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Ch 4. Reactions of Ions and Molecules in Aqueous Solutions
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Ch 4. Reactions of Ions and Molecules in Aqueous Solutions

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  1. Ch 4. Reactions of Ions and Molecules in Aqueous Solutions Tanguay HC1 Chapter 4

  2. 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 ratio describing the composition of the mixture 4.1. Special terminology applies to solutions

  3. 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

  4. 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

  5. Your turn! The solubility of NaCl is 39.0 g / 100 g water at 100 ºC. If 10.0 g are dissolved in 50.0 g water at this temperature, the solution is: • saturated • unsaturated • supersaturated • none of these 4.1. Special terminology applies to solutions

  6. 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

  7. Ionic compounds in water • Water molecules arrange themselves around the ions and dissociate them from the lattice. • The separated ions are “hydrated” and conduct electrical current (act as electrolytes) • Polyatomic ions remain intact in the dissociation process. 4.2 Ionic Compounds Conduct Electricity When Dissolved in Water

  8. Molecular compounds in water • The solute particles are surrounded by the water, but the molecules are not dissociated 4.2. Ionic compounds conduct electricity when dissolved in water

  9. Electrical conductivity • Strong electrolyte – aqueous solution that conducts electricity because solute is 100% dissociated into ions • Weak electrolyte –aqueous solution that weakly conducts electricity due to low ionization • Non-electrolyte – an aqueous solution that doesn’t conduct electricity because solute does not dissociate into ions 4.2. Ionic compounds conduct electricity when dissolved in water

  10. 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

  11. 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

  12. Your turn! Which of the following would not be expected to produce Cl-(aq) when dissolved? • PCl3(aq) • NaCl(aq) • HCl(aq) • none of the above • all produce Cl-(aq) 4.2. Ionic compounds conduct electricity when dissolved in water

  13. 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

  14. Your turn! How many ions form on the dissociation of Al2(SO4)3? • 2 • 3 • 4 • 5 • none of the above 4.2. Ionic compounds conduct electricity when dissolved in water

  15. 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

  16. Writing ionic equations Since strong electrolytes exist as dissociated ions in solution, we can show this in an equation. • identify the strong electrolytes • distinguish counting subscripts (those present only to make charges cancel) from characteristic subscripts-- counting subscripts become multipliers • separate the ions in the strong electrolytes • show the states as recorded in the molecular equations 4.2. Ionic compounds conduct electricity when dissolved in water

  17. 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

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

  19. 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

  20. 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

  21. The Arrhenius definition of acids • An acid is a substance that ionizes in a reaction with water to form the hydroniumion, 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

  22. 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

  23. 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

  24. Arrhenius bases • Base- substance that produces hydroxide ions in water • Molecular bases undergo an ionization (hydrolysis)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

  25. 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 “basicanhydrides” 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

  26. 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 are strong electrolytes and “strong bases”. • Ia hydroxides and Ca, Ba, and Sr hydroxides. 4.3.Acids and bases are classes of compounds with special properties

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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. A reaction will exist if… • A precipitate (insoluble product) forms from soluble reactants • An acid reacts with a base • A weak electrolyte product is formed from strong electrolyte reactants • A gas is formed from a mixture of reactions 4.5. Ionic reactions can often be predicted

  36. 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

  37. 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

  38. 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

  39. 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 of Ca2+, Sr2+, and Ba2+ • 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

  40. 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

  41. 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

  42. 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

  43. Predicting acid-base reactions • Neutralization: metathesis reaction in which acid + metal hydroxide or metal oxide forms water and salt • NaOH(aq) + HCl(aq)→H2O(l) + NaCl(aq) • Acid-base reaction: reaction of weak base and acid transferring a H+ ion, driven by the formation of a weaker acid. • HCl(aq) + NH3(aq) →NH4Cl(aq) 4.5. Ionic reactions can often be predicted

  44. + 2H+(aq)+2Cl-(aq) Ca2+ (aq)+2OH- (aq) → 2H2O(l) + Ca 2+(aq)+ 2Cl-(aq) Learning check Determine the molecular, total ionic and net ionic equations • Molecular Equation • Total Ionic Equation (TIE) • Net Ionic Equation (NIE) 2HCl(aq) + Ca(OH)2(aq) → 2H2O(l) +CaCl2(aq) H+(aq) + OH- (aq)→H2O(l) 4.5. Ionic reactions can often be predicted

  45. Your turn! Which of the following is not a product of the reaction: NH3(aq) +HCN(aq) →? • NH3CN(aq) • NH4+(aq) • CN-(aq) • None of the above 4.5. Ionic reactions can often be predicted

  46. Your turn! Which is the net ionic equation for the reaction: NaOH(aq) + HF(aq)→? • Na+(aq)+ OH-(aq) + H+(aq) + F-(aq) →H2O(l) + NaF(aq) • OH-(aq) + H+(aq) →H2O(l) • OH-(aq) + HF(aq) →H2O(l) + F-(aq) • Na+(aq)+ OH-(aq) + HF(aq) →H2O(l) + NaF(aq) • None of the above 4.5. Ionic reactions can often be predicted

  47. Metathesis and gas formation • If the product of a metathesis reaction is one of the following, formation of a gas is a driving force. • Gases formed by metathesis: H2S, HCN • Unstable compounds that decompose and form a gas: • H2CO3 (H2O & CO2(g)) • NH4OH (H2O & NH3(g)) • H2SO3 (H2O & SO2(g)) 4.5. Ionic reactions can often be predicted

  48. Metathesis overview • Precipitation: 2 solutions form solid product • Neutralization: acid + metal hydroxide or oxide form water and a salt • Gas-forming: metathesis reaction forms one of these products: • HCN, H2S, H2CO3(aq), H2SO3(aq), NH4OH(aq) • Check for a driving force: formation of weak electrolyte or non-electrolyte 4.5. Ionic reactions can often be predicted

  49. Your turn! Which of the following combinations will not react? • Na2CO3 (aq) + HCl(aq) • Na2CO3(aq) + CaCl2(aq) • NaCl(aq) + H2C3O2(aq) • None of these • All of these 4.5. Ionic reactions can often be predicted

  50. In solutions, solutes are dispersed in a larger volume Molarity expresses the relationship between the moles of solute and the volume of the solution Molarity (M)=moles solute/L solution Hence, a 6.0M solution of HCl contains 6.0 mole HCl in a liter of solution Molar concentrations 4.6. The composition of a solution is described by its concentration