Intersection 10: Acids and Bases

11/7/06

Reading: 16.1 (p765-770) 16.3-16.7 (p773-794)

Exam 1, Problem 12 Regrade

Please turn in your exams by noon on Tuesday, 11/14

Outline

• Equilibrium wrap up– From last week– Two everyday examples– Practice questions

• Acids and Bases– History– Models– pH Scale– Dissociation– Identifying acids and bases

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Equilibrium

What are the characteristics of an equilibrium reaction? Use each of the following words in a sentence that describes an equilibrium reaction:

Where does the “equal” in equilibrium come from?

products and reactants

dynamic

completion

concentrations

rates

Keq

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Can Equilibrium be Changed?

Fe(NO3)3 + KSCN ↔ Fe(SCN)+2 + KNO3 H < 0 red

Use LeChâtelier's Principle to predict what you will see:

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CaCO3(s) ↔ CaO(s) + CO2(g)     ΔH > 0

Using each method, explain what will happen to the concentration of CO2 if solid lime (CaO) is added to the system?

Q trumps LeChâtelier

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Equilibrium is Everywhere

• Iodine thermometer

Pictures from: jchemed.chem.wisc.edu/.../ 2003/Aug/abs878_1.html

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Equilibrium is Everywhere

Salting the roads

Is ice in equilibrium?

Picture from: www.glrc.org/story. php3?story_id=1377

http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml

What happens when salt is added to snowy winter roads?

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Question 1

Apatite, Ca5(PO4)3OH is the mineral in teeth.

Ca5(PO4)3OH(s)  5 Ca+2(aq)  + 3PO4-4(aq)  +  OH-(aq)

On a chemical basis explain why drinking milk strengthens young children's teeth.

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Problem 1

Given the following equilibrium

H2 + I2 2 HI Keq = 25

If you have 1 mol H2, 2 mol I2 and 3 mol HI in a 1 L flask, will you make more H2 or HI?

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CrO4-2(aq) + 2H+(aq) ↔ Cr2O7

-2(aq) + H2O(l)

Explain what will happen to the equilibrium if water is added to this system?

Question 2

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From: www.funsci.com/fun3_en/ acids/acids.htm

Acids and Bases

What makes something acidic/basic?

What do you know about acids and bases?

Who can name the most?

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2000 Top 20 Chemicals Produced in US*

*It does not include minerals which do not require processing, such as salt and sulfur, and petrochemical feedstocks, such as ethane and butane, which are considered products of oil companies.

http://scifun.chem.wisc.edu/chemweek/Sulf&top/Sulf&Top.html

Chemical 109 kg 109 kg

1. Sulfuric acid 39.62 11. Nitric acid 7.99

2. Ethylene 25.15 12. Ammonium nitrate 7.49

3. Lime 20.12 13. urea 6.96

4. Phosphoric acid

16.16 14. Ethyl benzene 5.91

5. Ammonia 15.03 15. Styrene 5.41

6. Propylene 14.45 16. Hydrochloric acid

4.34

7. Chlorine 12.01 17. Ethylene oxide 3.87

8. Sodium hydroxide

10.99 18. Cueme 3.74

9. Sodium carbonate

10.21 19. Ammonium sulfate

2.60

10. Ethylene chloride

9.92 20. 1,3-butatdiene 2.01

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History of Acids and Alkalies

www.catskillarchive.com/ dwellers/g.htmnefertiti.iwebland.com/ timelines/topics/drink.htm

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…a Brief History

The only acid know to the ancient Egyptians, Greeks, and Romans was______? It was made by air oxidation of fermented fruit juice (wine)

Among the alkalies known to the ancients were potash (potassium carbonate) obtained from____, soda (sodium carbonate) made by evaporation of alkaline waters, and lime (calcium oxide) made by roasting________. Caustic potash and caustic soda (potassium and sodium hydroxides) were made by the action of lime on soda and potash.

Kauffman, G. B. "The Bronsted-Lowry Acid-Base Concept" J. Chem Ed. 1988, 65, 2831.

