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CVA Biology I - B10vrv1022

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Copyright - Adapted from Pearson

Copyright - Adapted from Pearson

Published in: Technology, Business

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  • 1. Lesson OverviewLesson Overview Properties of WaterProperties of WaterLesson OverviewLesson Overview2.2 Properties of Water2.2 Properties of Water
  • 2. Lesson OverviewLesson Overview Properties of WaterProperties of WaterTHINK ABOUT ITLooking back at Earth from space,an astronaut called it “the blueplanet,” referring to the oceans ofwater that cover nearly threefourths of Earth’s surface.The very presence of liquid watertells a scientist that life may alsobe present on such a planet.Why should life itself beconnected so strongly tosomething so ordinary that weoften take it for granted?There is something very specialabout water and the role it plays inliving things.
  • 3. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe Water MoleculeHow does the structure of water contribute to its unique properties?
  • 4. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe Water MoleculeHow does the structure of water contribute to its unique properties?Because water is a polar molecule, it is able to form multiple hydrogenbonds, which account for many of water’s special properties.
  • 5. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe Water MoleculeWater is one of the few compounds found in a liquid state over most ofEarth’s surface.Like other molecules, water (H2O) is neutral. The positive charges on its 10protons balance out the negative charges on its 10 electrons.
  • 6. Lesson OverviewLesson Overview Properties of WaterProperties of WaterPolarityBecause of the angles of itschemical bonds, the oxygen atomis on one end of the molecule andthe hydrogen atoms are on theother.With 8 protons in its nucleus, anoxygen atom has a much strongerattraction for electrons than doesa hydrogen atom with its singleproton.
  • 7. Lesson OverviewLesson Overview Properties of WaterProperties of WaterPolarityThere is a greater probability offinding the shared electrons inwater close to its oxygen atomthan near its hydrogen atoms.As a result, the oxygen end of themolecule has a slight negativecharge and the hydrogen end ofthe molecule has a slight positivecharge.
  • 8. Lesson OverviewLesson Overview Properties of WaterProperties of WaterPolarityA molecule in which the chargesare unevenly distributed is saidto be “polar,” because themolecule is a bit like a magnetwith two poles.The charges on a polar moleculeare written in parentheses, (–) or(+), to show that they are weakerthan the charges on ions suchas Na+and Cl–.
  • 9. Lesson OverviewLesson Overview Properties of WaterProperties of WaterHydrogen BondingBecause of their partial positiveand negative charges, polarmolecules such as water canattract each other.The attraction between ahydrogen atom on one watermolecule and the oxygen atomon another is known as ahydrogen bond.
  • 10. Lesson OverviewLesson Overview Properties of WaterProperties of WaterHydrogen BondingWater is able to form multiplehydrogen bonds, which accountfor many of its special properties.Hydrogen bonds are not asstrong as covalent or ionic bonds,and they can form in othercompounds besides water.
  • 11. Lesson OverviewLesson Overview Properties of WaterProperties of WaterCohesionCohesion is an attraction betweenmolecules of the same substance.Because a single water moleculemay be involved in as many asfour hydrogen bonds at the sametime, water is extremely cohesive.
  • 12. Lesson OverviewLesson Overview Properties of WaterProperties of WaterCohesionCohesion causes water molecules to be drawn together, whichis why drops of water form beads on a smooth surface.Cohesion also produces surface tension, explaining why someinsects and spiders can walk on a pond’s surface.
  • 13. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAdhesionAdhesion is an attraction between molecules of differentsubstances.The surface of water in a graduated cylinder dips slightly in thecenter, forming a curve called a meniscus, because theadhesion between water molecules and glass molecules isstronger than the cohesion between water molecules.
  • 14. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAdhesionAdhesion between water and glassalso causes water to rise in anarrow tube against the force ofgravity. This effect is calledcapillary action.Capillary action is one of the forcesthat draws water out of the roots ofa plant and up into its stems andleaves.Cohesion holds the column ofwater together as it rises.
  • 15. Lesson OverviewLesson Overview Properties of WaterProperties of WaterHeat CapacityBecause of the multiple hydrogen bonds between water molecules, ittakes a large amount of heat energy to cause those molecules to movefaster and raise the temperature of the water.Water’s heat capacity, the amount of heat energy required to increaseits temperature, is relatively high.Large bodies of water, such as oceans and lakes, can absorb largeamounts of heat with only small changes in temperature. This protectsorganisms 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.
  • 16. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutions and SuspensionsHow does water’s polarity influence its properties as a solvent?
