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Chapter 14

Chapter 14. Mixtures and Solutions. 14.1 Types of Mixtures. What is a Mixture? A combination of 2 or more kinds of matter, each retains its own composition and properties . Homogeneous : a mixture with uniform composition (ex: salt water).

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Chapter 14

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  1. Chapter 14 Mixtures and Solutions

  2. 14.1 Types of Mixtures • What is a Mixture? • A combination of 2 or more kinds of matter, each retains its own composition and properties. • Homogeneous: a mixture with uniform composition (ex: salt water). • Heterogeneous: a mixture without uniform composition (ex: dirty water).

  3. Types of Mixtures • Solutions • A homogeneous mixture in a single phase. • Properties: • uniform distribution of particles • won’t settle out • transparent • can’t be filtered out (small particle size)

  4. Types of Mixtures • The nature of solutions: • Solute: the part that gets dissolved. • Solvent: the part that does the dissolving. • Aqueous: (aq) a solution that contains water as the solvent. • Tinctures: solutions that contains alcohol as the solvent • Examples: I2 in alcohol, phenolphthalein solutions

  5. Salts Dissolve to Form Molecules (Non-electrolytes Ions Electrolytes Solutions • Solutions can be electrolytes or non-electrolytes. • What is an electrolyte? • Salts. Anything that dissolves in water and conducts electricity. • Solutes are classified according to whether they dissolve to form neutral molecules or charged ions.

  6. Solutions • 3 Types of solutions • Gaseous solutions - air • Liquid solutions – vinegar (acetic acid dissolved in water); soft drinks (solutions of a gas, CO2, dissolved in water. • Solid solutions – alloys such as sterling silver – 92% silver, 8% copper; white gold – gold containing nickel, tin, zinc or copper.

  7. Suspensions • A heterogeneous mixture of the largest particles that settle out. • Example – a jar of muddy water, Italian dressing

  8. Colloids • Colloids contain intermediate size particles that remain in suspension because they are too small to settle out. • Example – the large particles settle out of the muddy water, but the water remains cloudy. The cloudy water cannot be filtered because the particles are too small and remain in suspension due to the constant movement of the liquid molecules. • Colloids include – mayonnaise (solid emulsion), foam, smoke (solid dispersed in gas), fog (liquid dispersed in gas)

  9. Colloid or Solutions? S C S S S C S C

  10. Matter Pure Substances Mixtures Elements Compounds Homogeneous Heterogeneous Solutions Colloids Suspensions Classification of Matter Fill in the flow chart with the following words: Mixtures, Matter, Pure Substances, Homogeneous, Heterogeneous, elements, compounds, suspensions, colloids, solutions

  11. 14.2 The solution process • Factors affecting the rate of dissolving • Degree of Solubility: the amount of substance required to form a saturated solution in a certain amount of solvent at a certain temperature. • solute + solvent ↔ solution (equilibrium)

  12. Factors affecting the rate of dissolving • If you wish to dissolve a substance, you can help by: • crush it (increase surface area) • stir it • heat it

  13. Factors affecting solubility • 1. Types of solvents and solutes –“Like dissolves like” Polar/ionic vs. nonpolar • water oil • salt gasoline • sugar Styrofoam

  14. “Like dissolves Like” • Ionic substances dissolve in polar substances – salt dissolves in water • Non polar substances dissolve in non polar substances – fats, oils, gasoline dissolve • Immiscible substances do not dissolve in each other (salad dressing – oil and vinegar) • Miscible substances do dissolve in each other (gasoline and benzene)

  15. S P Factors affecting solubility • 2. Pressure (gases only) • As pressure increase, solubility increases. • Henry’s law: solubility is proportional to pressure. • Effervescence: the escape of a gas from a solution (a carbonated soft drink effervesces when the bottle is opened and the pressure is reduced)

  16. Factors affecting solubility • 3. Temperature • For most solids, solubility increases as temperature increases • For gases, solubility decreases as temperature increases S T S T

  17. Heats of Solution • Solubility, the nature of solute and solvent, and the energy changes during solution formation Dissolving an ionic compound in water Na+ Na Cl O-2 O-2 Cl Na Na+ H+ H+ H+ H+ Cl O-2 Cl- O-2 Na Cl- Na Cl H+ H+ H+ H+ Cl- Cl- Step #1 Step #2 Step #3 Breakup the Breakup the Formation of Formation of the solvent the solution Solute (endothermic) (endothermic) (exothermic)

  18. Heats of Solution • If step #1 plus step #2 are more than step #3, then the overall reaction is endothermic. Energy Level Diagram E 3 2 1 Time

  19. 2 3 E 1 Time Heats of Solution • If step #1 plus step #2 are less than step #3, then the overall reaction is exothermic. Energy Level Diagram

  20. Heat of Solution/Hydration • Heat of Solution: The amount of heat absorbed or released when a solute dissolves in a solvent. • Heat of Hydration: energy released when ions are surrounded by water molecules. • The # of water molecules used depends on the size and charge of the ion. • ↑ Heat released (more negative) as the size of the ion ↓ Li+1 -523 kJ/mole vs Na+1 -418 kJ/mole • ↑ Heat released (more negative) as the charge of the ion ↑ Na+1 -418 kJ/mole vs Mg+2 -1949 kJ/mole Li and Mg are close to the same size, so... charge means more

