Student Worksheet for Liquids, Solids, and Solutions

Transcription

1 Student Worksheet for Liquids, Solids, and Solutions Attempt to work the following practice problems after working through the sample problems in the videos. Answers are given on the last page(s). Relevant Equations Boiling Point Elevation: Tb = i Kbm Freezing Point Depression: Tf = ikfm Vapor Pressure Changes: PA = i XAP A Osmotic Pressure: π = imrt= nrt V * Mole Fraction: Molality: Molarity: Moles A Total Number of Moles kilograms of solvent Liters of Solution Number of Moles = Grams Given Molecular Weight Where, Tb is Boiling Temperature, Tf is Freezing Temperature, i is the number of ions in solution, K is the constant for freezing or melting, m is molality, M is molarity, R is the constant, T is Temperature, XA is the mole fraction, PA is the new vapor pressure, P A is the vapor pressure of pure liquid, π is the osmotic pressure. *Refer to the Ideal Gas Law The R constant is always LAtm/molK 2017 Supercharged Science 1

2 1. Classify each of the following solution types as unsaturated, saturated, or supersaturate: a) All moles of solute have reacted with all moles of solvent. b) There are excess moles of solute, but no excess solvent. c) There are excess moles of solvent, but no excess solute. 2. Ionic solutions are composed of solutes that the atoms are polar/nonpolar (circle one) and found in columns of the periodic table. 3. Explain why polar and nonpolar compounds do not interact. 4. What is the molarity of a solution that has an osmotic pressure of 75.2 atm at 23 C if 2 electrolytes per mole of solute are released in the solution? 5. If a solution has a freezing point that is depressed by 5.2 C after the addition of CaCl2, and the K f is 1.86 C/m, what was the molality of the solution? 2017 Supercharged Science 2

3 6. How many moles of NaHCO3 should be dissolved in 100g of water to decrease its vapor pressure of atm at 23 C to atm? 7. What is the new boiling point of an aqueous solution after the 150g of NaCl have been dissolved in 500 g of H2O? The Kb is C/m. 8. If 500 ml of a 0.2 M glucose solution is allowed to cross a semipermeable membrane, and creates a pressure of 1.3 atm at 273K, what was the total volume of the osmosis chamber? 9. What molality of ether solution would be required for acetic acid to have a C boiling point? The normal boiling point of acetic acid is C. The Kb is 3.07 C/m Supercharged Science 3

4 10. If a 3M ionic solution exerts an osmotic pressure of 72.6 atm at 293 K, how many ions are in the solution. 11. If the dissolving of 200 grams of CaCO3 caused a freezing point depression of 10 C, how much solvent was present in the solution? The Kf is 2.53 C/m. 12. What is the new vapor pressure of a solution that consists of 175 grams of MgCl2 and 500 g of C3H6O? The initial pressure is 11.1 atm. 13. In general terms, explain why the addition of a solute raises the boiling point and decreases the freezing point Supercharged Science 4

5 14. What is the new freezing point of a 2m solution of H2SO4, assuming that the solute disassociates to HSO4 -? The Kf of water is 1.86 C/m. 15. We put antifreeze in our cars to prevent freezing and overheating. If the solution consists of 50% water and 50% propylene glycol (C 3 H 8 O 2 ), what temperature range can your car engine withstand. Assume 100 ml were used. The density of water is 1 g/ml. The density of propylene glycol is 1.04 g/ml Supercharged Science 5

6 1. Classify each of the following solution types as unsaturated, saturated, or supersaturate: a) All moles of solute have reacted with all moles of solvent. Saturated b) There are excess moles of solute, but no excess solvent. Unsaturated c) There are excess moles of solvent, but no excess solute. Super saturated 2. Ionic solutions are composed of solutes that the atoms are polar/nonpolar (circle one) and found in columns _1,2,3,15,16, and 17 of the periodic table. 3. Explain why polar and nonpolar compounds do not interact. Polar molecules are formed from dipole interactions. The dipole moments are created from electronegativity differences between atoms that are attached to each other. Nonpolar molecules do not have a significant electronegativity difference, so while there is a brief disruption of electron-protein locations, it is not significant enough for interactions. Think of the polar molecule as being like a magnet and the nonpolar molecule being like an insulated surface. The two will not interact together. 4. What is the molarity of a solution that has an osmotic pressure of 75.2 atm at 23 C if 2 electrolytes per mole of solute are released in the solution? Π= imrt Solving for M. M= π irt Don t forget to convert to K by adding 273. M= 75.2 ( ) = 1.54M 5. If a solution has a freezing point that is depressed by 5.2 C after the addition of CaCl2, and the Kf is 1.86 C/m, what was the molality of the solution? Tf = ikfm Solving for m. m= ΔTf i Kf = 5.2 (3 1.86) = 0.93m 2017 Supercharged Science 6

