![]() Examinethe molecular models and explain the difference in viscosity.Ħ. Compare the viscosities of hexane and 2-pentanol. Examinethe molecular models and explain the difference in viscosity.ĥ. Compare the viscosities of octane and 2,2,4-trimethylpentane (isooctane). Examinethe molecular models and explain the difference in viscosity.Ĥ. Compare the viscosities of hexane and octane. Examine the molecular models, and decide what properties ofmolecules affect viscosity.ģ. Use the times obtained from the stopwatch to determine therelative viscosities of the five liquids.Ģ. The four liquids in the demonstration are vegetable oil,water, ethylene glycol and 2-propanol. The molecules invegetable oil form no hydrogen bonds, but their large size meansthat the London forces are very strong and the liquid is extremelyviscous.ĭemonstration Notes:Warnings, Safety Information, etc.ġ. Rubbing alcohol and ethylene glycol(HOCH 2CH 2OH) molecules will have similarLondon forces, but with two hydroxyl groups, ethylene glycolmolecules form twice as many hydrogen bonds as those of2-propanol, so ethylene glycol is more viscous. Rubbingalcohol molecules (2-propanol) are significantly larger than thoseof water, so their greater London forces result in a higherviscosity. Eachof the first three substances can form hydrogen-bonds. The same general principles apply in this demonstration. ![]() However, 1-pentanol is much moreviscous, due to the hydrogen-bonding between the OH groups at theend of the molecules. Both have similar sizes and shapes, so theLondon forces should be similar. Compare the hexane and1-pentanol molecules. This is due to thehydrogen-bonding in water, a much stronger intermolecularattraction than the London force. In general, branch-chained isomers are lessviscous and have lower boiling points than straight-chainisomers.Īlthough water molecules are much smaller than hexanemolecules, water is more viscous than hexane. Although the sizes of the octane and2,2,4-trimethylpentane (called isooctane because it is an isomer of octane) molecules are similar, the more compact isooctanemolecule experiences smaller forces than the straight-chainn-octane molecule. Since hexane issmaller than octane, its intermolecular forces are weaker and itflows more rapidly. All molecules experience London forces, dueto the polarizability of the electron cloud. The rate of flow of a liquid depends on the magnitude of theintermolecular forces and the shapes of the molecules. Obtain the times when the meniscus passesthe zero and three milliliter mark. Viscosity isinversely proportional to the elapsed time.įrom the stopwatch, obtain the times when the meniscus passesthe zero and three milliliter mark. With the following movies, it is possible to determine therelative viscosities of the water, hexane, octane, 2,2,4-trimethylpentane (isooctane) and 1-pentanol from measurements of the times when the meniscuspasses the zero and 3 mL marks on the pipet. This is an introductory movie showing, in wider angle, themanner in which the experiment is performed. The greater the length of the capillary tube, the longer ittakes for the water to flow through the apparatus. Note that theflow rate is greatest in the apparatus with the shortest capillarytube. (Note: the viscosity of the liquids, not the pipets, is being tested.) Capillary Length Testįour funnels, each containing ten milliliters of water, areconnected to differing lengths of capillary tubing. Since viscosity is the resistance toflow, the liquid on the left is least viscous, and the viscosityincreases from left to right. The flow of liquid from four pipets is started simultaneouslyto test their viscosity. The narrow point is responsible for restriction of liquidflow. Intermolecular forces, polarity, polar molecules, physicalproperties, gases and liquids, bonding, solids and liquids,organicĪpparatus, Labeled Samples (water, rubbing alcohol, ethyleneglycol, vegetable oil), and Tip of Pipet The rate offlow depends on the size and shape of the molecules as well as onthe types of intermolecular forces involved.īubble: An air bubble moving in a liquid in a test tubeis demonstrated. Theexperiment is set up so that the times at which the liquid reachesthe 0 mL and 3 mL marks on the pipet may be observed. Measuring relative viscosity: The rate of flow of sixdifferent liquids through a Mohr pipet is determined. Thelonger the capillary tube, the slower the rate of flow of thewater. When the liquids are released, they are observed to flowat different rates.Ĭapillary length test: Four funnels are filled withwater and attached to capillary tubing of various lengths. Qualitative test: Four pipets are filled with differentliquids. Viscosity of Liquids Viscosity of Liquids
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |