Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 Properties of Water Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Water Molecule The unequal sharing of electrons causes the water molecule to be polar. The hydrogen end of the molecule is slightly positive and the oxygen end is slightly negative. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Hydrogen Bonds Because of their partial positive and negative charges, polar molecules can attract each other. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Adhesion is an attraction between molecules of different substances. Copyright Pearson Prentice Hall

Solutions and Suspensions A mixture is a material composed of two or more elements or compounds that are physically mixed but not chemically combined. Copyright Pearson Prentice Hall

Solutions and Suspensions Two types of mixtures can be made with water solutions suspensions Copyright Pearson Prentice Hall

Solutions and Suspensions All the components of a solution are evenly distributed throughout the solution. solute—the substance that is dissolved. solvent—the substance in which the solute dissolves. Copyright Pearson Prentice Hall

Solutions and Suspensions When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules. Na+ Cl - Water When an ionic compound such as sodium chloride is placed in water, water molecules surround and separate the positive and negative ions. Copyright Pearson Prentice Hall

Solutions and Suspensions Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out easily. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH Acids, Bases, and pH A water molecule is neutral, but can react to form hydrogen and hydroxide ions. H2O   H+ + OH- Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH The pH scale  Chemists devised a measurement system called the pH scale to indicate the concentration of H+ ions in solution. The pH scale ranges from 0 to 14. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH The pH Scale At a pH of 7, the concentration of H+ ions and OH- ions is equal. Sea water Human blood Pure water Milk Normal rainfall The concentration of H+ ions determines whether solutions are acidic or basic. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH Acids An acid is any compound that forms H+ ions in solution.  Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH Bases A base is a compound that produces hydroxide ions (OH- ions) in solution.  Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH Buffers  The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5. Controlling pH is important for maintaining homeostasis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 A molecule in which the charges are unevenly distributed is called a polar molecule. cohesive molecule. hydrogen molecule. covalent molecule. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 A dissolved substance is called a solvent. solution. solute. Suspension. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 A compound that produces hydroxide ions in solution is called a(an) base. buffer. acid. salt. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 Hydrogen bonds between water molecules result from adhesion between water molecules. magnetic attractions between water molecules. uneven electron distribution in each water molecule. ionic bonds in the water molecule. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2-2 On a pH scale, a value of 2 means that the solution has equal concentrations of H+ and OH- ions. the same concentration of H+ ions as pure water. higher concentration of H+ than in pure water. lower concentration of H+ than in pure water. Copyright Pearson Prentice Hall

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