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Ch 5. Reactions of Ions and Molecules in Aqueous Solutions

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

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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. 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

  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 • Strongelectrolyte – 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! 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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”. • Group IA or Group IIA hydroxides/oxides 4.3.Acids and bases are classes of compounds with special properties

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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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) NR (No reaction) Learning Check: Predict the products of the following: 4.5. Ionic reactions can often be predicted

  34. 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

  35. 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

  36. + 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

  37. 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

  38. 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

  39. 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

  40. Learning check: • What is the molarity of a solution created by dissolving 10.2g KNO3 in enough water to make 350 mL solution? • What mass of KNO3 are found in 25.33 mL of .0500M KNO3 solution? 0.29 M 0.128 g MM KNO3 = 101.1033 g/mol 4.6. The composition of a solution is described by its concentration

  41. Your turn! If 10.0 g NaCl (58.443 g/mol) are dissolved in 75.0 mL. What is the molarity? a) 0.133 M b) 2.28 M c) 7.5 M d) 0.00228M e) None of the above 4.6. The composition of a solution is described by its concentration

  42. Dilution • Adding solvent to a solution creates a less concentrated solution • moles of solute do not change, hence CstockVstock= CnewVnew • C=concentration • V=volume • Using volumetric glassware ensures that the volumes are known precisely 4.6. The composition of a solution is described by its concentration

  43. Dilution allows molecules more room • Adding solvent does not change how many moles of solute are present • The total volume does change • The concentration of the solution is decreased while the actual amount of solute is unchanged 4.6. The composition of a solution is described by its concentration

  44. Learning Check • What volume of 12.1M HCl are needed to create 250. mL of 3.2 M HCl? • 25 mL of 6 M HCl are diluted to 500 mL with water. What is the molarity of the resulting solution? 66 mL 0.3 M 4.6. The composition of a solution is described by its concentration

  45. Solution stoichiometry • What volume of 2.00M HCl is needed to react 25.2 g Na2CO3 (MM=105.9887) completely? • How many moles of BaSO4 will form if 20.0 mL of 0.600 M BaCl2 is mixed with 30.0 mL of 0.500 M MgSO4? • BaCl2(aq) + MgSO4(aq)→BaSO4(s) + MgCl2(aq) 0.0120 mol 4.7. Molarity is used for problems in solution stoichiometry

  46. Your turn! What mass of Na2CO3 (MM=105.9887) can be neutralized with 25.00 mL of 3.11 M HCl? a) 53.0 g b) 1.65(102) g c) 8.24 g d) 4.12 g e) None of these 4.7. Molarity is used for problems in solution stoichiometry

  47. Titration • Is the controlled addition of one reactant (titrant) to a known quantity of another (titrate) until the reaction is complete • Often, an indicator is used to signal the reaction completion • Endpoint: the volume of titrant required to complete the reaction . 4.8. Chemical analysis and titration are applications of solution stoichiometry

  48. Titration in practice: 4.8. Chemical analysis and titration are applications of solution stoichiometry

  49. Solving titration problems • Write the balanced equation • Calculate the moles of the known component • M×L = moles or mass/MM=moles • Use stoichiometry to determine moles of the unknown • Convert moles to desired quantity 4.8. Chemical analysis and titration are applications of solution stoichiometry

  50. Path for working titration problems 4.8. Chemical analysis and titration are applications of solution stoichiometry

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