Chapter 14 Acids and Bases

Transcription

1 Chapter 14 Acids and Bases

2 General Properties of Acids 1. An acid tastes sour - acidus = Latin, sour; acetum= Latin, vinegar 2. An acid turns indicator dye litmus from blue to red. 3. An acid reacts with certain metals (Fe, Sn, Zn, Mg). 4. An acid is an electrolyte. 5. An acid reacts with bases to form salts and water

3 1. HNO2 is named A) hydronitric acid. B) hydronitrous acid. C) nitric acid. D) nitrous acid. E) hydrogen nitrite. NO3 - = nitrate NO2 - = nitrite

4 Common Acids Name Formula Uses Strength Perchloric HClO4 explosives, catalysts Strong Nitric HNO3 explosives, fertilizers, dyes, glues Strong Sulfuric Hydrochloric Phosphoric H2SO4 HCl H3PO4 explosives, fertilizers, dyes, glue, batteries metal cleaning, food prep, ore refining, stomach acid fertilizers, plastics, food preservation Strong Strong Moderate Chloric HClO3 explosives Moderate Acetic HC2H3O2 plastics, food preservation, vinegar Weak Hydrofluoric HF metal cleaning, glass etching Weak Carbonic H2CO3 soda water, blood buffer Weak Hypochlorous HClO sanitizer Weak Boric H3BO3 eye wash Weak

5 Sources of Acids SO3 + H2O > H2SO4 Sulfuric Acid NO2 + H2O > HNO3 Nitric Acid CO2 + H2O > H2CO3 Carbonic Acid 2 NaCl + H2SO > Na2SO4 + 2 HCl Hydrochloric Acid

6 General Properties of Bases 1. A base tastes bitter 2. A base turns indicator dye litmus from red to blue. 3. A base feels slippery or soapy when mixed with a small amount of water 4. A base reacts with acids to form salts and water

7 2. What is the chemical formula for the base calcium hydroxide? A) CaOH B) CaH C) CaH2 D) Ca(OH)2 E) Ca2(OH) Ca 2+ OH -

8 Common Bases Name Formula Common Name Uses Strength Sodium Hydroxide NaOH Lye, Caustic Soda soap, plastic production, petroleum refining Strong Potassium Hydroxide KOH Caustic Potash soap, cotton processing, electroplating Strong Calcium Hydroxide Ca(OH)2 Slaked Lime cement Strong Sodium Bicarbonate NaHCO3 Baking Soda food preparation, antacids Weak Magnesium Hydroxide Mg(OH)2 Milk of Magnesia antacids Weak Ammonium Hydroxide NH4OH Ammonia Water fertilizers, detergents, explosives Weak

9 Sources of Bases CaO + H2O > Ca(OH)2 Calcium hydroxide Li2O + H2O > 2 LiOH Lithium hydroxide 2 Na + 2 H2O > 2 NaOH + H2 Sodium hydroxide Ca + 2 H2O > Ca(OH)2 + H2

10 Molecular Definitions of Acids and Bases

11 Acids and Bases in Solution Acids ionize in water to form H + ions. (More precisely, the H+ from the acid molecule is donated to a water molecule to form hydronium ion, H3O + ) Bases dissociate in water to form OH- ions. (Bases, such as NH3, that do not contain OH- ions, produce OH- by pulling H + off water molecules.) In the reaction of an acid with a base, the H + from the acid combines with the OH- from the base to make water. The cation from the base combines with the anion from the acid to make a salt. acid + base salt + water

12 Arrhenius Theory

13 3. Which of the following can act as an Arrhenius base? A) Ca(OH)2 B) H2O C) KOH D) H2SO4 E) Two of the above

14 Brønsted-Lowry Theory Brønsted-Lowry Acid-Base Reactions involve transfer of protons. A Brønsted-Lowry Acid is a proton donor. A Brønsted-Lowry Base is a proton acceptor.

15 Brønsted-Lowry Theory An acid-base reaction involves proton transfer: H-A + [B:]- -> A:- + H-B [H-A] + B: -> [A:]- + [H-B] + [H-A:]- + B: -> [:A:] 2- + [H-B] + [H-A] + + B: -> A: + [H-B] +

16 Brønsted-Lowry Acids A Brønsted-Lowry Acid is a proton donor. Any material with a H is a potential proton donor, but because of molecular structure, one or more protons are sometimes more likely to be transferred.

17 Molecular Models of Selected Acids

18 4. Which of the following can act as a Brønsted Lowry acid? A) NH3 B) NaOH C) BF3 D) HBr E) Two of the above

19 Ionization of an Acid The ionization of an acid in water is more accurately written as: HCl + H2O > Cl - + [H3O] proton donor proton acceptor chloride ion hydronium ion

20 Ionization of an Acid

21 Brønsted-Lowry Bases A Brønsted-Lowry Base is a proton acceptor. Any material with a lone pair of electrons is a potential proton acceptor, but because of molecular structure, one or more atoms with lone pairs may be more likely to accept a proton.

