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End Show Slide 1 of 44 2.2 Properties of Water Copyright Pearson Prentice Hall Earth, the “blue planet”, has water covering nearly ¾ of its surface. The.

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Presentation on theme: "End Show Slide 1 of 44 2.2 Properties of Water Copyright Pearson Prentice Hall Earth, the “blue planet”, has water covering nearly ¾ of its surface. The."— Presentation transcript:

1 End Show Slide 1 of Properties of Water Copyright Pearson Prentice Hall Earth, the “blue planet”, has water covering nearly ¾ of its surface. The very presence of liquid water tells a scientist that life may also be present on such a planet. Why is this so? There is something very special about water and the role it plays in living things!

2 End Show Slide 2 of 44 Copyright Pearson Prentice Hall H2OH2O Water is a molecule made up of 2 hydrogen atoms that are bonded through single covalent bonds to 1 oxygen atom. Like all molecules, a water molecule is neutral.

3 End Show 2-2 Properties of Water Slide 3 of 44 Copyright Pearson Prentice Hall The Water Molecule Polarity However the oxygen atom, with 8 protons in its nucleus, has a much stronger attraction for electrons than does the hydrogen atom with a single proton. Therefore, in each of the covalent bonds, the shared electrons spend a greater amount of time near the oxygen atom than near the hydrogen atom.

4 End Show 2-2 Properties of Water Slide 4 of 44 This type of covalent bond, where there is a greater probability of finding the shared electrons closer to one atom in the bond, is called a polar covalent bond. Copyright Pearson Prentice Hall

5 End Show 2-2 Properties of Water Slide 5 of 44 Copyright Pearson Prentice Hall The Water Molecule Why are water molecules polar? A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.

6 End Show 2-2 Properties of Water Slide 6 of 44 Copyright Pearson Prentice Hall The Water Molecule Since electrons in each oxygen to hydrogen bond will spend more time with the oxygen atom, the oxygen end of the molecule develops a slight negative charge and the hydrogen end develops a slight positive charge

7 End Show 2-2 Properties of Water Slide 7 of 44 Copyright Pearson Prentice Hall The Water Molecule Hydrogen Bonds Because of their partial positive and negative charges, polar molecules can attract each other.

8 End Show 2-2 Properties of Water Slide 8 of 44 Copyright Pearson Prentice Hall The Water Molecule The attraction between the hydrogen atoms on one molecule and the oxygen atom on another water molecule is a special Van der Waals force called a hydrogen bond. Hydrogen bonds are not true bonds and, so, are not as strong as covalent or ionic bonds.

9 End Show 2-2 Properties of Water Slide 9 of 44 Copyright Pearson Prentice Hall The Water Molecule Hydrogen bonds form between water molecules.

10 End Show 2-2 Properties of Water Slide 10 of 44 Copyright Pearson Prentice Hall The Water Molecule A single water molecule may be involved in as many as four hydrogen bonds at a time. Water’s ability to form multiple hydrogen bonds is responsible for many of its special properties.

11 End Show 2-2 Properties of Water Slide 11 of 44 Copyright Pearson Prentice Hall The Water Molecule Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Water's cohesion causes molecules on the surface of water to be drawn inward. That is, drops of water form beads on a smooth surface.

12 End Show 2-2 Properties of Water Slide 12 of 44 Cohesion also explains why some insects and spiders can walk on a pond's surface. There is a increase in attraction between water molecules at the surface of a sample. Water therefore has a high surface tension. Copyright Pearson Prentice Hall

13 End Show 2-2 Properties of Water Slide 13 of 44 Copyright Pearson Prentice Hall The Water Molecule Adhesion is an attraction between molecules of different substances. Water adheres to many surfaces due to hydrogen bonding between the water molecules and the surface molecules. The meniscus in a graduated cylinder exists because of the adhesion between water molecules and glass molecules.

14 End Show 2-2 Properties of Water Slide 14 of 44 Copyright Pearson Prentice Hall The Water Molecule Adhesion between water and glass also causes water to rise in a narrow tube against the force of gravity. This effect is called capillary action. Capillary action is one of the forces that draw 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.

15 End Show 2-2 Properties of Water Slide 15 of 44 The Water Molecule Because of hydrogen bonding and the attraction water molecules have for each other, large amounts of heat energy must be added for them to move faster (which is what causes an increase in temperature.) This means, water’s heat capacity (the amount of heat energy required to increase temperature) is relatively high. Copyright Pearson Prentice Hall Heat Capacity

16 End Show 2-2 Properties of Water Slide 16 of 44 The water molecule Large bodies of water (lakes, oceans) then can absorb a lot of heat with little change in temperature. At the cell level, water can absorb heat and regulate the temperature of the cell. Copyright Pearson Prentice Hall

17 End Show 2-2 Properties of Water Slide 17 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Water, being a polar molecule, has electric charges on its surface. This allows water to be an excellent solvent – it readily dissolves most other substances!

18 End Show 2-2 Properties of Water Slide 18 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Living systems are in part composed of mixtures involving water. A mixture is a material composed of two or more elements or compounds that are physically mixed but not chemically combined. Two types of mixtures can be made with water. solutions suspensions

19 End Show 2-2 Properties of Water Slide 19 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Solutions All the components of a solution are evenly distributed throughout the solution. In a salt–water solution, salt is evenly distributed throughout the water. Salt is the solute—the substance that is dissolved. Water is the solvent—the substance in which the solute dissolves.

