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Acids and Bases

Explore the core properties of acids and bases, including their distinctive tastes and reactive nature. Delve into the Arrhenius and Bronsted-Lowry theories, which explain acid-base behavior and neutralization reactions. Learn about strong and weak electrolytes, conductivity differences, and the importance of oxyacids. Discover the concept of conjugate acid-base pairs and amphoterism, which describes substances that can act as both acids and bases. This comprehensive overview enhances understanding of acid-base chemistry, its applications, and underlying principles.

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Acids and Bases

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  1. Acids and Bases

  2. Acid/Base Properties • In the past, we have classified acids and bases according to their observed properties ACIDSBASES • Sour taste bitter taste • Watery feel slippery feel • Reactive with metals can be corrosive • Water soluble may be soluble in H2O

  3. Extending Acid/Base Theories • Arrhenius Theory (Svante Arrhenius 1859-1927) • Proposed that when salts dissolve in water, they dissociate completely into ions Acids- dissolve in water to produce H+(aq) ions Eg. HCl, HNO3 , H3PO4 , H2SO4 , HF Bases- dissolve in water to produce OH-(aq) ions Eg. NaOH , Ca(OH)2 , Mg(OH)2 Neutralization- acid + base  water + a salt HCl(aq) + NaOH(aq)  HOH(ℓ) + NaCl(aq)

  4. HELP WANTED Extending Acid/Base Concepts Although Arrhenius theory is very successful and useful for explaining acid/base chemistry, it has limitations WHY is Na2CO3(aq) BASIC?!? Bronsted-Lowry Theory (1923 Johannes Bronsted, Thomas Lowry) • Independently noted that some acid-base neutralization reactions can occur without dissolving ions in water Eg. HCl(g) + NH3(g)  NH4Cl(s) • They concluded that acid/base reactions simply involve the transfer of a hydrogen ion from one molecule to another

  5. Acid Base Arrhenius (grade 11) Bronsted-Lowry Extending Acid/Base Concepts According to Bronsted-Lowry definitions: ACIDS- are proton (H+) donors BASES- are proton (H+) acceptors Comparing theories Produces H+ in solution Produces OH– in solution HCl  H+ + Cl– NaOH  OH– + Na+ H+ donor H+ acceptor HCl+NaOHH2O+NaCl

  6. + H H - H N + H Cl N H H + Cl H H Extending Acid/Base Concepts Bronsted-Lowry theory could be used to explain neutralization reactions that could not be explained by Arrhenius theory. HCl is an acid because it donates H+, NH3 accepts H+ and therefore is the base (NH4+ and Cl– then form an ionic compound) So, Na2CO3 is basic because… CO32-(aq) + H2O  HCO31-(aq) + OH1-(aq)

  7. Strong vs. Weak Electrolytes • DEMO conductivity of acids and bases 1.0 mol/L HCl(aq) and 1.0 mol/L CH3COOH(aq) 1.0 mol/L NaOH(aq) and 1.0 mol/L NH3(aq) • The conductivity of these solutions varies eventhough they are all of the same concentration • Substances that dissolve in water and completely dissociate into ions are called strong electrolytes • Acids/Bases that dissolve in water and completely dissociate into ions are called strong acids/bases

  8. Strong vs. Weak Electrolytes Hydronium ion • Some strong acids and bases: HCl(aq) + H2O(ℓ)  H3O+(aq) + Cl1-(aq) NaOH(s) + H2O(ℓ)  Na1+(aq) + OH1-(aq) fully dissociated!

  9. Strong vs. Weak Electrolytes • Some substances are highly water soluble, yet they do not fully dissociate into ions upon dissolution. These substances are weak electrolytes • Acids and bases that do not fully dissociate into ions upon dissolving are weak acids/bases • When weak acid/bases are dissolved in water, a chemical equilibriumis established in the solution

  10. Strong vs. Weak Electrolytes • Weak acid/base equilibria(CLICK HERE!) CH3COOH(aq) + H2O(ℓ)  H3O+(aq) + CH3COO1-(aq) NH3(aq) + H2O(ℓ)  NH4+(aq) + OH1-(aq) • The reactant sides of these equilibria are favoured, so complete dissociation of the acid/base molecules does not occur.

  11. Oxyacids • Oxyacids are mineral acids which contain oxygen combined with another non-metal • Eg. HNO3(aq), H2SO4(aq), H3PO4(aq) Monoprotic diprotoic triprotic • The relative strength (ability to donate protons) of an oxyacid increases with the number of oxygen atoms that are not bonded to an hydrogen atom in the acid molecule. • Eg. H2SO4(aq) sulfuric acid is stronger than H2SO3(aq)

  12. Oxyacids • The ionization of polyprotic acids can be expressed using more than one chemical equation. Eg. H3PO4(aq)ionization: • H3PO4(aq) + H2O(ℓ) H3O+(aq) + H2PO41-(aq) • H2PO41-(aq) + H2O(ℓ) H3O+(aq) + HPO42-(aq) • HPO42-(aq) + H2O(ℓ) H3O+(aq) + PO43-(aq)

  13. Conjugate Acid/Base Pairs CH3COO1-(aq) is the conjugate base of CH3COOH(aq) H3O+(aq) is the conjugate acid of H2O(ℓ) • In any equilibrium expression involving a weak acid/base more than one Bronsted/Lowry acid and base can be identified CH3COOH(aq) + H2O(ℓ)  H3O+(aq) + CH3COO1-(aq) Conjugate acid/base pair Conjugate acid/base pair- two substances that differ from each other by just one proton (H+).

  14. Conjugate Acid/Base Pairs HCN(l) + H2O  CN–(aq) + H3O+(aq) Forward: HCN is acid, H2O is base HCN(l) + H2OCN–(aq) + H3O+(aq) Reverse: H3O+ is acid, CN– is base • Relative strengths of conjugate acid/base pairs • The conjugate base of a weak acid must be a strong base • The conjugate base of a strong acid must be a weak base • The conjugate acid of a weak base must be strong acid • The conjugate acid of a strong base must be a weak acid Q. Explain whether you would expect a solution of NH4Cl(aq) to be acidic or basic. For more lessons, visit www.chalkbored.com

  15. Amphoterism • Any substance that can behave either as an acid or a base is amphoteric (amphiprotic) Eg. Bicarbonate buffer in blood, HCO31-(aq) HCO31- + OH1- H2O + CO32- (as an acid) HCO31- + H3O+ H2CO3 + H2O (as a base)

  16. Homework p.532 #1, 2 p.549 #2, 3 Read p.532 to 549 for next class

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