Precipitation Reactions

Precipitation Reactions

Precipitation Reactions Precipitation reactions are reactions in which a solid forms when we mix two solutions. 1) reactions between aqueous solutions of ionic compounds 2) produce an ionic compound that is insoluble in water 3) The insoluble product is called a precipitate.

Precipitation Reactions 2 NaI(aq) + Pb(NO3)2(aq) PbI2(s) + 2 NaNO3(aq)

What does it mean when a substance is soluble?

Compounds Containing the Following Ions Are Mostly Soluble Solubility Rules Exceptions Li +, Na +, K +, NH4 + NO3 -, C2H3O2 -, ClO4 - None None Cl -, Br -, I - Ag +, Hg2 2+, Cu +, Pb 2+ SO4 2 - Ca 2+, Sr 2+, Ba 2+,Pb 2+ Compounds Containing the Following Ions Are Mostly Insoluble Exceptions OH - Group I cations, Ca 2+, Sr 2+, Ba 2+ S 2 - Group I cations, Ca 2+, Sr 2+, Ba 2+, NH4 + CO3 2 -, PO 4 3 - Group I cations, NH4 +

2 NaI(aq) + Pb(NO3)2(aq) PbI2(s) + 2 NaNO3(aq)

No Precipitate Formation = No Reaction KI(aq) + NaCl(aq) KCl(aq) + NaI(aq) all ions still present, therefore, no reaction KI(aq) KCl(aq) + NaI(aq) NaCl(aq)

Process for Predicting the Products of a Precipitation Reaction 1. Determine which ions are present in each aqueous reactant. 2. Determine formulas of possible products. 3. Determine solubility of each potential product in water. 4. If neither product will precipitate, write no reaction after the arrow. 5. If any of the possible products are insoluble, write their formulas as the products of the reaction using (s) after the formula to indicate solid. Write any soluble products with (aq) after the formula to indicate aqueous. 6. Balance the equation. Remember to only change coefficients, not subscripts

Practice Predict the products and balance the equation: K2CO3(aq) + NiCl2(aq) K2CO3(aq) + NiCl2(aq) KCl (?) + NiCO3(?) K2CO3(aq) + NiCl2(aq) 2 KCl (?) + NiCO3(?) K2CO3(aq) + NiCl2(aq) 2 KCl (aq) + NiCO3(s)

Practice Predict the products and balance the equation: KCl(aq) + AgNO3(aq) KCl(aq) + AgNO3(aq) KNO3(?) + AgCl(?) KCl(aq) + AgNO3(aq) KNO3(aq) + AgCl(s)

Practice Predict the products and balance the equation: Na2S(aq) + CaCl2(aq) Na2S(aq) + CaCl2(aq) NaCl(?) + CaS(?) Na2S(aq) + CaCl2(aq) 2 NaCl(?) + CaS(?) Na2S(aq) + CaCl2(aq) 2 NaCl(aq) + CaS(aq) No Reaction!!!!!

Practice Predict the products and balance the equation: (NH4)2SO4(aq) + Pb(C2H3O2)2(aq) (NH4)2SO4(aq) + Pb(C2H3O2)2(aq) NH4C2H3O2(?) + PbSO4(?) (NH4)2SO4(aq) + Pb(C2H3O2)2(aq) 2 NH4C2H3O2(?) + PbSO4(?) (NH4)2SO4(aq) + Pb(C2H3O2)2(aq) 2 NH4C2H3O2(aq) + PbSO4(s)

Ionic Equations Equations that describe the chemicals put into the water and the product molecules are called molecular equations. 2 KOH(aq) + Mg(NO3)2(aq) 2 KNO3(aq) + Mg(OH)2(s) Equations that describe the material s structure when dissolved are called complete ionic equations. Aqueous strong electrolytes are written as ions. Insoluble substances, weak electrolytes, and nonelectrolytes are written as molecules.