  21. Heat of Solution/Hydration • Dissociation - separation of ions;caused by the action of the solvent. • Hydration- the process of solute particles being surrounded by water. • Remember: polar/ionic dissolves polar/ionic (like dissolves like). O2 and CO2 are nonpolar. They don’t dissolve very much in water (just enough for sodas)

  22. Solubility Curves and Tables • Solubility Rules: • soluble (definition): more than 1 g of solute dissolves per 100 g of water • slightlysoluble: between 0.1 and 1 g dissolves • insoluble: less than 0.1 g dissolves d = decomposes ni - not isolated - not been found to form

  23. Saturated, unsaturated, and supersaturated solutions • Saturated Solution: • Holds as much solute as it can at a given temperature and certain amount of solvent. • Temperature must be stated when determining solubility. • For gases, pressure must also be stated when determining solubility.

  24. Saturated, unsaturated, and supersaturated solutions • Unsaturated Solution • The solution is currently dissolving less than the maximum amount of solute at a given temperature. • Supersaturated Solution • The solution currently holds more than the maximum amount of solute at a given temperature. How is this possible? These solutions are created by saturating a hot solution and allowing it to cool undisturbed.

  25. Solubility Problems • Ex1: What is the solubility of potassium chlorate at 50.0 oC in 100.0 ml of water? • Ex2: What temperature will result in a saturated solution of 80.0 grams of sodium nitrate and 100.0 grams of water? 20.0 g of potassium chlorate in 100.0 grams of water 10.0 oC

  26. Solubility Problems • Ex3: If 40.0 grams of ammonium chloride are placed in 100.0 grams of water at 50.0 oC, is the solution saturated or unsaturated? If saturated, how much salt remains undissolved? If unsaturated, how much more salt can be dissolved? • Ex4: If 80.0 grams of potassium nitrate are placed in 100.0 grams of water at 44.0°C, is the solution saturated or unsaturated? If saturated, how much salt remains undissolved? If unsaturated, how much more salt can be dissolved? The solution is unsaturated and can hold 10.0 more grams of ammonium chloride. The solution is saturated with 5.0 grams of potassium nitrate undissolved

  27. Solubility Problems • Ex5: What is the solubility of sodium chloride at 90.0 oC in 50.0 ml of water? • At this temperature the 100.0 ml of water can hold 40.0 grams of this salt. So, if half as much water is present, half as much salt will dissolve. 40.0 g = x 100.0 ml 50.0 ml x = 20.0 grams of sodium in 50.0 grams of water

  28. Solubility Problems • Ex6: What is the solubility of potassium nitrate at 50.0 oC in 200.0 ml of water? 80.0 g = x 100.0 ml 200.0 ml x = 160.0 grams of potassium nitrate in 200.0 grams of water

  29. Solubility Problems • Ex7: What is the solubility of ammonium chloride at 90.0 oC in 68.2 ml of water? 70.0 g = x 100.0 ml 68.2 ml x = 47.7 grams of ammonium chloride in 68.2 grams of water

  30. 14.3 Concentrations of solutions • Dilute vs. Concentrated • Dilute: a small amount of solute in a large amount of solvent. • Concentrated: a large amount of solute in a small amount of solvent. • Do not confuse with saturated and unsaturated. For example, “a saturated solution may be either dilute or concentrated.”

  31. % by Mass of a Solute in Solution • Example: Suppose we have a solution that contains 50.0 ml of alcohol (solute) and 50.0 ml of water (solvent). If the density of the alcohol is 0.800 g/mL, calculate the following percent solutions. General Formula  solute * 100 = % by mass solution

  32. Three ways to calculate the % solution: #1 Volume of solute x 100  Total Volume of solution (50.0 ml / 100.0 ml) x 100 = 50.0 %

  33. Three ways to calculate the % solution: # 2 Weight of solute x 100  Total Volume of solution • D = M/ V  M = DV  M = (.800 g/ml)(50.0 ml)  M = 40.0 g solute (40.0 g / 100.0 ml) 100 = 40.0 %

  34. Three ways to calculate the % solution: #3 Weight of solute x 100 Weight of solution D = M/V  M = DV  M = (.800 g/ml)(50.0 ml)  M = 40.0 g solute D = M/V  M = DV  M = (1.00 g/ml)(50.0 ml)  M = 50.0 g solvent (40.0 g / 90.0g) 100 = 44.0 %

  35. Molarity • A method used to calculate concentration. • Molarity (M) = moles solute Liters of solution • Note: If given grams, use the periodic table to find the number of moles • When you talk about a solution with a label of 6 M HCl, we say, “ Six molar solution.”

  36. Molarity • What is the Molarity of a solution made by dissolving 20.0 g of H2SO4 to a volume of 400.0 ml?

  37. Molality • Another method used to calculate concentration. molality (m) = moles solute kg of solvent • When you talk about a solution with a label of 6 m HCl, we say, “ Six molal solution.”

  38. Molality • What is the molality of a solution made by dissolving 3.5 g of Ca(OH)2 in 350 g of water?

  39. Dilutions • CoVo = CnVn • Ex. How many mL of water would you need to add to 6.0 M H2SO4 so you could make 2.00 L of a 2.50 M solution?

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