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Chapter 4

Chapter 4. Aqueous reactions and solution stoichiometry. Aqueous Chemistry. Virtually all chemistry that makes life possible occurs in solution Common tests for sugar, cholesterol, and iron are all done in solution. Solution Vocabulary. Solution: Homogeneous mix of 2+ substances

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Chapter 4

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  1. Chapter 4 Aqueous reactions and solution stoichiometry

  2. Aqueous Chemistry • Virtually all chemistry that makes life possible occurs in solution • Common tests for sugar, cholesterol, and iron are all done in solution.

  3. Solution Vocabulary • Solution: Homogeneous mix of 2+ substances • Solvent: dissolving medium (water, oil, liquid nitrogen), present in larger qty. • Solute: what is being dissolved (salt, sugar, sodium hydroxide), present in smaller qty. • Aqueous Solution: When water is the dissolving medium (Making Kool-Aid) • Electrolytes: substance that dissolves in water to yield a solution that conducts electricity. (salt water)

  4. Solution Solvent Solute Soft drink (l) H2O Sugar, CO2 Air (g) N2 O2, Ar, CH4 Soft Solder (s) Pb Sn 4.1

  5. 4.1 General Properties of Solutions • One of the properties of water is its ability to dissolve MANY different substances. • Polar: unequal distribution of charges makes water polar, allowing it to dissolve solutes.

  6. Ions dissolving in water Ionic substances such as salts dissolve in water to release cations (+) and anions (-). Ex: NaCl -> Na+ , Cl- The dissociation of NaCl is called hydration.

  7. Solvation- The process in which an ion or a molecule is surrounded by solvent molecules arranged in a specific manner. • Hydration – solvation with water as solvent

  8. A Note On Dissociation • You must memorize the charges or all the ions and poly atomic ions in order to predict how molecules will dissociate. If you don’t know them by now you are in trouble. Make flash cards and study!

  9. Solubility • The amount of a substance that dissolves in a given volume of solvent at a given temperature. • If ionic compounds are not greatly attracted to the ions in water then that compound will be less soluble in water.

  10. What is not soluble in water? • Like dissolves like • In general polar (unequal distribution of charges) and ionic substances are expected to be more soluble in water than nonpolar substances.

  11. Electrolyte Vocabulary • Ionization: the process of adding or removing electrons from an atom or molecule. Which gives the atom a net charge. • Complete Ionization: substances that only exist as ions in solution

  12. Strong and Weak electrolytes • Strong electrolyte: ionize completely in water (single arrow). Are good conductors of electricity • Ex: Strong acids, strong bases and salts.

  13. Weak Electrolytes • Ionize partially in water (double arrows). Poor conductors of electricity • Ex: weak acids (acetic acid shown), weak bases, partially soluble salts. And thus The reaction is reversible

  14. Non-electrolytes • Do not IONIZE in water or conduct electricity. They are covalent compounds that are not acids or bases. • Dissolve in water as molecules instead of ions. Sugar (C12H22O11)

  15. Identify the strong and weak electrolytes.

  16. nonelectrolyte weak electrolyte strong electrolyte An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. 4.1

  17. Molecular Compounds

  18. Homework • Chang pg 157 # ‘s 1 2 4 7 11 • BL Pg 145 #’s 3, 5, 6, 7, 8

  19. 4.2 Precipitate Reactions • Reactions that result in the formation of an insoluble substance. • (-) anion • (+) cation Ag(NO3)2 (aq) + 2NaI (aq)  AgI2 (s) + 2NaNO3(aq)

  20. Question How would each molecule dissociate? Label cations and anions. NiSO4 Ca(NO3)2 Na3PO4 Al2(SO4)3

  21. Answer Ni 2+ SO42- Ca2+ (NO3)2 - Na3+PO43- Al23+(SO4)32-

  22. Solubility Rules to Memorize • You must memorize the following rules. • You will have a pop quiz on solubility rules in the next week. • If you do not pass with 85% you must write all the rules out 5 times each.

  23. Solubility Rules (memorize) Solubility Rules (memorize) 1. NH4+ and alkali metal (group IA) salts are soluble. 2. Nitrate, NO3-, acetate C2H3O2-, chlorate, ClO3-, perchlorate ClO4 salts are soluble. 3. Chloride, Cl-, bromide, Br-,iodide, I-, salts are soluble. EXCEPT: Ag+, Hg22+, Pb2+ (AgBr, Hg2I2, PbCl2) 4. Sulfate, SO42- , salts are soluble. EXCEPT: PbSO4, HgSO4, CaSO4, BaSO4, AgSO4, SrSO4 5. Most Hydroxide, OH- ,salts are slightly soluble. Hydroxide salts of Group I elements are soluble (Li, Na, K, Rb, Cs, Fr). Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble.

  24. Use Solubility Rules to Classify as Soluble or Insoluble • Sodium carbonate Na2CO3 • Lead Sulfate PbSO4 • Cobalt (II) hydroxide • Barium nitrate • Ammonium phosphate

  25. Answer • Sodium carbonate Na2CO3 Soluble (#1) • Lead Sulfate PbSO4 Insoluble (#4) • Co(OH)2 Insoluble (#5) • Ba(NO3)2 Soluble (#2) • Ammonium phosphate (NH4)3PO4 • New Polyatomic: PO4-3 Phosphate

  26. Goal • Use solubility rules to predict whether a precipitate will form when electrolytic solutions are mixed. • Hint: find products that have insoluble salt(s). This implies a precipitate reaction.

