Intro to Acids and Bases

1. Intro to Acids and Bases (again!)

2. Naming acids • An acid is loosely defined as a compound that produces hydrogen ions(H+) when dissolved in water • Acids are named depending on the anion in the compound Add H+ Add H+ Add H+ _______ ide (chloride, Cl-) ________ate (chlorate, ClO3-) _________ite (chlorite, ClO2-) Anion (example) Acid (example) hydro____ic acid (hydrochloric acid, HCl) _______ic acid (chloric acid, HClO3) _______ous acid (chlorous acid, HClO2)

4. Writing Formulas Acids

5. Names and formulas for Bases • A base is a compound that produces hydroxide ions (OH-) when dissolved in water • Bases are named in the same way as other ionic compounds—thename of the cation is followed by the name of the anion • Examples - Sodium hydroxide (NaOH); potassium hydroxide (KOH)

6. Strengths of Acids and Bases • The strength of an acid/base depends on how well the ions dissociate • Influenced by • Polarity (more polar = stronger) • Bond strength (Stronger bonds = weaker acid/bases because they don’t dissociate) • Stability of anion (more stable = stronger) • Strong ≠ high concentration • Strength measures the degree of separation • Concentration refers to how many particles are present

7. Strength of Acids/Bases • Strong acids/bases – completely dissociate, strong electrolytes • Examples you should know: HNO3, H2SO4, HCl, HBr, HI; KOH, NaOH • Weak acids/bases – don’t completely dissociate and are weak electrolytes • Generally, organic acids like acetic acid (vinegar) • Not many weak bases; i.e. NH3

8. Defining Acids and Bases • Multiple ways to define acids and bases • Arrhenius acids/bases • Acids are hydrogen-containing compounds that yield hydrogen ions (H+) in aqueous solution • Bases yield hydroxide ions (OH-) in aqueous solution

9. Arrhenius Acids • H+ is also known as a proton • Acids can be monoprotic, diprotic, or triprotic • Monoprotic: HNO3 → H+ + NO3- • Ionization yields one hydrogen ion • Diprotic: H2SO4 → 2H+ + SO42- • Complete ionization yields 2 hydrogen ions • Triprotic: H3PO4 → 3H+ + PO43- • Complete ionization yields 3 hydrogen ions

10. Nonionizable Hydrogen H O H C C O- H+ Ionizable Hydrogen H Arrhenius Acids • Not all the hydrogens in an acid may be released as hydrogen ions • Not all hydrogen-containing compounds are acids • Only hydrogens joined to very electronegative elements with very polar bonds, are ionizable in water Ethanoic Acid

11. Arrhenius Bases • Bases formed with group one metals are very soluble and caustic • NaOH → Na+(aq) + OH-(aq) • KOH → K+(aq) + OH-(aq) • Bases of group 2 metals are very weak • Examples are Ca(OH)2 and Mg(OH)2

12. Bronsted-Lowry Acids and Bases • Arrhenius definition is not very comprehensive • Ammonia (NH3) is a base, but there is no hydroxide (OH-) in the compound to ionize • The Bronsted-Lowry theory defines an acid as a hydrogen-ion donor, and a base as a hydrogen-ion acceptor NH3(aq) + H2O(l) → NH4+(aq) + OH-(aq) Hydrogen ion aceptor, Bronsted-Lowry Base Hydrogen ion donor, Bronsted-Lowry Acid Makes the solution basic

13. conjugate acid-base pair NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Conjugate Acid Conjugate Base Base Acid conjugate acid-base pair Conjugate Acids and Bases • A conjugate acid is the particle formed when a base gains a hydrogen ion • A conjugate base is the particle that remains when an acid has donated a hydrogen ion • A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion • Acids have conjugate bases while bases have conjugate acids

14. HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) conjugate acid-base pair Conjugate Acid Conjugate Base Acid Base • A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion H3O+ • Water can both accept AND donate a hydrogen ion • A substance that can act as both an acid and a base is said to be amphoteric • Amino Acids as an example – building block of protein conjugate acid-base pair

15. Lewis Acids and Bases • Acids accept a pair of electrons during a reaction while a base donates a pair of electrons • Lewis acid – a substance that can accept a pair of electrons to form a covalent bond • Lewis base – a substance that can donate a pair of electrons to form a covalent bond • MUCH broader, more inclusive definition than any of the others NH3 + BF3 → NH3BF3 Identify the Lewis Acid and the Lewis Base in the above equation

17. Base Acid H+ + H2O → H3O+ H+

18. Acid-Base Definitions Review

19. Reactions of Acids/Bases (Arrhenius and B.L kinds) • Single replacement • Double replacement

20. Single Replacement Reactions • A + BC = AB + C • A chemical change in which one element replaces a second element in a compound • Acids react strongly with most metals – reactivity with metals used to be a common way to classify acids • Hydrogen from the acid is always the cation replaced by the metal • Examples: 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) 2Al (s) + 6HNO3 (aq)  2Al(NO3)3(aq) + 3H2(g)

21. Single Replacement Reactions Activity Series of Metals Decreasing reactivity • Notice that aluminum is higher on the activity series of metals than hydrogen • A reactive metal will replace any metal listed below it in the activity series 2Al (s) + 6HNO3 (aq)  2Al(NO3)3(aq) + 3H2(g) Cu+ HNO3 No reaction

22. Practice Problems • 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) 2Al (s) + 6HNO3 (aq)  2Al(NO3)3(aq) + 3H2(g) Ca (s) + H2SO4(aq)  CaSO4 + H2(g) Pt (s) + HCl(aq)  N.R. 2Na (s) + H2SO4(aq)  Na2SO4 + H2(g)

23. Double Replacement Reactions • AB + CD = AC + BD • The ions of two compounds exchange places in an aqueous solution to form two new compounds • Often produce a precipitate, a gas, or molecular compound such as water • Precipitation (forms a solid or gas as a product) • Acid/Base (forms water as product); also known as a neutralization reaction • Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) + 2H2O(l)

24. Reactions in Aqueous SolutionAcid-Base reactions • Acids and bases react to form water and a salt, a generic name for an ionic compound • H3PO4 + 3Fe(OH)2  Fe3(PO4)2 + 6H2O • H2SO4+ Ca(OH) 2  CaSO4 + 2H2O