  • 17. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutions and SuspensionsHow does water’s polarity influence its properties as a solvent?Water’s polarity gives it the ability to dissolve both ionic compounds andother polar molecules.
  • 18. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutions and SuspensionsWater 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 compoundsthat are physically mixed together but not chemically combined.Living things are in part composed of mixtures involving water.Two types of mixtures that can be made with water are solutions andsuspensions.
  • 19. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutionsIf a crystal of table salt is placed in water, sodium and chloride ions onthe surface of the crystal are attracted to the polar water molecules.
  • 20. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutionsIons break away from the crystal and are surrounded by watermolecules.The ions gradually become dispersed in the water, forming a type ofmixture called a solution.
  • 21. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutionsAll the components of a solution are evenly distributed throughout thesolution.In a saltwater solution, table salt is the solute—the substance that isdissolved.Water is the solvent—the substance in which the solute dissolves.
  • 22. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSolutionsWater’s polarity gives it the ability to dissolve both ionic compounds andother polar molecules.Water easily dissolves salts, sugars, minerals, gases, and even othersolvents such as alcohol.When a given amount of water has dissolved all of the solute it can, thesolution is said to be saturated.
  • 23. Lesson OverviewLesson Overview Properties of WaterProperties of WaterSuspensionsSome materials do not dissolve when placed in water, but separate intopieces so small that they do not settle out. Such mixtures of water andnondissolved material are known as suspensions.Some of the most important biological fluids are both solutions andsuspensions.Blood is mostly water. It contains many dissolved compounds, but alsocells and other undissolved particles that remain in suspension as theblood moves through the body.
  • 24. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAcids, Bases, and pHWhy is it important for cells to buffer solutions against rapid changesin pH?
  • 25. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAcids, Bases, and pHWhy is it important for cells to buffer solutions against rapid changesin pH?Buffers dissolved in life’s fluids play an important role in maintaininghomeostasis in organisms.
  • 26. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAcids, Bases, and pHWater molecules sometimes split apart to form hydrogen ions andhydroxide ions.This reaction can be summarized by a chemical equation in which doublearrows are used to show that the reaction can occur in either direction.
  • 27. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAcids, Bases, and pHIn pure water, about 1 water molecule in 550 million splits to form ions inthis way.Because the number of positive hydrogen ions produced is equal to thenumber of negative hydroxide ions produced, pure water is neutral.
  • 28. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe pH ScaleChemists devised a measurement system called the pH scale toindicate 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. Purewater has a pH of 7.
  • 29. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe pH ScaleSolutions with a pH below 7 are called acidic because they have moreH+ions than OH–ions. The lower the pH, the greater the acidity.Solutions with a pH above 7 are called basic because they have moreOH–ions than H+ions. The higher the pH, the more basic the solution.
  • 30. Lesson OverviewLesson Overview Properties of WaterProperties of WaterThe pH ScaleEach step on the pH scale represents a factor of 10. For example, a literof a solution with a pH of 4 has 10 times as many H+ions as a liter of asolution with a pH of 5.
  • 31. Lesson OverviewLesson Overview Properties of WaterProperties of WaterAcidsAn acid is any compound that forms H+ions in solution.Acidic solutions contain higher concentrations of H+ions than pure waterand have pH values below 7. Strong acids tend to have pH values thatrange from 1 to 3. Hydrochloric acid (HCl) is a strong acid produced bythe stomach to help digest food.
  • 32. Lesson OverviewLesson Overview Properties of WaterProperties of WaterBasesA base is a compound that produces hydroxide (OH–) ions in solution.Basic, or alkaline, solutions contain lower concentrations of H+ions thanpure water and have pH values above 7. Strong bases, such as the lye(commonly NaOH) used in soapmaking, tend to have pH values rangingfrom 11 to 14.
  • 33. Lesson OverviewLesson Overview Properties of WaterProperties of WaterBuffersThe pH of the fluids within most cells in the human body must generallybe kept between 6.5 and 7.5 in order to maintain homeostasis. If the pHis lower or higher, it will affect the chemical reactions that take placewithin the cells.One of the ways that organisms control pH is through dissolvedcompounds called buffers, which are weak acids or bases that canreact with strong acids or bases to prevent sharp, sudden changes inpH.
  • 34. Lesson OverviewLesson Overview Properties of WaterProperties of WaterBuffersAdding acid to an unbuffered solution causes the pH of the unbufferedsolution to drop. If the solution contains a buffer, however, adding theacid will cause only a slight change in pH.

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