Properties of Water: Unique and Essential

1. Lesson Overview 2.2 Properties of Water

2. THINK ABOUT IT • “the blue planet,” • The very presence of liquid water tells a scientist that life may also be present on such a planet.

3. The Water Molecule • Water has very unique properties! • Water is one of the few compounds found in a liquid state over most of Earth’s surface. • Like other molecules, water (H2O) is neutral • Because water is a polar molecule, it is able to form multiple hydrogen bonds, which account for many of water’s special properties.

4. Polarity • Polar Molecule-The oxygen atom is on one end of the molecule and the hydrogen atoms are on the other.

5. Polar- molecule with uneven charges • oxygen- slight negative charge • hydrogen -slight positive charge.

6. Hydrogen Bonding • Polar molecules such as water can attract each other. • Hydrogen bond -attraction between a hydrogen atom on one water molecule and the oxygen atom on another • Hydrogen bonds are not as strong as covalent or ionic bonds

7. Cohesion • Cohesion -attraction between molecules of the same substance. • A single water molecule may be involved in as many as four hydrogen bonds at the same time, water is extremely cohesive.

8. Cohesion • Cohesion causes water molecules to be drawn together, which is why drops of water form beads on a smooth surface. • Cohesion also produces surface tension, explaining why some insects and spiders can walk on a pond’s surface. • lizard

9. Adhesion • Adhesion is an attraction between molecules of different substances. • meniscus- caused because the adhesion between water molecules and glass molecules is stronger than the cohesion between water molecules.

10. Adhesion • Adhesion-Capillary action is 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.

11. Heat Capacity • Because of the multiple hydrogen bonds between water molecules, it takes a large amount of heat energy to cause those molecules to move faster and raise the temperature of the water. • Water’s heat capacity- the amount of heat energy required to increase its temperature, is relatively high. • 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. • water capacity

12. Solutions and Suspensions • Water’s polarity gives it the ability to dissolve both ionic compounds and other polar molecules. When a given amount of water has dissolved all of the solute it can, the solution is said to be saturated. • If a crystal of table salt is placed in water, sodium and chloride ions on the surface of the crystal are attracted to the polar water molecules.

13. Solutions • Ions break away from the crystal and are surrounded by water molecules. • The ions gradually become dispersed in the water, forming a type of mixture called a solution.

14. 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 in which the solute dissolves. • When a given amount of water has dissolved all of the solute it can, the solution is said to be saturated.

15. Solutions and Suspensions • Water is not always pure; it is often found as part of a mixture. • A mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. • Living things are in part composed of mixtures involving water.

16. Suspensions • Suspensions- mixtures of water and nondissolved particles that do not settle out. • Some of the most important biological fluids are both solutions and suspensions. • Blood is mostly water. It contains many dissolved compounds, but also cells and other undissolved particles that remain in suspension as the blood moves through the body. • blood

17. Acids, Bases, and pH • Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases • Dissolve in water to release hydrogen ions into solution: • Bases feel slippery, change litmus blue, and become less basic when mixed with acids. • Dissolve in water to release hydroxide ions (OH-) into solution • NaOH H2O OH- + Na+

18. pH • Acids the concentration of hydrogen ions H+ • Bases the concentration of hydrogen ions H+ • more OH- ions(accepts H+)   • The acidity or basicity of something, therefore, can be measured by its hydrogen ion concentration.

19. pH scale • For example, a solution with [H+] = 1 x 10-7 moles/liter has a pH equal to 7 • pH scale ranges from 0 to 14. • Acids- pH between 0 and less than 7 (lower pH means higher [H+]). • Bases- pH greater than 7 and up to 14 are bases (higher pH means lower [H+]). • Neutral pH = 7, for example, pure water.

20. pH

21. Neutralization • A neutralization reaction of an acid  with a base  will always produce water and a salt 

22. Acids, Bases, and pH • Acid–base homeostasis is the part of human homeostasis concerning the proper balance between acids and bases, called body pH. The body is very sensitive to its pH level, so strong mechanisms exist to maintain it. 

23. Buffers • The pH of the fluids within most cells in the human body is kept between 6.5 and 7.5 in order to maintain homeostasis. • Buffer-controls pH • usually a weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH

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

25. Exercise Exercise has many short-term (acute) and long-term effects on the body: • Increased activity leads to increased carbon dioxide and hydrogen levels in the blood. ( metabolism) • They lower blood pH, increasing acidity, beyond optimal levels. • The brain stimulates the heart rate to increase: • remove excess carbon dioxide • lungs & kidneys.

26. BLOOD pH • If the pH of the body gets too low (below 7.4), acidosis results. This can be serious, because many of the chemical reactions that occur in the body, especially those involving proteins, are pH-dependent. (enzymes) • Ideal pH of the blood = 7.4. • If the pH drops below 6.8 or rises above 7.8, death may occur.

27. Buffering Systems There are three primary systems that regulate the H+ concentration in the body fluids to prevent acidosis or alkalosis: (1) the chemical acid-base buffer systems of the body fluids, which immediately combine with acid or base to prevent excessive changes in H+ concentration; (2) the respiratory center, which regulates the removal of CO2 (and, therefore, H2CO3) from the extracellular fluid; and (3) the kidneys, which can excrete either acid or alkaline urine, thereby readjusting the extracellular fluid H+ concentration toward normal during acidosis or alkalosis.

29. In the lungs, the reaction is reversed and produces carbon dioxide gas, which you exhale. As it enters the blood, carbon dioxide (CO2) reacts with water to produce carbonic acid (H2CO3), which is highly soluble. This chemical reaction enables the blood to carry carbon dioxide to the lungs. video

30. Homeostasis Acidosis is an “abnormal condition of” (-osis) too much body “acid.” Because a person exhales just enough CO 2 , there isn’t time for too much CO 2 to accumulate within the erythrocytes and build up too much carbonic acid, H 2 CO 3 , or H + ions. When a person hyperventilates too much CO 2 is exhaled from the body. Thus, not enough CO 2 is left to react with H 2 O inside the erythrocytes. There is not enough carbonic acid (H 2 CO 3 )or hydrogen ion (H + ) produced. The resulting state is alkalosis .

31. Acid Base Balance