CHAPTER 13 SOLUTIONS Problems 1 8 11 15 20 30 37 88 107 110 131 132 13 2 SOLUTIONS HOMOGENEOUS MIXTURES solution homogeneous mixture of substances present as atoms ions and or molecules solute component present in smaller amount solvent component present in greater amount Example Identify the solute and solvent in each of the following a saline solution NaCl water solute solvent b carbonated water water CO2 gas solute solvent Note Unless otherwise stated the solvent for most solutions considered in this class will almost always be water A concentrated solution has a large quantity of solute present for a given amount of solution A dilute solution has a small quantity of solute present for a given amount of solution 13 4 SOLUTIONS OF GASES IN WATER HOW SODA POP GETS ITS FIZZ TEMPERATURE EFFECTS and the SOLUBILITY OF GASES in solution Example What happens if soda is left outside in the summer At higher temperatures gas molecules move than molecules at lower temperatures faster or slower These gas molecules encounter the surface between liquid and air more quickly They escape from the liquid more quickly Fewer gas molecules in the liquid Thus as temperature increases the solubility of a gas in a liquid CHEM 139 Tro Chapter 13 F2012 increases decreases page 1 of 16 PRESSURE EFFECTS and the SOLUBILITY OF GASES in solution Henry s Law The solubility of a gas is proportional to partial pressure of the gas above liquid The greater the partial pressure of a gas above a liquid the greater the solubility of the gas in the liquid The greater number of gas molecules above a liquid More of the molecules will go into the liquid The higher the solubility of the gas in the liquid lower gas pressure higher gas pressure Ex 1 Why does a can or a 2 L bottle of soda hiss when it is first opened At the molecular level the bubbles that form in carbonated water or soda are CO2 molecules coming out of solution as the partial pressure of CO2 gas above the liquid decreases CHEM 139 Tro Chapter 13 F2012 page 2 of 16 13 3 SOLUTIONS OF SOLIDS DISSOLVED IN WATER HOW TO MAKE ROCK CANDY THE FORMATION OF A SOLUTION As a solute crystal is dropped into water the water solvent molecules pull apart the solute Water molecules surround the solute e g NaCl forming a solvent cage The Na and Cl ions are now hydrated surrounded by water molecules The solute is now dissolved in the solvent and cannot be seen because the ions are far apart like the particles in a gas The NaCl crystals above dissolve in water and exist as hydrated Na and Cl ions In a chemical equation NaCl is shown as NaCl aq meaning it exists as Na and Cl ions The RATE OF DISSOLVING can be increased by 1 heating the solution solvent molecules move faster break up the solute more frequently break apart solute more quickly 2 stirring the solution solvent encounters solute molecules more often solvent breaks apart solute more quickly 3 grinding the solute into smaller particles increases the surface area of the solute more solute surface for solvent to break it up solvent breaks apart solute more quickly CHEM 139 Tro Chapter 13 F2012 page 3 of 16 Like dissolves like rule miscible two liquids mix soluble a solid will dissolve in a liquid immiscible two liquid don t mix insoluble a solid won t dissolve in a liquid polar liquid solvent nonpolar liquid solvent polar liquid solvent miscible immiscible nonpolar liquid solvent immiscible miscible polar solid solute soluble insoluble nonpolar solid solute insoluble soluble ionic compound Check Solubility Rules insoluble Ex 1 Indicate whether the following is soluble insoluble or miscible immiscible in the substances indicated a NaCl is in ethanol C2H5OH b NaCl is in olive oil Ex 1 True or False a Stirring will increase the rate of dissolving of lithium chromate in water Explain why b Sugar will dissolve faster in hot tea than in cold tea Explain why c A sample of water will mix faster in hot olive oil than cold olive oil Explain why CHEM 139 Tro Chapter 13 F2012 page 4 of 16 SOLUBILITY AND SATURATION Unsaturated Saturated and Supersaturated Solutions If a solid is soluble in a solvent more solid dissolves in the solvent at higher temperatures unsaturated saturated contains less than the maximum amount of solute that a solvent can hold at a specific temperature contains the maximum amount of solute that a solvent can hold at a specific temperature supersaturated contains more than the maximum amount of solute that a solvent should be able to hold at specific temperature A supersaturated NaC2H3O2 solution recrystallizing after addition of more solute Preparing a supersaturated solution How can a solution hold more solute than it should be able to hold If a given amount of solute is dissolved in a solvent at a higher temperature and the solution is allowed to cool without being disturbed the solute will remain in solution But the solution is unstable and the solute will come out of solution i e recrystallize if the solution is disturbed e g by adding more solute scratching the glass etc For some substances the recrystallization process is exothermic The solution releases heat when it recrystallizes Hot packs used to warm hands and feet in winter For some substances the recrystallization process is endothermic The solution absorbs heat when it recrystallizes and becomes colder Cold packs used for sports injuries CHEM 139 Tro Chapter 13 F2012 page 5 of 16 Ex 1 Check all of the statements below that are true a Both stirring and heating will increase the rate of dissolving NaCl in water b A cup of hot tea can be made sweeter than a cup of cold tea c A cup of cold water will contain more dissolved O2 gas than a cup of boiling water d Adding a few granules of sugar to a cup of coffee produces a saturated solution e More sugar will dissolve in vegetable oil if the container is shaken Ex 2 A student dislikes the taste of the tap water in her apartment She had read that dissolved calcium and magnesium salts are usually the cause of bad tasting tap water She also heard that one can purify water by boiling purify it so she decides to boil a pot of her tap water to improve the taste Explain if and why the student will be happy with the results of her tap water after boiling What types of solute s can or cannot be removed by boiling water SOLUTION CONCENTRATIONS solution homogeneous mixture of substances present as atoms ions and or molecules solute component present in smaller amount solvent component present in greater amount A