Presentation on theme: "Chapter 8 Reactions in Aqueous Solutions. Will the reaction occur? Driving forces –Forming a solid (precipitate) –Transfer of electrons –Forming water."— Presentation transcript:
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: AgNO 3(s) H2OH2O Na + (aq) + Cl - (aq) NaCl (S)
Precipitates If you mix NaCl (aq) and AgNO 3 (aq), what possible products could form? NaCl (aq) and AgNO 3 (aq) ? The anions (Cl - and NO 3 - )change places. NaCl (aq) and AgNO 3 (aq) NaNO 3(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: KNO 3 –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? 1.Write the formulas of the possible products (Inside and outside) 2.Use the solubility chart to determine if any of the products are INSOLUBLE. 3.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
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) + AgNO 3 (aq) NaNO 3(aq) + AgCl (s) The complete ionic equation shows all strong electrolytes (aq) as ions. Na + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq) Na + (aq) + NO 3 - (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 NO 3 - ) Na + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq) Na + (aq) + NO 3 - (aq + AgCl (s) Net ionic equation: Cl - (aq) + Ag + (aq) AgCl (s)
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, HNO 3 and H 2 SO 4
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 H 2 O + NaCl Complete ionic equation H + +Cl - + Na + + OH - H 2 O(l) + Na + + Cl - Net ionic equation H + +OH - H 2 O(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 O 2 is a reactant or product.
Oxidation Reduction Ca (s) + Cl 2(g) CaCl 2(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 2 electrons
Oxidation Reduction This happens in two steps: Ca Ca e- Cl + e- Cl - Draw a picture of this reaction: Mg (s) + CuCl 2(s) Cu (s) + MgCl 2(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) H 2(g) + ZnCl 2(aq)
Synthesis Reactions Synthesis– 2 or more substances combine to form one, bigger molecule. General formula… Example: Combustion of Ca Ca + O 2 CaO
Decomposition Reactions Decomposition– one substance splits to form several smaller molecules/atoms. General formula… Example: Breaking water molecules. What equation will it have? (its a reaction that results in Hydrogen gas, H 2, and Oxygen,O 2 ) Usually requires energy input (heat, electricity, etc), because we are breaking bonds.
Combustion – a substance combines with oxygen. When they react they release energy, water vapor and carbon dioxide. Will need to balance these Ex: C 2 H 5 OH + O 2 CO 2 + H 2 O
Classifying reactions Practice: Classify this reaction in as many ways as possible 2Ca + O 2 2CaO This is classified as a synthesis and combustion. It is also an oxidation- reduction reaction.