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Later, during the middle ages, the alchemists learned to make aqua frotis (nitric acid), aqua regia (a nitric-hydrochloric acid mixture), and oil of vitriol (sulfuric acid).

…a Brief History

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…Glauber

Mid-1600's Johann Rudolph Glauber

2 NaCl + H2SO4 2 HCl + Glauber’s salt (Na2SO4)

Acid + base = salt + water KOH + HNO3 KNO3 + H2O

“Liquor fixus (KOH or K2CO3 solution) and spiritus acidus nitri (HNO3) are in their nature…totally unlike, foes and adversaries of each other…and when the two are brought together…and the one part has overcome and killed the other, neither a fiery liquor nor a spiritus acidus can be found in their dead bodies, but the same has been made, as both were before and from which they were derived namely ordinary saltpeter (KNO3).”

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… All Acids and Alkali Theory

Otto Tachenius and Francois Sylvius tried to simplify the chemistry of life processes by reducing all chemical interactions within the living organism to acid-base reactions.   

 What evidence can you think of to support or

discredit the theory of Tachenius and Sylvius?

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Boyle (1663) noted that acids, in addition to their sour taste, had exceptional solvent power, the ability to color certain blue vegetable dyes red, and a precipitating action on dissolved sulfur.  

Alkalies, on the other hand, had a slippery feel and detergent properties, the ability to dissolve oils and sulfur, and the capacity to counteract acids and destroy their properties.  Boyle's tests showed that some substances were neutral and did not classify either as acids or alkalies."

… Boyle

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… Lemery

Nicholas Lemery (1675) described acids as having sharp spiky atoms, which produced a pricking sensation on the skin, and alkalies as being made up of round particles, which made them feel slippery or soapy.  

 When acids and bases were mixed, he pictured the

sharp needles of the acids as penetrating the porous alkali globules, thus producing salts, which were neither stinging nor slippery to the touch.  

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Acids: Oxygen or Hydrogen?

Antoine Lavoisier named the gaseous element oxygen in 1777.  When sulfur or phosphorus was burned in oxygen, the products dissolved in water to form acids, so he concluded that oxygen was the element common to all acid materials.   

Claude Louis Berthollet (1789) showed that prussic acid (HCN) did not contain oxygen

Humphry Davy proved Lavoisier's error more convincingly with muriatic acid (HCl), a very strong acid.  

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Dualistic TheoryFollowing the development of the battery by Alessandro Volta

(1800), chemists began to use this new device to decompose all kinds of substances.   Jons Jacob Berzelius and William Hisinger (1803) found that when salt solutions were subjected to electrolysis, bases were found at the negative pole and acids at the positive pole.  They interpreted this to mean that acids and bases must carry opposite electrical charges.

 Berzelius concluded that acid-base reactions were simply the

result of electrical attractions. His dualistic theory (1812) explained all chemical interactions in terms of neutralization of opposite electrical charges

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Arrhenius Model

Svante August Arrhenius, during his study of electro-chemistry, observed that solutions of salts, acids, and bases were the only liquids that would conduct an electric current.  He suggested (1884) that when these compounds dissolved in water they dissociated into charged particles, which he called "ions."   

According to the Arrhenius theory acids are compounds that produce hydrogen ions in water solution:  HCl H+ + Cl- and bases are substances that provide hydroxide ions in water solution:  NaOH Na+ + OH-

(PhD describing this work received lowest possible rating from his University)

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H+ ions in water…Hydronium?

HCl(aq) H+ (aq) (proton) + Cl-

(aq)

H3O+ (aq) (hydronium)

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H2O

Hydronium

H3O+ (H2O)6 ref 1

H3O+ (H2O)20 ref 2

H9O4 + ref 3

H5O2+ ref 4

1 Zavitsas, A.A. (2001) Properties of water solutions of electrolyes and nonelectrolytes J. Phys. Chem. B 105 7805-7815.

2 Hulthe, G.; Stenhagen, G.; Wennstrom, O.; Ottosson, C.H. (1997) Water cluster studied by electrospray mass spectroscopy. J. Chromatogr. A 512 155-165.

