Chapter 4 Chemical Reactions: An Introduction

1. Chapter 4 Chemical Reactions: An Introduction

2. Suggested Problems for Chapter 4 4.9, 4.12, 4.17, 4.18, 4.23, 4.25, 4.28, 4.29, 4.32, 4.37, 4.39, 4.44, 4.47, 4.55, 4.59, 4.65. 4.73, 4.75, 4.79, 4.95, 4.97, 4.131

3. Figure 4.1: Reaction of potassium iodide solution and lead (II) nitrate solution. Photo courtesy of James Scherer.

4. Electrolytes

5. Figure 4.2: Motion of ions in solution.

6. Figure 4.3: Testing the electrical conductivity of a solution: water.Photo courtesy of American Color.

7. Figure 4.3: Testing the electrical conductivity of a solution: sodium chloride.Photo courtesy of American Color.

8. Figure 4.4: Comparing strong and weak electrolytes: HCl. Photo courtesy of American Color.

9. Figure 4.4: Comparing strong and weak electrolytes: NH3. Photo courtesy of American Color.

10. Methanol Li

11. The Role of Water as a Solvent: The Solubility of Ionic Compounds Electrical conductivity - The flow of electrical current in a solution is a measure of the solubility of ionic compounds or a measurement of the presence of ions in solution. Electrolyte - A substance that conducts a current when dissolved in water. Soluble ionic compound dissociate completely and may conduct a large current, and are called strong Eeectrolytes. NaCl(s) + H2O(l) Na+(aq) + Cl -(aq) When sodium chloride dissolves into water the ions become solvated, and are surrounded by water molecules. These ions are called “aqueous” and are free to move through out the solution, and are conducting electricity, or helping electrons to move through out the solution

12. Fig. 4.2

14. The Solubility of Ionic Compounds in Water The solubility of ionic compounds in water depends upon the relative strengths of the electrostatic forces between ions in the ionic compound and the attractive forces between the ions and water molecules in the solvent. There is a tremendous range in the solubility of ionic compounds in water! The solubility of so called “insoluble” compounds may be several orders of magnitude less than ones that are called “soluble” in water, for example: Solubility of NaCl in water at 20oC = 365 g/L Solubility of MgCl2 in water at 20oC = 542.5 g/L Solubility of AlCl3 in water at 20oC = 699 g/L Solubility of PbCl2 in water at 20oC = 9.9 g/L Solubility of AgCl in water at 20oC = 0.009 g/L Solubility of CuCl in water at 20oC = 0.0062 g/L

16. Types of Chemical Reactions • Most reactions fall under three basic types 1) Precipitation Reactions 2) Acid-Base Reactions 3) Oxidation-Reduction Reactions (RedOx)

17. Precipitation

18. Solubility • Soluble = ability to dissolve in a liquid • Insoluble = inability to dissolve in a liquid • Not all Ionic Compounds are water soluble • Not all molecular compounds are insoluble!

19. Reactions Involving Ions:Molecular vs. Ionic Equations • Chemical Reaction can be expressed by: • Molecular Equation (balanced chemical equation) • Complete Ionic Equation (showing all ions in reaction) • Net Ionic Equation (showing only those ions directly involved in reaction) • Consider Copper (III) sulfate reacts with sodium hydroxide to form copper (III) hydroxide and sodium sulfate (all in water). • Express reaction in molecular, complete ionic, • and net ionic equations

20. 8 Simple Rules For Common Ionic Compounds

21. (Taken from Cornell University – Adapted by Daley – Sing to Rhythm of 99 Bottles)  Potassium, sodium, and ammonium salts,  Whatever they may be, Can always be depended on For solubility. Asked about the nitrates or acetates The answer is always clear, They each and all are soluble, Is all we want to hear.  Most every chloride's soluble At least we've always read Save silver, mercurous mercury And (slightly) chloride of lead. Take the Bromide and iodide salts There soluble as can be Save silver, mercury, and lead That precipitate as you see Every single sulfate Is soluble ,  'Tis said 'Cept barium and strontium And calcium and lead.  Song For Solubility!! Hydroxides of metals won't dissolve That is, all but three Potassium, sodium and ammonium Dissolve quite readily. And then you must remember That you must not "forgit" Calcium, barium, strontium Dissolve a little bit.  The carbonates are insoluble,  It's lucky that it's so, Or else, our marble buildings Would melt away like snow.  (Repeat with feeling)  Only note is that all Lithium salts are Soluble too!!!

22. Predicting Whether a Precipitation Reaction Occurs; Writing Equations: a) Calcium Nitrate and Sodium Sulfate solutions are added together. Molecular Equation Ca(NO3)2 (aq) + Na2SO4 (aq) CaSO4 (s) + NaNO3 (aq) Total Ionic Equation Ca2+(aq)+2 NO3-(aq) + 2 Na+(aq)+ SO4-2(aq) CaSO4 (s) + 2 Na+(aq+) 2 NO3-(aq) Net Ionic Equation Ca2+(aq) + SO-4(aq) CaSO4 (s) Spectator Ions are Na+ and NO3- b) Ammonium Sulfate and Magnesium Chloride are added together. In exchanging ions, no precipitates will be formed, so there will be no chemical reactions occurring! All ions are spectator ions!

23. Precipitation Reactions: Will a Precipitate Form? If we add a solution containing potassium chloride to a solution containing ammonium nitrate, will we get a precipitate? KCl(aq) + NH4NO3 (aq) = K+(aq) + Cl-(aq) + NH4+(aq) + NO3-(aq) By exchanging cations and anions we see that we could have potassium chloride and ammonium nitrate, or potassium nitrate and ammonium chloride. In looking at the solubility table it shows all possible products as soluble, so there is no net reaction! KCl(aq) + NH4NO3 (aq) = No Reaction! If we mix a solution of sodium sulfate with a solution of barium nitrate, will we get a precipitate? From the solubility table it shows that barium sulfate is insoluble, therefore we will get a precipitate! Na2SO4 (aq) + Ba(NO3)2 (aq) BaSO4 (s) + 2 NaNO3 (aq)