Ionic Equations Equations that describe the chemicals put into the water and the product molecules are called molecular equations. 2 KOH(aq) + Mg(NO3)2(aq) 2 KNO3(aq) + Mg(OH)2(s) Equations that describe the material s structure when dissolved are called complete ionic equations. Aqueous strong electrolytes soluble ionic compounds strong acids and bases Nonelectrolytes insoluble ionic compounds weak acids and bases new molecular compounds 2K + (aq) + 2OH (aq) + Mg 2+ (aq) + 2NO3 (aq) 2K + (aq) + 2NO3 (aq) + Mg(OH)2(s)

Ionic Equations Equations that describe the chemicals put into the water and the product molecules are called molecular equations. 2 KOH(aq) + Mg(NO3)2(aq) 2 KNO3(aq) + Mg(OH)2(s) 2K + (aq) + 2OH (aq) + Mg 2+ (aq) + 2NO3 (aq) 2K + (aq) + 2NO3 (aq) + Mg(OH)2(s)

Ionic Equations Ions that are both reactants and products are called spectator ions. 2 K + (aq) + 2 OH (aq) + Mg 2+ (aq) + 2 NO3 (aq) 2 K + (aq) + 2 NO3 (aq) + Mg(OH)2(s) An ionic equation in which the spectator ions are removed is called a net ionic equation. 2 OH (aq) + Mg 2+ (aq) Mg(OH)2(s)

Write the ionic and net ionic equation K2SO4(aq) + 2 AgNO3(aq) 2 KNO3(aq) + Ag2SO4(s) 2K + (aq) + SO4 2- (aq) + 2Ag + (aq) + 2NO3 - (aq) 2K + (aq) + 2NO3 - (aq) + Ag2SO4(s) 2 Ag + (aq) + SO4 2 (aq) Ag2SO4(s)

Acids and Bases

Acids and Bases in Solution Acids ionize in water to form H + ions. (More precisely, the H+ from the acid molecule is donated to a water molecule to form hydronium ion, H3O + ) Bases dissociate in water to form OH- ions. (Bases, such as NH3, that do not contain OH- ions, produce OH- by pulling H + off water molecules.) acid + base salt + water

Molecular Models of Selected Acids

Acid-Base Reactions Also called neutralization reactions because the acid and base neutralize each other s properties 2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l) Note that the cation from the base combines with the anion from the acid to make the water soluble salt. The net ionic equation for an acid-base reaction is 2 H + (aq) + 2 OH-(aq) 2 H2O(l) acid + base a salt + water

Common Acids Name Formula Uses Strength Perchloric HClO4 explosives, catalysts Strong Nitric HNO3 explosives, fertilizers, dyes, glues Strong Sulfuric Hydrochloric Phosphoric H2SO4 HCl H3PO4 explosives, fertilizers, dyes, glue, batteries metal cleaning, food prep, ore refining, stomach acid fertilizers, plastics, food preservation Strong Strong Moderate Chloric HClO3 explosives Moderate Acetic HC2H3O2 plastics, food preservation, vinegar Weak Hydrofluoric HF metal cleaning, glass etching Weak Carbonic H2CO3 soda water, blood buffer Weak Hypochlorous HClO sanitizer Weak Boric H3BO3 eye wash Weak

Common Bases Name Formula Common Name Uses Strength Sodium Hydroxide NaOH Lye, Caustic Soda soap, plastic production, petroleum refining Strong Potassium Hydroxide KOH Caustic Potash soap, cotton processing, electroplating Strong Calcium Hydroxide Ca(OH)2 Slaked Lime cement Strong Sodium Bicarbonate NaHCO3 Baking Soda food preparation, antacids Weak Magnesium Hydroxide Mg(OH)2 Milk of Magnesia antacids Weak Ammonium Hydroxide NH4OH Ammonia Water fertilizers, detergents, explosives Weak

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) HCl(aq) NaOH(aq) NaCl(aq) + H2O(l)

Write the molecular, ionic, and net-ionic equation for the acid-base reactions. HNO3(aq) + Ca(OH)2(aq) HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + H2O(l) 2HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2H2O(l) 2H + (aq) + 2NO3 - (aq) + Ca 2+ (aq) + 2OH - (aq) Ca 2+ (aq) + 2NO3 - (aq) + 2H2O(l) 2H + (aq) + 2OH - (aq) 2H2O(l) HCl(aq) + Ba(OH)2(aq) 2HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2H2O(l) 2H + (aq) + 2OH-(aq) 2H2O(l)

Write the molecular, ionic, and net-ionic equation for the acid-base reactions. H2SO4(aq) + Sr(OH)2(aq) H2SO4(aq) + Sr(OH)2(aq) SrSO4(s) + 2 H2O(l) 2H + (aq) + SO4 2- (aq) + Sr 2+ (aq) + 2OH - (aq) SrSO4 (s) + 2H2O(l) 2H + (aq) + SO4 2- (aq) + Sr 2+ (aq) + 2OH-(aq) SrSO4 (s) + 2H2O(l)

