Chapter 4 Reactions in Aqueous Solution

A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount Water is always the solvent (96% H2SO4) Solution Solvent Solute Soft drink (l) H2O Sugar, CO2 Air (g) N2 O2, Ar, CH4 Soft Solder (s) Pb Sn

Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation.

Water’s power as an ionizing solvent results from the distribution of its electrons and its overall shape. A polar molecule is one that has a + end and a - end. Water is one of the most polar molecules. d+ d- H2O

Solvation is the process in which an ion is surrounded by solvent molecules arranged in a specific manner. Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner. d+ d- H2O

An electrolyte is a substance that, when dissolved in water forms ions, and hence, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved does not form ions, and hence, results in a solution that does not conduct electricity.

Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water. Strong Electrolyte – 100% dissociation NaCl (s) Na+ (aq) + Cl- (aq) H2O CH3COOH CH3COO- (aq) + H+ (aq) Reversible reaction - Chemical equilibrium

Strong Electrolytes Are… Strong acids: HCl, HBr, HI, HNO3, HClO4, HClO3, H2SO4 Strong bases: Group 1A metal hydroxide [LiOH, KOH, NaOH, RbOH, CsOH] Heavy group 2A metal hydroxides [Ca(OH)2, Sr(OH)2, Ba(OH)2]

Acids HCl + NaOH = NaCl + H2O base Acid Gives OH- Gives H+ Arrhenius Accepts H+ Lowry- Brønsted Gives electrons Accepts electrons Lewis

Acids Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) There are only seven strong acids: Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO3) Sulfuric (H2SO4) Chloric (HClO3) Perchloric (HClO4)

Acids that ionize to form one H+ ion are called monoprotic acids Acids that ionize to form one H+ ion are called monoprotic acids. Common monoprotic acids include HCl, HNO3 and HC2H3O2. Acids that ionize to form two H+ ions are called diprotic acids. A common diprotic acid is H2SO4.

Bases Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water. Brønsted and Lowry defined them as proton acceptors.

Common bases are NaOH, KOH, and Ca(OH)2 Common bases are NaOH, KOH, and Ca(OH)2. Compounds that do not contain OH– ions can also be bases. Proton transfer to NH3 (a weak base) from water (a weak acid) is an example of an acid–base reaction. Since there is a mixture of NH3, H2O, NH4+, and OH– in solution, We write: NH3(aq) + H2O(l)  NH4+(aq) + OH–(aq)

Strong and Weak Acids and Bases • Strong acids and strong bases are strong electrolytes. • They are completely ionized in solution. • Strong bases include: Group 1A metal hydroxides, Ca(OH)2, Ba(OH)2, and Sr(OH)2. • Strong acids include: HCl, HBr, HI, HClO3, HClO4, H2SO4, and HNO3. • We write the ionization of HCl as: HCl  H+ + Cl– • Weak acids and weak bases are weak electrolytes. • They are partially ionized in aqueous solution. • HF(aq) is a weak acid; most acids are weak acids. • We write the ionization of HF as: HF  H+ + F–

Acid-Base Reactions In an acid–base reaction, the acid donates a proton (H+) to the base.

Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water: CH3COOH(aq) + NaOH(aq) CH3COONa(aq) + H2O(l)

Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq)  Na+(aq) + Cl−(aq) + H2O(l)

Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq)  Na+(aq) + Cl−(aq) + H2O(l) H+(aq) + OH−(aq)  H2O(l)

The balanced molecular equation is: The complete ionic equation is: The net ionic equation is:

volume of solution in liters Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution: moles of solute volume of solution in liters Molarity (M) =

Mixing a Solution To create a solution of a known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute. The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask.

Dilution One can also dilute a more concentrated solution by Using a pipet to deliver a volume of the solution to a new volumetric flask, and Adding solvent to the line on the neck of the new flask.

Dilution The molarity of the new solution can be determined from the equation Mc  Vc = Md  Vd where Mc and Md are the molarity of the concentrated and dilute soln., respectively, and Vc and Vd are the volumes of the two solutions.

Using Molarities in Stoichiometric Calculations

Titration Titration is an analytical technique in which one can calculate the concentration of a solute in a solution.

Titration

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.