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Intermolecular forces. In our experiment we want to find out how intermolecular forces are present in our samples, how they interact with each other. We will experiment the relationships between molecular structures and their physical properties: volatili

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Introduction

Name: Vladimir Koloskov Section: Chem 111/102 Date submitted: 09/15/2011 Team member: Jake Harding Experiment #16: Intermolecular Forces-The Relationship Between Physical Properties and Structure Introduction The forces holding molecules together are generally called intermolecular forces. The energy required to break molecules apart is much smaller than a typical bond-energy, but intermolecular forces play important roles in determining the properties of a substances. In our experiment we want to find out how intermolecular forces are present in our samples, how they interact with each other. We will experiment the relationships between molecular structures and their physical properties: volatility, viscosity and solubility. Data Part A: Relative Volatilities of Samples. A. Volatility n-decane n-heptane n-pentane third second first B. Volatility n-butanol ethanol methanol third second first C. Volatility n-butanol Deionized water n-pentane second third first B. Relative Viscosities of Materials. VISCOSITY N- Hexane Deionized water Glycerol Middle Lowest Highest C. Mutual Slubilities of Liquids water ethanol n-hexane n-butyl acetate Ethylene glycol Water - M I I M Ethanol 1 - M M M n-hexane 2 3 - M I n-bytul acetate 4 5 6 - I Ethylene glycol 7 8 9 10 - D.

Middle

sulfate hexahydrate, and naphthalene. We took twelve small tubes, carefully cleaned them and put water in six of them and n-hexane in another six. Discussion From our first experiment we can see that the liquid, n-pentane, which has a shorter chain of carbon molecule in it and a lighter mass evaporated the fastest and a heavier liquid, n-decane, took longest time to evaporate. These compounds are held by dispersion forces which are a type of intermolecular forces. After finishing our second experiment with different liquids, alcohol, we saw that the first one to evaporate was n-methanol and the last was n-butanol. Methanol evaporated first because it is smaller compound with a lighter weight. But we see that these three compounds have different intermolecular forces such as: dispersion forces, dipole-dipole forces and hydrogen bonding. When we finished our last step of our first experiment, n-pentane evaporated first because this liquid does not have any hydrogen bonding comparing to another two liquids. Second experiment showed us that glycerol was the most viscous out of three liquids and water was least viscous after being placed in boiling water.

Conclusion

Water from sodium chloride solution will evaporate and we will end up with sodium chloride. We will distill the solution of iodine and n-pentane to get iodine and then condense pentane vapor and we will get n-pentane. 3. C=O bond will make it polar just like water and it will be soluble in water and C-C-C chain is nonpolar just like hexane and will make it soluble in it. 4. The reason for different boiling point is that ethanol is a liquid and has a very strong hydrogen bond that's why it requires more energy on another hand it's isomer, dimethyl ether, which is a gas, requires less energy because it has no hydrogen bonding . Boiling points: Dimethyl ether: -24 °C, 249 K, -11 °F Ethanol: 78 °C, 351 K, 172 °F Conclusion After we finished all our experiences we identified intermolecular forces within pure substances, as well as attractive forces between different substances in a mixture. We made qualitative comparison of physical properties of liquids and solids such as volatility, viscosity and solubility and correlated trends in physical properties with strength of intermolecular attractive forces. Reference: Department of Chemistry (2010). Laboratory Experiments in General Chemistry: Chem 110 and Chem 111, Version 9.0: Towson University

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