SECTION 2 2 PROPERTIES OF WATER Biology I

SECTION 2 -2 PROPERTIES OF WATER Biology I Flora

The Water Molecule Neutral (10 p and 10 e) Held together by covalent bonds It is a polar molecule A molecule in which the charges are unevenly distributed is called a polar molecule ex: electronegativity

Hydrogen Bonds Due to their partial negative and positive charges, polar molecules can attract each other Attraction between hydrogen atoms on one molecule and oxygen atoms on a nearby molecule is an example of a hydrogen bond. Responsible for cohesion – attraction between molecules of the same substance – Ex: 2 H 2 O

Cont. Hydrogen Bonds Adhesion – attraction between molecules of different substances – Ex: meniscus in graduated cylinder

Solutions and Suspensions Solutions can be pure or can be mixtures Mixture – material composed of two or more elements or compounds that are physically mixed together, but not chemically combined – Ex: pepper and salt; sugar and sand

Suspensions vs. Solutions Solution – all components are evenly distributed throughout the solution – Ex: Na. Cl in water Solute – substance that is dissolved (Na. Cl) Solvent – the substance that dissolves the solute (water)

Suspensions vs. Solutions Cont. Suspensions – mixture of water and nondissolved materials Ex: cells in blood

p. H Scale – (potential of hydrogen); scale to indicate the concentration of hydrogen ions in a solution Ranges from 0 -14 0 to 6 – acidic 8 -14 basic 7 – neutral: hydrogen ions (H+) and hydroxide ions (OH-) are equal.

Acids Acid – any compound that forms hydrogen ions in solution Acidic solutions have higher concentration of hydrogen ions

Bases Base – compound that produces hydroxide ions in solution Basic solutions contain lower concentrations of hydrogen ions

Buffers Buffer – weak acids or bases that react with strong acids or bases to resist changes in p. H – Ex: body homeostasis (6. 5 -7. 5)