aqueous reactions and solution stoichiometry
Post on 20-Mar-2016
35 Views
Preview:
DESCRIPTION
TRANSCRIPT
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 + waterStrong 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 soluteMolarity = -------------------------------
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 SO4
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.
• 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.
top related