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Ch 5. Reactions of Ions and Molecules in Aqueous Solutions

Ch 5. Reactions of Ions and Molecules in Aqueous Solutions

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Ch 5. Reactions of Ions and Molecules in Aqueous Solutions

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  1. Ch 5. Reactions of Ions and Molecules in Aqueous Solutions Brady & Senese 5th Ed.

  2. Link to Sections 4.1. Special terminology applies to solutions 4.2. Ionic compounds conduct electricity when dissolved in water 4.3. Acids and bases are classes of compounds with special properties 4.4. Naming acids and bases follows a system 4.5. Ionic reactions can often be predicted 4.6. The composition of a solution is described by its concentration 4.7. Molarity is used for problems in solution stoichiometry 4.8. Chemical analysis and titration are applications of solution stoichiometry

  3. Solutions • solution –ahomogeneous mixture in which the two or more components mix freely • solvent - the component present in the largest amount • solute – the substance dissolved in the solvent. The solution is named by the solute. • concentration - a solute-to-solvent or solute-to-solution ratio describing the composition of the mixture 4.1. Special terminology applies to solutions

  4. Relative concentration terms The dilute solution on the left has less solute per unit volume than the (more) concentrated solution on the right 4.1. Special terminology applies to solutions

  5. Examples of Solutions The solute and solvent in a solution can be a solid, liquid, and/or a gas.

  6. Solubility • saturated –no more solute can be dissolved at the current temperature in the given amount of solvent • solubility - the amount of solute that can dissolve in the specified amount of solvent at a given temperature (usually g solute/ 100 g solvent or moles solute/L solution) • unsaturated- contains less solute than the solubility allows • supersaturated- contains more solute than solubility predicts 4.1. Special terminology applies to solutions

  7. Unsaturated Solutions Unsaturated solutions Contain less than the maximum amount of solute. Can dissolve more solute. Dissolved solute

  8. Saturated Solutions Saturated solutions Contain the maximum amount of solute that can dissolve. Generally contain undissolved solute in the container.

  9. Supersaturated solutions are unstable • Most solid solutes are more soluble at higher temperatures. • Careful cooling of saturated solutions may result in a supersaturated solution • often form a precipitate (ppt.) 4.1. Special terminology applies to solutions

  10. Effect of Temperature on Solubility Solubility: Depends on temperature. Of most solids increases as temperature increases. Of gases decreases as temperature increases.

  11. Solubility and Pressure Henry’s Law states The solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid. At higher pressures, more gas molecules dissolve in the liquid.

  12. Water as a polar solvent Polar molecules have an asymmetrical shape Have an electron rich area (often containing lone pairs) Have an electron poor area Water is polar O is electron rich H is electron poor

  13. Water Water Is the most common solvent. Is a polar molecule. Forms hydrogen bonds between the hydrogen atom in one molecule and the oxygen atom in a different water molecule.

  14. Formation of a Solution Na+ and Cl- ions Ions on the surface of a NaCl crystal are attracted to polar water molecules. Are hydrated in solution with many H2O molecules surrounding each ion.

  15. When NaCl(s) dissolves in water, the reaction can be written as H2O NaCl(s) Na+(aq) + Cl-(aq) solid separation of ions Equations for Solution Formation

  16. Water and Potassium Cyanide Potassium Cyanide is a powerful poison and ionic compound

  17. In water, Strong electrolytes produce ions and conduct an electric current. Weak electrolytes produce a few ions. Nonelectrolytes do not produce ions. Solutes and Ionic Charge

  18. Strong electrolytes are ionic compounds as well as strongly acidic/basic molecules Dissociate in water producing positive and negative ions. Conduct an electric current in water. H2O 100% ions NaCl(s) Na+(aq) + Cl− (aq) H2O CaBr2(s) Ca2+(aq) + 2Br− (aq) Strong Electrolytes

  19. Weak electrolyte are weakly acidic/basic molecules Dissociates only slightly in water. In water forms a solution of a few ions and mostly undissociated molecules. HF(g) + H2O(l) H3O+(aq) + F- (aq) NH3(g) + H2O(l) NH4+(aq) + OH- (aq) Weak Electrolytes

  20. Nonelectrolytes Nonelectrolytes are nonacidic/ nonbasic molecules. Dissolve as molecules in water. Do not produce ions in water. Do not conduct an electric current.