20 End Show 2-2 Properties of Water Slide 20 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules. Na + Cl - Water How Substances Dissolve

21 End Show 2-2 Properties of Water Slide 21 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Ions break away from the crystal and are surrounded by water molecules. Na + Cl - Water

22 End Show 2-2 Properties of Water Slide 22 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions The ions gradually become evenly dispersed in the water, forming a solution. Na + Cl - Water

23 End Show 2-2 Properties of Water Slide 23 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Water's polarity gives it the ability to dissolve both ionic compounds and other polar molecules, such as sugar. Water is the greatest solvent on Earth.

24 End Show 2-2 Properties of Water Slide 24 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Suspensions Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out.

25 End Show 2-2 Properties of Water Slide 25 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions The movement of water molecules keeps the small particles suspended. Such mixtures of water and nondissolved material are known as suspensions.

26 End Show 2-2 Properties of Water Slide 26 of 44 Copyright Pearson Prentice Hall Solutions and Suspensions Some of the most important biological fluids are both solutions and suspensions. The blood that circulates through your body is mostly water, which contains many dissolved compounds. Blood also contains cells and other undissolved particles that remain in suspension as the blood moves through the body.

27 End Show 2-2 Properties of Water Slide 27 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH What are acidic solutions? What are basic solutions?

28 End Show 2-2 Properties of Water Slide 28 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Some water molecules in every sample dissociate (break apart) naturally to form hydrogen (H + ) and hydroxide ions (OH - ). Water remains neutral because the number of positive hydrogen ions (H + ) produced is equal to the number of negative hydroxide ions (OH - ) produced. When water reacts with other substances or other substances dissolve in water, this balance between ions can be upset.

29 End Show 2-2 Properties of Water Slide 29 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH The pH scale Chemists devised a measurement system called the pH scale to indicate the concentration of H + ions in solution. The pH scale ranges from 0 to 14.

30 End Show 2-2 Properties of Water Slide 30 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH At a pH of 7, the concentration of H + ions and OH - ions is equal. Pure water has a pH of 7. The pH Scale Human blood Milk Sea water Normal rainfall Pure water

31 End Show 2-2 Properties of Water Slide 31 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Solutions with a pH below 7 are called acidic because they have more H + ions than OH - ions. The lower the pH, the greater the acidity. Acid rain Tomato juice Lemon juice Stomach acids The pH Scale

32 End Show 2-2 Properties of Water Slide 32 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Solutions with a pH above 7 are called basic because they have more OH - ions than H + ions. The higher the pH, the more basic the solution. The pH Scale Soap Bleach Oven cleaner Ammonia solution

33 End Show 2-2 Properties of Water Slide 33 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Acids An acid is any compound that forms H + ions in solution. Acidic solutions contain higher concentrations of H + ions than pure water and have pH values below 7.

34 End Show 2-2 Properties of Water Slide 34 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Strong acids tend to have pH values that range from 1 to 3. The hydrochloric acid produced by the stomach to help digest food is a strong acid.

35 End Show 2-2 Properties of Water Slide 35 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Bases A base is a compound that produces hydroxide ions (OH - ions) in solution. Basic, or alkaline, solutions contain lower concentrations of H + ions than pure water and have pH values above 7.

36 End Show 2-2 Properties of Water Slide 36 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Strong bases, such as lye, tend to have pH values ranging from 11 to 14.

37 End Show 2-2 Properties of Water Slide 37 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Buffers The pH of the fluids within most cells in the human body must generally be kept between pH 6.5 and pH 7.5. If the pH is lower or higher, it will affect the chemical reactions that take place within the cells.

38 End Show 2-2 Properties of Water Slide 38 of 44 Copyright Pearson Prentice Hall Acids, Bases, and pH Controlling pH is important for maintaining homeostasis. One of the ways that the body controls pH is through dissolved compounds called buffers. Buffers are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH. Buffers play an important role in maintaining homeostasis in organisms.

39 End Show - or - Continue to: Click to Launch: Slide 39 of 44 Copyright Pearson Prentice Hall 2-2

40 End Show Slide 40 of 44 Copyright Pearson Prentice Hall 2-2 A molecule in which the charges are unevenly distributed is called a a.polar molecule. b.cohesive molecule. c.hydrogen molecule. d.covalent molecule.

41 End Show Slide 41 of 44 Copyright Pearson Prentice Hall 2-2 A dissolved substance is called a a.solvent. b.solution. c.solute. d.Suspension.

42 End Show Slide 42 of 44 Copyright Pearson Prentice Hall 2-2 A compound that produces hydroxide ions in solution is called a(an) a.base. b.buffer. c.acid. d.salt.

43 End Show Slide 43 of 44 Copyright Pearson Prentice Hall 2-2 Hydrogen bonds between water molecules result from a.adhesion between water molecules. b.magnetic attractions between water molecules. c.uneven electron distribution in each water molecule. d.ionic bonds in the water molecule.

44 End Show Slide 44 of 44 Copyright Pearson Prentice Hall 2-2 On a pH scale, a value of 2 means that the solution has a.equal concentrations of H + and OH - ions. b.the same concentration of H + ions as pure water. c.higher concentration of H + than in pure water. d.lower concentration of H + than in pure water.

45 END OF SECTION


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