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Chapter 4 Aqueous Reactions and Solution Stoichiometry

Chemistry, The Central Science , 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten. Chapter 4 Aqueous Reactions and Solution Stoichiometry. John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Solutions:.

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Chapter 4 Aqueous Reactions and Solution Stoichiometry

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  1. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 4Aqueous Reactions and Solution Stoichiometry John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc.

  2. Solutions: • Homogeneous mixtures of two or more pure substances. • The solvent is present in greatest abundance. • All other substances are solutes.

  3. Dissociation • When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. • This process is called dissociation.

  4. Electrolytes • Substances that dissociate into ions when dissolved in water. • Anon-electrolyte may dissolve in water, but it does not dissociate into ions when it does so.

  5. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes.

  6. Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases.

  7. Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water.

  8. Strong Electrolytes Are… • Strong acids

  9. Strong Electrolytes Are… • Strong acids • Strong bases

  10. Strong Electrolytes Are… • Strong acids • Strong bases • Soluble ionic salts

  11. Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed.

  12. Precipitation Reactions Common Solubility Laws (p. 127) Note: All common ionic compounds of the alkali metal ions, NH4+, and NO3- are soluble in water

  13. Precipitation Reactions To predict whether a precipitate forms when two solutions of soluble aqueous compounds are mixed: • Note ions in the reactants • Consider all possible combinations (no +/+ or -/- combos) • Use table 4.1 to determine if any of these combinations are insoluble Ex: Mix Fe2(SO4)3 (aq) + LiOH (aq)

  14. Metathesis comes from a Greek word that means “to transpose” AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions

  15. Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions “Square-dancing” Switch your partners! AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions

  16. Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions “Square-dancing” Switch your partners! AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions

  17. To complete and balance Use chemical formulas of reactants to determine the ions that are present Write the chemical formulas of products by rearranging and combining cations and anions Balance the product chemical formulas Balance the entire equation AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions

  18. Solution Chemistry • It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). • If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction.

  19. The molecular equation lists the reactants and products in their molecular form. Note that everything is aqueous, except the AgCl. What does that mean? AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Molecular Equation

  20. In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. Note: everything is broken up except the AgCl. Why? Ag+(aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl(s) + K+(aq) + NO3- (aq) Ionic Equation

  21. To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl(s) + K+(aq) + NO3-(aq) Net Ionic Equation

  22. To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag+(aq) + Cl-(aq) AgCl(s) Net Ionic Equation

  23. To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl(s) + K+(aq) + NO3-(aq) Net Ionic Equation

  24. Writing Net Ionic Equations • Write a balanced molecular equation. • Dissociate all strong electrolytes. • Cross out anything that remains unchanged from the left side to the right side of the equation. • Write the net ionic equation with the species that remain.

  25. Writing Net Ionic Equations

  26. Stoichiometry – Determining the mass of a product formed • Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO3 solution to precipitate all the Ag+ in the form of AgCl.

  27. Stoichiometry – Determining the mass of a product formed • When aqueous solutions of Na2SO4 and Pb(NO3)2 are mixed PbSO4 precipitates. Calculate the mass of PbSO4 formed when 1.25 L of 0.0500 M Pb(NO3)2 & 2.00 L of 0.0250M Na2SO4 are mixed.

  28. Acids: Neutralization Reactions • Substances that increase the concentration of H+ when dissolved in water (Arrhenius). • Proton donors (Brønsted–Lowry).

  29. Acids There are only seven strong acids: • Hydrochloric (HCl) • Hydrobromic (HBr) • Hydroiodic (HI) • Nitric (HNO3) • Sulfuric (H2SO4) • Chloric (HClO3) • Perchloric (HClO4)

  30. Bases: • Substances that increase the concentration of OH− when dissolved in water (Arrhenius). • Proton acceptors (Brønsted–Lowry).

  31. Bases The strong bases are the soluble salts of hydroxide ion: • Alkali metals • Calcium • Strontium • Barium

  32. Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H+) to the base.

  33. Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) Neutralization Reactions

  34. When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq) Na+ (aq)+ Cl- (aq)+ H2O (l) Neutralization Reactions

  35. When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq) Na+ (aq)+ Cl- (aq)+ H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH- (aq) Na+ (aq) + Cl- (aq) + H2O (l) Neutralization Reactions

  36. Neutralization Reactions Observe the reaction between Milk of Magnesia, Mg(OH)2, and HCl.

  37. These metathesis reactions do not give the product expected. The expected product decomposes to give a gaseous product (CO2 or SO2). CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) NaHCO3 (aq) + HBr (aq) NaBr (aq)+ CO2 (g) + H2O (l) SrSO3 (s) + 2 HI(aq) SrI2 (aq) + SO2 (g) + H2O (l) Gas-Forming Reactions

  38. This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! Just as in the previous examples, a gas is formed as a product of this reaction: Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g) Gas-Forming Reactions

  39. Neutralization reactions • When volume of a 1.00 M HCl solution is needed to neutralize 25.0 mL of 0.350 M NaOH?

  40. Neutralization reactions • In a certain experiment, 28.0 mL of 0.250 M HNO3 and 53.0 mL of 0.320 M KOH are mixed. Calculate the amount of water formed in the resulting reaction. What is the concentration of H+ or OH- s in excess after the reaction goes to completion?

  41. Titration The analytical technique in which one can calculate the concentration of a solute in a solution.

  42. Titration

  43. Neutralization reactions A student carries out an experiment to standardize a sodium hydroxide solution. To do this the student weighs out a 1.3009-g sample of potassium hydrogen phthalate or KHP(KHC8O4O4 . KHP (molar mass 204.22 g/mol) has one acidic hydrogen. The student dissolves the KHP in distilled water, adds phenolphthalein as an indicator, and titrates the resulting solution with the sodium hydroxide to the phenolphthalein endpoint. The difference between the final & initial buret readings indicates that 41.20 mL of the sodium hydroxide is required to react exactly with the 1.3009 g of KHP. Calculate the concentration of the sodium hydroxide solution.

  44. Neutralization reactions An environmental chemist analyzed the effluent from an industrial process known to produce the compounds carbon tetrachloride and benzoic acid (HC7H5O2), a weak monoprotic acid. A sample of this effluent weighing 0.3518 g was shaken with water, and the resulting aqueous solution required 10.59 mL of 0.1546 M NaOH for neutralization. Calculate the mass percent of HC7H5O2 in the original sample.

  45. Oxidation-Reduction Reactions • An oxidation occurs when an atom or ion loses electrons. • A reduction occurs when an atom or ion gains electrons.

  46. Oxidation-Reduction Reactions One cannot occur without the other.

  47. Terminology for Redox Reactions • OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. • REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. • OXIDIZING AGENT—electron acceptor; species is reduced. • REDUCING AGENT—electron donor; species is oxidized.  When you go to a travel agent, who ends up traveling?  YOU, or the agent? 

  48. You can’t have one… without the other! • Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. • You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! ose lectrons xidation ain lectrons eduction GER!

  49. 2Mg (s) + O2 (g) 2MgO (s) 2Mg 2Mg2+ + 4e- O2 + 4e- 2O2- 2Mg + O2 + 4e- 2Mg2+ + 2O2- + 4e- 2Mg + O2 2MgO Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) 4.4

  50. 4.4

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