Change in Volume, H-Bonding (Ethanol and Water)
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Required Training |
Required PPE |
---|---|
UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
Equipment |
Chemicals |
Two 250 mL Volumetric flask with |
DI water and YELLOW food coloring |
500 mL Volumetric flask |
Absolute ethanol and BLUE food coloring |
Digital Thermometer |
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Funnel (optional) |
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Procedure:
1) Pour the water solution into the larger flask followed by slowly adding the ethanol without allowing the two to mix and without using a funnel:
a. The volume is about 500 mL.
b. Two color layers are visible.
2) Mix well and note:
a. The volume decreases due to the “tightening” of the hydrogen bond structure.
b. The solution changes color.
Discussion:
The volume deficit should be about 17.5 mL. If 95% ethanol is used, the shrinkage is still about 15 mL. The structure of liquid water is open because of hydrogen bonding (that is to say, a network holds water molecules with specific orientations towards each other). Crudely we can say that the open (relatively low-density) structure of liquid water is broken much like when ice freezes. The more dense form is reflected in a more compact volume.
Hazards:
Ethanol is flammable. Avoid spills, but if one occurs, isolate ethanol from any sources of ignition. Wash affected areas with copious amounts of water.
Disposal (by Storeroom):
The mixture will be disposed as hazardous waste.