  21. Ionic equations show dissociated ions • hydrated ions, with the symbol (aq), are written separately • Na2SO4(s)→ 2Na+(aq) + SO42-(aq) • you might encounter the equation as: • Na2SO4(s)→ 2Na+ + SO42- • Accepted because only 2 states allow for dissociated ions (plasma and aqueous). Aqueous is far more common • It is vague and not preferred 4.2. Ionic compounds conduct electricity when dissolved in water

  22. Learning check Write the equations that illustrate the dissociation of the following: • Na3PO4(aq)→ • Al2(SO4)3(aq) → • CaCl2(aq) → • Ca(MnO4)2(aq) → 3Na+(aq) + PO43-(aq) 2Al3+(aq) + 3SO42-(aq) Ca2+(aq) + 2Cl-(aq) Ca2+(aq) + 2MnO4-(aq) 4.2. Ionic compounds conduct electricity when dissolved in water

  23. Your turn! How many ions form on the dissociation of Na3PO4? • 1 • 2 • 3 • 4 • none of the above 4.2. Ionic compounds conduct electricity when dissolved in water

  24. Writing chemical equations • Molecular equation: • Balanced, shows states, all substances electrically neutral • AgNO3(aq) + KCl(aq)→AgCl(s) + KNO3(aq) • Ionic equation: • Balanced, shows states, shows strong electrolytes as dissociated ions, net charges balance • Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)→AgCl(s) + K+(aq) + NO3-(aq) • Net ionic equation: • Balanced, shows states, eliminates spectator ions from the ionic equation, net charges balance • Ag+(aq) + Cl-(aq)→AgCl(s) 4.2. Ionic compounds conduct electricity when dissolved in water

  25. Learning check: • Write the ionic equations for each: • BaCl2(aq) + Pb(NO3)2(aq)→PbCl2(s) + Ba(NO3)2(aq) • Ba2+(aq) + 2Cl-(aq) + Pb2+(aq) + 2NO3-(aq) →PbCl2(s) + Ba2+(aq) + 2NO3-(aq) • Na2CO3(aq) +CaCl2(aq) →CaCO3(s) +2NaCl(aq) • 2Na+(aq) + 2CO32-(aq) + Ca2+(aq) + 2Cl-(aq) → CaCO3(s)+ 2Na+(aq) + 2Cl-(aq) 4.2. Ionic compounds conduct electricity when dissolved in water

  26. Writing net ionic equations • Show only those ions that were changed by the process • Omits spectator ions: • When we compare the reactant to product spectator ions are those ions that are not changed in any way 4.2. Ionic compounds conduct electricity when dissolved in water

  27. Write the following as net ionic equations: Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq)→PbI2(s) + 2K+(aq) + 2NO3-(aq) Ba2+(aq)+ 2Cl-(aq) + 2Na+(aq) + SO42-(aq)→BaSO4(s) + 2Na+(aq))+ 2Cl-(aq) 2Na+(aq))+ 2Cl-(aq) + Hg22+(aq) + 2NO3-(aq)→ 2Na+(aq) + 2NO3-(aq) + Hg2Cl2(s) Learning check: Pb2+(aq) + 2I-(aq)→PbI2(s) Ba2+(aq)+ SO42-(aq)→BaSO4(s) 2Cl-(aq) + Hg22+(aq)→Hg2Cl2(s) 4.2. Ionic compounds conduct electricity when dissolved in water

