9.6: Solutions (Exercises)

Additional Exercises

1. Calcium nitrate reacts with sodium carbonate to precipitate solid calcium carbonate:

   \[Ca(NO_3)_{2(aq)} + Na_2CO_{3(aq)} \rightarrow CaCO_{3(s)} + NaNO_{3(aq)}\]

   1. Balance the chemical equation.
   2. How many grams of Na₂CO₃ are needed to react with 50.0 mL of 0.450 M Ca(NO₃)₂?
   3. Assuming that the Na₂CO₃ has a negligible effect on the volume of the solution, find the osmolarity of the NaNO₃ solution remaining after the CaCO₃ precipitates from solution.

2. The compound HCl reacts with sodium carbonate to generate carbon dioxide gas:

   \[HCl_{(aq)} + Na_2CO_{3(aq)} \rightarrow H_2O_{(ℓ)} + CO_{2(g)} + NaCl_{(aq)}\]

   1. Balance the chemical equation.
   2. How many grams of Na₂CO₃ are needed to react with 250.0 mL of 0.755 M HCl?
   3. Assuming that the Na₂CO₃ has a negligible effect on the volume of the solution, find the osmolarity of the NaCl solution remaining after the reaction is complete.

3. Estimate the freezing point of concentrated aqueous HCl, which is usually sold as a 12 M solution. Assume complete ionization into H⁺ and Cl⁻ ions.

4. Estimate the boiling point of concentrated aqueous H₂SO₄, which is usually sold as an 18 M solution. Assume complete ionization into H⁺ and HSO₄⁻ ions.

5. Seawater can be approximated by a 3.0% m/m solution of NaCl in water. Determine the molarity and osmolarity of seawater. Assume a density of 1.0 g/mL.

6. Human blood can be approximated by a 0.90% m/m solution of NaCl in water. Determine the molarity and osmolarity of blood. Assume a density of 1.0 g/mL.

7. How much water must be added to 25.0 mL of a 1.00 M NaCl solution to make a resulting solution that has a concentration of 0.250 M?

8. Sports drinks like Gatorade are advertised as capable of resupplying the body with electrolytes lost by vigorous exercise. Find a label from a sports drink container and identify the electrolytes it contains. You should be able to identify several simple ionic compounds in the ingredients list.

9. Occasionally we hear a sensational news story about people stranded in a lifeboat on the ocean who had to drink their own urine to survive. While distasteful, this act was probably necessary for survival. Why not simply drink the ocean water? (Hint: See Exercise 5 and Exercise 6 above. What would happen if the two solutions in these exercises were on opposite sides of a semipermeable membrane, as we would find in our cell walls?)

Answers

1.  

   1. Ca(NO₃)₂(aq) + Na₂CO₃(aq) → CaCO₃(s) + 2NaNO₃(aq)
   2. 2.39 g
   3. 1.80 osmol

2.

 

a. 2HCl (aq) + Na₂CO₃(aq) → H₂O(ℓ) + CO₂(g) + 2NaCl (aq)

 

b. 10.0 g

 

c. 1.51 M

3. −45.6°C

4. 118°C

5. 0.513 M; 1.026 osmol

6. molarity = 0.15 M; osmolarity = 0.31 M

7. 75.0 mL

8. magnesium chloride, calcium chloride (answers may vary)

9. The osmotic pressure of seawater is too high. Drinking seawater would cause water to go from inside our cells into the more concentrated seawater, ultimately killing the cells.