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Section 6.4—Solubility & Precipitation

Section 6.4—Solubility & Precipitation. How can we make sure everything that’s added to the sports drink will dissolve?. A Review of Double-Replacement Reactions. Cl. Ag. Na. N. N. Na. O. O. Cl. O. O. Ag. O. O. Double Replacement Reactions.

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Section 6.4—Solubility & Precipitation

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  1. Section 6.4—Solubility & Precipitation How can we make sure everything that’s added to the sports drink will dissolve?

  2. A Review of Double-Replacement Reactions

  3. Cl Ag Na N N Na O O Cl O O Ag O O Double Replacement Reactions The cations from two compounds replace each other. NaCl + AgNO3 AgCl + NaNO3 Two ionic compounds switch ions

  4. Double Replacement Reactions General format of a double replacement reaction:

  5. Products of a Double Replacement 1 Combine the cation of the first reactant with the anion of the second reactant Ca Cl2 + Ag NO3

  6. Products of a Double Replacement 2 Combine the cation of the second reactant with the anion of the first reactant Ca Cl2 + Ag NO3

  7. Products of a Double Replacement 3 Remember to write cations first … & balance charges with subscripts when writing formulas Only leave subscripts that are in the original compound there if they are a part of a polyatomic ion! Ca Cl2 + Ag NO3 + + Ca Cl2 Ag NO3 Ca(NO3)2 AgCl

  8. Precipitation Reactions

  9. Precipitation Reactions • A precipitation reaction is when 2 soluble substances are mixed together and they form an insoluble substance 2 soluble chemicals: NaOH and Cu(NO3)2

  10. Precipitation Reactions • A precipitation reaction is when 2 soluble substances are mixed together and they form an insoluble substance 2 soluble chemicals: NaOH and Cu(NO3)2 2 soluble chemical: NaNO3 1 insoluble chemical (the precipitate): Cu(OH)2

  11. Why do some things dissolve and others don’t?

  12. Remember the dissolving process? • Substances are dissolved by a process called hydration • The solvent and solute need to break intermolecular forces within themselves • New intermolecular forces are formed between the solvent and solute • The solvent “carries off” the solute particles

  13. - - O H H + Review--Dissolving Ionic Compounds - + Ionic compound water Water molecules are polar and they are attracted to the charges of the ions in an ionic compound. + - When the intermolecular forces are stronger between the water and the ion than the intramolecular between the ions, the water carries away the ion. + - + - + -

  14. - - + O + H H + Review--Dissolving Ionic Compounds - + Ionic compound water As more ions are “exposed” to the water after the outer ions were “carried off”, more ions can be “carried off” as well. - - + - + -

  15. - O H H + Review--Dissolving Ionic Compounds - + Ionic compound water + - These free-floating ions in the solution allow electricity to be conducted - + - + - + -

  16. - 2- O H H + What about with stronger ionic bonds? 2- 2+ Ionic compound water Ion charge can affect strength of ionic bond—the higher the charges, the stronger the bond. 2+ 2- 2+ 2- 2+ (How closely the two ions can pack together also affects ionic bond strength) 2- 2+ 2-

  17. - O H H + What about with stronger ionic bonds? 2- 2+ Ionic compound water If the connection between the water and the ions is not similar in strength or stronger than the ion-ion and water-water connections that are being broken… 2- 2+ 2- 2+ 2- 2+ 2- 2+ 2-

  18. - O H H + What about with stronger ionic bonds? 2- 2+ Ionic compound water If the connection between the water and the ions is not similar in strength or stronger than the ion-ion and water-water connections that are being broken… 2- 2+ 2- 2+ 2- 2+ The water won’t be able to carry the ions away…it won’t dissolve the solid. 2- 2+ 2-

  19. Solubility Rules

  20. Solubility Rules Table This table, found at the end of Chpt 6 and in the Appendix, can help you figure out which compounds dissolve (those that are soluble) and which form precipitate (insoluble)

  21. Let’s Practice #1 NaNO3 AgCH3COO CaBr2 Ba(OH)2 Cu(OH)2 Example: Decide whether each is soluble or not

  22. Let’s Practice #1 Soluble Not soluble Soluble Soluble Not Soluble NaNO3 AgCH3COO CaBr2 Ba(OH)2 Cu(OH)2 Example: Decide whether each is soluble or not

  23. Let’s Practice #2 Remember to indicate compounds that dissolve with “aq” for “aqueous” and compounds that don’t dissolve with “s” for “solid” Example: Write the products for this reaction Na2CrO4 (aq) + BaCl2 (aq) 

  24. Let’s Practice #2 Remember to indicate compounds that dissolve with “aq” for “aqueous” and compounds that don’t dissolve with “s” for “solid” Example: Write the products for this reaction Na2CrO4 (aq) + BaCl2 (aq)  2 NaCl (aq) + BaCrO4 (s)

  25. Let’s Practice #3 Remember to indicate compounds that dissolve with “aq” for “aqueous” and compounds that don’t dissolve with “s” for “solid” Example: Write the products for this reaction NaCH3COO (aq) + KCl (aq) 

  26. Let’s Practice #3 Remember to indicate compounds that dissolve with “aq” for “aqueous” and compounds that don’t dissolve with “s” for “solid” Example: Write the products for this reaction NaCH3COO (aq) + KCl (aq)  NaCl (aq) + KCH3COO (aq) When everything dissolves, there is no net reaction!

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