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Review of Solubility and Precipitation Reactions

Review of Solubility and Precipitation Reactions. Aqueous Solutions. Compounds dissolved into water. Can contain molecules or ions in a solution. How do you distinguish between ion or molecule?. DISSOCIATION !!. The ability of a compound to breakdown in a solution into individual ions

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Review of Solubility and Precipitation Reactions

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  1. Review of Solubility and Precipitation Reactions

  2. Aqueous Solutions Compounds dissolved into water. Can contain molecules or ions in a solution. How do you distinguish between ion or molecule?

  3. DISSOCIATION !! • The ability of a compound to breakdown in a solution into individual ions • Ionic Compounds • Break down into cations and anions • Electrical conductors—ions flow through solution • Molecular Compound • Compound remains intact as “molecules,” no breakdown • Generally NOT electrical conductors

  4. Solubility • How much solute dissolves in a solution to produce a saturated solution • Temperature and Pressure dependent • Increase with increasing temperature • Increases with decreasing temperature (ex. Water in lake) • Pressure increases, solubility increases (ex. Soda can)

  5. Which compounds are soluble in water? 1) BaCl2 2) Pb (NO3)2 3) Na2S 4) BaCO3 5) PbS

  6. Precipitation Prediction • Write the reactants in ionic from • breakdown into ionic form if compounds are soluble • leave as molecules if insoluble • Determine the solubility of the products. • Use solubility Rules

  7. Precipitation Predictions (cont.) 3) Check to see if one product is insoluble in water. • Product will fall out of solution, identified as precipitate 4) Write the net ionic equation • Displays which ions are directly involved in the reaction, produce the precipitate • Ions existing on BOTH sides of the equation are “spectator ions” (do NOT participate in precipitate formation) • Spectator ions are eliminated

  8. Example 1: MgSO4 + KOH Write the net ionic equation. Will a precipitate form?

  9. Chemical Equilibrium so far----- • Gases • Acids and Bases • Slightly soluble Salts • Many ionic compounds—only a small fraction dissolves

  10. Ksp/Solubility Equilibria

  11. Solubility Equilibrium • Type of equilibrium between ionic solid and a saturated solution • Equilibrium exists between ions and solid • Saturated vs. concentrated solutions are NOT the same thing • Saturation---at equilibrium

  12. Solubility Product Constant (Ksp)

  13. Example 1: • BaSO4(s)  Ba+2(aq) + SO4-2(aq) • Indicates salt exists in “solubility equilibrium”—some dissolves, some does not

  14. Solubility vs. Solubility Constant • Solubility— • How much compound can be dissolved • Molarity of a saturated solution • How much ionic solid can dissolve in a liter of solution • Solubility Product/constant • Numerical value of equilibrium constant • Specific for an equation representing ionic substance dissolving in water

  15. Solubility Product Constant (Ksp) • Equilibrium constant for slightly soluble salts • Indicates equilibrium between solid salt and the ions found in a solution when it dissociates • Expression represents the product of the concentrations of ions in equilibrium • Temperature dependent • Values found in table along with solubility equation (p. 678, Appendix C—p.A18)

  16. Example 2: Write a Ksp expression for an equilibrium in a saturated aqueous solution of iron (III) phosphate and for an equilibrium in a separate aqueous solution of chromium (III) hydroxide.

  17. Ksp and Solution Molarity • Ksp is an equilibrium constant, NOT concentration • Molarity/concentration separate from Ksp • Ksp values • Considered estimates due to ion attractions to other ions in solution and Ksp values not exact • Used only for slightly soluble salts • Increase concentration of ions, increase Ksp value

  18. 2 Classic Ksp Problems Finding solubility of a chemical substance if given its solubility product (Ksp). Given the molar solubility of a chemical substance, find the solubility product (Ksp).

  19. Example 3: Determine the molar solubility of CaF2 given that Ksp= 3.9x10-11

  20. Example 4: • Based on a Ksp value of 1.4 x 10-5 at 25°C for silver sulfate, calculate this compound’s molar solubility at 25°C. • Ag2SO4(s)2Ag+(aq) + SO4-2(aq)

  21. Example 5: Given that the molarity solubility of MgF2= 2.1x10-3 M, calculate Ksp for MgF2.

  22. Example 6: • Without any calculations, arrange the following in order of INCREASING molar solubility. • MgF2, CaF2, PbCl2, PbI2

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