3 Zundel, G.; Metzger, H. (1968) Energiebander der tunnelnden Ubershub-Protenon in flussigen Sauren. Eine IR-spektrokpische Untersuchung der Natur der Gruppierungen H5O2

+ Z. Phys. Chem. 58 225-245.4 Wicke, E.; Eigen, M. Ackermann, Th. (1954) Uber den Zustand des Protons (Hydroniumions) in waBriger

Losung Z. Phys. Chem. 1 340-364.

Figures: http://itl.chem.ufl.edu/2045/lectures/lec_x.htmlhttp://cwx.prenhall.com/petrucci/medialib/media_portfolio/17.html

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Acid Base Reactions

HCl (aq) + NaOH (aq)

HNO3 (aq) + KOH (aq)

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H2O (l) + NaCl (aq)

H2O (l) + KNO3 (aq)

Bronsted-Lowry Model

Edward Franklin (1905) : NH4Cl + NaNH2 NaCl + 2 NH3

Thomas Martin Lowry in England and Johannes Nicholas Bronsted in Denmark (1923) independently arrived at a more inclusive definition of the neutralization reaction as the transfer of a hydrogen ion (a proton) from an acid to a base.

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Bronsted Lowry Practice

HCl + NH3

Acid: proton donor; Base: proton acceptor; Conjugate acid; conjugate base

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HCl (aq) + NaOH (aq)

HNO3 (aq) + KOH (aq)

H2O (l) + NaCl (aq)

H2O (l) + KNO3 (aq)

NH4Cl

Acids and Bases: Comparing Definitions

Arrhenius Bronsted

Acid provider of H+ in water proton donor

Base provider of OH- in water proton acceptor

Neutralization formation of water proton transfer

Equation H+ + OH- H2O HA + B BH + A

Limitations water only proton transfer

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If baseballs were really “base”balls….

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Measurement of Acids and Bases

pH = -log[H3O+]

HCl + H2O →  H3O+ + Cl-

A 1.0 M solution of HCl would produce 1.0 M H3O+

pH = -log [H3O+]

     = -log[ 1.0M]

     = 0

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pH [H3O+] pH [H3O+]

0 1 M 8 1x10-8

1 0.1 9 1x10-9

2 0.01 10 1x10-10

3 0.001 11 1x10-11

4 1x10-4 12 1x10-12

5 1x10-5 13 1x10-13

6 1x10-6 14 1x10-14

7 1x10-7

How do you measure base [OH-]?

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Water undergoes an equilibrium process called autoionization.2 H2O(l) → H3O

+(aq)  +  OH-

(aq)

• Write out the expression for the equilibrium constant (Kw) of this reaction.

• In water, the [H3O+] and [OH-] ions are always in equilibrium

with water having an equilibrium constant (Kw) of 1x10-14

• In pure water [H3O+] = [OH-] = 1x10-7 M.  What about the pH?

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pOH

pOH = - log[OH-] Remember that a low pH corresponds to a high

concentration of H3O+ (acidic) solution. Therefore, a low

pOH corresponds to a high concentration of OH- (basic) solution.

Kw =       [H3O+]*[OH-] = 1 x10-14

        -log ([H3O+]*[OH-]) = - log (1 x10-14)

 -log [H3O+] - log[OH-] = 14

                     pH + pOH = 14

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pH [H3O+] pOH [OH-]

battery acid, concentrated HF 0 1 M 14 1x10-14

HCl secreted by stomach lining 1 0.1 13 1x10-13

lemon juice, gastric acid, vinegar 2 0.01 12 1x10-12

grapefruit, orange juice, soda 3 0.001 11 1x10-11

tomato juice, acid rain 4 1x10-4 10 1x10-10

soft drinking water, black coffee 5 1x10-5 9 1x10-9

urine, saliva 6 1x10-6 8 1x10-8

"pure water" 7 1x10-7 7 1x10-7

sea water 8 1x10-8 6 1x10-6

baking soda 9 1x10-9 5 1x10-5

Great Salt Lake, milk of magnesia 10 1x10-10 4 1x10-4

ammonia solution 11 1x10-11 3 1x10-3

soapy water 12 1x10-12 2 1x10-2

bleaches, oven cleaner 13 1x10-13 1 1x10-1

liquid drain cleaner 14 1x10-14 0 1

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Question 3: Can you explain the following?

