Reactions in Aqueous Solutions Chemistry 101 Chapter 7 Reactions in Aqueous Solutions

Aqueous solution: solvent is water Reactions in Aqueous Solutions Ionic compounds (Salt) Aqueous solution: solvent is water

Reactions in Aqueous Solutions Chemical reactions that occur in water. In our body reactions occur in the aqueous solution.

Water in our body About 60% of our body. Most of the reactions occur in aqueous solution. Participates in many biochemical reactions. Transports reactants and products from one place in our body to another. 5. Eliminates the waste materials from cells and our body (urine).

Why does a chemical reaction occur? Several driving forces: Formation of a solid Formation of water Transfer of electrons Formation of a gas

Why does a chemical reaction occur? Several driving forces: Formation of a solid Formation of water Transfer of electrons Formation of a gas

Precipitation reactions Formation of a solid Precipitation reactions Precipitate KI + Pb(NO3)2  ?

Ionic Compounds When an ionic compound dissolves in water, ions are produced. Each ion is surrounded by water molecules. Ions Hydrated by H2O Hydration

Soluble solid: it completely dissolves in water (ions are formed). Ionic Compounds Soluble solid: it completely dissolves in water (ions are formed). Slightly soluble solid: it partially dissolves in water. Insoluble solid: it does not dissociate in water (almost). Note: the terms insoluble and slightly soluble mean such a miniscule amount dissolves that you can’t see any decrease in the amount of solid present.

Soluble Insoluble Solubility Rules Memorize these RULES! Preceding rules trump following rules.

Solubility Rules Another way of showing the same rules.

Electrolytes + - Electrolyte: conducts an electric current. Na+ Cl- bulb Electrolyte: conducts an electric current. Ionization (Dissociation) NaCl → Na+ + Cl- strong electrolytes: molecules dissociate completely into ions (NaCl). weak electrolytes: molecules dissociate partially into ions (CH3COOH). nonelectrolytes: molecules do not dissociate into ions (DI water).

Precipitation reactions Formation of a solid Precipitation reactions Precipitate KI + Pb(NO3)2  ?

Aqueous Solution (ionic compounds) aqueous solution: solvent is water H2O Dissociation (Ionization) KI(s) K+(aq) + I-(aq) KI K+ I- H2O Pb(NO3)2 Pb(NO3)2(s) Pb2+(aq) + 2NO3-(aq) Pb2+ NO3- NO3-

Aqueous Solution (ionic compounds) sometimes the ions react with each other. Positive ions will interact with negative ions. KI Pb(NO3)2 K+ I- Pb2+ NO3- 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq) Sometimes they stick together to form a solid (precipitate).

total charge on left side = total charge on right side Molecular equation: 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq) Complete Ionic equation: 2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq) 2K+(aq) + Pb2+(aq) + 2I-(aq) + 2NO3-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq) Pb2+(aq) + 2I-(aq)  PbI2(s) Net ionic equation: Spectator ions 2As3+(aq) + 3s2-(aq)  As2S3(s) total charge on left side = total charge on right side balanced equation

Complete ionic equation Example Pb(NO3)2(aq) + Na2SO4(aq)  ? Pb(NO3)2(aq) + Na2SO4(aq)  PbSO4(s) + NaNO3(aq) Balance it: Pb(NO3)2(aq) + Na2SO4(aq)  PbSO4(s) + 2 NaNO3(aq) Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO42-(aq)  PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq) Complete ionic equation

Pb2+(aq) + SO42-(aq)  PbSO4(s) Example Pb2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + SO42-(aq)  PbSO4(s) + 2 Na+(aq) + 2 NO3-(aq) The ions that do not react are called spectator ions. Net ionic equation: Pb2+(aq) + SO42-(aq)  PbSO4(s)

Practice Molecular equation 3 KOH(aq) + Fe(NO3)3(aq)  ? Balancing Complete ionic equation Net ionic equation

Why does a chemical reaction occur? Several driving forces: Formation of a solid Formation of water Transfer of electrons Formation of a gas

