Chapter 4 Aqueous Reactions and Solution Stoichiometry CHEMISTRY The Central Science 9th Edition Chapter 4 Aqueous Reactions and Solution Stoichiometry Chapter 4

Electrolytic Properties Aqueous solutions, have the potential to conduct electricity. Conducting ability depends on the number of ions in solution. There are three types of solution: Strong electrolytes, Weak electrolytes, and Nonelectrolytes. Chapter 4

General Properties of Aqueous Solutions Electrolytic Properties Prentice Hall © 2003 Chapter 4

General Properties of Aqueous Solutions Ionic Compounds, Molecular Compounds in Water Ions dissociate in water. In solution, each ion is surrounded by water molecules. Transport of ions through solution causes flow of current. Molecular compounds in water (e.g., CH3OH): no ions are formed. Chapter 4

Strong and Weak Electrolytes Strong electrolytes: completely dissociate in solution Weak electrolytes: produce a small concentration of ions in solution. These ions exist in equilibrium with the unionized substance Chapter 4

Precipitation Reactions

Exchange (Metathesis) Reactions Metathesis reactions involve swapping ions in solution: AX + BY  AY + BX. leads to a change in solution if one of three things occurs: an insoluble solid is formed (precipitate), weak or nonelectrolytes are formed, or an insoluble gas is formed. Chapter 4

Ionic equation: used to highlight reaction between ions. Ionic Equations Ionic equation: used to highlight reaction between ions. Molecular equation: all species listed as molecules: HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq) Complete ionic equation: lists all ions: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  H2O(l) + Na+(aq) + Cl-(aq) Net ionic equation: lists only nonspectator ions: H+(aq) + OH-(aq)  H2O(l) Chapter 4

Acids with one proton are called monoprotic (e.g., HCl). Acid = substances that ionize to form H+ in solution (e.g. HCl, HNO3, CH3CO2H, lemon, lime, vitamin C). Acids with one proton are called monoprotic (e.g., HCl). Acids with two protons are called diprotic (e.g., H2SO4). Acids with many protons are called polyprotic. Chapter 4

Acid-Base Reactions Bases Bases = substances that react with the H+ ions formed by acids (e.g. NH3, Drano™, Milk of Magnesia™). Chapter 4

Strong and Weak Acids and Bases Strong acids and bases are strong electrolytes. They completely ionize in solution. Weak acids and bases are weak electrolytes. They partially ionize in solution. Chapter 4

Identifying Strong and Weak Electrolytes Water soluble and ionic = strong electrolyte (probably). Water soluble and a strong acid/base (covalent) = strong electrolyte. Water soluble and a weak acid/base (covalent) = weak electrolyte. Otherwise, the compound is probably a nonelectrolyte. Chapter 4

Acid-Base Reactions Identifying Strong and Weak Electrolytes Prentice Hall © 2003 Chapter 4

HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq) Neutralization Reactions and Salts Neutralization occurs when an acid and a base are mixed: HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq) Neutralization between acid and metal hydroxide produces water and a salt. Chapter 4

2HCl(aq) + Na2S(aq)  H2S(g) + 2NaCl(aq) Acid-Base Reactions with Gas Formation Sulfide and carbonate ions can react with H+ in a similar way to OH- 2HCl(aq) + Na2S(aq)  H2S(g) + 2NaCl(aq) 2H+(aq) + S2-(aq)  H2S(g) HCl(aq) + NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g) Chapter 4

Ca(s) +2H+(aq)  Ca2+(aq) + H2(g) Oxidation and Reduction When a metal undergoes corrosion it loses electrons to form cations: Ca(s) +2H+(aq)  Ca2+(aq) + H2(g) Oxidized: atom, molecule, or ion becomes more positively charged. Oxidation is the loss of electrons. Reduced: atom, molecule, or ion becomes less positively charged. Reduction is the gain of electrons. Chapter 4

Oxidation-Reduction Reactions Oxidation and Reduction Chapter 4

Oxidation-Reduction Reactions Oxidation and Reduction

Oxidation of Metals by Acids and Salts Oxidation Numbers Nonmetal usually have negative oxidation numbers Metals usually have positive oxidation numbers Oxidation of Metals by Acids and Salts Metals are oxidized by acids to form salts: Mg(s) +2HCl(aq)  MgCl2(aq) + H2(g) Metals can also be oxidized by other salts: Fe(s) +Ni2+(aq)  Fe2+(aq) + Ni(s) Chapter 4

Activity Series Activity series: a list of metals arranged in decreasing ease of oxidation. Chapter 4

Concentrations of Solutions Molarity Chapter 4

Concentrations of Solutions Dilution MdiluteVdilute = moles = MconcentratedVconcentrated Chapter 4

Solution Stoichiometry and Chemical Analysis Prentice Hall © 2003 Chapter 4

Solution Stoichiometry and Chemical Analysis Titrations

Titration What do we do? Take a known volume of the HCl solution, measure the mL of NaOH required to react completely with the HCl. Suppose we know the molarity of a NaOH solution and we want to find the molarity of an HCl solution. Chapter 4

End of Chapter 4: Aqueous Reactions and Solution Stoichiometry Prentice Hall © 2003 Chapter 4