Slide 1 / 208 Slide 2 / 208 Acids and Bases Slide 3 / 208 Table of Contents: Acids and Bases Click on the topic to go to that section Properties of Acids and Bases · Conjugate Acid and Base Pairs · Amphoteric Substances · Strong Acids and Bases · Auto-Ionization of Water · pH · Weak Acids and Bases · Polyprotic acids · The Relationship Between K a and K b · Acid-Base Properties of Salt Solutions · Factors Affecting Acid Strength ·
Slide 4 / 208 Properties of Acids and Bases Return to the Table of contents Slide 5 / 208 Properties of Acids What is an Acid? Acids release hydrogen ions into solutions Acids neutralize bases in a neutralization reaction. Acids corrode active metals. Acids turn blue litmus to red. Acids taste sour. Slide 6 / 208 Properties of Bases Bases release hydroxide ions into a water solution. Bases neutralize acids in a neutralization reaction. Bases denature protein. Bases turn red litmus to blue. Bases taste bitter.
Slide 7 / 208 Arrhenius Acids and Bases Arrhenius's definition of acids and bases dates back to the 1800's. It is now considered obsolete since it only relates to reactions in water - aqueous solutions. Arrhenius defined acids and bases this way: An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions . HCl + H 2 O H 3 O + + Cl - H 3 O + is called a hydrated proton or a hydronium ion. A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions . NH 3 + H 2 O NH 4+ + OH - Slide 8 / 208 Brønsted-Lowry Acids and Bases The Brønsted-Lowry definition dates back to the early 1900's and is considered the modern definition of acids and bases. This definition is more general and it works for all reactions; not just in those in water An acid is a proton, H + , donor. A base is a proton, H + , acceptor. NH 3 + HCl NH 4+ + Cl - Slide 9 / 208 Brønsted-Lowry Acids and Bases A Brønsted-Lowry acid: must have a removable (acidic) proton or must transfer a proton to another substance NH 3 + HCl NH 4+ + Cl - A Brønsted-Lowry base: must have a pair of nonbonding electrons or must accept a proton H N H + HCl NH 4+ + Cl - H
Slide 10 / 208 Brønsted-Lowry Acids and Bases HCl +H 2 O Cl - + H 3 O + HCl donates the proton and acts as a Brønsted-Lowry acid. H 2 O accepts the proton and acts as a Brønsted-Lowry base. Slide 11 / 208 Lewis Acids Brønsted-Lowry acids replaced Arrhenius acids because the former were more general: Arrhenius acids could only be defined in aqueous (water) solutions. Brønsted-Lowry acids don't have that limitation. Arrehenius acids - only substances dissolved in H 2 O Similarly, Brønsted-Lowry acids are limited to substances that gain or lose hydrogen. Brønsted-Lowry acids - only substances that gain or lose H + The most general approach is that of Lewis acids; which do not require an aqueous environment or an exchange of hydrogen. Slide 12 / 208 Lewis Acids Lewis acids are defined as electron-pair acceptors. Atoms with an empty valence orbital can be Lewis acids. CH 3 CH 3 H + OH 2 H 3 C C O H 3 C C + H CH 3 CH 3 Lewis Acid
Slide 13 / 208 Lewis Bases Lewis bases are defined as electron-pair donors. Anything that could be a Brønsted-Lowry base is a Lewis base. Lewis bases can interact with things other than protons, however. Therefore, this definition is the broadest of the three. CH 3 CH 3 H H 3 C C O H 3 C C + + OH 2 CH 3 H CH 3 Lewis Base Slide 14 / 208 1 A Brønsted-Lowry base is defined as a substance that __________. A increases [H+] when placed in H 2 O B decreases [H+] when placed in H 2 O C increases [OH-] when placed in H 2 O acts aa s proton acceptor D E acts as a proton donor Slide 15 / 208 2 A Brønsted-Lowry acid is defined as a substance that __________. A increases K a when placed in H 2 O B decreases [H + ] when placed in H 2 O C increases [OH - ] when placed in H 2 O D acts as a proton acceptor E acts as a proton donor