Acids and Bases Acids: sour Bases: bitter or salty

Acids and Bases Arrhenius definition: Acid: produces H3O+ (H+) in water. CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) H3O+ (Hydronium ion): H+(aq) + H2O(l) H3O+(aq) Base: produces OH- in water. H2O NaOH(s) Na+(aq) + OH-(aq) NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

Weak acid and base: it is partially ionized in aqueous solution. Acids and Bases Weak acid and base: it is partially ionized in aqueous solution. produces less H+ and OH- CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Strong acid and base: it is completely ionized in aqueous solution. HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq) NaOH(aq) + H2O(l) Na+(aq) + OH-(aq) produces more H+ and OH-

Acid-Base Reactions Neutralization Strong acid + Strong base → Salt + H2O NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) +  Na+(aq) + Cl-(aq) + H2O(l) H+(aq) + OH-(aq) H2O(l) The only chemical change is the formation of water.

Why does a chemical reaction occur? Several driving forces: Formation of a solid Formation of water Transfer of electrons Formation of a gas

e- 2Na(s) + Cl2(g) 2NaCl(s) Na → Na+ + e- Cl + e- → Cl- Oxidation and Reduction reactions (redox) e- 2Na(s) + Cl2(g) 2NaCl(s) Na → Na+ + e- Cl + e- → Cl-

oxidation: it is the loss of electrons. Oxidation and Reduction reactions (redox) oxidation: it is the loss of electrons. reduction: it is the gain of electrons. Na → Na+ + e- Cl + e- → Cl- Remember – LEO says GER. Loss of Electrons is Oxidation Gain of Electrons is Reduction.

Metal + Nonmetal : Transfer of electrons Oxidation and Reduction reactions (redox) Metal + Nonmetal : Transfer of electrons Oxidation and Reduction reactions (redox) Oxidation and reduction always occur together. (The lost e- must go somewhere!)

oxidation: it is the loss of electrons. Oxidation and Reduction reactions (redox) oxidation: it is the loss of electrons. reduction: it is the gain of electrons. Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s) redox reaction Zn(s)  Zn2+(aq) + 2e- Zn is oxidized (reducing agent) Cu2+(aq) + 2e-  Cu(s) Cu2+ is reduced (oxidizing agent)

oxidation: is the gain of oxygen / loss of hydrogen. Oxidation and Reduction reactions (redox) oxidation: is the gain of oxygen / loss of hydrogen. reduction: is the loss of oxygen / gain of hydrogen. CH4(s) + 2O2(g)  CO2(g) + 2H2O(g) redox reaction C gains O and loses H is oxidized (reducing agent) O gains H Is reduced (oxidizing agent) single replacement reaction and combustion reactions  redox reactions double replacement reactions  non redox

2 Al(s) + Fe2O3(s)  2 Fe(s) + Al2O3(s) Oxidation and Reduction reactions (redox) Example 2: 2 Al(s) + Fe2O3(s)  2 Fe(s) + Al2O3(s) Called the Thermite reaction. Let’s just say it’s vigorous! is oxidized is reduced

Cu(s) + 2 Ag+(aq)  2 Ag(s) + Cu2+(aq) Oxidation and Reduction reactions (redox) Example 3: Cu(s) + 2 Ag+(aq)  2 Ag(s) + Cu2+(aq) is oxidized is reduced

Zn(s) + 2 HCl(aq)  H2(g) + ZnCl2(aq) Oxidation and Reduction reactions (redox) Example 4: Zn(s) + 2 HCl(aq)  H2(g) + ZnCl2(aq) Zn(s) + 2 H+(aq)  H2(g) + Zn2+(aq) is oxidized is reduced Note: this reaction also shows the fourth driving force of a reaction, namely, the formation of a gas.

Practice: 2 Mg(s) + O2(g)  2 MgO(s) Oxidation and Reduction reactions (redox) Practice: 2 Mg(s) + O2(g)  2 MgO(s)

Classification of chemical reactions Precipitation Reactions Oxidation-Reduction Acid-Base Combustions Synthesis (combination) (Reactants are elements.) Decomposition (Analysis) (Products are elements.)