How is vsepr used to classify molecules? What are the units used for the ideal gas law? How does Charle's law relate to breathing? What is the ideal gas law constant? How do you calculate the ideal gas law constant? How do you find density in the ideal gas law?
Does ideal gas law apply to liquids? Impact of this question views around the world. If bottled gas escapes into a building, it collects near the floor. This presents a much more serious fire hazard than a natural-gas leak because it is more difficult to rid the room of the heavier gas. As shown in Table This general rule holds true for the straight-chain homologs of all organic compound families.
Larger molecules have greater surface areas and consequently interact more strongly; more energy is therefore required to separate them. For a given molar mass, the boiling points of alkanes are relatively low because these nonpolar molecules have only weak dispersion forces to hold them together in the liquid state. An understanding of the physical properties of the alkanes is important in that petroleum and natural gas and the many products derived from them—gasoline, bottled gas, solvents, plastics, and more—are composed primarily of alkanes.
This understanding is also vital because it is the basis for describing the properties of other organic and biological compound families. For example, large portions of the structures of lipids consist of nonpolar alkyl groups. Lipids include the dietary fats and fatlike compounds called phospholipids and sphingolipids that serve as structural components of living tissues. For more information about lipids, see Chapter 17 "Lipids".
These compounds have both polar and nonpolar groups, enabling them to bridge the gap between water-soluble and water-insoluble phases. This characteristic is essential for the selective permeability of cell membranes. Tripalmitin a , a typical fat molecule, has long hydrocarbon chains typical of most lipids. Compare these chains to hexadecane b , an alkane with 16 carbon atoms. Without referring to a table, predict which has a higher boiling point—hexane or octane.
If 25 mL of hexane were added to mL of water in a beaker, which of the following would you expect to happen? Without referring to a table or other reference, predict which member of each pair has the higher boiling point. Help Creative Commons. Creative Commons supports free culture from music to education. Their licenses helped make this book available to you. These are most often phosphate, ammonium or carboxylate, all of which are charged when dissolved in an aqueous solution buffered to pH 7.
Some biomolecules, in contrast, contain distinctly hydrophobic components. In a biological membrane structure, lipid molecules are arranged in a spherical bilayer: hydrophobic tails point inward and bind together by van der Waals forces, while the hydrophilic head groups form the inner and outer surfaces in contact with water.
Interactive 3D Image of a lipid bilayer BioTopics. Because the interior of the bilayer is extremely hydrophobic, biomolecules which as we know are generally charged species are not able to diffuse through the membrane— they are simply not soluble in the hydrophobic interior. The transport of molecules across the membrane of a cell or organelle can therefore be accomplished in a controlled and specific manner by special transmembrane transport proteins, a fascinating topic that you will learn more about if you take a class in biochemistry.
A similar principle is the basis for the action of soaps and detergents. Soaps are composed of fatty acids, which are long typically carbon , hydrophobic hydrocarbon chains with a charged carboxylate group on one end,. Fatty acids are derived from animal and vegetable fats and oils. In aqueous solution, the fatty acid molecules in soaps will spontaneously form micelles , a spherical structure that allows the hydrophobic tails to avoid contact with water and simultaneously form favorable van der Waals contacts.
Interactive 3D images of a fatty acid soap molecule and a soap micelle Edutopics. Because the outside of the micelle is charged and hydrophilic, the structure as a whole is soluble in water.
Micelles will form spontaneously around small particles of oil that normally would not dissolve in water like that greasy spot on your shirt from the pepperoni slice that fell off your pizza , and will carry the particle away with it into solution.
We will learn more about the chemistry of soap-making in a later chapter section Synthetic detergents are non-natural amphipathic molecules that work by the same principle as that described for soaps.
The physical properties of alcohols are influenced by the hydrogen bonding ability of the -OH group. The -OH groups can hydrogen bond with one another and with other molecules. Hydrogen bonding raises the boiling point of alcohols. This is due to the combined strength of so many hydrogen bonds forming between oxygen atoms of one alcohol molecule and the hydroxy H atoms of another. The longer the carbon chain in an alcohol is, the lower the solubility in polar solvents and the higher the solubility in nonpolar solvents.
This table shows that alcohols in red have higher boiling points and greater solubility in H 2 O than haloalkanes and alkanes with the same number of carbons. It also shows that the boiling point of alcohols increase with the number of carbon atoms. Solubility Virtually all of the organic chemistry that you will see in this course takes place in the solution phase. Example Exercise 2. Solutions Illustrations of solubility concepts: metabolic intermediates, lipid bilayer membranes, soaps and detergents Because water is the biological solvent, most biological organic molecules, in order to maintain water-solubility, contain one or more charged functional groups.
Interactive 3D Image of a lipid bilayer BioTopics Because the interior of the bilayer is extremely hydrophobic, biomolecules which as we know are generally charged species are not able to diffuse through the membrane— they are simply not soluble in the hydrophobic interior.
Soaps are composed of fatty acids, which are long typically carbon , hydrophobic hydrocarbon chains with a charged carboxylate group on one end, Fatty acids are derived from animal and vegetable fats and oils. Interactive 3D images of a fatty acid soap molecule and a soap micelle Edutopics Because the outside of the micelle is charged and hydrophilic, the structure as a whole is soluble in water.
Hydrogen Bonding and Solubility The physical properties of alcohols are influenced by the hydrogen bonding ability of the -OH group. Hydrogen Bonding of Methanol Hydrogen bonding raises the boiling point of alcohols. References Schore, Neil E.
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