Acid pH [H3O+]

0.1 M HCl 1.0 0.1 M

0.1 M acetic acid CH3COOH 2.9 1.26x10-3

0.1 M nitric acid HNO3 1.0 0.1 M

0.1 M nitrous acid HNO2 2.2 6.3 x10-3

0.1 M hypochlorous acid HOCl 4.2 6.3 x10-5

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Problem 2

HA(aq) +  H2O(l)  →  A- (aq)  +   H3O+

(aq)    

What is the expression for the equilibrium constant?

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Ka = ([H3O+][A-]) [HA]

Find the Ka if a 0.1 M HNO2 measures a pH = 2.2

Vocabulary

Strong (16 definitions):

Weak (10 definitions):

Favorable reaction..

ionizing freely in solution

ionizing only slightly in solution

Strong Reaction

exothermic

spontaneous

product favored

goes to completion

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Strong Acids BasesAn acid that dissociates completely (the equilibrium is shifted all of the way

to its conjugate base and hydronium ion) is said to be a strong acid.

HCl(aq) +  H2O(l) →   H3O+

(aq) + Cl-(aq)

acid                                           conj. base

An acid that does not dissociate completely (an equilibrium is established in solution between the acid, its conjugate base, and hydronium ion) is said to be a weak acid.

HClO2(aq) + H2O(l)  ↔  H3O+

(aq) + ClO2- (aq)     

acid                                          conj base

Ka = ([H3O+][ClO2

-]) / [HClO2]

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Strong BasesA base that dissociates completely (the equilibrium is shifted all of

the way to its conjugate acid and hydroxide) is said to be a strong base.

NaOH(aq) +  H2O(l) →   OH-(aq) + Na+

(aq)

base                                             conj. acid

A base that does not dissociate completely (an equilibrium is established in solution between the base, its conjugate acid, and hydroxide) is said to be a weak base.

(CH3)3N(aq)  +  H2O(l)   ↔ (CH3)3NH+(aq)  + OH-

(aq)    base                            conj. acid

Kb = ([(CH3)3NH+][OH-]) / [(CH3)3N]

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Strong Acid

Weak Acid

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There are six strongly dissociating acids:HCl HNO3

HBr HClO4

HI H2SO4 

There are also five bases that dissociate completely in solution (strong):LiOH Ca(OH)2

NaOH Ba(OH)2

KOH You should commit the strong acids and bases to memory.Appendix F in your text book lists Ka and Kb values for many weakly

dissociating acids and bases.

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Problem 3

Trimethylamine (CH3)3N has a Kb of 6.5 x10-5.  Write out its chemical reaction with water:  What is the [OH-] of a 0.010 M solution of triethylamine?  What is the pOH?  What is the pH?

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What kinds of hydrogen atoms (protons) are acidic?

H-halogen (HF, HCl, HBr, HI)

H2O

H2S (Ka1 = 8.9x10-8)

Oxoacids (H-polyatomic ions) (H2CO3, HNO3, etc.) HCN

O

C

HO

C

CC

O

OH

OH

H

H

OH

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Organic Acids

CR

O

OH

+ H2O

CR

O

O-

+ H3O+

RCOOH

CR

O-

O

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Bases

OH

R3N

H2N CH C

CH3

OH

O

H2N CH C

CH2

OH

O

CH2

C

OH

O

HN

C OH

O

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Collecting Samples

Obtain Whirl pack bags

How do you fill the bags?

How many samples should you take?

How to store samples?

Filter (acid wash all glassware)

You may need special sampling techniques!

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Blanks

• Field blank– Controls for contamination during travel

• Lab Blank– Controls for contamination during analysis

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