9.2 Reactions in Aqueous Solutions Ms. Munir

Introduction When 2 aqueous ionic compounds are mixed together, there are 2 possible outcomes: the compounds will remain in solution without reacting, one aqueous ionic compound will chemically react with the other. It’s a DD rxn: WX + YZ → WZ + YX A DD rxn is recognized by the formation of: precipitate gas water

Double Displacement Reactions That Produce a Precipitate A DD rxn resulting in the formation of an insoluble substance is called a precipitation reaction. Solubility guidelines are used to predict solubility of various compounds. What would happen if you mix lead (II) nitrate with potassium iodide? Write a balanced chemical.

Example 1 Which of the following pairs of aqueous solutions produce a precipitate when mixed together? Write the balanced chemical equation if you predict a precipitate. Write “NR” if you predict that no reaction takes place. potassium carbonate and copper(II) sulfate ammonium chloride and zinc sulfate

Solution – part a Ammonium sulfate is soluble. Potassium sulfate is soluble. Copper (II) carbonate is insoluble. Precipitate forms: K2CO3(aq) + CuSO4(aq) → K2SO4(aq) + CuCO3(s) Ammonium sulfate is soluble. Zinc chloride is soluble. Thus, no precipitate forms. NH4Cl(aq) + ZnSO4(aq) → NR

Double Displacement Reactions That Produce a Gas DD rxns are responsible for producing a number of gases. These gases include hydrogen hydrogen sulfide (a poisonous gas that smells like rotten eggs) sulfur dioxide (a reactant in forming acid rain) carbon dioxide ammonia

A Reaction that Produces Hydrogen Gas The alkali metals form bonds with hydrogen to produce compounds called hydrides. Hydrides react readily with water to produce hydrogen gas. LiH(s) + H2O(l) → LiOH(aq) + H2(g)

A Reaction that Produces Hydrogen Sulfide Gas Sulfides react with certain acids, such as hydrochloric acid, to produce hydrogen sulfide gas. K2S(aq) + 2HCl(aq) → 2KCl(aq) + H2S(g)

A Reaction that Produces Sulfur Dioxide Gas Some reactions produce a compound that, afterward, decomposes into a gas and water. These are two step reactions: Na2SO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2SO3(aq) H2SO3(aq) → SO2(g) + H2O(l) Therefore, the net reaction is Na2SO3(aq) + 2HCl(aq) → 2NaCl(aq) + SO2(g) + H2O(l)

A Reaction that Produces Carbon Dioxide Gas The reaction of a carbonate with an acid produces carbonic acid. Carbonic acid decomposes rapidly into carbon dioxide and water. Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2CO3(aq) H2CO3(aq) → CO2(g) + H2O(l) The net reaction is Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)

A Reaction that Produces Ammonia Gas Ammonia gas is very soluble in water. You can detect it easily, however, by its sharp, pungent smell.

Double Displacement Reactions That Produce Water In a neutralization reaction, water results when an H+ ion from the acid bonds with an OH− ion from the base. H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l) Most metal oxides are bases. Therefore, a metal oxide will react with an acid in a neutralization reaction to form a salt and water. Non-metal oxides are acidic. Therefore, a non-metal oxide will react with a base.

Representing Aqueous Ionic Reactions with Net Ionic Equations In a reaction there is reshuffling of ions. Some ions combine together to form a precipitate while others do not. The ions that do not involve in precipitate formation are referred to as spectator ions.

Total ionic equation The reaction between silver nitrate and sodium chloride can be represented by the following chemical equation: AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s) This equation can be written by using ions used to form soluble reactants and products. This is called total ionic equation. The insoluble products do not dissociate into ions!!!! Ag+(aq)+NO3−(aq)+Na+(aq)+Cl−(aq)→Na+(aq)+NO3−(aq)+AgCl(s)

Spectator ions appear on both sides of the equation. Total ionic equation with slashes through the spectator ions: Eliminate the spectator ions: Ag+(aq) + Cl−(aq) → AgCl(s) An ionic equation that is written this way, without the spectator ions, is called a net ionic equation.

Example 2 A chemical reaction occurs when the following aqueous solutions are mixed: sodium sulfide and iron(II) sulfate. Identify the spectator ions. Then write the balanced net ionic equation. Solution: Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) The total ionic equation is: The net ionic equation is: Fe2+(aq) + S2−(aq) → FeS(s)

Homework P347 #1-7 McGrawHill P 428 #1-7 Nelson