Slide 1 / 174 Acids and Bases PSI Chemistry covers the material approximately up to slide 75. Slide 2 / 174 Properties of Acids · Acids release hydrogen ion(s) into (aqueous) solution · Acids neutralize bases in a neutralization reaction. · Acids corrode active metals. · Acids turn blue litmus to red. · Acids taste sour. Slide 3 / 174 Properties of Bases · Bases release a hydroxide ion(s) into a water solution. · Bases neutralize acids in a neutralization reaction. · Bases denature protein. · Bases turn red litmus to blue. · Bases taste bitter.
Slide 4 / 174 Arrhenius Acids and Bases A definition of acids and bases from the 1800's Considered obsolete now since it only relates to reactions in water, aqueous solutions. He defined acids and bases this way: · An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions. · A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. Slide 5 / 174 Brønsted-Lowry Acids and Bases A more modern definition: formulated in the early 1900's More general since it works for all reactions; not just in water · An acid is a proton, H + , donor. · A base is a proton, H + , acceptor. Slide 6 / 174 Brønsted-Lowry Acids and Bases A Brønsted-Lowry acid: must have a removable (acidic) proton or must transfer a proton to another substance A Brønsted-Lowry base: must have a pair of nonbonding electrons or must accept a proton
Slide 7 / 174 1 A Bronsted-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 D acts as a proton acceptor E acts as a proton donor Slide 8 / 174 2 A Bronsted-Lowry acid is defined as a substance that __________. A increases K a when placed in H 2 O decreases [H + ] when placed in H 2 O B increases [OH - ] when placed in H 2 O C D acts as a proton acceptor E acts as a proton donor Slide 9 / 174 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 + H 3 O + is called a hydrated proton or a hydronium ion. It is also written as H +
Slide 10 / 174 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. · Similarly, Brønsted-Lowry acids are limited to substances that gain or lose hydrogen. But there are acids and bases that don't. · The most general approach is that of Lewis acids; which don't require an aqueous environment or an exchange of hydrogen. Slide 11 / 174 Lewis Acids · Lewis acids are defined as electron-pair acceptors. · Atoms with an empty valence orbital can be Lewis acids. Slide 12 / 174 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.
Slide 13 / 174 3 Which of the following compounds could never act as an acid? 2- A SO 4 - HSO 4 B H 2 SO 4 C D NH 3 CH 3 COOH E Slide 14 / 174 4 According to the following reaction model, which 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 15 / 174 5 According to the following reaction, which reactant is acting as 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 16 / 174 6 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. - + H 3 O + H 3 PO 4 + H 2 O → H 2 PO 4 Acid A Base B Neither C D Both None of the above E Slide 17 / 174 7 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. - + H 3 O + H 3 PO 4 + H 2 O → H 2 PO 4 A Acid Base B Both C Neither D E None of the above Slide 18 / 174 8 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. - + H 3 O + H 3 PO 4 + H 2 O → H 2 PO 4 A Acid Base B C Both Neither D None of the above E
Slide 19 / 174 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. Slide 20 / 174 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 21 / 174 Conjugate Acids and Bases remove H + HNO 2 (aq) + H 2 O(l) NO 2 - (aq) + H 3 O - (aq) conjugate Conjugate Acid 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 22 / 174 Amphoteric Substances If a substance can act both as an acid and base, it is known as amphoteric. For example, water can act as a base or acid depending on the situation. ↔ Cl - + H 3 O + HCl + H 2 O Above, water accepts a proton, thus acting as a base. ↔ NH 4 + + OH - NH 3 +H 2 O Above, water donates a proton, thus acting as an acid. Slide 23 / 174 9 A substance that is capable of acting as both an acid and as a base is __________. A autosomal B conjugated C amphoteric D saturated E miscible Slide 24 / 174 Amphoteric Substances Another term for amphoteric is amphiprotic. For each of the following substances, write two equations, one showing it as a Bronsted-Lowry acid and another showing it as a Bronsted-Lowry base. - HCO 3 - HSO 4 H 2 O
Slide 25 / 174 What is the conjugate acid of NH 3 ? 10 A NH 3 + NH 2 B + NH 3 C + NH 4 D NH 4 OH E Slide 26 / 174 11 + , What are the conjugate bases of HClO 4 , H 2 S, PH 4 - ? HCO 3 A + , HS-, PH 3 - , CO 3 - ClO 4 - , HS - , PH 3 , CO 3 2- ClO 4 B 2- , HS 2- , PH 3 3- , CO 3 2- ClO 4 C Slide 27 / 174 Acid and Base Strength Acid Base · Strong acids are 100% - HCl Cl completely dissociated in ionized - H 2 SO 4 HSO 4 in H 2 O Base strength increases - HNO 3 NO 3 water. H 3 O + H 2 O - SO 4 2- HSO 4 - H 3 PO 4 H 2 PO 4 HF F- · Their conjugate bases are HC 2 H 3 O 2 C 2 H 3 O 2 - - Acid strength increases H 2 CO 3 HCO 3 quite weak. Negligible Weak g n o r t S H 2 S HS - Negligible k a e W Strong - HPO 4 2- H 2 PO 4 NH 4 + NH 3 - CO 3 2- HCO 3 HPO 4 2- PO 4 3- - H 2 O OH - O 2- OH 100% - H 2 H protonated - CH 4 CH 3 in H 2 O
Slide 28 / 174 Acid and Base Strength Acid Base 100% HCl Cl - ionized - H 2 SO 4 HSO 4 in H 2 O Base strength increases - HNO 3 NO 3 + H 2 O H 3 O - SO 4 2- HSO 4 · Weak acids only H 3 PO 4 H 2 PO 4 - HF F- dissociate partially in water. HC 2 H 3 O 2 C 2 H 3 O 2 - - Acid strength increases H 2 CO 3 HCO 3 Negligible Weak g n o r t S H 2 S HS - Negligible k a e W Strong - HPO 4 2- H 2 PO 4 · Their conjugate bases are NH 4 + NH 3 - CO 3 2- HCO 3 weak bases. HPO 4 2- PO 4 3- - H 2 O OH OH - O 2- 100% H 2 H - protonated - CH 4 CH 3 in H 2 O Slide 29 / 174 Acid and Base Strength Acid Base 100% HCl Cl - ionized - H 2 SO 4 HSO 4 in H 2 O Base strength increases HNO 3 NO 3 - + H 2 O H 3 O - SO 4 2- HSO 4 - H 3 PO 4 H 2 PO 4 · Substances with negligible HF F- - HC 2 H 3 O 2 C 2 H 3 O 2 acidity do not dissociate in - Acid strength increases H 2 CO 3 HCO 3 Negligible Weak g n o r t S k a e W Strong - H 2 S HS water. They will not readily - HPO 4 2- H 2 PO 4 + NH 3 NH 4 give up protons. - CO 3 2- HCO 3 2- PO 4 3- HPO 4 - H 2 O OH OH - O 2- · Their conjugate bases are 100% - H 2 H protonated CH 4 CH 3 - exceedingly strong. in H 2 O Slide 30 / 174 Strong Acids The seven strong acids are: · HCl hydrochloric acid · HBr hydrobromic acid · HI hydroiodic acid · HNO 3 nitric acid · H 2 SO 4 sulfuric acid · HClO 3 chloric acid · HClO 4 perchloric acid Memorize this list.
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