Acid-Base Reactions

Review Acids are proton (H +1 ion) donors. ◦ H 2 SO 4 (aq) + H 2 O(l)  HSO 4 -1 (aq) + H 3 O +1 (aq)  In this reaction, H 2 SO 4 (aq) donates a proton to H 2 O.  H 2 SO 4 (aq) is the acid in this reaction. Bases are proton acceptors. ◦ CH 3 NH 2 (aq) + H 2 O(l)  CH 3 NH 3 +1 (aq) + OH -1 (aq)  In this reaction, CH 3 NH 2 (aq) accepts a proton from H 2 O.  CH 3 NH 2 (aq) is the base in this reaction. A conjugate base is the species formed when an acid gives up one proton. ◦ H 2 PO 4 -1 is the conjugate base of H 3 PO 4. A conjugate acid is the species formed when a base accepts one proton. ◦ NH 4 +1 is the conjugate acid of NH 3.

Acid-Base Reactions Neutralization reaction ◦ acid + base  salt + water  HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l)  H 2 SO 4 (aq) + 2 KOH(aq)  K 2 SO 4 (aq) + 2 H 2 O(l)  HNO 3 (aq) + NH 4 OH(aq)  NH 4 NO 3 (aq) + H 2 O(l) Contrary to what the name suggests, neutralization rxns do not always result in a neutral solution. ◦ Depends on the relative strengths of the acid and base that react.

Acid-Base Reactions Salt – an ionic compound ◦ Formed during an acid-base neutralization rxn  Cation comes from base.  Anion comes from acid. NaCl is a salt. ◦ Formed from a rxn between HCl and NaOH ◦ HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l) Mg(ClO 3 ) 2 is a salt. ◦ Formed from a rxn between HClO 3 and Mg(OH) 2 ◦ 2 HClO 3 (aq) + Mg(OH) 2  Mg(ClO 3 ) 2 (aq) + 2 H 2 O(l)

Parent Acids and Parent Bases To determine the parent acid of a salt: ◦ Identify the anion and its charge. ◦ Add as many H +1 ions to the anion as are indicated by its charge. EXAMPLES: ◦ What is the parent acid of KI?  The anion is I -1.  The parent acid is HI. ◦ What is the parent acid of CuSO 4 ?  The anion is SO  The parent acid is H 2 SO 4. ◦ What is the parent acid of Mg 3 (PO 4 ) 2 ?  The anion is PO  The parent acid is H 3 PO 4.

Parent Acids and Parent Bases To determine the parent base of a salt: ◦ Identify the cation and its charge. ◦ Add as many OH -1 ions as are indicated by its charge. EXAMPLES: ◦ What is the parent base of KCl?  The cation is K +1.  The parent base is KOH. ◦ What is the parent base of Ca(NO 3 ) 2 ?  The cation is Ca +2.  The parent base is Ca(OH) 2. ◦ What is the parent base of Fe 2 (SO 4 ) 3 ?  The cation is Fe +3.  The parent base is Fe(OH) 3.

Acid-Base Reactions Determine the “parent acid” and “parent base” of each salt. ◦ NaNO 3 ◦ LiBr ◦ Fe(CN) 3 ◦KC2H3O2◦KC2H3O2 ◦ (NH 4 ) 2 S ◦ HNO 3 + NaOH ◦ HBr + LiOH ◦ HCN + Fe(OH) 3 ◦ HC 2 H 3 O 2 + KOH ◦ H 2 S + NH 4 OH

Acidic and Basic Salts Salts can form acidic, basic, or neutral solutions. ◦ In order to determine what type of solution a salt will form, we must compare the strengths of its parent acid and parent base. Strong acid + strong base  neutral salt Strong acid + weak base  acidic salt Weak acid + strong base  basic salt Weak acid + weak base  varies

Acidic and Basic Salts Is a solution of NaCl acidic, basic, or neutral? ◦ The parent acid of NaCl is HCl.  HCl is a strong acid. ◦ The parent base of NaCl is NaOH.  NaOH is a strong base. ◦ Conclusion: NaCl forms a neutral solution.

Acidic and Basic Salts Is a solution of KF acidic, basic, or neutral? ◦ The parent acid of KF is HF.  HF is a weak acid. ◦ The parent base of KF is KOH.  KOH is a strong base. ◦ Conclusion: KF forms a basic solution.

Acidic and Basic Salts Is a solution of Fe(NO 3 ) 3 acidic, basic, or neutral? ◦ The parent acid of Fe(NO 3 ) 3 is HNO 3.  HNO 3 is a strong acid. ◦ The parent base of Fe(NO 3 ) 3 is Fe(OH) 3.  Fe(OH) 3 is a weak base. ◦ Conclusion: Fe(NO 3 ) 3 forms an acidic solution.

Titrations Acid-base titration = a neutralization reaction done for the purpose of determining the concentration of an acidic or basic solution. ◦ EXAMPLE: A solution of HCl with an unknown concentration is reacted with an NaOH solution of known concentration until the HCl solution is completely neutralized.  The concentration of the HCl solution can be calculated from how much NaOH solution was used in the titration.

Titrations Titrant – the solution whose concentration is known. Analyte – the solution whose concentration is unknown. Equivalence point – the point at which stoichiometrically equal amounts of titrant and analyte have been mixed.

Titrations Formula for use with acid-base titrations: ◦ a x [A] x V a = b x [B] x V b  a = number of H +1 ions the acid can donate  [A] = molar concentration of the acid  V a = volume of the acid solution  b = number of H +1 ions the base can accept  [B] = molar concentration of the base  V b = volume of the base solution

Titrations 25.0 mL of an HCl soln with unknown concentration are titrated with M NaOH. ◦ It takes 32.0 mL of the NaOH soln to neutralize the acid soln. ◦ What was the [acid]? a x [A] x V a = b x [B] x V b 1 x [A] x 25.0 mL = 1 x M x 32.0 mL 25.0 mL x [A] = 3.20 M*mL [A] = M

Titrations 20.0 mL of an HNO 3 soln of unknown concentration is titrated with M Ca(OH) 2. ◦ It takes 18.1 mL of the Ca(OH) 2 soln to neutralize the acid soln. ◦ What was [acid]? a x [A] x V a = b x [B] x V b 1 x [A] x 20.0 mL = 2 x M x 18.1 mL 20.0 mL x [A] = 9.05 M*mL [A] = M