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) –NaClO 4 → Na + (aq) + ClO 4 - (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. –CH 3 COOH → CH 3 COO - (aq) + H + (aq)

Electrolytic solutions CH 3 COOH is very soluble, but a weak electrolyte. Ba(OH) 2 is not very soluble, but is a strong electrolyte.

Ionic solutionMolecular 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(NO 3 ) 2 (aq) → PbI 2 (aq) + 2KNO 3 (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(CH 3 COO) 2 + 2HCl → CaCl 2 + 2CH 3 COOH 2Na 3 PO 4 + 3H 2 SO 4 → Na 2 SO 4 + 2H 3 PO 4 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: HClO 4, HClO 3, HCl, HBr, HNO 3 and H 2 SO 4 - 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: Cd 2+ ( aq ) + 2NO 3 - ( aq ) + 2Na + ( aq ) + S 2- ( aq )→ CdS( s ) + 2Na + ( aq ) + 2NO 3 - ( 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 Na 2 SO 4 is 2.0 M of Na + ions and 1.0 M of SO 4 2- 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. M 1 V 1 = M 2 V 2

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.