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General Chemistry Principles, Patterns, and Applications, 2011

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6. Why is heat evolved when sodium hydroxide pellets are dissolved in water? Does this process correspond to<br />

simple dissolution or a chemical reaction? Justify your answer.<br />

7. Which process(es) is the simple formation of a solution, <strong>and</strong> which process(es) involves a chemical reaction?<br />

a. mixing an aqueous solution of NaOH with an aqueous solution of HCl<br />

b. bubbling HCl gas through water<br />

c. adding iodine crystals to CCl 4<br />

d. adding sodium metal to ethanol to produce sodium ethoxide (C 2 H 5 O − Na + ) <strong>and</strong> hydrogen<br />

gas<br />

8. Using thermochemical arguments, explain why some substances that do not form a solution at room<br />

temperature will form a solution when heated. Explain why a solution can form even when ΔH soln is positive.<br />

9. If you wanted to formulate a new compound that could be used in an instant cold pack, would you select a<br />

compound with a positive or negative value of ΔH soln in water? Justify your answer.<br />

10. Why is entropy the dominant factor in the formation of solutions of two or more gases? Is it possible for two<br />

gases to be immiscible? Why or why not?<br />

A N S W E R S<br />

1. Homogeneous mixtures: aqueous ammonia, liquid decongestant, vinegar, <strong>and</strong> gasoline. Heterogeneous<br />

2.<br />

3.<br />

4.<br />

5.<br />

6.<br />

mixtures: seawater <strong>and</strong> fog.<br />

7. All are chemical reactions except dissolving iodine crystals in CCl 4 .<br />

13.2 Solubility <strong>and</strong> Molecular Structure<br />

L E A R N I N G O B JE C T I V E<br />

1. To underst<strong>and</strong> the relationship between solubility <strong>and</strong> molecular structure.<br />

When a solute dissolves, its individual atoms, molecules, or ions interact with the solvent, become solvated, <strong>and</strong> are<br />

able to diffuse independently throughout the solution (part (a) in ). This is not, however, a unidirectional process. If<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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