Solutions of Electrolytes and Nonelectrolytes SAMPLE PROBLEM 8.1 Indicate whether solutions of each of the following contain only ions, only molecules, or mostly molecules and a few ions: a. Na 2 SO 4, a strong electrolyte b. CH 3 OH, a nonelectrolyte a. A solution of Na 2 SO 4 contains only the ions Na + and SO 4 2. b. A nonelectrolyte such as CH 3 OH dissolves only as molecules. Boric acid, H 3 BO 3, is a weak electrolyte. Would you expect a boric acid solution to contain only ions, only molecules, or mostly molecules and a few ions?
SAMPLE PROBLEM 8.2 Electrolyte Concentration In body fluids, concentrations of electrolytes are often expressed as milliequivalents (meq) per liter. A typical concentration for Ca 2+ in the blood is 8.8 meq/l. a. How many moles of calcium ion are in 0.50 L of blood? b. If chloride ion is the only other ion present, what is its concentration in meq/l? a. Using the volume and the electrolyte concentration (in meq/l), we can find the number of equivalents in 0.50 L of blood: We can then convert equivalents to moles (for Ca 2+ there are 2 Eq per mole): b. If the concentration of Ca 2+ is 8.8 meq/l, then the concentration of Cl must be 8.8 meq/l to balance the charge. A Ringer s solution for intravenous fluid replacement contains 155 meq Cl per liter of solution. If a patient receives 1250 ml of Ringer s solution, how many moles of chloride were given?
Saturated Solutions SAMPLE PROBLEM 8.3 At 20 C, the solubility of KCl is 34 g/100 g of water. In the laboratory, a student mixes 75 g of KCl with 200. g of water at a temperature of 20 C. a. How much of the KCl can dissolve? b. Is the solution saturated or unsaturated? c. What is the mass of any solid KCl in the bottom of the container? a. KCl has a solubility of 34 g of KCl in 100 g of water. Using solubility as a conversion factor, the maximum amount of KCl that can dissolve in 200. g of water is calculated as follows: b. Because 75 g of KCl exceeds the amount that can dissolve in 200. g of water, the KCl solution is saturated. c. If we add 75 g of KCl to 200. g of water and only 68 g of KCl can dissolve, there is 7 g of solid (undissolved) KCl on the bottom of the container. At 50 C, the solubility of NaNO 3 is 110 g/100 g of water. How many grams of NaNO 3 are needed to make a saturated NaNO 3 solution with 50. g of water at 50 C?
Factors Affecting Solubility SAMPLE PROBLEM 8.4 Indicate whether the solubility of the solute will increase or decrease in each of the following situations: a. dissolving sugar using 80 C water instead of 25 C water b. effect on the dissolved O 2 in a lake as it warms a. An increase in the temperature increases the solubility of the sugar. b. An increase in the temperature decreases the solubility of O 2 gas. At 10 C, the solubility of KNO 3 is 30 g/100 g H 2 O. Would you expect the solubility of KNO 3 to be higher or lower at 40 C? Explain.
SAMPLE PROBLEM 8.5 Formation of an Insoluble Salt Solutions of BaCl 2 and K 2 SO 4 are mixed and a white solid forms. a. Write the net ionic equation. b. What is the white solid that forms? a. STEP 1 STEP 2 BaSO 4 (s) is insoluble. STEP 3 STEP 4 b. BaSO 4 is the white solid. Predict whether a solid might form in each of the following mixtures of solutions. If so, write the net ionic equation for the reaction. a. NH 4 Cl(aq) + Ca(NO 3 ) 2 (aq) b. Pb(NO 3 ) 2 (aq) + KCl(aq)
Calculating Mass Percent SAMPLE PROBLEM 8.6 What is the mass percent of a solution prepared by dissolving 30.0 g of NaOH in 120.0 g of H 2 O? STEP 1 Given 30.0 g of NaOH and 120.0 g of H 2 O Need mass percent (m/m) of NaOH STEP 2 Plan The mass percent is calculated by using the mass in grams of the solute and solution in the definition of mass percent. STEP 3 Equalities/Conversion Factors STEP 4 Set Up Problem The mass of the solute and the solution are obtained from the data:
Calculating Mass Percent (Continued) SAMPLE PROBLEM 8.6 What is the mass percent (m/m) of NaCl in a solution made by dissolving 2.0 g of NaCl in 56.0 g of H 2 O?
Calculating Percent Concentration SAMPLE PROBLEM 8.7 A student prepared a solution by dissolving 5.0 g of KI in enough water to give a final volume of 250 ml. What is the mass/volume percent (m/v) of the KI solution? STEP 1 Given 5.0 g of KI and 250 ml of solution Need mass/volume percent (m/v) of KI STEP 2 Plan The mass/volume percent is calculated by using the mass in grams of the solute and the volume in ml of the solution in the definition of mass/volume percent. STEP 3 Equalities/Conversion Factors Write the mass/volume percent expression. STEP 4 Set Up Problem Substitute solute and solution quantities into the mass/volume percent expression. What is the mass/volume percent (m/v) of Br 2 in a solution prepared by dissolving 12 g of bromine (Br 2 ) in enough carbon tetrachloride to make 250 ml of solution?