Gas-Evolving Reactions

Gas-Evolving Reactions Some reactions form a gas directly from the ion exchange: K2S(aq) + H2SO4(aq) K2SO4(aq) + H2S(g) Other reactions form a gas by the decomposition of one of the ion exchange products into a gas and water. K2SO3(aq) + H2SO4(aq) K2SO4(aq) + H2SO3(aq) H2SO3 H2O(l) + SO2(g)

Gas-Evolving Reactions NaHCO3(aq) + HCl(aq) NaCl(aq) + CO2(g) + H2O(l) NaHCO3(aq) NaCl(aq) + CO2(g) + H2O(l) HCl(aq)

A reaction which forms a gas by the decomposition of one of the ion exchange products into a gas and water. NaHCO3(aq) + HCl(aq) NaCl(aq) + H2CO3(aq) H2CO3 H2O(l) + CO2(g) carbonic acid

Practice Write the ionic and net ionic equation for Na2CO3(aq) + 2 HCl(aq) 2 NaCl(aq) + CO2(g) + H2O(l) 2Na + (aq) + CO3 2- (aq) + 2H + (aq) + 2Cl - (aq) 2Na + (aq) + 2Cl - (aq) + CO2(g) + H2O(l) CO3 2 (aq) + 2 H + (aq) CO2(g) + H2O(l)

Compounds that Undergo Gas-Evolving Reactions Reactant Reactant Exchange Product Gas Formed Example Metal sulfide Metal hydrogensulfide Acid H2S H2S K2S (g) + HCl (aq) H2S (g) + KCl (aq) Metal carbonate Metal hydrogencarbonate Acid H2CO3 CO2 K2CO3 (aq) + HCl (aq) CO2 (g) + H2O (l) + KCl (aq) Metal sulfite Metal hydrogensulfite Acid H2SO3 SO2 K2SO3 (aq) + HCl (aq) SO2 (g) + H2O (l) + KCl (aq) Ammonium salt Base NH4OH NH3 KOH (aq) + NH4Cl (aq) NH3 (g) + H2O (l) + KCl (aq)

Practice Predict the products and balance the equations Na2CO3(aq) + 2 HNO3(aq) 2 NaNO3(aq) + H2O (l) + CO2(g) 2 HCl(aq) + Na2SO3(aq) 2 NaCl (aq) + H2O (l) + SO2 (g) H2SO4(aq) + CaS(aq) CaSO4(aq) + H2S(g)

Redox Reactions

Oxidation/Reduction Basic Definitions e- X Y X loses electrons X is oxidized X is the reducing agent X increases its oxidation number Y gains electron Y is reduced Y is the oxidizing agent Y decreases its oxidation number

Oxidation and Reduction at the Atomic Level

Redox Reactions Oxidation/reduction reactions involve transferring electrons from one atom to another. Also known as redox reactions Many involve the reaction of a substance with O2(g). 4 Fe(s) + 3 O2(g) 2 Fe2O3(s) Fe 0 + O 0 Fe +3 + O -2

Combustion as Redox 2 H2(g) + O2(g) 2 H2O(g) H 0 + O 0 H +1 + O -2

Redox without Combustion 2 Na(s) + Cl2(g) 2 NaCl(s) Cl 0 + Na 0 Cl -1 + Na +1

Reactions of Metals with Nonmetals Consider the following reactions: 4 Na(s) + O2(g) 2 Na2O(s) 2 Na(s) + Cl2(g) 2 NaCl(s) The reactions involve a metal reacting with a nonmetal. In addition, both reactions involve the conversion of free elements into ions. Na 2 O = 2 Na + + O 2- NaCl = Na + + Cl -

Oxidation Reduction Oxidation and reduction must occur simultaneously. 2 Na(s) + Cl2(g) 2 Na + Cl (s) Na is oxidized Cl is reduced Na is the reducing agent Cl2 is the oxidizing agent

Another Spontaneous Redox Reaction governed by the activity series Zn0 + CuSO4 Zn0 + Cu2+ Cu0 + ZnSO4 Zn2+ + Cu0

Zn 0 + Cu 2+ Zn 2+ + Cu 0 electrons Zn 2+ NO3 - NO3 - Cu 2+

A Voltaic Cell