Chapter 8 : SOLUTIONS Section 1 – Solutions and Other Mixtures Section 2 – How Substances Dissolve Section 3 – Solubility and Concentration 1 - Solutions and Other Mixtures Key Questions • What is a heterogeneous mixture? • What is a homogeneous mixture? State Standards • CLE.3202.1.5 : Evaluate pure substances and mixtures Heterogeneous Mixtures • Does not appear uniform ( microscope needed ) • Does not have a fixed composition – Amounts of each component vary in distinct samples • Another example – Granite – Mixture of minerals – Different types of Granite – Internet Break?? Oil and Water • Do oil and water mix? • Maybe but will separate quickly – Depends on type of oil • Immiscible or Miscible? – Oil and Water are IMMISCIBLE – Alcohol and Water are MISCIBLE Suspensions • Orange Juice – another heterogeneous mixture • Suspensions have large particles that settle out • Particles may also be filtered out Colloids • Colloids are suspensions with particles too small to settle out – they remain suspended always • Can scatter light – Tyndall Effect – FOG!! Common Colloids • FOG!!!! • Emulsions: Colloids made of liquids that do not normally mix • Mayo ( oil droplets in vinegar ) • Milk/Cream ( oil droplets in water ) • Lotions, creams, many cosmetics Homogeneous Mixtures • Appear uniform even when using a microscope – May look like pure substance but they are not • They are Solutions – components are uniformly spread throughout each other • Solute – substance being dissolved • Solvent – substance dissolving the solute Homogeneous Mixtures • Example – SALTWATER • Water is SOLVENT / Salt is SOLUTE Solutions • Miscible liquids mix – form solutions – Solids not always involved • Water is not always involved ( can mix alcohols ) in liquid solutions • Other states of matter can form solutions – Solids can dissolve in other solids – Metal ALLOYS ( Brass is Zn and Cu ) – Tooth Fillings ( used to be Ag/Hg but now are plastics ) How is Crude Oil turned into Gasoline? 1 - Solutions and Other Mixtures Key Questions • What is a heterogeneous mixture? • What is a homogeneous mixture? State Standards • CLE.3202.1.5 : Evaluate pure substances and mixtures 2 - How Substances Dissolve Key Questions • Why is water called the universal solvent? • Why do substances dissolve? State Standards • CLE.3202.TE.3 : Explain the relationship between the properties of a material and the use of the material in the application of a technology • CLE.3202.1.6 : Distinguish between common ionic and covalent compounds Water : A Common Solvent • Water is called the universal solvent because many substances can dissolve in water • Water can dissolve ionic compounds • A polar molecule has partially charged + and – areas ( water is polar ) – Charge is not evenly distributed in polar molecules Dissolving – Depends of Forces • Polar water molecules pull ionic crystals apart – Na+, Cl- attracted more to water “poles” than each other • Dissolving depends on forces between particles – Goto go.hrw.com and enter keyword “HK8SOLF2” Like dissolves Like • This is a rule in chemistry!! • Water dissolves many molecular compounds – Recall that O in water pulls electrons away from H – This forms a Hydrogen Bond (pull H2O close together) – Water dissolves compounds with hydrogen bonds – Examples are alcohols, sugar, vitamin C Like dissolves Like • Nonpolar compounds ( liquids ) dissolve other nonpolar compounds • Nonpolars do not have their +/- charges separated • Why oils do not dissolve in water • But one oil WILL dissolve another oil The Dissolving Process • Kinetic Theory (molecules are always moving) • Dissolving occurs because: • Energy transferred from solvent to solute (collisions upon addition of solute) • Attractive forces between solute and solvent The Dissolving Process • Solutes with larger surface area dissolve faster – What is surface area of a sphere ? – ( 4πr2 ) • Small particles of salt will dissolve faster than a large chunk of salt The Dissolving Process • Stirring or shaking helps dissolve solids faster • Hot solvents dissolve solids faster than cold ones • Solutes affect the physical properties of a solution – Boiling & Melting temperature ( salted roads!! ) 2 - How Substances Dissolve Key Questions • Why is water called the universal solvent? • Why do substances dissolve? 3 – Solubility and Concentration Key Questions • What is solubility? • What happens when you add more solute to a saturated solution? • How do you describe how much of a solute is in a solution? State Standards • CLE.3202.Inq.3 : Use appropriate tools and technology to collect precise and accurate data • CLE.3202.Inq.6 : Communicate and defend scientific findings ( LAB!! ) Solubility in Water • The solubility of a substance is the maximum mass of a solute that can dissolve in 100 g of solvent at a certain temperature and standard atmospheric pressure • Different solutes have different solubilities • • • • Examples at 20 oC: Salt ( NaCl ) has solubility of 35.9 g / 100 g H2O Sodium Iodide ( NaI ) – 178 g / 100 g H2O Iron(II) Sulfide ( FeS ) – 0.0006 g / 100 g H2O Concentration • Concentration is the quantity of solute that is dissolved in a given volume of solution • Concentrated solution has a lot of solute • Dilute solution has small amount of solute • Qualitative terms – would like to know a value • Salt ( NaCl ) max solubility of 35.9 g / 100 g H2O • This gives a concentration of 0.359 g/mL at 20 oC Concentration • Salt ( NaCl ) max solubility of 35.9 g / 100 g H2O • This gives a concentration of 0.359 g/mL at 20 oC • Molarity is a common way to express this 𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚 = 𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝒍𝒊𝒕𝒆𝒓𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = 𝒎𝒐𝒍 𝑳 or M • Salt max solubility above becomes ~ 6.15 mol/L Saturated Solutions • In saturated solutions, dissolved solute is in equilibrium with undissolved solute • So, more solute added just settles to bottom • Unsaturated solutions can become saturated by adding enough solute Temperature and Pressure • Heating a saturated solution can dissolve more solute ( can also increase maximum solubility ) – Why solubility values given at 20 oC • Temperature and pressure affect gas solubility – Pressure inside sealed coke is higher then an open one 3 – Solubility and Concentration Key Questions • What is solubility? • What happens when you add more solute to a saturated solution? • How do you describe how much of a solute is in a solution? Gas Solubility Lab