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4.4 Water Properties

4.4 Water Properties

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4.4 Water Properties

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  1. 4.4 Water Properties

  2. Properties of Water • Result of H2O • being a polar molecule- Oxygen end has a slight negative charge; Hydrogen end has a slight positive charge. • Ability of water to form hydrogen bonds.

  3. 1. Cohesion • Like molecules attach to like molecules. • Water forms bonds with other water molecules. • Important in surface tension of water. • Movement of water up a straw and up the roots of a plant to the stem and leaves.

  4. 2. Adhesion • Unlike molecules are attracted to each other. • Water forms bonds with other substances. • Important in fighting the effects of gravity. • Water forms bonds with cells in the transport tubes so water can move up the stems to the leaves. • Why is this important to plants and us?

  5. Cohesion and adhesion

  6. 3.Temperature moderation • Because of hydrogen bonds water takes longer to heat up and longer to cool down. • Heat is transferred from the warm to colder substances. • This is why lakes and oceans moderate the temperatures of nearby land areas ,so coastal areas generally have less extreme temperatures than inland areas. • Also seen in sweating- When water molecules evaporate, the hydrogen bonds break releasing water into the air, cooling our bodies.

  7. 4. Low density of ice • Water is unique- solid form-ice is less dense than the liquid form. • As water cools the hydrogen bonds spread out.

  8. 5. Water is an excellent solvent Terms: • A solution is a uniform mixture of two or more substances. • A solvent (water) dissolves the other substance and is present in the greater amoun. • The solute is the substance that is dissolved and is present in a lesser amount (salt). • An aqueous solution is when water is the solvent.

  9. Water is the main solvent inside all cells, in blood, and in plant sap. • The positive sodium ions of NaCl (salt) attract the oxygen ends of the water molecules. The negative chloride ions attract the hydrogen ends of the water molecules. • The result is water molecules surround each ion, breaking the salt apart.

  10. Acids, bases and pH • In aqueous solutions the ions formed are: • positively charged hydrogen ions (H+) • and negatively charged hydroxide ions (OH-). • For the chemical processes of life to work a balance of H+ ions and OH- ions is critical. • Terms: • An acid is a compound that donates H+ ions to a solution. • A base is a compound that removes H+ ions from an aqueous solution.

  11. pH scale • The pH scale describes how acidic or basic a solution is. • The scale ranges from 0 (most acidic) to 14 (most basic) • Each pH unit represents a tenfold change in the concentration of H+ ions. For example, lemon juice at pH 2 has 10 times more H+ ions than an equal amount of grapefruit juice at pH 3. • Pure water has an equal amounts of H+ and OH- ions It is neutral with a pH of 7. • The pH of blood cells is 7.4

  12. pH scale

  13. Buffers • Even a slight change in pH can be harmful to organisms. • Many biological fluids contain buffers. • Buffers resist changes in pH by accepting H+ ions when pH levels rise and donating H+ ions when pH levels fall.

  14. Ch. 4 Review Questions • 4. A covalent bond forms whena. opposite ions attract.b. protons are shared between atoms.c. an electron is transferred from one atom to another.d. two atoms share a pair of electrons. • 5. Substances formed by a chemical reaction are calleda. reactants.b. products.c. chemical formulas.d. chemical equations. • 7. A solution with a pH of 9 isa. acidic.b. basic.c. neutral.d. higher in H+ ions than in OH- ions.

  15. 10. How are the number of electrons in an atom's highest energy level related to the reactivity of that atom? • 11. How is a potassium atom (K) different from a potassium ion (K+)? • 13. Explain what makes a water molecule polar. • 15. Describe how the properties of water molecules contribute to the upward movement of water through a tall tree. • 16. What is an aqueous solution? • 17. How does a buffer keep a solution from becoming too acidic?

  16. 21. Analyzing Data Use the data table to answer. a. Which sample in the table is most acidic? b. Which sample listed has a pH that is closest to neutral? c. Which sample, normal rainfall or baking soda solution has a greater amount of hydrogen ions (H+)?