Chem 1000                Chapter 7 Molecular Mixing

End-of Chapter Homework: Key terms: 3-5, 8-10. Review Questions: 1, 3, 6, 14, 15, 29-31. Problems: 1-3.

7.1 Submicroscopic Particles Electrically Attract One Another

Ch. 6: Within molecules, atoms are held together by ionic, polar or nonpolar covalent bonds

This chapter: Submicroscopic particles, including molecules, are attracted to each other

    The attractive force is electrostatic, but weaker than the bonds in Ch. 6

Table 7.1 Comparison of the different types of these attractive forces

Ions and Polar Molecules Attract One Another

Principle example NaCl dissolved in water:

    The H₂O molecules orient themselves so that the O atoms are closest to the Na⁺ ions

        and the H atoms are closest to the Cl^- ions

    This takes advantage of the O^(delta)- attraction to the Na⁺. and the H^(delta)+ attraction to Cl^-.

    Even though H₂O is neutral overall, it can participate in electrostatic attraction with ions

        with its centers of (delta)- and (delta)+

Fig 7.1 and 7.2: the   )))(((   indicates the electrostatic attraction

Polar Molecules Attract Other Polar Molecules

First example C₂H₆O molecules, dimethyl ether, Fig 7.3

    In the molecule there is a particularly polar bond, C-O with the polarity  ^(delta)+C-O^(delta)-

   Fig 7.3: (delta)+ on the C of one molecule attracts the (delta)- on the O of another molecule

Second example: H₂O, Fig 7.4. The O-H bond is polarized  ^(delta)-O-H^(delta)+

    Again, the (delta)+ on the H of one molecule attracts the (delta)- on the O of another molecule

    This attraction is unusually strong, and it has a special name, the hydrogen "bond"

        This is not a true bond as in Chapter 6, but a very strong attractive force

        Any molecule with an O-H bond can exhibit hydrogen bonding

    Other hydrogen bonds are found between molecules with N-H bonds and F-H bonds

Polar Molecules Can Induce Dipoles in Nonpolar Molecules - relatively weak attractions - skim

Atoms and Nonpolar Molecules Can Form Temporary Dipoles on Their Own - skim

7.2 A Solution Is a Single-Phase Homogeneous Mixture

Sucrose in Water, Fig 7.12 a polar substance, sucrose, initially a solid crystal is dissolved in water

    Water, also a polar substance, and sucrose become attracted to each other by hydrogen bonds

The result is a homogeneous solution, a uniform mixture

    In the solution, the crystals of sucrose break up, but not the sucrose molecules

    Both the sucrose molecules and water molecules remain intact

Fig 7.13 Examples of other solutions

Solvent: the component of the solution in the larger amount (water)

Solute: the component of the solution in the smaller amount (sucrose)

Concept check, p. 210.

Fig 7.14: unsaturated, saturated solutions - skim

P. 211: Concentration = amount of solute/amount of solution

Calculation corner, p. 212

P. 211: The mole. The mole is a number, a convenient number, 6.02 x 10²³.

P. 213: Whereas the number of grams tells you the mass of a substance

    The number of  moles tells you the number of molecules of a substance

    More on moles and why 6.02 x 10²³ in Ch. 9.

Fig 7.15: A mole of sucrose molecules is dissolved in a liter of solution. 

    P. 213: this solution is 1 molar of sucrose in water

    molarity = number of moles of solute/liter of solution

Fig 7.16 A solution of sucrose in water

    Although there are more grams of sucrose (200g vs 100g of water ),

    There are more molecules of water, thus water is the solvent (the larger amount)

    Calculations to convert grams to moles are in Ch. 9

Concept check, p. 213.

7.3 Solubility is a Measure of How Well a Solute Dissolves - skim

Solubility Changes with Temperature - skim

Gasses Are More Soluble at Low Temperature and High Pressures - skim

Nonpolar Gases Readily Dissolve in Perfluorocarbons - skim

7.4 Soap Works by Being Both Polar and Nonpolar

Dirt and grease are substances made of comparatively nonpolar molecules

Water alone is too polar to dissolve these molecules

    Oil (also nonpolar) and water don't mix

Dry cleaning solvents such as trichloroethane or turpentine are nonpolar substances

    they can dissolve dirt and grease

Water can dissolve dirt and grease if soap is mixed in

P. 222: a drawing of the two parts of a soap molecule

    A nonpolar end - left - with just C and H atoms. 

        (The polarity difference between C and H is very small)

    And a polar end - right - with C=O, C-O and O^- Na⁺ bonds

Fig 7.25: The nonpolar end attracts the nonpolar dirt and grease molecules

    And the polar end attracts the water molecules.

    The water (solvent) solution of soap-grease (solute)  can now be rinsed away

Detergents Are Synthetic Soaps - skim

Hard Water Makes Soap Less Effective - skip

Dec, 2002