  27. Example • Predict what will happen when the following pairs of solutions are mixed. (Hint: break it into ions) KNO3(aq) and BaCl2 (aq) Na2SO4(aq) and Pb(NO3)2(aq)

  28. Answer • KNO3(aq) and BaCl2 (aq) Reactants: K+ + NO3- + Ba2+ + Cl- Products: KCl + Ba(NO3)2 Both are soluble according to the rules and thus no precipitate forms. Rule #1 Rule # 2

  29. Na2SO4(aq) and Pb(NO3)2(aq) Reactants: Na+ + SO42- + Pb2+ + NO3- Products: NaNO3+ PbSO4 NaNO3 Soluble according to rule #1. PbSO4 Insoluble according to rule # 4

  30. Demonstrations Aqueous iron (III) nitrate reacts with sodium hydroxide

  31. Demonstrations CoCl2(aq) + Ca(OH)2(aq) 

  32. Predicting Precipitates • Predict the precipitate that forms when solutions mix and write a balanced chemical equation. • BaCl2 (aq) + K2SO4 (aq)  • Fe2(SO4)3 (aq) + LiOH (aq) 

  33. Answer BaCl2 (aq)+ K2SO4 (aq)  BaSO4 (s) + 2KCl Fe2(SO4)3 (aq) + 6LiOH (aq) 2Fe(OH)3 (s) + 3Li2SO4 (aq)

  34. Describing reactions • In this section we will talk about the types of equations used to represent reactions in solution. • Three types of equations: • Molecular • Complete ion • Net ionic

  35. precipitate Pb(NO3)2(aq) + 2NaI (aq) PbI2(s) + 2NaNO3(aq) Pb2+(aq) + 2NO3-(aq) + 2Na+ (aq) + 2I-( aq) PbI2 (s) + 2Na+ (aq) + 2NO3- (aq) Pb2+aq + 2I-aq PbI2 (s) PbI2 Precipitation Reactions Precipitate – insoluble solid that separates from solution molecular equation ionic equation net ionic equation Na+ and NO3- are spectator ions 4.2

  36. Molecular Equations/Chemical equation • Shows the complete chemical formula for reactants and products HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) Strong acid Strong Base Soluble Salt weak electrolyte Strong elect. Strong elect.

  37. Complete Ionic Equation Shows the formula of cations and anions for ionic compounds. H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  Na+(aq) + Cl-(aq) + H2O(l) Water (l) and solid (s) precipitates do not break down into ions Solids on reactant side can break down in water (i.e adding salt to water)

  38. Net Ionic Equation • Includes only those solutions components directly involved in the reaction. H+(aq) + OH-(aq)  H2O(l) Spectator ions: ions that appear in identical forms in reactants and product side of a chemical rxn that do not participate in the rxn directly. NOTE: The net ionic equation of any strong acid-base neutralization rxn is always like the above rxn.

  39. Write the three types of equations for the following rxn. Pb(NO3)2 (aq) + KI (aq) 

  40. Molecular Pb(NO3)2(aq) + 2KI (aq)  PbI2 (s) + 2KNO3 (aq) Complete Ionic Pb 2+ (aq) + 2NO3-1(aq) + 2K+ (aq) + 2I- (aq) PbI2 (s) + 2K+ (aq) + 2NO3- (aq) • Note subscripts that a re “multiplied” through become coefficients • Coefficients apply to all atoms in a compound Net Ionic Pb 2+ (aq) + 2I- (aq)  PbI2 (s)

  41. AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq) Write the net ionic equation for the reaction of silver nitrate with sodium chloride. Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3- Ag+ + Cl- AgCl (s) Writing Net Ionic Equations • Write the balanced molecular equation. • Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions. • Cancel the spectator ions on both sides of the ionic equation • Check that charges and number of atoms are balanced in the net ionic equation 4.2

  42. 4.2 Homework • Chang pg 156-157 #’s 9,10,12,15,18,19,21, 22, • BL: Pg 145 #’s 11, 12, 14, 15, 16, 19

  43. 4.3 Acids Substances that are able to donate a hydrogen ion (H+) and increase [H+] in aqueous solutions. MEMORIZE

  44. Properties of acids • Sour taste • Acids neutralize bases • Acids corrode active metals • Acids release a hydrogen ion into water (aqueous) solution • Strong acids conduct electricity

  45. Properties of Bases • Bitter taste • Slippery feel • Bases denature protein • Bases neutralize acids • Bases release a hydroxide ion into water solution • Strong bases conduct electricity

  46. Bases • Are soluble ionic compounds containing hydroxide ion (OH-). • When dissolved in water the cations and OH- ions separate and move independently. • MEMORIZE /LEARN

  47. Strong electrolytes • All of the strong bases and acids that you memorized are strong electrolytes because they ionize completely. • All weak acids and bases are weak electrolytes because they only partially ionize.

  48. Salts • Another name for an ionic compound. When a salt dissolves in water, it breaks up into its ions, which move about independently. • ionic substances are electrolytes • Result from acid base neutralizations Hand crafted Himalayan Salt Lamps bring beauty, harmony and health into your living and working space.

  49. Classify the following dissolved substances as strong or weak electrolytes: CaCl2 HNO3 C2H5OH HCHO2

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