Major Chemical Concept

To a large extent, the physical properties of a solid substance are determined by the type of bonding which holds the molecules, atoms or ions together. Solids may be classified as ionic, molecular, metallic or covalent network solids. The type of bonding affects physical properties of a solid. The type of bonding may be determined by studying its physical properties.

Level

This activity is suitable for basic, general, and honors students. Only the part involving sodium chloride and lauric acid is recommended for basic students, although doing the remainder as a guided teacher demonstration might be useful for these students.

Expected Student Background

Students should have some background in ionic and covalent bonding. Previous instruction in van der Waals forces, bonding in covalent network solids, and metallic bonding is not important, since this laboratory activity provides a natural lead into a discussion of these types of bonding.

Time

Teacher preparation requires about 40 min. Students should be able to complete the activity in about 50 min.

Safety

Usual safety precautions include safety goggles, gloves, aprons, and the availability of a fume hood. Students must be monitored during the conduct of the activity, especially if they do the conductivity testing. It is recommended that you perform the conductivity testing for students if a device powered by 120 V is used. If low-voltage battery-powered testers are available, then students can complete this. Monitor students to insure that no open flames are present while cyclohexane is being used. Have a suitable fire extinguisher available.

Materials

Nonconsumables

• 60 evaporating dishes
  
• 96 test tubes, 18 x 150 mm, rubber or cork stoppers to fit
  
• 12 test tube racks
  
• 12 ring stands, iron rings, triangles, wire gauzes, burners
  
• 12 crucible tongs
  
• 12 low-voltage conductivity testers
  
• 120 beakers, 50 mL (100-mL beakers may be used)
  
• 12 graduated cylinders, 10 mL
  
• 12 spatulas
  
• 12 plastic pens or other devices for crushing solids
  
• 12 beakers, 250 mL
  
• safety goggles (one per student)
  
• fume hood

  Consumables
  

• 48 g sodium chloride, NaCl
  
• 48 g silicon dioxide, SiO2 (silica gel or pure sand)
  
• 48 g lauric acid
  
• 48 g iron filings
  
• 360 mL cyclohexane (or charcoal lighter fluid)
  
• distilled water
  

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