26.07.2021 Views

General Chemistry Principles, Patterns, and Applications, 2011

General Chemistry Principles, Patterns, and Applications, 2011

General Chemistry Principles, Patterns, and Applications, 2011

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

When PbCl 2 is dissolved in hot water, its presence can be confirmed by its reaction with CrO 2− 4 , with which it<br />

forms a yellow precipitate:<br />

Pb 2+ (aq) + CrO 2− 4 (aq) → PbCrO 4 (s)<br />

The precipitate is used as a rust inhibitor <strong>and</strong> in pigments.<br />

a. What type of reaction does each equation represent?<br />

b. If 100 mL of a Pb 2+ solution produce 1.65 g of lead chromate, what was the concentration of the lead<br />

solution?<br />

c. What volume of a potassium chromate solution containing 0.503 g of solute per 250.0 mL is needed for this<br />

reaction?<br />

d. If all the PbCrO 4 originated from PbCl 2 , what volume of a 1.463 M NaCl solution was needed for the initial<br />

reaction?<br />

e. Why is there environmental concern over the use of PbCrO 4 ?<br />

3. ♦ Reactions that affect buried marble artifacts present a problem for archaeological chemists. Groundwater<br />

dissolves atmospheric carbon dioxide to produce an aqueous solution of carbonic acid:<br />

CO 2 (g) + H 2 O(l) → H 2 CO 3 (aq)<br />

This weakly acidic carbonic acid solution dissolves marble, converting it to soluble calcium bicarbonate:<br />

CaCO 3 (s) + H 2 CO 3 (aq) → Ca(HCO 3 ) 2 (aq)<br />

Evaporation of water causes carbon dioxide to be driven off, resulting in the precipitation of calcium<br />

carbonate:<br />

Ca(HCO 3 ) 2 (aq) → CaCO 3 (s) + H 2 O(l) + CO 2 (g)<br />

The reprecipitated calcium carbonate forms a hard scale, or incrustation, on the surface of the object.<br />

f. If 8.5 g of calcium carbonate were obtained by evaporating 250 mL of a solution of calcium bicarbonate<br />

followed by drying, what was the molarity of the initial calcium bicarbonate solution, assuming complete<br />

reaction?<br />

g. If the overall reaction sequence was 75% efficient, how many grams of carbonic acid were initially dissolved<br />

in the 250 mL to produce the calcium bicarbonate?<br />

4. How many Maalox tablets are needed to neutralize 5.00 mL of 0.100 M HCl stomach acid if each tablet<br />

contains 200 mg Mg(OH) 2 + 200 mg Al(OH) 3 ? Each Rolaids tablet contains 412 mg CaCO 3 + 80.0 mg Mg(OH) 2 .<br />

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

Saylor.org<br />

408

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!