18CH 18.1


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18CH 18.1

  1. 1. 18.1 Properties of Solutions
  2. 2. <ul><li>“ Like dissolves like.” </li></ul><ul><li>Materials with similar polarity are soluble in each other. Dissimilar ones are not. </li></ul><ul><li>Miscible </li></ul><ul><li>Liquids that are soluble in each other in all proportions such as ethanol and water. </li></ul><ul><li>Immiscible </li></ul><ul><li>Liquids that are not soluble in each other such as hexane and water. </li></ul>
  3. 3. Factors Affecting rate of solution <ul><li>Nature of solvent ( polar or non or ionic) </li></ul><ul><li>Temperature- for most, not all solids in a liquid, solubility increases with temp. </li></ul><ul><li>Agitation- more shaking or stirring, faster a solute dissolves ( solids in liquids) </li></ul><ul><li>Particle size- smaller the particle size, more surface area, so faster dissolving takes place </li></ul><ul><li>All these can be explained by understanding how solvation occurs </li></ul>
  4. 5. Solution of solids
  5. 6. Solubility <ul><li>Amount of solute that dissolves in a given amount of solvent at a particular temperature </li></ul><ul><li>Usually expressed in: </li></ul><ul><li>g of solute/100g of solvent </li></ul><ul><li>Solubility chart shows solubility of different solutes at different temperatures. (pg 504) </li></ul>
  6. 7. Few terms first.. <ul><li>Saturated- solution is holding max amount of solute for that solvent; if you try to add more solute, it does not dissolve </li></ul><ul><li>Unsaturated – solution is holding less than the max amount of solute </li></ul><ul><li>Supersaturated- solution is holding more solute than it should for that temp. ( we’ll talk about this later) </li></ul>
  7. 8. <ul><li>At saturation, the solute is in dynamic equilibrium. The concentration is constant. </li></ul><ul><li>Solute species are </li></ul><ul><li>constantly in </li></ul><ul><li>motion, moving </li></ul><ul><li>in and out of </li></ul><ul><li>solution. </li></ul>
  8. 9. The lines represent saturated solutions- solutions which are holding the maximum amount of solute possible for these conditions. Handout problems
  9. 10. Handout hints <ul><li>Make sure you read the axis of the graphs- this one is for 100g of water </li></ul><ul><li>If the problem asks for solubility in 200g of water, then you need to double your reading/or if it asks for solubility in 50g of water then you cut your reading in ½ ; You must always adjust your readings to the amount of solvent in the problem </li></ul>
  10. 11. <ul><li>If your reading is below the line for your solute, the solution is unsaturated; if it is above the line it, is either supersaturated, or you can calculate how much extra solute will precipitate out ( amount above the line) </li></ul>
  11. 12. Supersaturated Solutions <ul><li>At higher temperatures, more solute can be dissolved than at a lower temp. </li></ul><ul><li>So, if you heat up water and make a saturated solution, then slowly cool the solution down in an uncontaminated env. then more solute will be dissolved than should be for the lower temp- this is supersaturated </li></ul><ul><li>As soon as you add an additional crystal of solute, or scratch the glass of the container, the excess solute will precipitate out </li></ul>
  12. 13. Gases and solubility <ul><li>Look at the chart on pg.505 </li></ul>Notice- for gases, solubility decreases with temperature
  13. 14. <ul><li>This is why you seen tiny bubbles when heating up water ( long before it boils)- these are N 2 and O 2 coming out of solution </li></ul><ul><li>This is why thermal pollution can affect life in waterway- warmer the water, the less Oxygen (DO) can be dissolved in it, less oxygen available for living things </li></ul>
  14. 15. Pressure and solubility of gases <ul><li>Increasing the pressure of a gas above a liquid increases the concentration of the gas. </li></ul><ul><li>This shifts the equilibrium, driving more gas into the liquid. </li></ul>
  15. 16. Pressure and solubility of gases <ul><li>At constant temperature, the solubility of a gas is directly proportional to the pressure of the gas above the solution. </li></ul><ul><li>Henry’s Law </li></ul><ul><li>S 1 = S 2 </li></ul><ul><li>P 1 P 2 </li></ul><ul><li>This law is accurate to </li></ul><ul><li>within 1-3% for slightly soluble gases and pressures up to one atmosphere. </li></ul>
  16. 17. Henry’s Law problem <ul><li>If the solubility of a gas in water is .77g/L at 3.5 atm, what is the solubility at 1 atm? Assume temp stays same </li></ul><ul><li>.77g/L = S 2 </li></ul><ul><li>3.5 atm 1.0 atm </li></ul><ul><li>.77g/L x 1 atm = S 2 </li></ul><ul><li>3.5 atm </li></ul><ul><li>.22g/L=S 2 </li></ul>