05 chemical elements_and_water


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05 chemical elements_and_water

  1. 1. Chemical Elements and Water
  2. 2. Atoms and Ions <ul><li>An atom is a single particle of a chemical element </li></ul><ul><li>If an atom either gains or loses electrons it becomes an ion </li></ul><ul><li>Atoms are uncharged particles and ions are charged – they have either positive or negative charges </li></ul><ul><li>For example, if a sodium atom (Na) loses an electron it becomes a sodium ion (Na + ) </li></ul><ul><li>This is important for when we discuss solubility later </li></ul>
  3. 3. Elements Found in Living Organisms <ul><li>Living organisms contain many chemical elements, some in large quantities and some in very small amounts </li></ul><ul><li>The 3 most common chemical elements of life are carbon, hydrogen, and oxygen (CHO) </li></ul><ul><li>They are part of all the main organic compounds in living organisms </li></ul><ul><li>Organic compounds: </li></ul><ul><ul><li>contain carbon </li></ul></ul><ul><ul><li>found in living organisms </li></ul></ul><ul><ul><ul><li>carbohydrates, lipids, amino acids are all organic molecules </li></ul></ul></ul><ul><li>Other elements needed by living things: </li></ul><ul><li>Nitrogen (AA and proteins) </li></ul><ul><li>Calcium (bones) </li></ul><ul><li>Phosphorus (Nucleic acids) </li></ul><ul><li>Iron (blood) </li></ul><ul><li>Sodium (Na+/K+ pumps) </li></ul>
  4. 5. Examples of Chemical Elements and Their Roles Used in neurons (nerve cells) for the transmission of nerve impulses Sodium Needed to make hemoglobin and thus to carry oxygen in blood Iron Part of the phosphate groups in ATP and DNA molecules Phosphorus Needed to make the mineral that strengthens bones and teeth Calcium Part of the amine groups of amino acids and therefore proteins Nitrogen Role in Plants or Animals Element
  5. 6. The Significance of Water to Living Organisms <ul><li>Water is of immense importance to all living organisms </li></ul><ul><li>It is used by them in many different ways </li></ul><ul><li>These uses can be explained by referring to the properties of water </li></ul><ul><li>Water is used a coolant </li></ul><ul><ul><li>Refer to thermal properties </li></ul></ul><ul><li>Water is used as a transport medium </li></ul><ul><ul><li>Refer to cohesion, solvent properties, and thermal properties </li></ul></ul><ul><li>Water is used as a habitat </li></ul><ul><ul><li>Hydrogen bonding, refer to cohesion, transparency, and thermal properties </li></ul></ul>
  6. 7. Polarity and Hydrogen Bonding in Water <ul><li>Water molecules consist of 2 hydrogen atoms bonded to an oxygen atom </li></ul><ul><li>The hydrogen atoms have a slight positive (+) charge and the oxygen atom has a slight negative (-) charge </li></ul><ul><li>So, water molecules have 2 poles (they are dipoles) – a positive hydrogen pole and a negative oxygen pole </li></ul><ul><li>This feature of a molecule is called polarity </li></ul><ul><li>A bond can form between the positive pole of one water molecule and the negative pole of another </li></ul><ul><li>This is called a hydrogen bond </li></ul><ul><li>In liquid water, many of these bonds form </li></ul><ul><li>Hydrogen bonds provide water with much of its basic properties </li></ul>
  7. 8. Water molecules form Hydrogen bonds slightly positive charge slightly negative charge hydrogen bond between (+) and (-) areas of different water molecules
  8. 9. Thermal Properties: Heat Capacity <ul><li>Water has a high heat capacity </li></ul><ul><li>This means that large amounts of energy are needed to raise its temp </li></ul><ul><li>The energy is needed to break one of the hydrogen bonds </li></ul><ul><li>This heat energy is given out again when the water is cooled </li></ul><ul><li>The temperature of water tends to remain quite stable </li></ul><ul><li>This is useful for organisms such as fish that use water as a habitat </li></ul><ul><li>Blood, which is mainly composed of water, can carry heat from warmer parts of the body to cooler parts </li></ul>
