8 - 1 Acid-Base Reactions If an acid reacts with a metal, a salt of that acid and hydrogen is produced.  aluminum + sulfuric acid → aluminum sulfate + hydrogen 2Al(s) + 3H 2 SO 4 (aq) → Al 2 (SO 4 ) 3 (aq) + 3H 2 (g) 2Al(s) + 6H + (aq) → 2Al 3+ (aq) + 3H 2 (g)

8 - 2  In the case of this single replacement reaction, the metal must be more active than the hydrogen it is trying to replace. If the metal is not more reactive, there will be no reaction. When an acid reacts with a salt, a new salt and a new acid is produced.  silver nitrate + hydrochloric acid → silver chloride + nitric acid

8 - 3 AgNO 3 (aq) + HCl(aq) → AgCl(s) + HNO 3 (aq) Ag + (aq) + Cl - (aq) → AgCl(s)  All double replacement (metathesis) reactions must produce a phase change for the reaction to occur. The phase change may result from: Formation of a precipitate: A precipitate forms when the inter-ionic attractions are greater than the attraction between the ions and the water.

8 - 4 Formation of a gas: Gases may form directly from the reaction itself or from the decomposition of one of the products. Formation of a molecular species: The formation of unionized molecules in a solution removes the ions from the solution. An example of this is water formed when an acid and a base neutralize each other.

8 - 5 Common Gases Formed Some common gases formed in double replacement reactions are given below.  any acid + any sulfide → salt + hydrogen sulfide HNO 3 (aq) + K 2 S(aq) → H 2 S(g) + KNO 3 (aq) H + (aq) + S 2- (aq) → H 2 S(g)

8 - 6  any carbonate + any acid → carbon dioxide + water + salt Ba(HCO 3 ) 2 (aq) + H 2 SO 4 (aq) → BaSO 4 (s) + 2H 2 O(l) + CO 2 (g) Ba 2+ (aq) + 2HCO 3 - (aq) + H + (aq) + HSO 4 - (aq) → BaSO 4 (s) + 2H 2 O(l) + 2CO 2 (g)

8 - 7  any sulfite + any acid → sulfur dioxide + water + salt MgSO 3 (aq) + 2HClO 4 (aq) → Mg(ClO 4 ) 2 (aq) + H 2 SO 3 (aq) SO 3 2- (aq) + 2H + → H 2 O(l) + SO 2 (g)

8 - 8  any ammonium salt + strong base → salt + water + ammonia NH 4 Br(aq) + LiOH(aq) → LiBr(aq) + NH 4 OH(aq) NH 4 + (aq) + OH - (aq) → NH 3 (g) + H 2 O(l)

8 - 9 More Acid-Base Reactions When writing acid-base reactions, be sure to account for states. Co(OH) 2 (s) + HNO 3 (aq) →  Co(OH) 2 (s) + H + (aq) → Co 2+ (aq) + H 2 O(l) Mn(OH) 2 (s) + HIO 4 (aq) →  Mn(OH) 2 (s) + 2H + (aq) → Mn 2+ (aq) + 2H 2 O(l)

LiNO 2 (aq) + H 2 O(l)  NO 2 - (aq) + H 2 O(l) HNO 2 (aq) + OH - (aq) CsF(aq) + HBr(aq) →  F - (aq) + H + (aq) → HF(aq) Al(OH) 3 (s) + HI(aq) →  Al(OH) 3 (s) + 3H + (aq) → Al 3+ (aq) + 3H 2 O(l)

NH 3 (aq) + HBrO 4 →  NH 3 (aq) + H + (aq) → NH 4 + (aq) HCN(aq) + KOH(aq) →  H + (aq) + OH - (aq) → H 2 O(l)

Net Ionic Equation WrapUp Formulas for reactants and products are written to show the predominant form of each substance as its exists in an aqueous solution.  Strong acids, strong bases, and soluble salts are written in ionized or dissociative form.  Weak acids, weak bases, gases, water, organic compounds, and insoluble salts are always written molecular form.

Questions that determine how a species is to be written. Does the solute dissolve in water?  If no, write the molecular formula. If yes, continue. i.e. I 2, AgCl, C 6 H 12 O 6

Does the solute dissociate or ionize?  If yes, write the ionic form. If no, write the molecular formula. i.e. HCl, NaOH The only substances that should be written in ionic form are:  Soluble salts, strong acids, and strong bases.

Important Reactants and Products H 2 SO 4 written as a reactant or product must be written: H 2 SO 4 (aq) → H + (aq) + HSO 4 - (aq) When the following gases are formed as products, they decompose and must be written as:  H 2 SO 3 (aq) → SO 2 (g) + H 2 O(l)  H 2 CO 3 (aq) → CO 2 (g) + H 2 O(l)

 NH 4 OH(aq) → NH 3 (g) + H 2 O(l) The only exception to this rule is when H 2 SO 3, H 2 CO 3, or NH 4 OH are formed from hydrolysis.  In the case of hydrolysis, the concentrations that result are so small that their decomposition does not take place.

Selective Solubility Which of the following will be more soluble in an acidic solution than in a basic solution? CaCO 3  CaCO 3 would be more soluble in an acidic solution because CO 3 2- is a relatively strong conjugate base of H 2 CO 3.  CaCO 3 (s) + 2H + (aq) → Ca 2+ (aq) + CO 2 (g) + H 2 O(l)

BaF 2  BaF 2 would be more soluble in an acidic solution because F - is a strong conjugate base of HF. BaF 2 (aq) + 2H + (aq) → 2HF(aq) + Ba 2+ (aq) AgCl  Cl - is an extremely weak conjugate base which results in no HCl being formed. However, AgOH is insoluble which would make AgCl more soluble in an acidic solution.

Acidic and Basic Anhydrides Anhydride means without water. When a nonmetallic oxide hydrolyzes, it forms an acid.  SO 2 is an acidic anhydride because when it reacts with water, sulfurous acid is formed.  SO 2 (g) + H 2 O(l) → H 2 SO 3 (aq)

 Cl 2 O is the acidic anhydride of HClO.  2HClO(aq) → Cl 2 O(aq) + H 2 O(l) When a metallic oxide hydrolyzes, it forms a base.  Na 2 O is a basic anhydride because when it reacts with water, sodium hydroxide is formed.  Na 2 O(s) + H 2 O(l) → 2NaOH(aq)

 CuO is the basic anhydride of Cu(OH) 2.  CuO(s) + H 2 O(l) → Cu(OH) 2 (s) Remember that in the case of hydrolysis, the concentrations of H 2 SO 3, H 2 CO 3, and NH 4 OH are so small that their decomposition does not take place.