A Slippery Dilemma Demonstration
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ward
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science
Recommended Grade Level(s):
Appropriate for: Grades 7+
Time Requirements:
Prep Time: 15–20 minutes
Activity Time: 35–40 minutes
Teaching Topics & Concepts:
• Human impact on the environment
• Experimental protocol
Materials:
• Each student group will need
– A jar of pond water, hay infusion, or sample of mixed protozoa (20 mL will be needed for each group)
– Access to samples of four salt solutions.
These can be shared. Each group will need 1mL of each
A – 119 g/L of Sodium Chloride and Water
B – 59.5 g/L of Sodium Chloride and Water
C – 29.75 g/L of Sodium Chloride and Water
D – 14.9 g/L of Sodium Chloride and Water
– A well slide with coverslip
– Pipettes
– Microscope
– Test tubes and rack
– Vital stain (optional)
– Protist slowing agent (optional)
Safety
• Always read the SDS for all chemicals before handling them.
• Wear safety glasses, gloves and lab coat or apron.
!
Background
Your class has been asked to help the town determine if it is using too much salt on the roads and sidewalks. Every year the town
puts down salt to keep the roads from becoming slippery, but much of this salt runs off into local ponds and lakes. Some citizens are
concerned that the salt is damaging the local ecosystem. Based on the town's annual usage, it is estimated that the runoff has a
concentration of 119 g/L; the roads would be unsafe with concentrations below 14.9 g/L. The higher concentrations make the roads
safer, so you are being asked to assess the levels with the lowest impact and make a recommendation.
Procedure:
1. Obtain the following materials and equipment so you can analyze the effects of the salt solutions on the pond water:
a. Microscope
b. Well slide
c. Cover slip
d. Six pipettes
e. Vital stain
