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.
Chapter 4 HW • Visualizing: 1,3,5,7,9,10 • Electrolytes: 11,13,15,17 • Pp rx and net ionic eq: 19,23,25 • Acid-base rx: 29,35,37,39 • Redox: 49,51,53 • Molarity: 61,65,67,71 • Titrations : 77,81,85
Aqueous Solutions Water is the dissolving medium, or solvent.
Some Properties of Water • Water is “bent” or V-shaped. • The O-H bonds are covalent. • Water is a polar molecule. • Hydration occurs when salts dissolve in water.
Solutions: • Homogeneous mixtures of two or more pure substances. • The solvent is present in greatest abundance. • All other substances are solutes.
A Solute • dissolves in water (or other “solvent”) • changes phase(if different from the solvent) • is present in lesser amount (if the same phase as the solvent)
A Solvent • retains its phase(if different from the solute) • is present in greater amount (if the same phase as the solute)
Polar Water Molecules Interact with the Positive and Negative Ions of a Salt
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.
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.
Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes.
Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases.
Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water.
Strong Electrolytes Are… • Strong acids
Strong Electrolytes Are… • Strong acids • Strong bases
Strong Electrolytes Are… • Strong acids • Strong bases • Soluble ionic salts
Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak- conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution
Strong Electrolytes • Soluble salts- eg. NaCl, Pb(ClO3)2 • Strong acids- eg. HCl, H2SO4 • Strong bases- eg. NaOH, KOH
Weak or Nonelectrolytes • Insoluble or only slightly soluble salts. Eg. AgCl, CaSO4 • Weak Acids- eg. CH3COOH, HF • Weak Bases- eg. NH3, amines • Water
September 23-Section 4.2Precipitation Reactions *SOLUBILITY *PRECIPITATION REACTIONS *DOUBLE REPLACEMENT (METATHESIS –EXCHANGE ) REACTION • NET IONIC EQUATIONS • SPECTATOR IONS
Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed.
SOLUBILITY • The amount of a substance that can be dissolved in a given quantity of solvent at a given temperature. Example Solubility of KNO3 65 g/100 ml H2O of KNO3 at 40 C *It is determined experimentally.
Solubility Rules – Used to determine what reaction occurs, if any: 1. Separate all ions. 2. Determine all possible compounds formed. 3. Determine which, if any, of the compounds will precipitate. 4. Write the appropriate chemical equation.
Rules for Solubility of Ionic Compounds in Water • All common Group 1 and ammonium salts are soluble. • All nitrates, chlorates, and acetates are soluble except silver acetate. • All halide salts (except fluorides) are soluble except those of silver, mercury (I), and lead. • All sulfates are soluble except those of silver, mercury (I or II), lead, calcium, strontium, and barium. • Calcium, strontium, and barium hydroxides (as well as group 1 hydroxides) are soluble; other hydroxides generally are not. • Most other ionic compounds are generally insoluble.
Double Replacement (Metathesis) Reactions • Metathesis or double displacement/replacement reactions involve swapping ions in solution: • AX + BYAY + BX. • Metathesis reactions will lead 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.
The molecular equation lists the reactants and products in their molecular form. AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Molecular Equation
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
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
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
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
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.
Examples: Write the molecular, complete ionic and net ionic equations for each of the following reactions. • Aqueous solutions of sodium sulfide and calcium nitrate are mixed.
2. Aqueous solutions of barium chloride and potassium sulfate are mixed.
3. Aqueous solutions of silver nitrate and ammonium chloride are mixed.
Homework • Page 157 answer: 4.7 to 4.9 • Page 158 4.19 to 4.28 odd • Read Section 4.3
September 24- Section 4.3 Acid – Bases Reactions • Strong and weak Acid and Bases • Neutralization Reactions
Classify as strong, weak or nonelectrolyte CaCl2 HNO3 C2H5OH HC2H3O2
Rank the following solutions in order of increasing electrical conductivity • Ca(NO3)2 • C6 H12 O6 • NaC2 H3O2 • HC2 H3O2
Acids: • Substances that increase the concentration of H+ when dissolved in water (Arrhenius). • Proton donors (Brønsted–Lowry).
Acids There are only seven strong acids: • Hydrochloric (HCl) • Hydrobromic (HBr) • Hydroiodic (HI) • Nitric (HNO3) • Sulfuric (H2SO4) • Chloric (HClO3) • Perchloric (HClO4)
Acids • Dissociation = pre-formed ions in solid move apart in solution. • Ionization = neutral substance forms ions in solution. • Acids= substances that ionize toform H+ in solution(e.g. HCl,HNO3,CH3CO2H, lemon, lime, vitamin C). Proton donors. • Acids with one acidic proton are called monoprotic (e.g., HCl). • Acids with two acidic protons are called diprotic (e.g., H2SO4). • Acids with many acidic protons are called polyprotic.
Bases: • Substances that increase the concentration of OH− when dissolved in water (Arrhenius). • Proton acceptors (Brønsted–Lowry).
Bases • Bases = substances that react with the H+ ions formed by acids (e.g. NH3, Drano™, Milk of Magnesia™). Proton acceptors (Bronsted-Lowry).
Strong and Weak Acids and Bases • Strong acids and bases are strong electrolytes. • They are completely ionized in solution. • Strong acids are HCl, HBr, HI, HNO3, H2SO4, HClO3 and HClO4. • Strong bases are group 1 hydroxides and soluble group 2 hydroxides. • Weak acids and bases are weak electrolytes. • They are partially ionized in solution.
Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H+) to the base.
Neutralization Reactions and Salts • Neutralization occurs when a solution of an acid and a base are mixed: • HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) • We form a salt (NaCl) and water. • Salt = ionic compound whose cation comes from a base and anion from an acid. • Neutralization between acid and metal hydroxide produces water and a salt. • In net ionic equations, strong acids and bases are written dissociated, while weak acids and bases are written associated (non-dissociated)
Neutralization Reactions Observe the reaction between Milk of Magnesia, Mg(OH)2, and HCl.