  9. 10. The Importance of Ice Floating <ul><li>If ice sank to the bottom of a body of water as it cooled… </li></ul><ul><ul><li>Ponds and lakes would freeze up from the bottom </li></ul></ul><ul><ul><li>Fish and other organisms would be trapped in the small amount of water that is left </li></ul></ul><ul><ul><li>There would be no access to the nutrients are the muddy bottom </li></ul></ul><ul><li>Ice atop a body of water, insulates the water below </li></ul><ul><ul><li>Life persists under the frozen surface </li></ul></ul>
  10. 11. Thermal Properties: Boiling and freezing points <ul><li>The boiling point of water is relatively high because to change it from a liquid to a gas all of the hydrogen bonds between the water molecules have to be broken </li></ul><ul><ul><li>In natural habitats on Earth, water rarely boils </li></ul></ul><ul><ul><li>Living organisms could not survive if the water inside them boiled </li></ul></ul><ul><li>Water also freezes at a relatively high temperature but because it becomes less dense as it cools to freezing point, ice forms at the surface first </li></ul><ul><ul><li>The ice that forms on the surface of lakes or seas insulates the water underneath, so living organisms can survive there </li></ul></ul>
  11. 12. Thermal Properties: The Cooling Effect of Evaporation <ul><li>Water can evaporate at temps below boiling point </li></ul><ul><li>Hydrogen bonds have to be broken to do this </li></ul><ul><li>The heat energy needed to break the bonds is taken from the liquid water, cooling it down </li></ul><ul><li>Evaporation of water from plant leaves ( transpiration ) and from human skin ( sweat ) has useful cooling effects </li></ul>
  12. 13. Cohesion <ul><li>Water molecules stick to each other because of the hydrogen bonds that form between them </li></ul><ul><li>Strong pulling forces can be exerted to suck columns of water up to the tops of the tallest trees in their transport systems </li></ul><ul><ul><li>These columns of water rarely break </li></ul></ul>
  13. 14. <ul><li>Trees have specialized structures to transport water: xylem and phloem “plumbing” </li></ul><ul><li>Water molecules are “dragged” from the roots to the top of the tree by capillary action (adhesion) and cohesion: hydrogen bonds help water molecules hydrogen bond to each other </li></ul>
  14. 15. <ul><li>Adhesion refers to attraction to other substances . </li></ul><ul><ul><li>Water is adhesive to any substance with which it can form hydrogen bonds . </li></ul></ul><ul><ul><li>Think water climbing up capillary tubes… </li></ul></ul>Adhesion
  15. 16. Cohesion <ul><li>At a surface, the cohesion of water molecules can make it difficult for small objects to break through </li></ul><ul><ul><li>surface tension </li></ul></ul><ul><ul><ul><li>a measure of the force necessary to stretch or break the surface of a liquid </li></ul></ul></ul><ul><li>Some animals such as mosquito larvae use the surface of water as a habitat </li></ul><ul><li>Though they are denser than water they remain on the surface and do not sink because of the high surface tension of water caused by cohesion </li></ul>
  16. 17. Solvent Properties <ul><li>Many different substances dissolve in water because of its polarity </li></ul><ul><li>Inorganic particles such as sodium ions and organic substances such as glucose can dissolve </li></ul>Water’s polarity “pulls” apart the ions of a particular substance (above NaCl). The positive hydrogen ends are attracted to the anions of a substance and the negative oxygen ends are attracted to the cations of a substance
  17. 18. Like dissolves like: water can interact with other polar molecules
  18. 19. <ul><li>Water transports molecules dissolved in it </li></ul><ul><ul><li>Blood , a water-based solution, transports molecules of nutrients and wastes within organisms </li></ul></ul><ul><ul><li>Nutrients dissolved in water get transported through plants </li></ul></ul><ul><ul><li>Unicellular organisms that live in water absorb needed dissolved substances </li></ul></ul>
  19. 20. Transparency <ul><li>The fact that water is clear allows light to pass through it </li></ul><ul><ul><li>Aquatic plants can receive sunlight </li></ul></ul><ul><ul><li>Light can pass through the eyeball to receptor cells in the back </li></ul></ul>
  20. 21. pH, Acids, Bases, Buffers
  21. 22. <ul><li>An acid is a substance that increases the hydrogen ion concentration in a solution. </li></ul><ul><ul><li>When hydrochloric acid is added to water, hydrogen ions dissociate from chloride ions: </li></ul></ul><ul><ul><ul><li>HCl -> H + + Cl - </li></ul></ul></ul><ul><li>Addition of an acid makes a solution more acidic. </li></ul>1. Organisms are sensitive to changes in pH
