Molecular View of Reactions in Aqueous Solutions CHAPTER 5

1. Molecular View of Reactions in Aqueous Solutions CHAPTER 5 Chemistry: The Molecular Nature of Matter, 6th edition By Jesperson, Brady, & Hyslop

2. CHAPTER 5: Molecular View of Reactions • Learning Objectives • Define a solution, solute, solvent • Solubility Rules • Concentration • Dilution • Solution Stoichiometry • Writing chemical equations for reactions in solutions • Definition/basics of solution chemistry of Acids & Bases • Titrations

3. Solutions Definition • For reaction to occur • Reactants needs to come into physical contact • Happens best in gas or liquid phase • Movement occurs Solution • Homogeneous mixture • Two or more components mix freely • Molecules or ions completely intermingled • Contains at least two substances Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

4. Solutions Examples of Solutions

5. Solutions Solutes and Solvents Solvent • Medium that dissolves solutes • Component present in largest amount • Can be gas, liquid, or solid • Aqueous solution—water is solvent Solute • Substance dissolved in solvent • Solution is named by solute • Can be gas—CO2 in soda • Liquid—ethylene glycol in antifreeze • Solid—sugar in syrup Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

6. Solutions Electrolytes In Water… • Strong electrolytes produce ions and conduct an electric current. • Weak electrolytes produce a few ions. • Nonelectrolytes do not produce ions. Brady & Senese 5th Ed

7. Solutions Acids & Bases • Arrhenius Theory • Acids produce hydronium when dissolved in water • Bases produce hydroxide when dissolved in water • Bronsted-Lowry Theory • Acids are proton (H+) donors. • Bases are proton (H+) acceptors. Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

8. Solutions Acids & Bases • 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) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

9. Solutions Writing Solution Chemical Equations • 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 Brady & Senese 5th Ed

10. Solutions Writing Solution 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 ionsfrom the ionic equation, net charges balance • Ag+(aq) + Cl-(aq) →AgCl(s) Brady & Senese 5th Ed

11. Solutions Criteria for Balancing Ionic & Net Ionic Equations Material Balance • There must be the same number of atoms of each kind on both sides of the arrow Electrical Balance • The net electrical charge on the left must equal the net electrical charge on the right • Charge does not have to be zero Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

12. Solutions 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 Brady & Senese 5th Ed Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

13. Solutions Solubility & Temperature Solubility: • Depends on temperature. • Of most solids increases as temperature increases. • Of gases decreases as temperature increases. Brady & Senese 5th Ed

14. Solutions Solubility & Pressure • Henry’s Law states • The solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid. • At higher pressures, more gas molecules dissolve in the liquid. Brady & Senese 5th Ed

15. Solutions Concentration • In solutions, solutes are dispersed in a larger volume • Molarityexpresses 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 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

16. Solutions Dilution • Can take solution of higher concentration and dilute it to a lower concentration. • Amount of MOLES does NOT change Remains the same Large Volume Dilute Solution Small Volume Concentrated Solution Add solvent • moles of solute do not change, hence CstockVstock= CnewVnew • C=concentration • V=volume VdilMdil = VconcMconc Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E Brady & Senese 5th Ed

17. Solutions Solubility Rules • 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+ Brady & Senese 5th Ed

18. Solutions Solubility Rules • A general idea as to whether a fair amount of solid will dissolve is achieved using solubility rules • 5.All metal hydroxides (ionic compounds containing OH−) and all metal oxides (ionic compounds containing O2−) are insoluble except those of Group IA and Group IIA • 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) • 6. All salts that contain PO43−, CO32−, SO32−, and S2− are insoluble, except those of Group IA and NH4+. Brady & Senese 5th Ed

19. Solutions Solution Stoichiometry • Often work with solutions when conducting reactions • How do we determine amounts needed to completely react one compound? • Like any other stoichiometry problem • Now use volume and molarity to obtain moles of each substance. • Sometimes we need to know concentrations of ions • Important for net ionic reaction stoichiometry • Molar concentration of particular ion equals molar concentration of salt multiplied by number of ions of that kind in one formula unit of salt. Brady & Senese 5th Ed Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

20. Solutions Titrations • Is the controlled addition of one reactant (titrant) to a known quantity of another reactant of unknown concentration (analyte) 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 Brady & Senese 5th Ed

21. Solutions Titrations Brady & Senese 5th Ed