Ch4

Aqueous Reactions and Solution Stoichiometry Chapter 4 Aqueous Solutions A solution is a homogeneous mixture In an aqueous solution, water is the solvent. Dissolving NaCl in Water Electrolytes Electrolytes dissolve in water to form ions. Electrolytes are: Soluble ionic compounds such as NaCl and AgNO3 Acids such as HCl and HNO3 Bases such as NaOH Nonelectrolytes What kinds of compounds are nonelectrolytes? Dissolving Nonelectrolytes CH3OH(l) ? CH3OH(aq) Identify each substance in water as a strong electrolyte, weak electrolyte, or nonelectrolyte. Explain. (Water molecules have been left out) Dissolving Electrolytes NaCl(s) ? Na+(aq) + Cl-(aq) Mg(NO3)2(s) ? Mg2+(aq) + 2NO3-(aq) KOH(s) ? HCl(g) ? Aqueous Reactions often Involve Electrolytes Double-Displacement Reactions also called Exchange or Metathesis Single-Displacement Reactions a type of oxidation-reduction reaction Double-Displacement Reactions (Exchange) AB + CD ? AD + CB Examples: NaCl(aq) + AgNO3(aq) ? NaNO3(aq) + AgCl(s) HCl(aq) + NaOH(aq) ? NaCl(aq) + H2O(l) The latter is also called neutralization reaction Double-Displacement Reactions (Exchange) AB + CD ? AD + CB Different types (that you need to know) Precipitation Reaction (a solid forms) 3. Acid-Base Neutralization Reactions Mixing Two Aqueous Solutions Cl- Na+ Cl - Cl- Na+ Na+ Ag+ Ag+ NO3- NO3- Ag+ NO3- NaCl(aq) AgNO3(aq) Precipitation Reactions AgNO3(aq) + NaCl(aq) ? AgCl(s) + NaNO3(aq) Precipitation Reactions AgNO3(aq) + NaCl(aq) ? AgCl(s) + NaNO3(aq) Complete Ionic Equation: Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) ? AgCl(s) + Na+(aq) + NO3-(aq) What are the spectator ions? Precipitation Reactions AgNO3(aq) + NaCl(aq) ? AgCl(s) + NaNO3(aq) Complete Ionic Equation: Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) ? AgCl(s) + Na+(aq) + NO3-(aq) What are the spectator ions? Precipitation Reactions AgNO3(aq) + NaCl(aq) ? AgCl(s) + NaNO3(aq) Net Ionic Equation: Leave out the spectator ions: Ag+(aq) + Cl-(aq) ? AgCl(s) Net Ionic Equation (Leave out spectators) Na+ NO3- Na+ NO3- AgClAgCl AgCl NO3- Na+ Ag+(aq) + Cl-(aq) ? AgCl(s) Solubility Rules ???????.do not memorize Gas-forming Reactions AB + CD ? AD + CB Gas-Forming Reaction Na2CO3(aq) + 2HCl(aq) ? H2CO3(aq) + 2NaCl(aq) H2CO3(aq) ? CO2(g) + H2O(l) Overall Reaction: Na2CO3(aq) + 2HCl(aq) ? CO2(g) + H2O(l)+2NaCl(aq) Gas-forming Reactions AB + CD ? AD + CB 2. Gas-Forming Reaction Na2CO3(aq) + 2HCl(aq) ? CO2(g) +H2O(l)+2NaCl(aq) When a carbonate or bicarbonate reacts with an acid in water, carbon dioxide is produced along with water and a salt (ionic compound). Neutralization Reactions AB + CD ? AD + CB 3. Neutralization Reactions Acid + Base ? Salt + water HCl(aq) + Mg(OH)2(s) ? Stomach acid Neutralization Reactions AB + CD ? AD + CB Neutralization Reactions Acid + Base ? Salt + water 2HCl(aq) + Mg(OH)2(s) ? MgCl2(aq) + 2H2O(l) Oxidation-Reduction Reactions ?Charge? on atom changes from reactants to products. ? Electrons are exchanged Example: 2Na + Cl2 ? 2NaCl 2Na ? 2Na+ + 2e- (Oxidation) Cl2 + 2e- ? 