Qualitative Test

CCA! Volume 5

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Qualitative Test

The viscosities of water, 2-propanol (rubbing alcohol), ethylene glycol (antifreeze) and vegetable oil are compared.

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Narrative
The flow of liquid from four pipets is started simultaneously to test their viscosity. Since viscosity is the resistance to flow, The liquid on the left is least viscous, and the viscosity increases from left to right.

Discussion
Four pipets are filled with different liquids. From left to right the liquids are water, 2-propanol (rubbing alcohol), ethylene glycol (antifreeze) and vegetable oil. When the liquids are released, they are observed to flow at different rates.

Each of the first three substances can form hydrogen-bonds. Rubbing alcohol molecules (2-propanol) can hydrogen bond and they are significantly larger than water molecules, so their greater London forces result in a higher viscosity. Rubbing alcohol and ethylene glycol (HOCH₂CH₂OH) molecules will have similar London forces, but with two hydroxyl groups, ethylene glycol molecules form twice as many hydrogen bonds as those of 2-propanol, so ethylene glycol is more viscous. The molecules in vegetable oil form no hydrogen bonds, but their large size means that the London forces are very strong and the liquid is extremely viscous.