Chapter 4 Aqueous Reactions and Solution Stoichiometry - PowerPoint PPT Presentation

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Chapter 4 Aqueous Reactions and Solution Stoichiometry

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  1. Chapter 4Aqueous Reactions and Solution Stoichiometry

  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. • Anonelectrolyte 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. Composition of Solutions • Molarity – moles of solute per volume of solution • Solute – what is being dissolved • Solvent – the dissolving agent • Will describe other ways of describing or showing concentration in chapter 11

  12. Calculation of Molarity I • Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution.

  13. Calculation of Molarity II • Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough water to make 26.8 mL of solution.

  14. Concentration of Ions I • Give concentration of each type of ion in the following solutions: • a. 0.50 M Co(NO3)2 • b. 1 M Fe(ClO4)3

  15. Concentration of Ions II • Calculate the number of moles of Cl- ions in 1.75x10-3 M ZnCl2

  16. Concentration & Volume • Typical blood serum is about 0.14 M NaCl. What volume of blood contains 1.0 mg NaCl?

  17. Solutions of Known Concentration • To analyze the alcohol content of a certain wine, a chemist needs 1.00 L of an aqueous 0.200 M K2Cr2O7 (potassium dichromate) solution. How much solid K2Cr2O7 must be weighed out to make this solution?

  18. Dilution • Dilution – adding water to a stock solution to provide a solution of desired concentration. • M1V1=M2V2- • M1 is molarity of the stock solution, M2 is molarity of the diluted solution, V1 is the volume of the stock solution (your unknown usually), V2 volume of the diluted solution • Remember this equation! You will use this all the time in the next 7 chapters. • The Monte Vista equation

  19. Concentration & Volume • What of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H2SO4 solution? Also describe in detail how you would do this in the lab.

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

  21. Solubility Rules for Common Ionic Compounds • Mainly water soluble • NO3 - all nitrates are soluble • CH3COO- all acetates are soluble • Cl- all chlorides are soluble except AgCl, Hg2Cl2, and PbCl2 • Br- all bromides are soluble except AgBr, Hg2Br2,PbBr2, & HgBr2 • I- all iodides are soluble except AgI, Hg2I2,PbI2, and HgI2 • SO42- all sulfates are soluble except CaSO4, SrSO4,BaSO4, PbSO4, Hg2SO4,and Ag2SO4 • Mainly water insoluble • O2- all oxides are insoluble except those of the 1A elements • S2- all sulfides are insoluble except those of the 1A and 2A • elements and (NH4)2S • CO32- all carbonates are insoluble except those of the 1A elements and (NH4)2CO3 • PO43- all phosphates are insoluble except those of the 1A • elements and (NH4)3PO4 • OH- all hydroxides are insoluble except those of the 1A elements, NH4OH, Ba(OH)2, Sr(OH)2, and Ca(OH)2

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

  23. Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) ReactionsAKA - Replacement Reactions

  24. Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions AKA - Replacement Reactions

  25. 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.

  26. The molecular equation lists the reactants and products in their molecular form. AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Molecular Equation

  27. 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. Ag+(aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl(s) + K+(aq) + NO3- (aq) Ionic Equation

  28. 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

  29. 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

  30. 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

  31. 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.

  32. Writing Net Ionic Equations

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

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

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