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 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.