Chemistry 121 Ch. 4 In-Class Exercise In this exercise we will discuss solutions. Since water is the most common solvent, we will focus on aqueous solutions. Solutes (the minor components of solutions) can be categorized according to their ability to affect the electrical conductivity of the solution. An aqueous solution of an electrolyte conducts electricity. An aqueous solution of a nonelectrolyte does not conduct electricity. 1. Classify each of the following solutes as electrolytes or nonelectrolytes. sodium chloride, glucose, ethanol, lead nitrate, sucrose, methanol Electrolyte Nonelectrolyte 2. Determine which of the following solutions will conduct electricity. salt water, tap water, distilled water, a saline solution, a sugar solution Conducts Electricity Does not Conduct Electricity 1
When an electrolyte (usually an ionic compound) dissolves in water, the cations and anions are separated. In the solution, the cations and anions are surrounded (solvated) by water molecules. This is denoted by the symbol (aq) which stands for aqueous. Example: sodium sulfate is an electrolyte. Na2SO4(s) ---> 2 Na + (aq) + SO4 2- (aq) 3. Write a balanced equation for the solvation reaction of a. sodium chloride b. glucose (C6H12O6) c. ethanol (C2H5OH) d. lead(ii) nitrate e. sucrose (C12H22O12) f. methanol (CH3OH) 4. Draw a picture of the ions in a crystal (solid) of sodium sulfate. Make sure that the ions are of the appropriate size and are present in the appropriate ratio. 2
5. Draw a picture of a solution of sodium sulfate. Show the both ions and the water molecules. Make sure that the ions and molecules are of the appropriate size and are present in the appropriate ratio. The concentration of a solute in a solution is a measure of the amount of solute in a given volume of solution. The concentration can be expressed in many ways; in this course, we will use molarity as the unit of concentration in solutions. 6. When one mole of Na2SO4 is dissolved in water, a. mol of sodium ions are found in the solution. b. mol of sulfate ions are found in the solution. 7. When 10.0 g of Na2SO4 are dissolved in water, a. mol of sodium sulfate are found in the solution. b. mol of sulfate ions are found in the solution. c. mol of sodium ions are found in the solution. 3
The Molarity of an Electrolyte Dissolved in Water 8. When 10.0 g of Na2SO4 are dissolved in water, a. What is the molarity of sodium sulfate in the solution? b. What is the molarity of sulfate ions in the solution? c. What is the molarity of sodium ions in the solution? 9. When 10.0 g of glucose (C6 H12O6) are dissolved in water, how many moles of glucose are found in the solution? 4
A Nonelectrolyte Dissolved in Water 10. When 10.0 g of glucose (C6 H12O6) are dissolved in water, what is the molarity of glucose in the solution? 11. Which solution has the higher concentration of sodium ions, 0.50 M sodium chloride or 0.30 M sodium sulfate? Show work. 12. Which solution has the higher concentration of sodium ions, 50.0 g of sodium chloride in 500 ml of solution or 59.0 g of sodium sulfate in 500 ml of solution? Show work. 5
13. Determine the aluminum ion and chloride ion concentrations in 250 ml of 0.125 M AlCl3. 14. Determine the chromium ion and sulfate ion concentrations in a 300 ml solution that contains 5.00 g of chromium(iii) sulfate. 15. Determine the mass of sodium in 10.5 L of a 0.209 M solution of sodium phosphate. 16. Which of the following solutions has the highest concentration of chloride ions? a) 10.0 g of sodium chloride dissolved in 50.0 ml of solution. b) 15.0 g of calcium chloride dissolved in 100.0 ml of solution. c) 20.0 g of chromium(iii) chloride dissolved in 125.0 ml of solution. 6
17. A solution is prepared by dissolving 0.5482 g of iron(iii) nitrate in enough water to make 100.0 ml of solution. A 10.00-mL aliquot (portion) of this solution is then diluted to a final volume of 250.0 ml. What is the concentration of Fe 3+ ions in the final solution? Adapted from CHEMISTRY, A Guided Inquiry by Richard S. Moog and John J. Farrell, preliminary edition. 7