Lesson Overview Lesson Overview Properties of Water Lesson Overview 2.2 Properties of Water

Lesson Overview Lesson Overview Properties of Water THINK ABOUT IT Why study water in Biology? Biology is the study of living things, so why study something nonliving such as water?

Lesson Overview Lesson Overview Properties of Water The Water Molecule Water covers 3/4 of Earth’s Surface Single most abundant compound in living things Expands as it freezes Water is one of the few compounds found in a liquid state over most of Earth’s surface.

Lesson Overview Lesson Overview Properties of Water Polarity Electrically neutral Oxygen is on one end of the molecule and hydrogen is on the other. Oxygen has a stronger attraction for electrons

Lesson Overview Lesson Overview Properties of Water Polarity Oxygen has a negative charge Hydrogen has a positive charge. Polar Molecule: molecule in which the charges are unevenly distributed The molecule is a bit like a magnet with two poles.

Lesson Overview Lesson Overview Properties of Water Hydrogen Bonding Partial positive and negative charges attract each other Hydrogen Bonding: attraction between a hydrogen atom (+) and the oxygen atom (-)

Lesson Overview Lesson Overview Properties of Water Hydrogen Bonding Water is able to form multiple hydrogen bonds Hydrogen bonds are not as strong as covalent or ionic bonds.

Lesson Overview Lesson Overview Properties of Water Cohesion Cohesion: an attraction between molecules of the same substance Because a single water molecule may be involved in as many as four hydrogen bonds at the same time, water is extremely cohesive.

Lesson Overview Lesson Overview Properties of Water Cohesion Causes water molecules to be drawn together, which is why drops of water form beads on a smooth surface Produces surface tension, explaining why some insects and spiders can walk on a pond’s surface

Lesson Overview Lesson Overview Properties of Water Adhesion Adhesion: attraction between molecules of different substances Explains the formation of a meniscus

Lesson Overview Lesson Overview Properties of Water Adhesion Capillary Action: force that causes water to rise in a narrow tube against the force of gravity One of the forces that draws water out of the roots of a plant and up into its stems and leaves. Cohesion holds the column of water together as it rises.

Lesson Overview Lesson Overview Properties of Water Heat Capacity It takes a large amount of heat energy to cause molecules to move faster and raise the temperature of the water. Heat Capacity: amount of heat energy required to increase temperature of a substance The heat capacity of water is relatively high.

Lesson Overview Lesson Overview Properties of Water Heat Capacity Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature. At the cellular level, water absorbs the heat produced by cell processes, regulating the temperature of the cell.

Lesson Overview Lesson Overview Properties of Water The Water Molecule How does the structure of water contribute to its unique properties?

Lesson Overview Lesson Overview Properties of Water The Water Molecule How does the structure of water contribute to its unique properties? Because water is a polar molecule, it is able to form multiple hydrogen bonds, which account for many of water’s special properties.

Lesson Overview Lesson Overview Properties of Water Solutions and Suspensions Water is not always pure; it is often found as part of a mixture. Mixture: material composed of two or more elements or compounds that are physically mixed together but not chemically combined.

Lesson Overview Lesson Overview Properties of Water Solutions and Suspensions Living things are in part composed of mixtures involving water. Two types of mixtures that can be made with water are solutions and suspensions.

Lesson Overview Lesson Overview Properties of Water Solutions All the components of a solution are evenly distributed throughout the solution. In a saltwater solution, table salt is the solute— the substance that is dissolved. Water is the solvent—the substance that is doing the dissolving.

Lesson Overview Lesson Overview Properties of Water Solutions Water’s polarity gives it the ability to dissolve both ionic compounds and other polar molecules. Water easily dissolves salts, sugars, minerals, gases, and even other solvents such as alcohol. When a given amount of water has dissolved all of the solute it can, the solution is said to be saturated.

Lesson Overview Lesson Overview Properties of Water Suspensions Suspension: mixture of H 2 O and non-dissolved particles that do not settle out Example: Blood Mostly water Contains dissolved compounds, cells and other undissolved particles that remain in suspension

Lesson Overview Lesson Overview Properties of Water Acids, Bases, and pH Why is it important for cells to buffer solutions against rapid changes in pH?

Lesson Overview Lesson Overview Properties of Water Acids, Bases, and pH Why is it important for cells to buffer solutions against rapid changes in pH? Buffers dissolved in life’s fluids play an important role in maintaining homeostasis in organisms.

Lesson Overview Lesson Overview Properties of Water Acids, Bases, and pH Water molecules can split apart to form hydrogen ions and hydroxide ions.

Lesson Overview Lesson Overview Properties of Water The pH Scale pH scale: measurement system that indicates the concentration of H + ions in solution The pH scale ranges from 0 to 14. At a pH of 7, the concentration of H + ions and OH – ions is equal.

Lesson Overview Lesson Overview Properties of Water The pH Scale Acid: compound that will form H + ions in solution pH below 7 More H + ions than OH – ions The lower the pH, the greater the acidity.

Lesson Overview Lesson Overview Properties of Water The pH Scale Base: compound that will form OH - ions in solution pH above 7 More OH – ions than H + ions. The higher the pH, the more basic the solution.

Lesson Overview Lesson Overview Properties of Water The pH Scale Each step on the pH scale represents a factor of 10.

Lesson Overview Lesson Overview Properties of Water Buffers The pH in the human body must be kept between 6.5 and 7.5 in order to maintain homeostasis If the pH is lower or higher, it will affect the chemical reactions that take place within the cells.

Lesson Overview Lesson Overview Properties of Water Buffers Buffer: dissolved compounds in the body that help an organism control pH Weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH

Lesson Overview Lesson Overview Properties of Water Buffers Adding acid to an unbuffered solution causes the pH to drop. If the solution contains a buffer, however, adding the acid will cause only a slight change in pH.