  22. 23. <ul><li>Any substance that reduces the hydrogen ion concentration in a solution is a base . </li></ul><ul><li>Some bases reduce H+ directly by accepting hydrogen ions. </li></ul><ul><ul><li>Ammonia (NH 3 ) acts as a base when the nitrogen’s unshared electron pair attracts a hydrogen ion from the solution, creating an ammonium in (NH 4 + ). </li></ul></ul><ul><ul><ul><li>NH 3 + H + <=> NH 4 + </li></ul></ul></ul><ul><li>Other bases reduce H+ indirectly by dissociating to OH - that combines with H+ to form water. </li></ul><ul><ul><li>NaOH -> Na + + OH - OH - + H + -> H 2 O </li></ul></ul><ul><li>Solutions with more OH - than H + are basic solutions . </li></ul>
  23. 24. <ul><li>Some acids and bases (HCl and NaOH) are strong acids or bases. </li></ul><ul><ul><li>These molecules dissociate completely in water. </li></ul></ul><ul><li>Other acids and bases (NH 3 ) are weak acids or bases. </li></ul><ul><ul><li>For these molecules, the binding and release of hydrogen ions are reversible. </li></ul></ul><ul><ul><li>Carbonic acid (H 2 CO 3 ) is a weak acid: </li></ul></ul><ul><ul><ul><li>H 2 CO 3 <=> HCO 3 - + H + </li></ul></ul></ul>
  24. 25. pH scale <ul><li>the environment needs to be at a specific pH for many organisms to survive </li></ul><ul><ul><li>Ex: most cells have an internal pH of 7 (neutral) </li></ul></ul><ul><ul><li>If the pH changes, even slightly, this can disrupt the chemical reactions inside the cell </li></ul></ul><ul><ul><li>Blood pH =7.4, a person will die if pH reaches 7.8 or 7 for even a little while! </li></ul></ul>
  25. 26. <ul><li>The chemical processes in the cell can be disrupted by changes to the H+ and OH- concentrations away from their normal values near pH 7. </li></ul><ul><li>To maintain cellular pH values at a constant level, biological fluids have buffers . </li></ul><ul><li>Buffers resist changes to the pH of a solution when H+ or OH- is added to the solution. </li></ul><ul><ul><li>Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted. </li></ul></ul>
  26. 27. <ul><li>Buffers typically consist of a weak acid and its corresponding base. </li></ul><ul><ul><li>One important buffer in human blood and other biological solutions is carbonic acid . </li></ul></ul><ul><ul><li>The chemical equilibrium between carbonic acid and bicarbonate acts at a pH regulator. </li></ul></ul><ul><ul><li>The equilibrium shifts left or right as other metabolic processes add or remove H+ from the solution. </li></ul></ul>
  27. 28. <ul><li>Acid rain and acid fog can significantly affect life in streams, rivers and ponds </li></ul><ul><li>Their effects upon forest and terrestrial life are still controversial– acid rain can affect soils and mineral content. </li></ul>
  28. 29. Figure 3.10x1 Pulp mill
  29. 30. Figure 3.10x2 Acid rain damage to statuary, 1908 & 1968
  30. 31. <ul><li>Acid precipitation is caused primarily by sulfur oxides and nitrogen oxides in the atmosphere. </li></ul><ul><ul><li>These molecules react with water to form strong acids. </li></ul></ul><ul><ul><li>These fall to the surface with rain or snow. </li></ul></ul><ul><li>The major source of these oxides is the burning of fossil fuels (coal, oil, and gas) in factories and automobiles. </li></ul><ul><li>The presence of tall smokestacks allows this pollution to spread from its site of origin to contaminate relatively pristine areas. </li></ul><ul><ul><li>Rain in the Adirondack Mountains of upstate New York averages a pH of 4.2 </li></ul></ul>
  31. 32. <ul><li>The effects of acids in lakes and streams is more pronounced in the spring during snowmelt. </li></ul><ul><ul><li>As the surface snows melt and drain down through the snow field, the meltwater accumulates acid and brings it into lakes and streams all at once. </li></ul></ul><ul><ul><li>The pH of early meltwater may be as low as 3. </li></ul></ul><ul><li>Acid precipitation has a great impact on eggs and early developmental stages of aquatic organisms which are abundant in the spring. </li></ul><ul><li>Thus, strong acidity can alter the structure of molecules and impact ecological communities. </li></ul>Adapted from M. Goss by J. Naftzinger 2008