Ann Barker 1 Properties of Water

Ann Barker 2 Why is Water important? n Life probably evolved in water. n Living cells are 70-95% water n Water covers 3/4 of the earth. n Water naturally occurs in three states of matter. n Life depends on the properties of water.

Ann Barker 3 n Water is a polar molecule. Its polar bonds and asymmetrical shape give water opposite charges on opposite sides.

Ann Barker 4 Polarity n The polar molecules of water are held together by hydrogen bonds.

Ann Barker 5 Polarity n Polar water molecules are attracted to ions and polar compounds, making them soluble.

Ann Barker 6 Benefit to life: polarity n Many kinds of molecules can move freely in cells, permitting a diverse array of chemical reactions.

Ann Barker 7 Properties of water n 1. Cohesion n 2. Adhesion n 3. Surface tension n 4. Hydophilic n 5. Imbibition

Ann Barker 8 Properties of water n 6. High specific heat n 7. High Heat of vaporization n 8. Freezing and expansion of water n 9. Universal solvent n 10. Capillary action

Ann Barker 9 Properties of water--cohesion n 1. Cohesion--substances held together by hydrogen bonds--contributes to upward water transport in plants.

Ann Barker 10 Properties of water--adhesion n 2. Adhesion of water to vessel walls counteracts the downward pull of gravity. Adhesion is the clinging of water to hydrophilic substances (such as glass).

Ann Barker 11 Properties of water--surface tension n 3. Water has a strong surface tension because water molecules are held together by hydrogen bonds, water has a high degree of cohesion, or the ability to stick together.

Ann Barker 12 Properties of water--hydrophilic n 4. hydrophilic--property of having an affinity for water. – hydro-”water” – philo-”loving” – phobic-”fearing”

Ann Barker 13 n Ionic and polar substances are hydrophilic, but nonpolar compounds are hydrophobic. (not water soluble)

Ann Barker 14 Properties of water--imbibition n 5. Imbibition--process of water soaking into a porous hydrophilic substance (like in a sponge). Imbibition in seeds, allows germination.

Ann Barker 15 High specific heat n Water has a high specific heat, which means that it resists temperature changes when it absorbs or releases heat.

Ann Barker 16 High specific heat n A large body of water can act as a heat sink--absorbing heat from the sun during the day and summer and releasing heat during the night and winter as the water gradually cools.

Ann Barker 17 High heat of vaporization n 7. Vaporization (evaporation)= transformation from liquid to gas. For water to evaporate, hydrogen bonds must be broken which requires heat energy.

Ann Barker 18 Freezing and expansion of water n Water is densest at 4º C. n 8. As water cools from 4º C to freezing, it expands and becomes less dense than liquid water (ice floats.)

Ann Barker Universal solvent n Solution--a liquid that is a homogenous mixture of 2 or more substances. n Solvent--dissolving agent n Solute--substance dissolved in a solution

Ann Barker 20 Capillary action n 10. Two forces taken together-- cohesion and adhesion account for the ability of water to rise in thin vessels of tens or hundreds of feet up the roots, trunks, and branches of even the largest trees.

Ann Barker 21 Acids, Bases, and pH n Acids--substance that increases the H+ of a solution. n Bases--substance that increases the OH- of a solution; reduces the H of a solution.

Ann Barker 22 pH scale n pH scale is used to measure degree of acidity. It ranges from 0 to 14. n pH 7 is neutral n 7 is basic

Ann Barker 23 pH scale n Remember that the pH scale is a measure of hydrogen (H + ) ion concentration.

Ann Barker 24 pH n A low pH corresponds to a high concentration of hydrogen ions. n A high pH corresponds to a low concentration of hydrogen ions.

Ann Barker 25 pH scale n pH scale is a logarithmic scale. A change of one pH number actually represents a tenfold change in hydrogen ion concentration. ex. pH 3 is ten times more acid than pH 4.

Ann Barker 26 pH of body fluids n Most biological fluids have a pH between 6 and 8. –stomach acid with pH 1.5-2

Ann Barker 27 pH scale ACIDBASE NEUTRAL Each step on pH scale represents a factor of 10. pH 5 vs. pH 6 (10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different) : measures the number of H+ ions 10x Soren Sorensen ( )