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Chapter 13

Chapter 13. Water and Its Solutions. 13.1 Uniquely Water. Water – common substance with uncommon properties Simple molecule – vital to life *****Unique properties of H 2 O are due to three-dimensional arrangement and electron distribution. Water: The Molecular View. How is water different?.

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Chapter 13

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  1. Chapter 13 Water and Its Solutions

  2. 13.1 Uniquely Water • Water – common substance with uncommon properties • Simple molecule – vital to life *****Unique properties of H2O are due to three-dimensional arrangement and electron distribution

  3. Water: The Molecular View • How is water different? • liquid at room temperature • high melting/boiling pts • solid state LESS dense then liquid state

  4. Water: The Molecular View • water is a polar molecule • electrons are unequally shared • Bent structure allows a positive pole and a negative pole

  5. Intermolecular Forces in Water • Water molecules are attracted to each other – opposite poles line up

  6. Molecular Forces in Water • H2O molecules held together by covalent bonds (intra-molecular, solid lines) • and hydrogen bonds (inter –molecular, dashed lines)

  7. Hydrogen Bonding the attraction of hydrogen atoms in one molecule to an electronegative atom on another molecule

  8. Water: The Hydrogen Bonding Champion • Water will form hydrogen bonds with any molecule with O – H bonds • alcohols • proteins • nucleic acids • carbohydrates

  9. Water: Physical Properties Revisited • hydrogen bonds hold H2O molecules together and result in • H2O being a liquid at room temp • high boiling point

  10. Ice Floats • Solid H2O is less dense than liquid H2O • liquid H2O increases in density as it cools • When it hits maximum density @ 4o C volume begins to expand and density decreases

  11. Ice Floats Why does this happen? • below 4o C water molecules begin to form an open arrangement due to hydrogen bonding • volume expands and • density decreases

  12. Surface Tension • surface tension – force needed to overcome intermolecular attraction and break through the surface of a liquid • high surface tension = high resistance • H2O has high surface tension

  13. Capillarity How does a liquid travel UP a tube? • capillarity – competition between • inter-particle attractive forces • attractive forces between the liquid and the tube

  14. Water: Earth’s Thermostat • Specific heat is the amount of heat in joules needed to raise the temperature of 1 g substance 1oC. • Water has a high specific heat

  15. The Dissolving Process How does water dissolve ionic substances? • polar water molecules surround the ions • the + hydrogen pulls on the – ions • the - oxygen pulls on the + ions • this is called dissociation

  16. The Dissolving Process How water dissolves a covalent substance: • Water forms hydrogen bonds with the O-H group of covalent molecule • The hydrogen bond overcomes the intermolecular forces of the sugar molecule

  17. Like Dissolves Like How can you predict whether a substance will dissolve in another substance? • like dissolves like • solvent and solute must have similarities

  18. Like Dissolves Like • How is water like an ionic compound? • ionic compounds have charged (- & +) ions • water is polar (has partially charged ends)

  19. Like Dissolves Like • How is water like sugar? • both have O-H groups and form hydrogen bonds

  20. Concentrated Versus Dilute • weak and strong are used to describe acids and bases • chemists use concentrated and dilute to describe solutions

  21. Unsaturated Versus Saturated • unsaturated - a solution that has less than the maximum amount of solute dissolved • saturated – a solution that holds the maximum amount of dissolved solute

  22. Unsaturated Versus Saturated supersaturated – a solution that contains MORE than the maximum amount of dissolved solute --- unstable

  23. Molarity • molarity - # of moles of SOLUTE per liter of SOLUTION • used to determine the exact concentration of a solution • abbreviated --- M (= moles/liter)

  24. Molarity When making a solution you need to know: • the concentration • the amount of solute • total volume of solution needed Ex: How would you prepare 5.0 L of a 0.15 M sodium chloride solution?

  25. Molarity Ex: How would you prepare 5.0 L of a 0.15 M sodium chloride solution? 5.0 L solution X 0.15 mol NaCl X 58.5 g NaCl 1 1.0 L solution 1 mol NaCl = 43.9 g NaCl So you need to mix 43.9 g of NaCl with enough water to equal 5.0 L of solution

  26. Molarity Ex: How would you prepare 2.5 L of a 0.80 M KNO3 solution? 2.5 L solution X 0.80 mol KNO3 X 101 g KNO3 1 1.0 L solution 1 mol KNO3 = 202 g KNO3 So you need to mix 202 g of KNO3 with enough water to equal 2.5 L of solution

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