  28. Your turn! Consider the following reaction : Na2SO4(aq) + BaCl2(aq)→2NaCl(aq) + BaSO4(s) Which is the correct total ionic equation? • 2Na+(aq) + SO42- (aq) + Ba2+(aq)+ Cl22-(aq) → 2Na+(aq) +2Cl-(aq) + BaSO4(s) • 2Na+(aq) + SO42- (aq) + Ba2+(aq)+ 2Cl-(aq) → 2Na+(aq) +2Cl-(aq) + BaSO4(s) • 2Na+(aq) + SO42- (aq) + Ba2+(aq)+ Cl22-(aq) → 2Na+(aq) +2Cl-(aq) + Ba2+(s) + SO42-(s) • None of these 4.2. Ionic compounds conduct electricity when dissolved in water

  29. The Arrhenius definition of acids • An acid is a substance that ionizes in a reaction with water to form the hydronium ion, H3O+ • Strong acids are 100% ionized when dissolved, whereas weak acids are far less efficiently ionized 4.3.Acids and bases are classes of compounds with special properties

  30. What is H(aq)+? • It is common to encounter the hydrogen ion (H+) instead of the hydronium ion • The previous ionization is, for simplicity, also written as: H+ does not ever exist in aqueous solution- it is always attached to a water molecule as the hydronium ion 4.3.Acids and bases are classes of compounds with special properties

  31. Nonmetal oxides can be acids • Nonmetal oxides, or “acidicanhydrides” react with water to form acid solutions • SO2(g) + H2O(l)→H2SO3(aq) • CO2(g) + H2O(l) →H2CO3(aq) 4.3.Acids and bases are classes of compounds with special properties

  32. Arrhenius bases • Base- substance that produces hydroxide ions in water • Molecular bases undergo an ionization or dissocation reactionto form the hydroxide ions, and are weak bases • Many N-compounds are molecular bases • B(aq) + H2O(l)HB+(aq) + OH-(aq) 4.3.Acids and bases are classes of compounds with special properties

  33. Metal oxides and hydroxides are bases • Metal hydroxide solutions dissociate into metal and hydroxide ions and are strong bases. • NaOH(s)→Na+(aq) + OH-(aq) • Soluble metal oxides “basic anhydrides” react with water to form metal hydroxides that are strong bases • CaO(s) +H2O(l) → Ca2+(aq) + 2OH-(aq) 4.3.Acids and bases are classes of compounds with special properties

  34. Strong vs. weak • Some acids ionize 100% in water, and are termed “strong acids” and are also “strong electrolytes” • HCl, HClO4, HNO3, HBr, HI, H2SO4 • The very soluble metal hydroxides and oxides are strong electrolytes and “strong bases”. • Group IA and IIA metals with hydroxides or oxides. • NaOH, MgO, etc… 4.3.Acids and bases are classes of compounds with special properties

  35. Weak acids and bases are weak electrolytes 4.3.Acids and bases are classes of compounds with special properties

  36. Naming binary acids (aqueous) • prefix hydro- + nonmetal stem + the suffix –ic, followed by the word acid • Stem is first syllable of element name. i.e. Chlorine • P and S stems use 2 syllables phosphorus, sulfur • the name of the (aq) form differs from other states due to the ionization that occurs in water 4.4. Naming acids and bases follows a system

  37. Your turn! Which of the following is not named as an hydro___ic acid? • HCl • H2S • HNO3 • HF • all are named in this way 4.4. Naming acids and bases follows a system

  38. Oxoacids (aqueous) • named according to the anion suffix • anion ends in -ite, the acid name is -ous acid • ends in -ate, the acid name is -ic acid 4.4. Naming acids and bases follows a system

  39. HNO2 HCN HClO4 HF HMnO4 H2CO3 nitrous acid hydrocyanic acid perchloric acid hydrofluoric acid permanganic acid carbonic acid Learning check: Name each aqueous acid 4.4. Naming acids and bases follows a system

