CHAPTER 14: SOLUTIONS

Transcription

1 CHAPTER 4: SOLUTIONS Try these Problems, answers in Appendix I:,7,9,,3,5,7,23,43,47,49,5,53,59 solution - uniform mixture of two or more substances. A solution is composed of a solute dissolved in a solvent. solute - substance present in lesser amount. solvent - substance present in greatest amount. Water is the most common solvent. Physical states of solute and solvent can be solid, liquid or gas: CO 2 gas dissolved in liquid soda, gin and tonic (2 liquids), Brass is Cu & Zn (2 solids), salt water, air (N 2 & O 2 gases) 4. GASES IN SOLUTION Factors that affect solubility of gases in liquids: ) Temperature: Solubility of a gas in a liquid decreases as T increases. Gas molecules are moving faster so they find and escape from the surface of the liquid more quickly. What happens if you open a can of soda that has been sitting outside for a few hours on a hot Summer day? 2) Pressure: Solubility of a gas in a liquid increases as P increases. Henry's Law: Solubility of gas is proportional to partial P of gas above liquid. Higher pressure keeps the gas molecules from escaping by pushing down on them. Why does a can or a 2-L bottle of soda hiss when it is first opened? Factors that affect solubility of solids in liquids: ) Temperature: Solubility of a solid in a liquid increases as T increases. Molecules move faster and the solvent is more likely to pull apart the ions of an ionic solid. The solid also dissolves faster at higher temperatures. The solubility of a solid in a liquid is not affected by pressure. 4.2 LIQUIDS IN SOLUTION and 4.3 SOLIDS IN SOLUTION Like dissolves like rule Polar solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents Nonpolar and polar substances don t mix or dissolve in one another. Ionic solids usually dissolve in polar solvents check solubility rules on your periodic table to see if the solid dissolves in water. miscible: two liquids mix immiscible: two liquids don t mix soluble: solid will dissolve in liquid insoluble: solid won t dissolve in liquid Corwin Chapter 4: Solutions of 5

2 polar solvent nonpolar solvent polar liquid miscible immiscible nonpolar liquid immiscible miscible polar solid soluble insoluble nonpolar solid insoluble soluble ionic solid Check Solubility Rules! insoluble 4.4 THE DISSOLVING PROCESS As a solute crystal is dropped into a solution, the solvent molecules begin to attack and pull apart the solute molecules solvent molecules surround the solute molecules, forming a solvent cage This is a cool animation that shows how a salt dissolves in water: MASS PERCENT CONCENTRATION concentrated solution - a solution containing a relatively large amount of solute dilute solution - a solution containing a relatively small amount of solute. The concentration of a solution may be expressed as a mass/mass %: Mass Percent g solute g solution 00% g solute gsolute gsolvent 00% Note that the mass of solvent = mass of solution mass solute Corwin Chapter 4: Solutions 2 of 5

3 4.9 MOLAR CONCENTRATION = MOLARITY (M) Molarity M moles solute Liters of solution Units : M mol Liter Practice Problems Ex. : Indicate whether the following are soluble / insoluble in or miscible / immiscible with water: vegetable oil: NaCl: C 5 H 2 : AgI: HBr (l): grease (s): Br 2 (l): Mg(OH) 2 : Ex. 2 Circle all of the following that would be soluble in or miscible with vegetable oil: I 2 (s) KCl P 4 (s) water HBr (l) ) A solution is prepared by dissolving 2.3 g of Na 2 SO 4 in 7.6 g of water. a) The solute is, and the solvent is. b) What is the mass percent for this solution? Corwin Chapter 4: Solutions 3 of 5

4 2) If a normal IV glucose solution is 5.00 % glucose, what is the mass of solution that contains 5.0 g of glucose? 3) What mass of solute is required to prepare 50.0 g of a 2.50% KCl solution? 4) What mass of water is required to dissolve 5.00 g of NaOH to prepare a 0.0% NaOH solution? 5) Find the molarity of a solution prepared by dissolving moles of NaOH in 00.0 ml of solution: 6) Find the molarity of a solution prepared by dissolving 30.6 g of NaOH in 350 ml of solution. 7) How many moles of AgNO 3 are present in 55.7 ml of a M AgNO 3 solution. 8) Calculate the mass of NaCl needed to prepare 75 ml of a.50 M NaCl solution. Ex. : Answers vegetable oil: immiscible NaCl: soluble C 6 H 2 (l): immiscible Br 2 (l): immiscible AgI: insoluble HBr (l): miscible grease (s): insoluble Mg(NO 3 ) 2 : soluble Ex. 2 I 2 (s) KCl P 4 (s) grease (s) HBr (l) Corwin Chapter 4: Solutions 4 of 5

5 ) The solute is Na 2 SO 4, and the solvent is H 2 O. mass % = 2.3 g x 00% = 2.3g 7.6 g 2.3 g 83.9 g x 00% = 4.7 % 2) 3) 4) g solution mass solution 5.0 g glucose = 3.00x0 2 g solution 5.00 g glucose 2.50 g KCl mass solute 50.0g solution = 3.75 g KCl 00 g solution g water mass water 5.00 g NaOH = 45.0 g water 0.00 g NaOH 5) Find the molarity of a solution prepared by dissolving moles of NaOH in 00.0 ml of solution: 00 ml 000 ml = 0.00 L M = mol solute L solution = 0.250mol NaOH = 2.50 M NaOH 0.00L 6) Find the molarity of a solution prepared by dissolving 30.6 g of NaOH in 350 ml of solution g NaOH mol NaOH 40.0g NaOH = mol NaOH 350 ml = L 000mL M = mol solute L solution = mol NaOH = 2.9 M NaOH L 7) How many moles of AgNO 3 are present in 55.7 ml of a M AgNO 3 solution ml 000 ml moles AgNO3 = 0.04 moles AgNO 3 8) Calculate the mass of NaCl needed to prepare 75 ml of a.50 M NaCl solution. 75 ml 000 ml.50 mol 58.44g NaCl mol NaCl = 5.3 g NaCl Corwin Chapter 4: Solutions 5 of 5