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Acid-Base Reactions

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.

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Acid-Base Reactions

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  1. Acid-Base Reactions

  2. Review • Acids are proton (H+1 ion) donors. • H2SO4(aq) + H2O(l)  HSO4-1(aq) + H3O+1(aq) • In this reaction, H2SO4(aq) donates a proton to H2O. • H2SO4(aq) is the acid in this reaction. • Bases are proton acceptors. • CH3NH2(aq) + H2O(l)  CH3NH3+1(aq) + OH-1(aq) • In this reaction, CH3NH2(aq) accepts a proton from H2O. • CH3NH2(aq) is the base in this reaction. • A conjugate base is the species formed when an acid gives up one proton. • H2PO4-1 is the conjugate base of H3PO4. • A conjugate acid is the species formed when a base accepts one proton. • NH4+1 is the conjugate acid of NH3.

  3. Acid-Base Reactions • Neutralization reaction • acid + base  salt + water • HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) • H2SO4(aq) + 2 KOH(aq)  K2SO4(aq) + 2 H2O(l) • HNO3(aq) + NH4OH(aq)  NH4NO3(aq) + H2O(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.

  4. 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) + H2O(l) • Mg(ClO3)2 is a salt. • Formed from a rxn between HClO3 and Mg(OH)2 • 2 HClO3(aq) + Mg(OH)2 Mg(ClO3)2(aq) + 2 H2O(l)

  5. 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 CuSO4? • The anion is SO4-2. • The parent acid is H2SO4. • What is the parent acid of Mg3(PO4)2? • The anion is PO4-3. • The parent acid is H3PO4.

  6. 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(NO3)2? • The cation is Ca+2. • The parent base is Ca(OH)2. • What is the parent base of Fe2(SO4)3? • The cation is Fe+3. • The parent base is Fe(OH)3.

  7. Acid-Base Reactions • Determine the “parent acid” and “parent base” of each salt. • NaNO3 • LiBr • Fe(CN)3 • KC2H3O2 • (NH4)2S • HNO3 + NaOH • HBr + LiOH • HCN + Fe(OH)3 • HC2H3O2 + KOH • H2S + NH4OH

  8. 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

  9. 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.

  10. 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.

  11. Acidic and Basic Salts • Is a solution of Fe(NO3)3 acidic, basic, or neutral? • The parent acid of Fe(NO3)3 is HNO3. • HNO3 is a strong acid. • The parent base of Fe(NO3)3 is Fe(OH)3. • Fe(OH)3 is a weak base. • Conclusion: Fe(NO3)3 forms an acidic solution.

  12. 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.

  13. 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.

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

  15. Titrations • 25.0 mL of an HCl soln with unknown concentration are titrated with 0.100 M NaOH. • It takes 32.0 mL of the NaOH soln to neutralize the acid soln. • What was the [acid]? • a x [A] x Va = b x [B] x Vb • 1 x [A] x 25.0 mL = 1 x 0.100 M x 32.0 mL • 25.0 mL x [A] = 3.20 M*mL • [A] = 0.128 M

  16. Titrations • 20.0 mL of an HNO3 soln of unknown concentration is titrated with 0.250 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 Va = b x [B] x Vb • 1 x [A] x 20.0 mL = 2 x 0.250 M x 18.1 mL • 20.0 mL x [A] = 9.05 M*mL • [A] = 0.453 M

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