Can Hydrogel Crystals be Used as a Sensitive Humidity Indicator? (page 2)

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Author: Michael Calhoun

Research Questions

  • What is a hydrogel superabsorbent polymer crystal?
  • What is relative humidity and what is its relationship to weather?
  • Will a hydrogel superabsorbent polymer crystal absorb water vapor from the air?
  • Why was the hydrogel crystal kept in the sealed dry plastic container used as a control?
  • What happens when the crystal gel dries out? Is the hydrogel crystal reusable?
  • How does the hydrogel crystal compare to other humidity measuring devices?  

Terms, Concepts and Questions to Start Background Research

Hydrogel crystal,crystal, polymer, control, relative humidity, and superabsorbent polymer

Experimental Procedure

  • Conduct this experiment on a day in which the weather forecast is for high humidity.
  • Measure the length of several crystals that will be used in this science fair project as shown in the illustration in Figure 1, and recorded the measurements. If a small kitchen food scale is available weigh several crystals instead or in addition to measuring their length.

  • Place one or two hydrogel crystal into a clear dry sealable, plastic bag or container with a lid.
  • Place one of two crystals in various locations inside and outside of the house. Do not place the crystals in direct sunlight.
  • Allow the crystals to sit undisturbed for several hours or until there is a noticeable change in size and or appearance.
  • Carefully measure the change in size (or mass if a kitchen scale was used). For a more scientifically accurate investigation the entire process should be repeated twice more. Record the results in a table similar to the one shown below.
  • If there was a significant increase in the size and or mass of the crystal(s) this is an indication of high humidity, where as a small increase or no detectable change indicates either low or no humidity.  

Initial Size/Mass of Crystal  

Final Size/Mass of Crystal 

 Humidity (High, Low, None)
Trial 1
Trial 2
Trial 3
  • If a hygrometer or “Humidity Indicator Card” is available the investigator could augment this science fair project by comparing the increasing size (or mass) of the crystal(s) with the actual humidity in the air at various times during the day. A table similar to the one shown below can be used to display the results.

Size/Mass of Control Crystal(s)          


 Size/Mass of Test Crystal(s)          
0 hour
1st hour
2nd hour
3rd hour
4th hour
  • Use the data in the table to plot a line or bar graph of percent relative humidity along the Y-axis verses the changes in crystal size or mass along the X-axis.
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