2Cl- (Reduction) Oxidation-Reduction Reactions Oxidation: Loss of electrons Reduction: Gain of electrons Oxidation Numbers pp. 139-140 1. Atoms in elemental form: 0 2. Monatomic Ions in ionic compounds: ion charge 3. Atoms in Molecular Compounds: Oxygen -2 except in peroxide O22- Hydrogen +1 (when bonded to nonmetals) Fluorine -1 always Halogens -1 except when bonded to Oxygen 4. The oxidation numbers sum to zero for a compd. Oxidation Numbers Determine the oxidation number for each element in each substance. TiCl4 MnO4- CaH2 H2O CO2 O2 N2O4 Ag NH3 Oxidation Reactions (Redox Reactions) Which of the following reactions are oxidation-reduction reactions? 2Mg(s) + O2(g) ? 2MgO(s) CaCO3(s) ? CaO(s) + CO2(g) AgNO3(aq) + HCl(aq) ? AgCl(s) + HNO3(aq) 2AgNO3(aq) + Cu(s) ? Cu(NO3)2(aq) + 2Ag(s) Oxidation Reactions (Redox Reactions) Which of the following reactions are oxidation-reduction reactions? 2Mg(s) + O2(g) ? 2MgO(s) CaCO3(s) ? CaO(s) + CO2(g) AgNO3(aq) + HCl(aq) ? AgCl(s) + HNO3(aq) 2AgNO3(aq) + Cu(s) ? Cu(NO3)2 + 2Ag(s) Single-Displacement Reactions A + BC ? AC + B Examples: Zn(s) + Cu(NO3)2(aq) ? Zn(NO3)2(aq) + Cu(s) Mg(s) + 2HCl(aq) ? MgCl2(aq) + H2(g) 2Na(s) + 2H2O(l) ? 2NaOH(aq) + H2(g) Cl2(g) + 2NaBr(aq) ? 2NaCl(aq) + Br2(aq) Predicting Single-Displacement Reactions A + BC ? AC + B Which reaction will occur? Zn(s) +Cu(NO3)2(aq) ? Zn(NO3)2(aq) + Cu(s) or Cu(s) +Zn(NO3)2(aq) ? Cu(NO3)2(aq) + Zn(s) It depends on the relative activities of the metals. See Activity Series T 4.5 Which is more Reactive? Zn or Cu? Copper metal plates on Zinc (Zinc transfers electrons to copper!) Describe the electron transfer Single-Displacement Reactions A + BC ? AC + B Which reaction will occur? Zn(s) +Cu(NO3)2(aq) ? Zn(NO3)2(aq) + Cu(s) or Cu(s) +Zn(NO3)2(aq) ? Cu(NO3)2(aq) + Zn(s) Zinc metal is more active than copper so zinc metal will lose electrons to form Zn2+. Which is more Active, Zn or Mg? Which is more active, Ag or Cu? Rxn Place Cu, Zn, Mg and Ag in order from most active to least active. Zn > Cu Mg > Zn Cu > Ag Activity Series (T 4.5) Li (Most easily Oxidized: Most Active) K Ba Ca Na Mg* Al Mn Zn* Cr Fe Co Ni Sn Pb H2 Cu* Ag* Hg Pt Au (Ions are easily reduced to Metal: Least Active) Group Work Which of the following metals will react with HCl(aq) to form H2 gas? Silver Iron Concentrations of Solutions The concentration of a solution describes the relative amount of solute dissolved in the solvent. Chemistry often expresses solution concentrations in terms of molarity (M). Molarity = Moles/Liter Molarity What volume of a 0.40 M NaOH solution contains 0.040 mol of NaOH? Molarity What volume of a 0.40 M NaOH solution contains 0.040 mol of NaOH? Molarity How many moles of HCl are contained in 250 mL of a 0.10 M HCl solution? Molarity How many moles of HCl are contained in 250 mL of a 0.10 M HCl solution? Group Work M = mol/L What is the molarity of a solution that contains 36.5 grams of HCl dissolved in 250.0 mL of solution? What volume of a 0.80 M NaOH solution contains 4.0 mol of NaOH? Group Work M = mol/L What is the molarity of a solution that contains 36.5 grams of HCl dissolved in 250.0 mL of solution? 4.00 M What volume of a 0.80 M NaOH solution contains 4.0 mol of NaOH? 5.0 L Dilutions Moles of Solute before dilution = moles of solute after dilution molesi = molesf MiVi = MfVf Dilution What is the concentration of a solution prepared by diluting 2.0 mL of a 6.0 M HCl solution to a total volume of 100.0 mL?