Honors Unit 10 Notes Solutions

Transcription

1 Name: Honors Unit 10 Notes Solutions [Chapter 10] Objectives: 1. Students will be able to calculate solution concentration using molarity, molality, and mass percent. 2. Students will be able to interpret solubility curves and to predict the effect of temperature and pressure on the solubility of solids and gases. 3. Students will be able to calculate freezing points and boiling points of solutions based on the theory and equations describing colligative properties of solutions both for electrolytes and nonelectrolytes. Vocabulary Solution o Every solution contains a solute and a solvent. Solute Solvent o The solute gets dissolved in the solvent! Colloids o Colloids may look clear when dilute enough. o Examples: Tyndall effect o Causes the beam of light to become visible o Why you can see rays from the sun sometimes!

2 2 Suspension a mixture from which the particles settle out slowly upon standing o o Suspensions can be! o Examples: Concentration Concentration of a solution = the amount of in a given quantity of o A solution contains a relatively amount of solute vs. the solvent o A solution contains a relatively amount of solute vs. the solvent Concentrated and dilute aren t very quantitative though! Quantitative Concentration Values: 1. Molarity 2. Mass Percent 3. Molality Molarity (Review from Unit 4) Molarity (M) moles of solute liters of solution Example #1: What is the molarity of a solution made by dissolving 12.5 g of oxalic acid (H2C2O4) in 456 ml of solution?

3 Example #2: How many grams of sodium carbonate (Na2CO3) are needed to prepare L of an aqueous M solution? 3 Mass Percent mass of solute percent by mass *100 mass of solution Example #3: What is the percent by mass of the solute in a solution made by adding 1.20 g of methyl alcohol (CH3OH) to 16.8 g of water? Molality (m) Why use molality if you can use molarity instead? o Molarity varies with temperature due to the exapansion or contraction in the volume of the solution o Molality does not change with temperature since it s based on the mass of solvent added (instead of a volume). molesof solute Molality ( m ) kilogramsof solvent

4 Example #4: A solution contains 15.5 g of a compound, NH2CONH2, in 74.3 g of water. Calculate the molality of the solution. 4 Dilution of Solutions Dilutions are used to the concentration (or molarity) of a soln. Example #5: How would you prepare L of M Na2CO3 starting with 1.33 M solution? Example #6: Copper sulfate is widely used as a dietary supplement for animal feed. A lab technician prepares a stock solution of CuSO4 by adding g of CuSO4 to enough water to make ml of solution. An experiment requires a M solution of CuSO4. (a) What is the molarity of the CuSO4 stock solution prepared by the technician? (b) How would you prepare L of a M solution from the stock solution?

5 Solubility 5 Vocabulary two liquids that are soluble in each other (mix in all proportions) liquids that are insoluble in each other (do not mix) contains the maximum amount of dissolved solute contains less than the maximum amount of dissolved solute contains more solute than can theoretically be dissolved at a given temperature o A supersaturated solution is created when a warm, saturated solution is allowed to cool without the precipitation of the excess solute. o Testing for Saturation: Add crystal of a solid and watch for crystallization. the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature and pressure to produce a saturated soln. 1. Units: 2. Example: At 20 C, NaNO3 has a solubility of 74 g/100 grams of water. Factors which influence solubility: Like Dissolve Like The concentration of the solute in a saturated solution (the solubility) can be shown on a graph or curve called a solubility curve.

6 Solubility Curves Example #7: What mass of solute will dissolve in 100 g of water at the following temperatures? 6 a) KNO3 at 70 C b) NaCl at 100 C Example #8: At 20 C, if 100 grams of NaNO3 are dissolved in 100 grams of water, is this solution saturated, unsaturated, or supersaturated? Example #9: Which term - saturated, unsaturated, or supersaturated - best describes a solution that contains 70 g of NaNO3 per 50 g H2O at 30 C? Example #10: Which term - saturated, unsaturated, or supersaturated - best describes a solution that contains 70 g of dissolved KCl per 200 g H2O at 80 C? Example #11: Determine the molality of a saturated NaCl solution at 25 C.

7 Solubility of Gases 7 A. Effect of temperature Most gases become in liquids as the temperature. o Example: B. Effect of pressure Pressure has a major effect on the solubility of a gas in a liquid, but little effect on other systems. Henry s Law at low to moderate pressure the concentration of a gas with the pressure o Colligative Properties When adding a solute to a solvent, the properties of the solvent are modified: Vapor pressure Melting point Boiling point These changes are called Colligative means. o Depends only on the of dissolved particles, not on the of the dissolved particles. o Examples of colligative properties:

8 Boiling Point Elevation Boiling occurs when equals 8 The boiling point of a is than the boiling point of the. o Dissolving substances increases ( ) the boiling point of a solvent. Example: Formula for Boiling Point Elevation: kb = i= Van t Hoff factor= # of ions in solution (1 for all nonelectrolytes) m = ΔTb = Freezing Point Depression The freezing point of a is lower than the freezing point of the. o Dissolving substances lowers ( ) the freezing point of a solvent. o Example:

9 ***Example: Antifreeze (ethylene glycol in water) prevents car s radiator from boiling over in the summer (raises boiling point of water) & prevents car s radiator from freezing in the winter (lowers freezing point of water) 9 Formula for Freezing Point Depression: kf = i= Van t Hoff factor= # of ions in solution (1 for all nonelectrolytes) m = ΔTf = Electrolytes Soluble ionic compounds. When they dissolve in solution, they dissociate completely into ions and conduct Example: NaCl (aq) Covalent (molecular) molecules in aqueous solution: o Covalent particles don t dissociate in solution, so the # of molecules = # of particles ***The greater the product of molality and number of ions, the the boiling point elevation or freezing point depression!

10 Example #12: Calculate the boiling point of solution that contains 50.0 g of glucose, C6H12O6, in 400 g of water. The molal boiling point constant of water is 0.52 o C/m. 10 Example #13: Rank the following aqueous solutions in order of lowest to highest melting point: (1) m C6H12O6 (3) m HCl (2) m MgCl2 (4) m Al2(SO4)3