Using Mass/Volume Percent to Find Mass of Solute A topical antibiotic is 1.0% (m/v) Clindamycin. How many grams of Clindamycin are in 60. ml of the 1.0% (m /v) solution? STEP 1 Given 1.0% (m/v) Clindamycin Need grams of Clindamycin STEP 2 Plan STEP 3 Equalities/Conversion Factors The percent (m/v) indicates the grams of a solute in every 100 ml of a solution. The 1.0% (m/v) can be written as two conversion factors: SAMPLE PROBLEM 8.8 STEP 4 Set Up Problem The volume of the solution is converted to mass of solute using the conversion factor: Calculate the grams of KCl in 225 g of an 8.00% (m/m) KCl solution.
SAMPLE PROBLEM 8.9 Calculating Molarity What is the molarity (M) of 60.0 g of NaOH in 0.250 L of solution? STEP 1 Given 60.0 g of NaOH in 0.250 L of solution Need molarity (moles/l) STEP 2 Plan The calculation of molarity requires the moles of NaOH and the volume of the solution in liters. STEP 3 Equalities/Conversion Factors
Calculating Molarity (Continued) What is the molarity (M) of 60.0 g of NaOH in 0.250 L of solution? STEP 4 Set Up Problem SAMPLE PROBLEM 8.9 The molarity is calculated by dividing the moles of NaOH by the volume in liters. What is the molarity of a solution that contains 75.0 g of KNO 3 dissolved in 0.350 L of solution?
Using Molarity to Find Volume How many liters of a 2.00 M NaCl solution are needed to provide 67.3 g of NaCl? STEP 1 Given 67.3 g of NaCl from a 2.00 M NaCl solution SAMPLE PROBLEM 8.10 Need liters of NaCl solution STEP 2 Plan The volume of the NaCl solution is calculated using the moles of NaCl and molarity of the NaCl solution: STEP 3 Equalities/Conversion Factors The molarity of any solution can be written as two conversion factors:
Using Molarity to Find Volume (Continued) How many liters of a 2.00 M NaCl solution are needed to provide 67.3 g of NaCl? STEP 4 Set Up Problem SAMPLE PROBLEM 8.10 How many moles of HCl are present in 750 ml of a 6.0 M HCl solution?
Molarity of a Diluted Solution SAMPLE PROBLEM 8.11 What is the molarity of a solution prepared when 75.0 ml of a 4.00 M KCl solution is diluted to a volume of 0.500 L? STEP 1 Give Data in a Table We make a table of the molar concentrations and volumes of the initial and diluted solutions. For the calculation, units must be the same. STEP 2 Plan The unknown molarity can be calculated by solving the dilution expression for M 2 : STEP 3 Set Up Problem The values from the table are placed into the dilution expression: You need to prepare 600. ml of 2.00 M NaOH solution from a 10.0 M NaOH solution. What volume of the 10.0 M NaOH solution do you use?
SAMPLE PROBLEM 8.12 Volume of a Solution in a Reaction Zinc reacts with HCl to produce ZnCl 2 and hydrogen gas H 2 : How many liters of a 1.50 M HCl solution completely react with 5.32 g of zinc? STEP 1 Given 5.32 g of Zn and a 1.50 M HCl solution Need liters of HCl solution STEP 2 Plan We start the problem with the grams of Zn given and use its molar mass to calculate moles. Then we can use the mole mole factor from the equation and the molarity of the HCl as conversion factors:
Volume of a Solution in a Reaction (Continued) Zinc reacts with HCl to produce ZnCl 2 and hydrogen gas H 2 : SAMPLE PROBLEM 8.12 How many liters of a 1.50 M HCl solution completely react with 5.32 g of zinc? STEP 3 Equalities/Conversion Factors
Volume of a Solution in a Reaction (Continued) Zinc reacts with HCl to produce ZnCl 2 and hydrogen gas H 2 : SAMPLE PROBLEM 8.12 How many liters of a 1.50 M HCl solution completely react with 5.32 g of zinc? STEP 4 Set Up Problem We can write the problem setup as seen in our plan: Using the reaction in Sample Problem 8.12, how many grams of zinc can react with 225 ml of 0.200 M HCl solution?
Isotonic, Hypotonic, and Hypertonic Solutions SAMPLE PROBLEM 8.13 Describe each of the following solutions as isotonic, hypotonic, or hypertonic. Indicate whether a red blood cell placed in each solution will undergo hemolysis, crenation, or no change. a. a 5.0% (m/v) glucose solution b. a 0.2% (m/v) NaCl solution a. A 5.0% (m/v) glucose solution is isotonic. A red blood cell will not undergo any change. b. A 0.2% (m/v) NaCl solution is hypotonic. A red blood cell will undergo hemolysis. What is the effect of a 10% (m/v) glucose solution on a red blood cell?