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Chapter 8 : SOLUTIONS

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

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Chapter 8 : SOLUTIONS

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  1. Chapter 8 : SOLUTIONS Section 1 – Solutions and Other Mixtures Section 2 – How Substances Dissolve Section 3 – Solubility and Concentration

  2. 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

  3. 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??

  4. 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

  5. Suspensions • Orange Juice – another heterogeneous mixture • Suspensions have large particles that settle out • Particles may also be filtered out

  6. Colloids • Colloids are suspensions with particles too small to settle out – they remain suspended always • Can scatter light • Tyndall Effect • FOG!!

  7. 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

  8. 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

  9. Homogeneous Mixtures • Example – SALTWATER • Water is SOLVENT / Salt is SOLUTE

  10. 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 )

  11. How is Crude Oil turned into Gasoline?

  12. 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

  13. 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

  14. 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

  15. 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”

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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!! )

  21. 2 - How Substances Dissolve Key Questions • Why is water called the universal solvent? • Why do substances dissolve?

  22. 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!! )

  23. 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

  24. 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

  25. 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 • Salt max solubility above becomes ~ 6.15 mol/L or M

  26. 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

  27. 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

  28. 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?

  29. Gas Solubility Lab

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