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Ch.13 ions in aqueous solutions and colligative properties

Ch.13 ions in aqueous solutions and colligative properties. Dissociation – separation of ions that occurs when an ionic compound dissolves NaCl  Na + + Cl -.

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Ch.13 ions in aqueous solutions and colligative properties

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  1. Ch.13 ions in aqueous solutions and colligative properties • Dissociation – separation of ions that occurs when an ionic compound dissolves • NaCl Na+ + Cl-

  2. Write the equation for the dissolution of aluminum sulfate, Al2(SO4)3 in water. How many moles of aluminum ions and sulfate ions are produced by dissolving 1 mol of aluminum sulfate? What is the total number of moles of ions produced by dissolving 1 mol of aluminum sulfate?

  3. Precipitation reactions Solubility guidelines • sodium, potassium, and ammonium compounds are soluble in water. • Nitrates, acetates, and chlorates are soluble • Most chlorides are soluble, except those of silver, mercury (I), and lead. Lead(II) chloride is soluble in hot water. • Most sulfates are soluble, except those of barium, strontium, lead, calcium, and mercury.

  4. Most carbonates, phosphates, and silicates are insoluble, except those of sodium, potassium, and ammonium. • Most sulfides are insoluble, except hose of calcium, strontium, sodium, potassium, and ammonium.

  5. Net ionic equation – includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution. • The purpose is to show the actually reaction that occurred in the aqueous solution. • The product will be insoluble. • Ionic equation – includes all ions even if they do not participate in the reaction. • Spectator ions – ions that do not participate in the reaction.

  6. Steps • Write the equation • Split all soluble compounds into ions. • Cross out ions that appear on both sides of arrow. (a.k.a. the spectator ions) • Write out the left over ions and compounds  “your net ionic equation”

  7. Example • Identify the precipitate that forms when aqueous solutions of zinc nitrate and ammonium sulfide are combined. Write the equation for the possible double-displacement reaction. Then write the formula equation, overall ionic equation, and net ionic equation for the reaction.

  8. Ionization – ions are formed from solute molecules by the action of the solvent. This is different from dissociation because this is a molecule (not an ionic compound) forming ions. If the strength of a bond within the solute molecule is weaker than the attractive forces of the solvent molecules, then the covalent bond of the solute breaks and the molecule is separated into ions.

  9. Ex. HCl(aq)  H+ + Cl- The attraction between a polar HCl molecule and the polar water molecules is strong enough to break the HCl bond forming hydrogen ions and chloride ions.

  10. Hydronium Ion • H+ ion attracts other molecules or ions so strongly that it does not normally exist alone. • In an aqueous solution it bonds to H2O to form H3O+ or hydronium ions. • H+ + H2O  H3O+

  11. Strong Electrolyte • Any compound whose dilute aqueous solutions conduct electricity well; this is due to the presence of all or almost all of the dissolved compound in the form of ions.

  12. Weak electrolytes • Any compound whose dilute aqueous solutions conduct electricity poorly; this is due to the presence of a small amount of the dissolved compound in the form of ions.

  13. Review: Will a precipitate form if solutions of magnesium acetate and strontium chloride are combined? No because magnesium chloride and strontium acetate are soluble.

  14. Explain why HCl is a strong electrolyte and HF is a weak electrolyte. H-F covalent bond is stronger than the intermolecular force between water and HF.

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