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Science Dept.

Chemistry CHE 100 Notes
O. Water

  1. Polarity of the Water Molecule

    1. Chemical Formula

      1. H2O

      2. HOH

    2. Draw the Structural Formula

  2. Hydrogen Bonding in Water

    1. The positive end of a water molecule is attracted to either the negative end
      of another water molecule or an anion (negative ion) such as Cl1-

    2. The negative end of a water morecule is attracted to either the positive end
      of another water molecule or a cation (positive ion) such as Na1+

  3. Physical Properties

    1. Appearance

      1. Colorless

      2. Tasteless

      3. Odorless

    2. Density: N.B. Densest at 4oC

      1. 4oC water density = 1.000 g/cc

      2. 0oC water density = 0.99987 g/cc

      3. 0oC ice density = 0.917 g/cc

    3. Lakes and ponds freeze from the top down and not from bottom up, otherwise life would not exist in the lake. Water is unusual in this respect

  4. Preparation of Water

    1. Hydrocarbon + Oxygen --Energy--> Water + Carbon Dioxide + Energy

      1. CH4 + 2O2 --Energy--> 2H2O + CO2 + Energy

    2. Carbohydrate (respiration by animals and plants) + Oxygen ----> Water + Carbon Dioxide + Energy

      1. C12H22O11 + 12O2 ----> 11H2O + 12CO2 + Energy

    3. 2H2 + O2 --Energy--> 2H2O + Energy

    4. ACID + BASE ----> SALT + WATER

      1. HCl + KOH ----> K1+ + Cl1- + H2O ... a Neutralization Reaction

  5. Reactions with H2O

    1. Electrolysis of H2O

      1. 2H2O --elect. DC current--> 2H2 + O2 ... a Decomposition Reaction

    2. Reactions with certain metals eg Li K Ba Ca Na

      1. Ba +2H2O ----> Ba(OH)2 + H2(g) ... a Single Replacement

    3. A Nonmetal oxide + water ----> Acid

      1. SO2 + H2O ----> H2SO3 ... a Combination Reaction, creating sulfurous acid (later becoming sulfuric acid) part of the acid rain problem

    4. A Metal oxide + water ----> Base

      1. CaO + H2O ----> Ca(OH)2 ... a Combination Reaction

  6. Purification of Water for Water Supply

    1. Settling

      1. Use of a gelatinous floculant to remove clay, silt, organic matter

      2. CaO + H2O ---> Ca(OH)2

      3. 3Ca(OH)2 + Al2(SO4)3 ----> 3CaSO4 + 2Al(OH)3

      4. N.B. Al(OH)3 is an insoluble gelatonous ppt

    2. Filtering

      1. Through fine sand filters to remove particles of floculant

      2. Sand can be washed via a backflush

    3. Disinfection

      1. Chlorination either Cl2 or some hyprochlorite such as NaClO

      2. Sometimes ozone O3 is used as a disinfectant

      3. N.B. Chlorination can create chlorinated hydrocarbons

  7. Purification of Water for Laundry

    1. Ion Exchange Resins, for example Zeolite a natural substance, or a man made substance can be used

    2. Ca2+ ion in water causes hardness because it binds with soap or detergents and inactivates them

    3. Exchange the offending Ca2+ ion in water with Na1+ and tie up the Ca2+ with the Zeolite

    4. Na2Z + CaSO4 ----> CaZ + Na2SO4

  8. Purification of Water for Laboratory Purposes

    1. Distillation

  9. Purification of Water for Laboratory Purposes

    1. Use of Ion Exchange Resins

      1. Cation Exchange Part: Replaces cations (eg. Na1+) with H1+

      2. Anion Exchange Part: Replaces anions (eg. Cl1-) with OH1-

    2. The resultant production of H1+ and OH1- yields water, H2O

  10. Some Odds and Ends

    1. Hygroscopic: takes up water

      1. NaCl can take up water from the atmosphere, the reason is cakes in humid weather

    2. Hydrogen Peroxide

      1. H2O2 ----> H2O + O

      2. The lone O atom, called nascent oxygen is highly reactive

    3. Ozone

      1. O3 ---> O2 + O

      2. The lone O atom, called nascent oxygen is highly reactive

     

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