Chemistry - A Molecular Science

Chapter 10 Solutions

dishes by adding a detergent, agitating it to

accelerate the formation of micelles that

dissolve the hydrophobic dirt, and then rinsing the micelles and the captured oil and grease down the drain. Example 10.6 Which would form a better micelle, sodium acetate (NaC

H 2

O 3

) or sodium palmitate 2

(NaC

H 16

O 31

)? Explain. 2

CH^2

H^2 C

CH^2

H^2 C

CH^2

H^2 C

CH^2

H^2 C

CH^2

H^2 C

CH^2

C

H^2 C

CH^2

H^2 C

HC^3

O

O

Palmitate ion

HC^3

O C

O

Acetate ion

tail

The CH

group of the acetate ion is not hydroph 3

obic enough for acetate to form micelles.

Sodium acetate is soluble in water. The CH

(CH 3

) 214

chain of the palmitate ion is very

hydrophobic, so the ion makes an excellent micelle.

10.5

ELECTROLYTES

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solution ofelectrolytes

glowinglight bulb electrode

Figure 10.7 Solutions of electrolytes conduct electricity The light bulb glows if there are ions present in the solution. Cations migrate to the negative electrode and anions to the positive electrode. The migrati

on of ions results in current

passing through the solution from one electrode to the other in a process is called

electrolytic conduction.

In Chapter 8, we saw that ionic substances

form extended solids in which there are no

clearly defined ‘ionic molecules.’ Rather, each ion is surrounded by some number (the coordination number) of ions of opposite charge.

In this section, we consider the nature of

solutions composed of ionic substances disso

lved in water by examining their ability to

conduct electricity. Consider the apparatus shown in Figure 10.7. How brightly the light bulb glows depends upon how well charge fl

ows from one electrode to the other,

i.e.

, how

well charge flows through the solution. The m

ovement of charge through the solution is

due to the migration of ions, not free electrons. The light bulb does not glow when the electrodes are immersed in pure water or in

a 0.1 M sugar solution because there are no

ions in these solutions. The bulb glows very brightly when the solution is 0.1 M NaCl, but it does not glow at if solid sodium chloride is used. Thus, an aqueous solution of NaCl is a good conductor of electricity, but the solid is not. The difference between the solution and the solid is that the ions in solution are m

obile, while those in the solid are not. Conduction

in the solution results from a migration of ions as Na

1+ ions migrate toward the negative

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