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Dilution

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Dilution

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  1. Dilution

  2. Dilution • Adding water to a particular stock solution to achieve a desired molarity

  3. Dilution • Moles of solute after dilution = Moles of solute before dilution • Only water is added! Solute is not added or subtracted !

  4. Dilution • MV = MV • What volume of 16M H2SO4 must be used to prepare 1.5 L of 0.10 M H2SO4 solution?

  5. Types of Chemical Rxns • Precipitation rxns • Acid/Base rxns • Oxidation/Reduction rxns

  6. Precipitation Rxns • When two solutions are mixed and an insoluble substance forms • The solid is the precipitate

  7. Precipitation Rxns • Best way to predict products is to think about what products are possible

  8. Precipitation Rxns • In almost every case, when a solid containing ions dissolves in H2O, the ions separate and move independently.

  9. Hints that help... • 1. When ions form a solid, the compound must have a 0 net charge. (i.e. the products must contain a cation and anion)

  10. Hints that help... • 2. Most ionic materials contain only one type of cation and one type of anion.

  11. A rxn to try... • K2CrO4(aq) + Ba(NO3)2(aq) -->products?? • The product includes a yellow solid...

  12. Possible ions... • K+ CrO42- Ba2+ NO3- • Possible products • K2CrO4 KNO3 BaCrO4 Ba(NO3)2

  13. Only real possibilities... • KNO3 and BaCrO4 • An experienced chemist has more data-- CrO4 is a yellow ion

  14. The final result... • K2CrO4(aq) + Ba(NO3)2(aq) --> BaCrO4(s) + 2KNO3(aq)

  15. Solubility Rules for Salt • 1. Nitrate (NO3-) salts are soluble.

  16. Solubility Rules for Salt • 2. Salts containing alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4+) are soluble.

  17. Solubility Rules for Salt • 3. Most chloride, bromide, and iodide salts are soluble. Notable exceptions are salts with ions Ag+, Pb2+, and Hg22+

  18. Solubility Rules for Salt • 4. Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, HgSO4, and CaSO4.

  19. Solubility Rules for Salt • Most hydroxide salts precipitate (or dissolve only slightly). Impt soluble hydroxides are NaOH and KOH.

  20. Solubility Rules for Salt • Ba(OH)2, Sr(OH)2 and Ca(OH)2 are marginally soluble.

  21. Solubility Rules for Salt • Most sulfide (S2-), carbonate (CO32-) and phosphate (PO43-) salts precipitate.

  22. Describing Rxn in Sol’n

  23. Types of Equations • Molecular equation • shows the reactants and products of a reaction

  24. Molecular Eqn Example • AgNO3(aq) + KCl(aq) --> AgCl(s) + KNO3(aq) • Does not give clear picture of what occurs!

  25. Complete Ionic Eqn • All substances that are strong electrolytes (ionized) are represented as ions

  26. Complete Ionic Eqn • Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)-->AgCl(s) + K+(aq) + NO3-(aq)

  27. Notice! • The K+ and the NO3- ions do not participate in the reaction!!! • They are spectator ions.

  28. Net Ionic Eqns • Eliminate the spectator ions from the complete ionic equation.

  29. Net Ionic Eqns • Ag+(aq) + Cl-(aq) --> AgCl(s)

  30. Stoichiometry of ppt rxn • Same as stoichiometry that we already learned! • Must figure out rxn first! • Must get moles from M!