Slide 16 / 208 3 Which of the following compounds could never act as an acid? SO 42- A - HSO 4 B H 2 SO 4 C D NH 3 CH 3 COOH E Slide 17 / 208 4 According to the following reaction model, reactant is acting like an acid? H 2 O + H 2 SO 4 → H 3 O + + HSO 4- H 2 SO 4 A B H 2 O H 3 O + C - HSO 4 D None of the above E Slide 18 / 208 5 According to the following reaction, which reactant is acting like a base? H 3 O + + HSO 4- → H 2 O + H 2 SO 4 H 2 SO 4 A H 2 O B H 3 O + C - D HSO 4 None of the above E
Slide 19 / 208 6 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. H 3 PO 4 + H 2 O → H 2 PO 4- + H 3 O + Acid A B Base Neither C Both D None of the above E Slide 20 / 208 7 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. H 3 PO 4 + H 2 O → H 2 PO 4 - + H 3 O + A Acid Base B C Both D Neither None of the above E Slide 21 / 208 8 Which of the following cannot act as a Lewis base? Cl - A B NH 3 C BF 3 CN - D H 2 O E
Slide 22 / 208 9 In the reaction BF 3 + F - BF 4- BF 3 acts as a/an ____________ acid. Arrhenius A Bronsted-Lowry B Lewis C Arrhenius, Bronsted-Lowry, and Lewis D Arrhenius and Bronsted-Lowry E Slide 23 / 208 Conjugate Acid Base Pairs Return to the Table of contents Slide 24 / 208 Conjugate Acids and Bases The term conjugate comes from the Latin word “conjugare,” meaning “to join together.” Reactions between acids and bases always yield their conjugate bases and acids. remove H + HNO 2 (aq) + H 2 O(l) NO 2- (aq) + H 3 O + (aq) Conjugate Conjugate Acid Base base acid add H+
Slide 25 / 208 Conjugate Acids and Bases remove H + HNO 2 (aq) + H 2 O(l) NO 2- (aq) + H 3 O + (aq) Acid Conjugate Conjugate Base base acid add H+ After the acid donates a proton, the result is called its conjugate base. After the base accepts a proton, the result is called its conjugate acid. Slide 26 / 208 Acids in Water What Happens When an Acid Dissolves in Water? Which is the acid? Which is the base? Water acts as a Brønsted-Lowry base and takes a proton (H+) from the acid. As a result, the conjugate base of the acid and a hydronium ion are formed. H 3 O + + HSO 4- H 2 SO 4 + H 2 O Slide 27 / 208 10 In liquid ammonia, the reaction represented below occurs. In the reaction NH 4+ acts as 2NH 3 NH 4+ + NH 2- a catalyst A both an acid and a base B the conjugate acid of NH 3 C D the reducing agent the oxidizing agent E Question from the College Board
Slide 28 / 208 11 What are the conjugate bases of HClO 4 , H 2 S, PH 4+ , HCO 3- ? A ClO 4+ , HS-, PH 3- , CO 3- ClO 4- , HS - , PH 3 , CO 32- B ClO 42- , HS 2- , PH 33- , CO 32- C D ClO 4- , H 2 S - , PH 3 , CO 32- Slide 29 / 208 Acid and Base Strength Strong acids completely Acid Base dissociate in water. 100% HCl Cl - - ionized H 2 SO 4 HSO 4 Base strength increases in H 2 O - HNO 3 NO 3 Their conjugate bases are quite + H 2 O H 3 O - SO 4 2- HSO 4 weak. - H 3 PO 4 H 2 PO 4 HF F- - HC 2 H 3 O 2 C 2 H 3 O 2 Acid strength increases - H 2 CO 3 HCO 3 H 2 S HS - Weak Negligible Strong Weak Strong - HPO 4 2- H 2 PO 4 Acid + NH 3 NH 4 HCO 3 - CO 3 2- Proton 2- PO 4 3- HPO 4 - Negative ion H 2 O OH - O 2- OH - H 2 H 100% - CH 4 CH 3 protonated in H 2 O Slide 30 / 208 Acid and Base Strength Acid Base Weak acids only partially 100% HCl Cl - dissociate in water. ionized - H 2 SO 4 HSO 4 Base strength increases in H 2 O HNO 3 NO 3 - + H 2 O H 3 O Their conjugate bases are - SO 4 2- HSO 4 - weak bases. H 3 PO 4 H 2 PO 4 HF F- - HC 2 H 3 O 2 C 2 H 3 O 2 Acid strength increases H 2 CO 3 HCO 3 - H 2 S HS - Weak Negligible Strong Weak Strong - HPO 4 2- H 2 PO 4 + NH 3 Acid NH 4 - CO 3 2- HCO 3 Proton 2- PO 4 3- HPO 4 H 2 O OH - Negative ion - O 2- OH - H 2 H 100% - CH 4 CH 3 protonated in H 2 O
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