22 Bronsted Lowry Acid Base Reaction

23 Conjugate Pairs 1. In a Brønsted-Lowry reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in the reverse process 2. Each reactant and product are a conjugate pair. 3. The original base becomes a conjugate acid, and the original acid becomes a conjugate base

24 Conjugate Acid Base Pairs H-A + :B :A - + H-B + acid base conjugate conjugate base acid HCHO 2 + H 2 O CHO H 3 O + acid base conjugate conjugate base acid H 2 O + NH 3 : HO - + NH 4 + acid base conjugate conjugate base acid

25 Conjugate Pairs H2O and OH- are an acid/base conjugate pair. NH3 and NH4+ are an base/acid conjugate pair.

26 5. Identify the two Brønsted Lowry acids in the following reaction: H3PO4 + NH3 NH4 + + H2PO4 A) H3PO4 and NH3 B) H3PO4 and NH4 + C) H3PO4 and H2PO4 D) NH3 and NH4 + E) NH3 and H2PO4

27 6. What is the conjugate acid of H2C6H5O6? A) C6H5O6 3 B) HC6H5O6 2 C) H2C6H5O6 D) H3C6H5O6 E) H4C6H5O6 +

28 Lewis Acids and Bases electron pair donor = Lewis Base = nucleophile electron pair acceptor = Lewis Acid = electrophile Lewis acid-base reactions include all the previously described acid-base reactions plus additional types.

29 Molecules as Lewis Acids and Bases

30 The reaction of the Lewis acid BF3 with the Lewis base NH3 - +

31 Reactions of Acids and Bases

32 Acid-Base Reactions Also called neutralization reactions because the acid and base neutralize each other s properties 2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l) Note that the cation from the base combines with the anion from the acid to make the water soluble salt. The net ionic equation for an acid-base reaction is H + (aq) + OH-(aq) H2O(l) (as long as the salt that forms is soluble in water)

33 Neutralization - The reaction of an acid and a base HCl + NaOH > NaCl + H2O

34 7. What is the salt formed in the neutralization reaction between nitric acid and potassium hydroxide? A) KCl B) KNO2 C) KNO3 D) H2O E) KH HNO3 (aq) + KOH (aq) KNO3 (aq) + H2O (l)

35 Other Useful Acid-Base Reactions 1. Mg(OH)2 + 2 HCl > 4 H2O + MgCl2 2. CaCO3 + H2SO > H2O + CO2 + CaSO4 3. NaHCO3 + RCOOH > H2O + CO2 + RCOO - Na +

36 Titrations

37 A specific volume of the solution to be titrated is added to a flask. An indicator is added. A titrant (OF KNOWN CONCENTRATION) is added to the solution being titrated until the indicator changes colore. The volume of titrant added from the buret is measured. THE CONCENTRATION OF THE ORIGINAL SOLUTION IS THEN DETERMINED BY CALCULATION.

38 8. A 25.0 ml solution of 3.00 M hydrochloric acid requires 65.6 ml of NaOH solution to reach the endpoint. Calculate the original concentration of the NaOH. A) 1.14 M B) M C) M D) 3.00 M E) 3.43 M HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) How many moles of HCl reacted? How many moles of NaOH reacted? In what volume was the NaOH contained? What is the molarity of the NaOH solution? 3.00 mol HCl L HCl solution X X 1.00 L HCl solution 1.00 mol NaOH 1.00 mol HCl = mol NaOH M = mol/l = mol NaOH L NaOH solution = 1.14 M NaOH

39 9. A 25.0 ml solution of 3.00 M phosphoric acid requires 65.6 ml of NaOH solution to reach the endpoint. Calculate the original concentration of the NaOH. A) 1.14 M B) M C) M D) 3.00 M E) 3.43 M H3PO4 (aq) + 3 NaOH (aq) Na3PO4 (aq) + 3 H2O (l) How many moles of H3PO4 reacted? How many moles of NaOH reacted? In what volume was the NaOH contained? What is the molarity of the NaOH solution? 3.00 mol H3PO L H3PO4 solution X 1.00 L X H3PO4 solution 3.00 mol NaOH 1.00 mol H3PO4 = mol NaOH M = mol/l = mol NaOH L NaOH solution = 3.43 M NaOH

40 Why not use M1V1 = M2V2 for titrations?? HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) 3.00 mol HCl L HCl solution X X 1.00 L HCl solution 1.00 mol NaOH 1.00 mol HCl = mol NaOH H3PO4 (aq) + 3 NaOH (aq) Na3PO4 (aq) + 3 H2O (l) 3.00 mol H3PO L H3PO4 solution X 1.00 L X H3PO4 solution 3.00 mol NaOH 1.00 mol H3PO4 = mol NaOH

41 10. What volume of a M NaOH solution is required to reach the endpoint in the titration of ml sample of M H2SO4? H2SO4 (aq) + 2 NaOH (aq) Na2SO4 (aq) + 2 H2O (l) A) ml B) ml C) ml D) ml E) ml How many moles of H2SO4 reacted? How many moles of NaOH reacted? What volume of NaOH was needed? mol H2SO L H2SO4 solution X X 1.00 L H2SO4 solution 2.00 mol NaOH 1.00 mol H2SO mol NaOH X 1.00 L NaOH solution mol NaOH = mol NaOH = L NaOH solution

42 2 NaOH (aq) + H2SO4 (aq) Na2SO4 (aq) + 2 H2O (l) L solution A L solution B M M mol compound A mol/mol ratio mol compound B

43 The Big Picture of Stoichiometry Grams of A Grams of B Molar Mass Molar Mass Liters of a Solution of A Molarity Moles of A Moles of B Molarity Liters of a Solution of B Avogadro s Number Avogadro s Number Particles of A Particles of B Coefficients