UNIT 5

1. UNIT 5 Aqueous Reactions and Solution Stoichiometry Acid-Base Neutralization

2. Writing Equations for Reactions Involving Ions • There are three ways to write equations for reactions involving ions. • Molecular equation: • HCl (aq) + AgNO3 (aq)  AgCl (s) + HNO3 (aq) • Here no ions are shown but all reactants and products are identified and their physical states given. • Complete or Total Ionic Equation: • H+ (aq) + Cl- (aq) + Ag+ (aq) + NO3- (aq)  AgCl (s) + H+ (aq) + NO3- (aq) • Here ALL ions are shown as they exist in solution. Spectator ions do not participate in the reaction but are shown. • Net ionic equation: • Cl- (aq) + Ag+ (aq)  AgCl (s) • Here only ions which participate in the reaction are shown. Spectator ions are NOT shown.

3. Writing Equations for Reactions Involving Ions • Write the three equations for the reaction between solutions of barium nitrate and sodium phosphate. • Molecular equation: • 2Na3PO4 (aq) + 3Ba(NO3)2 (aq)  Ba3(PO4)2 (s) + 6NaNO3 (aq) • Complete or Total Ionic Equation: • 6Na+ (aq) + 2PO43- (aq) + 3Ba2+ (aq) + 6NO3- (aq)  Ba3(PO4)2 (s) + 6Na+ (aq) + 6NO3- (aq) • Net ionic equation: • 2PO43- (aq) + 3Ba2+ (aq)  Ba3(PO4)2 (s) • The net ionic equation says that ANY soluble compound with phosphate and ANY soluble compound with barium ion will react to form the barium phosphate precipitate.

4. Acid-Base Neutralization • Metathesis reactions are reactions of the form: AX + BY  AY + BX • If either of the POSSIBLE new compounds AY or BX is: • insoluble in water (a precipitate) • a weak electrolyte • a gas • then the metathesis reaction will occur. • Acid-base neutralization is a metathesis reaction. The product of the neutralization is either a weak electrolyte (usually water) or a gas.

5. Acid-Base Neutralization • Acid-base neutralization is a metathesis reaction between an acid and a base. • HX + BOH BX + HOH ( = H2O ) • Definitions of acids and bases • Acids • produce H+ in water (Arrhenius) • are proton donors (proton = H+) (Brønsted-Lowry) • Bases • produce OH- in water (Arrhenius) • are proton acceptors (Brønsted-Lowry)

6. Acid-Base Neutralization • Acid-base neutralization is a metathesis reaction between an acid and a base. • HX + BOH  BX + H2O • acid + base  water • (a weak electrolyte) • Acids are proton donors (proton = H+). • Bases are proton acceptors and are metal hydroxides, ammonia, the amines and alcohols: • HCl+ NH3 NH4+ + Cl-  NH4Cl(s) • acid + ammonia  salt

7. Acid-Base Neutralization • In a neutralization, the acid and the base are reactants. Identify the acid and the base in the following reactions (hint: look for the H+): • CH3OH + HBr CH3OH2+ + Br - • CH3NH2 + H2O  CH3NH3+ + OH- • Here, the acids had the H at the left of the formula (HBr, HOH). • (It is helpful to know the Lewis structures of ammonia and of water.)

8. Acid-Base Neutralization • Identify the acid and the base in the following reactions: • CH3CO2H + KOH  CH3CO2- K++ H2O • CH3COOH+ CH3Li  CH3CO2-Li++ CH4 • Organic acids (CO2H or COOH) have the acid H at the right of the formula. • Here are two more: • CH3OH+ NaH CH3O- Na++ H2 • C4H9Li + H2O  C4H10 + LiOH (Li+ and OH-)

9. Acid-Base Neutralization • KNOW THE STRONG ACIDS: HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4 by name AND formula. • These ionize completely in water. HCl(aq)  H+(aq) + Cl-(aq) • KNOW THE STRONG BASES: LiOH, NaOH, KOH, RbOH, CsOH (these are Group 1A metal hydroxides), Ca(OH)2, Sr(OH)2, and Ba(OH)2, by name AND formula. • These ionize completely in water. Ba(OH)2(aq)  Ba2+(aq) + 2OH-(aq) • 2HCl(aq) + Ba(OH)2(aq)  2H2O(l) + BaCl2(aq) • NET IONIC REACTION BETWEEN A STRONG ACID AND A STRONG BASE: H+(aq) + OH-(aq)  H2O(l)

10. Acid-Base Neutralization - Examples Acetic acid is neutralized by a solution of potassium hydroxide: M.E.: HC2H3O2 (aq) + KOH (aq) KC2H3O2 (aq) + H2O (l) Complete ionic equation: HC2H3O2(aq) + K+(aq) + OH-(aq) K+ (aq) + C2H3O2- (aq) + H2O (l) Net ionic equation: HC2H3O2(aq) + OH-(aq) C2H3O2-(aq) + H2O(l)

11. Acid-Base Neutralization - Examples Solid magnesium hydroxideis neutralized by hydroiodic acid: M.E.: Mg(OH)2 (s) + 2HI (aq) MgI2 (aq) + 2H2O (l) Complete ionic equation: Mg(OH)2 (s) + 2H+ (aq) + 2I- (aq) Mg2+ (aq) + 2I- (aq) + 2H2O (l) Net ionic equation: Mg(OH)2 (s) + 2H+ (aq)  Mg2+ (aq) + 2H2O (l)

12. Acid-Base Neutralization with Gas Formation Hydrochloric acidreacts with a solution of sodium sulfide. One of the products is a gas. Molecular Equation: 2HCl (aq) + Na2S (aq) 2NaCl (aq) + H2S (g) acid base salt gas The sulfide ion acts as a proton acceptor and is therefore the base. Complete ionic equation: 2H+(aq) + 2Cl-(aq) + 2Na+(aq) + S2-(aq) 2Cl-(aq) + 2Na+(aq) + H2S (g) Net ionic equation: 2H+(aq) + S2-(aq) H2S (g)

13. Acid-Base Neutralization Recognize the “gases in disguise:” H2SO3, H2CO3 and NH4OH. These compounds are unstable in water and decompose to form a gas and water. H2SO3 (aq) H2O (l) + SO2 (g) H2CO3 (aq) H2O (l) + CO2 (g) NH4OH (aq) H2O (l) + NH3 (g)

14. Acid-Base Neutralization Hydrochloric acidis neutralized by a solution of sodium sulfite. 2HCl (aq) + Na2SO3 (aq) 2NaCl (aq) + H2SO3 (aq) Molecular equation: 2HCl (aq) + Na2SO3 (aq) 2NaCl (aq) + H2O (l) + SO2 (g) The sulfite ion acts as a proton acceptor and is therefore the base. Complete ionic equation: 2H+(aq) + 2Cl-(aq) + 2Na+(aq) + SO32-(aq) 2Cl-(aq) + 2Na+(aq) + H2O(l) + SO2 (g) Net ionic equation: 2H+(aq) + SO32-(aq) H2O (l) + SO2 (g)