Transcript Slide 1
Aqueous Reactions and Solution Stoichiometry Aqueous Solutions • Aqueous solutions are solutions in which water does the dissolving. – Solute – material that is dissolved – Solvent – the material doing the dissolving Properties of Aqueous Solutions • Electrolytic properties – Ability to conduct an electric current – Ionic compounds are electrolytic solutions – Acids and bases are electrolytic Electrolytic Solutions • Ionic Compounds – Dissociate in water into their component ions – NaCl (s) → Na+ (aq) + Cl- (aq) Try These! • What dissolved species are present in a solution of: – KCN → K+ (aq) + CN- (aq) – NaClO4 → Na+(aq) + ClO4- (aq) Molecular Compounds • Molecular compounds are not made up of ions and therefore do not ionize in water. • They are non-conductors of electricity. Strong vs. Weak Electrolytes • Strong electrolytes – exist completely as ions in solution – HCl → H+(aq) + Cl- (aq) • Weak electrolytes – only a small fraction of the compound exists as ions in solution. – CH3COOH → CH3COO-(aq) + H+(aq) Electrolytic solutions • CH3COOH is very soluble, but a weak electrolyte. • Ba(OH)2 is not very soluble, but is a strong electrolyte. Ionic solution Molecular solution Solubility and Precipitation Reactions • These are reactions that result in the formation of an insoluble product. • A precipitate is a insoluble solid formed by a chemical reaction in a solution. • 2KI (aq) + Pb(NO3)2 (aq) → PbI2 (aq) + 2KNO3 (aq) Double Replacement Reactions (Metathesis Reactions) • These reactions can go to completion (are not reversible) if the following are produced: – Precipitate is formed (insoluble solid is formed) – Gas is formed – Formation of a primarily molecular species • Ca(CH3COO)2 + 2HCl → CaCl2 + 2CH3COOH • 2Na3PO4 + 3H2SO4 → Na2SO4 + 2H3PO4 • HCl + NaOH → NaCl + HOH Acid Base Neutralization Reactions • Acids react with bases to produce water and a salt. • Acid + base → salt + water Strong acids are written in ionic form and weak acids are written in molecular form. Common strong acids are: HClO4, HClO3, HCl, HBr, HNO3 and H2SO4 - memorize these! Total Ionic Equations • Formulas of the reactants and products are written to show the predominant form of each substance as it exists in an aqueous solution. • Soluble salts, strong acids and strong bases are written as separated ions. • Insoluble salts, suspensions, solids, weak acids and bases, gases and water are written as individual molecules. Total Ionic Equations • Example: Cd2+(aq) + 2NO3-(aq) + 2Na+(aq) + S2-(aq)→ CdS(s) + 2Na+(aq) + 2NO3-(aq) Net Ionic Equations • Cancel out all spectator ions that do not participate in the reaction. • The remaining equation is the net ionic equation. Redox Equation Balancing and Reactions • Loss of electrons is Oxidation • Gain of electrons is Reduction • LEO the Lion goes GER! Redox Equations • Assign the oxidation states of all elements in the compounds in the equation. • Identify which ones undergo oxidation and which ones undergo reduction. (Look for changes in oxidation from one side of the arrow to the other.) • Use this to balance the overall equation. Molarity • Molarity is the concentration of a substance in solution. moles of solute Molarity = ------------------------------- liters of solution Molarity of Electrolytes • When an ionic substance dissolves in water, the relative concentrations in the solution depend on the chemical formula of the compound. • A 1.0 M solution of NaCl is 1.0 M of Na+ ions and 1.0 M Cl- ions. • A 1.0 M solution of Na2SO4 is 2.0 M of Na+ ions and 1.0 M of SO42- ions. Dilution • Dilutions of solutions are frequently used when starting from a concentrated stock solution, or a concentrated solution of an acid, such as HCl. • M1V1 = M2V2 Titrations • This determines the concentration of an unknown solution using a known standard solution. • Acid base indicators are frequently used to determine the end point of a titration.