  40. Your turn! Which of the following is the correct name for HClO4(aq)? • chloric acid • hydrochloric acid • perchloric acid • none of the above 4.3.Acids and bases are classes of compounds with special properties

  41. Your turn! Which of the following is the correct name for H2SO3(aq)? • sulfuric acid • sulfurous acid • hydrosulfuric acid • none of the above 4.3.Acids and bases are classes of compounds with special properties

  42. Acid salts • polyprotic acids can be partially neutralized to form acid salts • acidic salt- contains an anion that is capable of furnishing additional hydrogen ions • The number of hydrogen atoms that can still be neutralized is also indicated in the name 4.4. Naming acids and bases follows a system

  43. A solution reaction will occur if: • A precipitate (insoluble product) forms from soluble reactants • An acid reacts with a base 4.5. Ionic reactions can often be predicted

  44. Metathesis (double replacement) reactions • AB + CD → AD + CB • Cations change partners • Charges on each ion don’t change • Formulas of the products are determined by the charges of the reactant ions • Metathesis reactions occur only if they form a weak electrolyte or non-electrolyte as a product (otherwise, all ions are spectator ions) 4.5. Ionic reactions can often be predicted

  45. counting subscript 2 2 Predicting metathesis reactions • Identify the ions involved: • Do not confuse counting subscripts (those present only to make charges cancel) with those that are characteristic of a polyatomic ion • Swap partners and make neutral with appropriate subscripts • Assign states using solubility rules • Balance the equation HCl(aq) + Ca(OH)2(aq) → CaCl2 + H2O (aq) (l) ions: H+, Cl- Ca2+ , OH- 4.5. Ionic reactions can often be predicted

  46. Solubility rules: soluble compounds • A general idea as to whether a fair amount of solid will dissolve is achieved using solubility rules • All compounds of the alkali metals (Group IA) • All salts containing NH4+, NO3−, ClO4−, ClO3−, and C2H3O2− • All chlorides, bromides, and iodides (salts containing Cl−, Br−, or I−) except when combined with Ag+, Pb2+, and Hg22+ • All sulfates (salts containing SO42−) except those of Pb2+, Ca2+, Sr2+, Hg22+, and Ba2+ 4.5. Ionic reactions can often be predicted

  47. Solubility rules: insoluble compounds • All metal hydroxides (ionic compounds containing OH−) and all metal oxides (ionic compounds containing O2−) are insoluble except those of Group IA and IIA • When metal oxides dissolve, they react with water to form hydroxides. The oxide ion, O2−, does not exist in water. For example, Na2O(s) +H2O(l)→ 2NaOH(aq) • All salts that contain PO43−, CO32−, SO32−, and S2− are insoluble, except those of Group IA and NH4+. 4.5. Ionic reactions can often be predicted

  48. Learning check: Which of the following compounds are expected to be soluble in water? Ca(C2H3O2)2 FeCO3 AgCl Yes No No 4.5. Ionic reactions can often be predicted

  49. Pb(NO3)2(aq) + Ca(OH)2(aq) → BaCl2(aq) + Na2CO3(aq) → Na3PO4(aq) + Hg2(NO3)2(aq) → NaCl(aq) + Ca(NO3)2(aq)→ Pb(OH)2(s) + Ca(NO3)2(aq) BaCO3(s) + NaCl(aq) NaNO3(aq) + (Hg2)3(PO4) 2(s) CaCl2(aq) + NaNO3(aq) NR (No reaction) Learning Check: Predict the products of the following: 4.5. Ionic reactions can often be predicted

  50. Your turn! Which of the following will be the solid product of the reaction of Ca(NO3)2(aq) + Na2CO3(aq)→? • CaCO3 • NaNO3 • Na(NO3)2 • Na2(NO3)2 • None of the above 4.5. Ionic reactions can often be predicted