 # Reactions in Aqueous Solutions

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Reactions in Aqueous Solutions
Chapter 8 Reactions in Aqueous Solutions

Will the reaction occur?
Driving forces Forming a solid (“precipitate) Transfer of electrons Forming water Forming a gas Will the reaction occur? Yes, if one of the above driving forces happens.

Dissolving ions A strong electrolyte completely separates into ions when it is mixed with water. Example: NaCl Complete the equation of silver nitrate dissolving in water: AgNO3(s)  NaCl(S) Na+(aq) + Cl-(aq) H2O

Precipitates If you mix NaCl(aq) and AgNO3 (aq) , what possible products could form? NaCl(aq) and AgNO3 (aq)  ? The anions (Cl- and NO3-)change places. NaCl(aq) and AgNO3 (aq)  NaNO3(aq) + AgCl(s) AgCl is a precipitate, so write an “(s)” A precipitate is an insoluble solid. Insoluble = it cannot dissolve in water. What is the driving force in this reaction?

Double replacement (continued)
A double replacement reaction happens when a precipitate forms. Reactants must be aqueous (dissolved in water) Example: NaCl dissolved would be shown as NaCl(aq) If something is “slightly soluble” it will also make a precipitate, so slightly soluble is almost the same as insoluble. Solubility chart on page 245 will show you when a precipitate will form.

Example Example: KNO3 Soluble or insoluble?
Rule #2: K+ salts are usually soluble. Answer: Soluble (No precipitate)

Will this double replacement actually happen??
Practice: Will this form a reaction? Write the formulas of the possible products (Inside and outside) Use the solubility chart to determine if any of the products are INSOLUBLE. If one or both products are insoluble, a chemical reaction will happen.

Examples: KNO3 and BaCl2 KOH and Fe(NO3)3 Na2SO4 and Pb(NO3)2

Annimation: http://www. mhhe

Double Replacement You should be able to write three types of chemical equations for double replacement: 1. Molecular equation 2. Complete ionic equation 3. Net ionic equation

Double Replacement The molecular equation shows the complete formulas of all reactants and products NaCl(aq) + AgNO3 (aq)  NaNO3(aq) + AgCl(s) The complete ionic equation shows all strong electrolytes (aq) as ions. Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s)

Double Replacement The net ionic equation shows only the chemicals participating in the reaction. Steps: Remove the “spectator ions” Spectator ions are the same on the reactant side and the product side (Na+ and NO3-) Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)Na+(aq) + NO3-(aq + AgCl(s) Net ionic equation: Cl-(aq) + Ag+(aq)  AgCl(s)

Acid-Base Reactions and Oxidation-Reduction Reactions
8.2 Acid-Base Reactions and Oxidation-Reduction Reactions

Arrhenius Acids and Bases
An Arrhenius Acid is a substance that produces H+ ions when dissolved in water. A “strong acid” is an acid that is a strong electrolyte. It completely separates into H+ and the anion. HCl  H+ + Cl- Strong acids: HCl, HNO3 and H2SO4

Arrhenius Acids and Bases
An Arrhenius Base produces OH ions when dissolved in water. A strong base completely separates into a metal cation and OH- NaOH  Na+ + OH-

Acid-Base Reaction Write the molecular equation, complete ionic equation and net ionic equation for the reaction of hydrochloric acid and sodium hydroxide. Molecular equation HCl + NaOH  H2O + NaCl Complete ionic equation H+ +Cl- + Na+ + OH-  H2O(l) + Na+ + Cl- Net ionic equation H+ +OH-  H2O(l)

Acid-Base Reaction When an acid and base are mixed, the products are always water and a salt. How do you know a reaction happened? The solution will be hot. An acid-base reaction is the reaction of H+ and OH-

Oxidation Reduction In an oxidation-reduction reaction, electrons move from one chemical to another. Common reactions: A metal and a nonmetal react Reactions between nonmetals where O2 is a reactant or product.

Oxidation Reduction Ca(s) + Cl2(g)  CaCl2(s)
2 electrons Ca(s) + Cl2(g)  CaCl2(s) Which chemical is losing electrons? How many electrons? Ca loses two electrons Which chemical is gaining electrons? How many electrons? Cl gains one electron

Oxidation Reduction This happens in two steps: Ca Ca2+ + 2e-
Cl + e-  Cl- Draw a picture of this reaction: Mg(s) + CuCl2(s)  Cu(s) + MgCl2(s) Which chemical loses electrons? How many? Which chemical gains electrons? How many?

8.3 Types of reactions & “How do we know IF it will happen?”

Classifying reactions
Looking at a chemical equation, be able to classify it… Based on driving force: 1. Precipitation reactions 2. Oxidation-reduction reactions 3. Acid-base reactions Types of oxidation-reduction reactions: 1. Combustion reactions 2. Synthesis reactions 3. Decomposition reactions 4. Single Replacement

Double Replacement AX+BY → AY +BX
Each anion changes places with the cation. Example: sodium sulfate + copper (II) chloride

Single Replacement: A+BX → AX +B A = a metal or group 7 element. B = metal, group 7 element or hydrogen X = anion A replaces B in the BX compound. Example: Zn(s) +2HCl(aq)  H2(g) + ZnCl2(aq)

Synthesis Reactions Synthesis– 2 or more substances combine to form one, bigger molecule. General formula… Example: Combustion of Ca Ca + O2  CaO

Decomposition Reactions
Decomposition– one substance splits to form several smaller molecules/atoms. General formula… Example: Breaking water molecules. What equation will it have? (it’s a reaction that results in Hydrogen gas, H2, and Oxygen,O2) Usually requires energy input (heat, electricity, etc), because we are breaking bonds.

Combustion Reactions

Combustion Reactions Combustion – a substance combines with oxygen. When they react they release energy, water vapor and carbon dioxide. Will need to balance these Ex: C2H5OH + O2  CO2 + H2O

Classifying reactions
Practice: Classify this reaction in as many ways as possible 2Ca + O2  2CaO This is classified as a synthesis and combustion. It is also an oxidation-reduction reaction.