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Factors Affecting Solubility

Factors Affecting Solubility. As T o , rate. 1. temperature. As size , rate. 2. particle size. More mixing, rate. 3. mixing. 4. nature of solvent/solute (“like dissolves like”, polar dissolves polar ). Measuring Concentration. Concentration …a measure of solute-to-solvent ratio

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Factors Affecting Solubility

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  1. Factors Affecting Solubility As To , rate 1. temperature As size , rate 2. particle size More mixing, rate 3. mixing 4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

  2. Measuring Concentration Concentration…a measure of solute-to-solvent ratio concentrated vs. dilute “lots of solute” “not much solute” “watery” Add water to dilute a solution; boil water off to concentrate it.

  3. mol C. Molality (m) = moles of solute M L kg of solvent Measuring Concentration“The amount of solute in a solution” A. Parts per million (ppm) also, ppb and ppt = g solute/1,000,000 g solution – commonly used for minerals or contaminants in water supplies B. Molarity (M) = moles of solute L of solution – used most often

  4. One mole, in solution.

  5. liter of solution Molarity

  6. Molarity • Find the molarity of a solution containing 75 g of MgCl2 in 250 ml of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 L water = 3.2M MgCl2

  7. mass of solvent only 1 kg water = 1 L water Molality

  8. Molality • Find the molality of a solution containing 75 g of MgCl2 in 250 ml of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

  9. Molality • How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 1.54 mol NaCl 1 kg water 0.500 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

  10. Factors Affecting Solubility As To , rate 1. temperature As size , rate 2. particle size More mixing, rate 3. mixing 4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

  11. Solubility (“Dissolution”) • Temperature -The solubility of most solids in water increases as the temperature of the sol’n increases. -The solubility of gases in water decreases with increasing temperature

  12. Solubility (“Dissolution”) Experiment 1: Add 1 drop of red food coloring Before AFTER Miscible – “mixable” two gases or two liquids that mix evenly Water HOT Water COLD Water HOT Water COLD A B A B

  13. Solubility (“Dissolution”) Experiment 2: Add oil to water and shake AFTER Before Immiscible – “does not mix” two liquids or two gases that DO NOT MIX Oil Water Water T0 sec T30 sec

  14. Gas Solubility CH4 2.0 O2 Higher Temperature …Gas is LESS Soluble CO Solubility 1.0 He 0 10 20 30 40 50 Temperature (oC)

  15. UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility: forming a “saturated” solution in equilibrium increasing concentration

  16. “Oil and Water Don’t Mix” • Oil is nonpolar • Water is polar “Like dissolves like”, nonpolar dissolves nonpolar, nonpolar does not dissolve polar Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 470

  17. Water Molecule Water is a POLAR molecule H+ d+ H2O d+ d- O2- H+ d-

  18. Na+ ions Water molecules Cl- ions Dissolving of NaCl in Water NaCl(s) + H2O  Na+(aq) + Cl-(aq)

  19. Ethanol is Polar d - H O d + H Polar bond C C H H H H Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 469

  20. H O H O H H C C H H H H Ethanol and Water are Soluble ‘Like dissolves like’ Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 469

  21. Cleaning Action of Soap Micelle Timberlake, Chemistry 7th Edition, page 573

  22. emulsifying agent (emulsifier): -- molecules w/both a polar AND a nonpolar end -- allows polar and nonpolar substances to mix e.g., soap detergent lecithin eggs MODEL OF A SOAP MOLECULE Na1+ NONPOLAR HYDROCARBON TAIL POLAR HEAD

  23. Oil Oil Oil Oil Oil Oil Oil Non-polar Water Water Water Water Water Water Water Water Water Water Water Water Water Water Water Water dissolved solid Polar red food coloring Interstitial Spaces "immiscible" Layer

  24. H2O + CO2 H2CO3 H2CO3 + CaCO3 Ca(HCO3)2 H2CO3 + MgCO3 Mg(HCO3)2 Water softner Clogged Pipes – Hard Water Step 1: Acid rain is formed carbonic acid Step 2: Acid rain dissolves limestone ‘hard’ water

  25. Pipes develop Scales Step 3: Hard water is heated and deposits scales Ca(HCO3)2 CaCO3(s) + H2O + CO2 Mg(HCO3)2 MgCO3(s) + H2O + CO2 D scales on pipes D

  26. Water Purification Cation Exchanger Anion Exchanger Deionized Water Hard Water H+ OH- H+ OH- H+ Mg2+ OH- Na+ H+ (b) (c) (a) OH- OH- Fe3+ H+ Ca2+ H+ OH- H+ OH- H+ OH- Hard water is softened by exchanging Na+ for Ca2+, Mg2+, and Fe3+. • The cations in hard water are exchanged for H+. • The anions in hard water are exchanged for OH-. • The H+ and OH- combine to give H2O. Corwin, Introductory Chemistry2005, page 361

  27. Source of electric power Pure water Pure water does not conduct an electric current Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 215

  28. Source of electric power Free ions present in water Ionic Solutions conduct a Current Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 215

  29. electrolytes: solutes that dissociate in solution -- conduct electric current because of free-moving ions e.g., acids, bases, most ionic compounds -- are crucial for many cellular processes -- obtained in a healthy diet -- For sustained exercise or a bout of the flu, sports drinks ensure adequate electrolytes. nonelectrolytes: solutes that DO NOT dissociate -- DO NOT conduct electric current (not enough ions) e.g., any type of sugar

  30. NaCl Na1+ + Cl1– CH3COOH CH3COO1– + H1+ Strong electrolytes exhibit nearly 100% dissociation. NOT in water: 1000 0 0 in aq. solution: 1 999 999 Weak electrolytes exhibit little dissociation. NOT in water: 1000 0 0 in aq. solution: 980 20 20 “Strong” or “weak” is a property of the substance. We can’t change one into the other.

  31. NaCl(aq) Na+ + Cl- HF(aq) H+ + F- Electrolytes Electrolytes - solutions that carry an electric current strong electrolyte weak electrolyte nonelectrolyte Timberlake, Chemistry 7th Edition, page 290

  32. Colligative Propertiesdepend on concentration of a solution Compared to solvent’s… a solution w/that solvent has a… …normal freezing point (NFP) …lower FP FREEZING PT. DEPRESSION …normal boiling point (NBP) …higher BP BOILING PT. ELEVATION

  33. Applications (NOTE: Data are fictitious.) 1. salting roads in winter water + a little salt –11oC 103oC water + more salt –18oC 105oC 2. antifreeze (AF) /coolant

  34. Effect of Pressure on Boiling Point

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