Introductory Chemistry

Quiz: Ions in solution.

Cracolice 2/e Ch 17.

Answer key
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1. Consider a solution obtained by saturation with silver sulfate, Ag2SO4.

Notes:
* If silver ions are a little unfamiliar to you, think of sodium ions. The issues here would come out the same whether we used sodium ions or silver ions.
* You may do the parts in any order. I suspect that some will find it best to start with part d. You might even check yourself on one part before going on to do the others.

a. Which of the following "lists" most closely reflects the state of the solute in the solution?

i. Ag+   Ag+   SO42-   SO42-
ii. Ag+   Ag+   Ag+   Ag+   SO42-   SO42-
iii. Ag22+   Ag22+   SO42-   SO42-

b. Which of the following statements is/are correct? Mark all that apply.

i. The silver ion concentration is less than the sulfate ion concentration.
ii. The sulfate ion concentration is twice the silver ion concentration.
iii. The sulfate and silver ion concentrations are equal.
iv. The silver ion concentration is twice the sulfate ion concentration.
v. The silver ion concentration is greater than the sulfate ion concentration.

c. Which of the following statements is/are correct? Mark all that apply.

In these statements, the square brackets, [ ], are used to mean "concentration of, in molarity". For example, [Na+] would be read "concentration of sodium ions (in molarity)". In the Cracolice book, this is formally introduced on page 513; it is also mentioned in the Ch 16-17 handout.

i. [Ag+] < [SO42-]
ii. [SO42-] = 2 [Ag+]
iii. [SO42-] = [Ag+]
iv. [Ag+] = 2 [SO42-]
v. [Ag+] > [SO42-]

You may do parts b and c in any order, as noted earlier. But after doing both as best you can, check this "hint"; move your cursor over the word "hint" at the end of this paragraph, and the hint message will appear, after a momentary delay, in a balloon right near it. Hint.

d. Write a balanced equation showing how this salt dissolves in water, dissociating into ions.

2. Make a similar sketch or list (similar to that in #1 part a) showing the chemical species in solution if you dissolve some methanol in water. Methanol is CH3OH, and is entirely covalent. (It is not acidic or basic.)

3. The reaction
2 NaOH (aq) + H2SO4 (aq) --> Na2SO4 (aq) + 2 H2O (l)
has a ΔH (heat given off) of -114 kJ. Now consider the reaction
Ba(OH)2 (aq) + 2 HCl (aq) --> BaCl2 (aq) + 2 H2O (l).
What ΔH would you expect for this reaction? Explain.

Not sure where to start? How do you focus on what is important? After doing what you can, check this "hint"; move your cursor over the word "hint" at the end of this paragraph, and the hint message will appear, after a momentary delay, in a balloon right near it. Hint.


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Last update: August 14, 2010