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Ch 17sec3

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Ch 17sec3

  1. 1. 17.3 Aqueous Solutions
  2. 2. 1. What is the difference between molecular and ionic compounds? <ul><li>2. What is a cation? </li></ul><ul><li>3. What is an anion? </li></ul><ul><li>4. Why are ionic compounds generally soluble in water? </li></ul>
  3. 3. Aqueous Solutions <ul><li>A solution is a homogenous mixture- it is stable; parts cannot be separated by filtering; one phase </li></ul><ul><li>Solutions have two parts: Solute and solvent </li></ul><ul><li>Solute - substance that gets dissolved </li></ul><ul><li>Solvent - substance that does the dissolving </li></ul><ul><li>Solutions with water as the solvent are called aqueous solutions </li></ul><ul><li>Solvents and solutes can be solids, liquids or gasses </li></ul>
  4. 4. Examples Notice- you can have more than one solute; usually the solvent is the substance in the greatest amount N 2 O 2, CO 2 , H 2 O, air water Na + , K + , Ca +2 , O 2, CO 2 blood water salt saltwater Solvent Solute Solution
  5. 5. Aqueous Solutions <ul><li>In aqueous solutions the solutes are usually ionic and/or polar covalent compounds ( remember water itself is polar) </li></ul><ul><li>“ Like dissolves Like” this means polar substances dissolve in polar substances and nonpolar substances dissolve in nonpolar substances </li></ul>
  6. 6. Which of the following would dissolve in water? <ul><li>A) Oil </li></ul><ul><li>B) CH 4 (methane) </li></ul><ul><li>C) LiCl </li></ul><ul><li>D) I 2 </li></ul>
  7. 7. Which of the following would not dissolve in water? <ul><li>He </li></ul><ul><li>MgSO 4 </li></ul><ul><li>NaHCO 3 </li></ul><ul><li>KCl </li></ul>
  8. 8. True or False <ul><li>In a saltwater solution the salt is the solvent. </li></ul>
  9. 9. Solution Process <ul><li>Solvation - process whereby solutes dissolve </li></ul><ul><li>In ionic compounds- the + ions are surrounded by the negative end of the water molecule (O), and the – ions are surrounded by the + end of the water molecule (H)- thus separating the ions from each other </li></ul><ul><li>Not all ionic compounds will dissolve- some have such a strong attraction to their ions they are said to be insoluble ( reference table) </li></ul>
  10. 10. Which substance will not dissolve in water ( use solubility chart)? <ul><li>KF </li></ul><ul><li>NH 4 Cl </li></ul><ul><li>Pb(OH) 2 </li></ul><ul><li>CaCl 2 </li></ul>
  11. 11. Solvation continued <ul><li>In molecular (covalently bonded) substances the + end of a polar solute will be attracted to the – end of the water molecule, and the – end of the polar solute will be attracted to the –end of the water molecule so dissolving takes place ; polar substances dissolve in polar substances-Like dissolves Like </li></ul><ul><li>Nonpolar substances, like oil will not dissolve in water- there is no + or – end to the nonpolar molecule; but nonpolar will dissolve in nonpolar substances- Like dissolves Like </li></ul><ul><li>Simulation 19 </li></ul>
  12. 12. Electrolytes <ul><li>Substances that conduct electricity in its aqueous or molten form are called electrolytes </li></ul><ul><li>Ionic compounds are electrolytes if they are soluble in water ( NaCl- yes; BaSO 4 -no, insoluble) </li></ul><ul><li>Compounds that do not conduct electricity in either the molten state or in aqueous form are called nonelectrolytes </li></ul>
  13. 13. Solution of solids <ul><li>While covalent compounds do not dissociate, they are solvated in solution. </li></ul>
  14. 14. Electrolytes continued <ul><li>Most molecular compounds are nonelectrolytes </li></ul><ul><li>A few very polar molecular compounds however will ionize in solution and so are electrolytes( HCl, NH 3, ) when they are dissolved in water </li></ul><ul><li>HCl (g) + H 2 0 (l) H 3 O + (aq) + Cl - (aq) </li></ul><ul><li>Simulation 20 </li></ul>
  15. 15. Electrolytes continued <ul><li>Not all electrolytes conduct electricity to the same degree- some are better conductors than others- there are weak electrolytes and strong electrolytes </li></ul><ul><li>What makes them weak or strong is how much many of the ions dissociate ( split up) when in solution. If almost all do, then it is a strong electrolyte; if only a few of the ions dissociate, then it is a weak electrolyte ( chart pg 485) </li></ul><ul><li>Conductivity testers can determine if a substance is an electrolyte </li></ul>
  16. 16. Strong Electrolytes <ul><li>Strong, inorganic acids </li></ul><ul><li>Strong inorganic bases </li></ul><ul><li>Soluble salts (ionic compounds) </li></ul>
  17. 17. Weak Electrolytes <ul><li>Heavy metal halides ( PbCl 2 ) </li></ul><ul><li>NH 3 (weak base) </li></ul><ul><li>Organic acids and bases </li></ul><ul><li>H 2 O </li></ul>
  18. 18. Nonelectrolytes <ul><li>Most organic compounds </li></ul><ul><li>Nonpolar molecules </li></ul>
  19. 19. Water of Hydration <ul><li>When water is an integral part of the crystalline structure of a substance, the water is called the water of hydration </li></ul><ul><li>A substance with water of hydration in it is called a hydrate </li></ul><ul><li>Examples: CuSO 4 . 5H 2 O </li></ul><ul><li>MgSO 4 . 7H 2 O (epsom salt) </li></ul>
  20. 20. Hydrates <ul><li>Water in hydrates is not held very tightly and so hydrates tend to have noticable vapor pressures ( from water leaving the crystal) </li></ul><ul><li>If the hydrate’s vapor pressure is higher than water vapor pressure, the hydrate will effloresce , which means it loses its water of hydration naturally-this is why some hydrates become coated with a white powder- it is the anhydrous form of the compound </li></ul>
  21. 21. Hydrates con’td <ul><li>Hygroscopic compounds are hydrates that remove water from the air- they have a low vapor pressure </li></ul><ul><li>They are used as desiccants - they remove moisture from the air (like from the shoebox of that expensive leather boots you got) </li></ul><ul><li>Deliquescent compounds are so hygroscopic (water loving) they remove enough from water from the air to turn into a solution. This occurs when their vapor pressure is much lower than water’s </li></ul><ul><li>CaCl 2 . H 2 O CaCl 2 . 2H 2 O </li></ul>
  22. 22. % Water in a Hydrate <ul><li>You can calculate the % water in a hydrate similar to % composition problems </li></ul><ul><li>Mass of Water x 100 </li></ul><ul><li>Total mass of Compound </li></ul>
  23. 23. Problem <ul><li>Find the % by mass of water in sodium carbonate decahydrate. ( Na 2 CO 3 . 10H 2 O) </li></ul><ul><li>10 x 18g/1mol= 180g water </li></ul><ul><li>2(23)+12+3(16) +180=286g Na 2 CO 3 . 10H 2 O </li></ul><ul><li>180g/286 x 100=62.9% </li></ul>
  24. 24. What is the % water in CuSO 4 . 5H 2 0 <ul><li>2 sig figs </li></ul>
  25. 25. What is the % water in CaCl 2 . 6H 2 O <ul><li>2 sig figs </li></ul>