a written "Consumer Report".


Students will be asked to compare the materials that did create beads and the materials that did not make beads when the Sodium Alginate was added. They are to use a periodic table and analyze the materials and their location on the table. From this, they are to predict how other elements would behave based on their data collected and the location on the periodic table.


This lesson can be taught to any group with basic lab skills. NO specific content prerequisites are noted.

Best Teaching Practices

  • Hands-on/Minds-on Learning
  • Communication skills
  • Inquiry approaches
  • On- going, embedded, authentic assessment

Alignment with Standards

NGSS Standards:

  • HS-LS2-1. Use mathematical and/or computational representations to support explanations of factors that affect carrying capacity of ecosystems at different scales.
  • HS-LS2-6. Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.

Common Core Standards:

  • RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.
  • WHST.9-10.1. Write arguments focused on discipline-specific content

Ohio Standards:

  • Science Inquiry and Application: Design and Conduct scientific Investigations, Formulate and revise explanations and models using logic and evidence
  • Chemistry: Intramolecular chemical bonding, Periodic table trends

Content Knowledge

Students will utilize technology in their presentations (PowerPoint. Prezi, etc.)

Students will be able to complete needed calculations and graphically represent data

Students will be able to make predictions


All of the salts used in this investigation were coded 0 or 1 for all safety areas. Recommended Flinn disposal is 26a which allows for disposal in the regular municipal trash. (Although there is a recommendation that each teacher checks with their municipal waste disposal for any specific regulations.)




Potting soil companies utilize this information when they create their potting soil products. Students are also introduced to the pervasiveness of the hydrogels in their world and will be able to apply the investigations to the materials they encounter daily.


As a group - Students will complete a presentation identifying the results of their investigation. Within this presentation, they will need to be able to describe their procedures, analyze and explain their results, use their data to determine the best formulation and justify their decisions. (See presentation guidelines)

Individual assessment – students will need to write their own “Consumer Report” that will explain the material selected, the justification for the material and analysis of cost. (See consumer report guidelines.)

Other Considerations

Grouping Suggestions: Groups of 2-4 are preferred.

Pacing/Suggested Time: This series of investigations would take five 45 minute periods. Teachers can shorten it by eliminating some of the presentations and having them submit their work without presenting. Also, portions of the investigative portion could be done as teacher demonstrations to eliminate the use of some class time.

Printable PDF Worksheets

Hydrogel: Preparation, characterization, and applications: A review
Article by Enas M. Ahmed, no changes made;
Attribution-NonCommercial-NoDerivs 3.0 Unported (CC BY-NC-ND 3.0)

Hydrogel Basics

Hydrogels - An Introduction

Hydrated Hydrogels Make Happy Plants

What Bead is Best?

Presentation and Debriefing Guidelines