7 6. How many moles of NaHCO3 should be dissolved in 100 g of water to decrease its vapor pressure of atm at 23 C to atm? PA = i XAP A Using XA to solve for moles. XA= PA ip A 0 = ( ) = 0.24 Moles of H2O= = 5.6 moles H 2O Moles A XA = Total Number of Moles 0.24 = X 5.6+X X = X 1.34 = 0.76X X= 1.77 moles of NaHCO3 7. What is the new boiling point of an aqueous solution after the 150g of NaCl have been dissolved in 500 g of H2O? The Kb is C/m. You must first find the molality of the solution. Moles of NaCl= m= kilograms of solvent = = 5.17m Tb = i Kbm = 2*0.512*5.17 = 5.3 C = 2.59 moles NaCl We know that water normally boils at 100 C. The new boiling point becomes: New Tb = Initial Tb + Tb = = C 2017 Supercharged Science 7

8 8. If 500mL of a 0.2 M glucose solution is allowed to cross a semipermeable membrane, and creates a pressure of 1.3 atm at 273K, what was the total volume of the osmosis chamber? Π = nrt V Solving for V and n. Molarity = Liters of Solution Moles of solute= Molarity * Liters of Solution V = nrt π = ( ) 1.3 = 1.73 L = 0.2 * 0.5 = 0.1 moles of glucose 9. What molality of ether solution would be required for acetic acid to have a C boiling point? The normal boiling point of acetic acid is C. The Kb is 3.07 kg/ C. Tb = i Kbm Solving for m. m= ΔTb ikb = = 0.46m 10. If a 3M ionic solution exerts an osmotic pressure of 72.6 atm at 293 K, how many ions are in the solution. Π= imrt Solving for i. i= = π MRT 72.6 ( ) = 1 electrolyte 2017 Supercharged Science 8

9 11. If the dissolving of 200 grams of CaCO3 caused a freezing point depression of 10 C, how much solvent was present in the solution? The Kf is 2.53 kg/ C. Tf = i Kfm Solving for m. m= ΔTf ikf = = 1.98m Before using the molality formula, you must first convert the grams of CaCO3 to moles. Moles CaCO3 = Grams Given Molecular Weight = 200 = 2 moles CaCO3 100 m= kilograms of solvent Solving for kilograms of solvent kilograms of solvent = moles of solute = m = 1.01 kg solvent 12. What is the new vapor pressure of a solution that consists of 175 grams of MgCl2 and 500 g of C3H6O? The initial pressure is 11.1 atm. PA = i XAP A You must first solve for XA by converting both compounds to moles. Moles of MgCl2 = Moles of C3H6O = XA= = Moles A Total Number of Moles 1.84 ( ) = 0.18 = 1.84 moles = 8.62 moles Now use the original formula to solve for PA PA = 3*0.18* 11.1 = 5.99 atm 2017 Supercharged Science 9

10 13. In general terms, explain why the addition of a solute raises the boiling point and decreases the freezing point. In respect to boiling point, it is easiest to think of the solute as acting as a shield from the atmosphere. They hover over the molecules of solvent, which prevents them from being able to escape/vaporize. The same concept can be used for freezing, but in a different way. When a substance freezes, the individual molecules create a lattice with each other. As the solute is floating around in the solvent, it blocks the solvent molecules from interacting with each other, which prevents the lattice from forming. 14. What is the new freezing point of a 2m solution of H2SO4, assuming that the solute disassociates to HSO4 -? The Kf of water is 1.86 C/m. Tf = i Kfm Solving for Tf = 2* 1.86*2 = 7.44 C New Tf = Initial Tf - Tf = = C 15. We put antifreeze in our cars to prevent freezing and overheating. If the solution consists of 50% water and 50% propylene glycol (C3H8O2), what temperature range can your car engine withstand. Assume 100 ml were used. The density of water is 1 g/ml. The density of propylene glycol is 1.04 g/ml. The Kf of H2O is 1.86 C/m. The Kb of H2O is C/m. The molality must first be calculated by finding out the number of grams of each, and then converting the grams of propylene glycol to moles. This can be done by using the density values. 50 ml H2O = 50 g H2O = 0.05 kg H2O 50 ml C3H8O2= 52 grams of propylene glycol Moles of C3H8O2 = = 0.68 m= kilograms of solvent = = m Tf = i Kfm = 2 * 1.86* = C 2017 Supercharged Science 10

11 Tb = i Kbm = 2 * * = 14 C Temperature range that your car s engine can withstand is C to 114 C Supercharged Science 11