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Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

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Page 1: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Biomedical Science

Health and Society, Malmö University

Sergey Shleev

Chemistry

“Acids, bases, pH, pK, pI”

Page 2: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Antoine Lavoisier (1743 - 1794)

Pioneer of analytical chemistryand chemical nomenclature

”One of the first defenition of acids” 1780

Nitrogen (N2) – kväve – (Greek: “no life”)

Hydrogen (H2) – väte – gas which is “water-former“ (Greek)

Oxygen (O2) – syrgas – gas which is "acid-former“(Greek: “becoming sharp”) H2SO4HClO4

Page 3: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

SimpleComplex

Nonmetals[S, P]

Metals[K, Na, Ca]Oxides

acidic[SO2, SO3, P2O5,]

basic[K2O, Na2O, CaO]

Acids

Bases[KOH, NaOH, Ca(OH)2]

Salts[KCl,,NaSO4]

oxoacids[HPO3, H4P2O7, H3PO4

H2SO3, H2SO4]nonoxo[HCl, HF,HCN, H2S]

Hydride

Metals[KH, NaH,

CaH2]

Nonmetals[PH3, SiH4]

Inorganic substances

Page 4: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Svante August Arrhenius (1859 - 1927)

”Theory of electrolytic dissociation” – 1887

Nobel Price in Chemistry – 1903

Arrhenius theory that describes aqueous solutions in terms of acids (which dissociate to give hydrogen ions)

and bases (which dissociate to give hydroxyl ions);the product of an acid and a base is a salt and water

This theory is still involved in our modern understanding ofelectrolytes, electrical conductivity of solutions, etc

HA H+ + A- AOH A+ + OH-

Page 5: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

HCl NH4OH

White

smoke

HCl + NH3 = NH4Cl

?

HCl + NH4OH = NH4Cl + H2O

??Al(OH)3 or H3AlO3

???[Al(H2O)6]3+

electrical conductivity of melts?

Page 6: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Johannes Nicolaus Brønsted (1879–1947)

Thomas Martin Lowry (1874–1936)

1923- formulation of the protonic definition ofacids and bases, both in solution and in gas phase

BH+ + OH- B + H2O

Page 7: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Gilbert Newton Lewis (1875–1946)

1923 - the electron-pair theory of acid-base reactions

the donation of electron pairs from bases and the acceptance by acids, rather than protons or other bonded substances

The theory spans both aqueous and non-aqueous reactions

Page 8: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Inorganic substances

SimpleComplex

nonmetals[S, P]

metals[K, Na, Ca]Oxides

acidic[SO2, SO3, P2O5,]

basic[K2O, Na2O, CaO]

Basic hydroxides

[KOH, NaOH]

Salts[NaSO4]

Acidic hydroxides

[HPO3, H4P2O7, H3PO4

H2SO3, H2SO4]

Hydride

metals[KH, NaH]

Amphoteric[Al]

Amphoteric[Al2O3]

Amphoteric

hydroxides

[Al(OH)3]

Nonmetals[PH3, SiH4]

Halides

Metalic[KCl, NaF]

Nonmetalic[HCl, HF]

Chelates[K3Fe(CN)6]

Page 9: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

HA H+ + A-

HA+H2O H3O+ + A-

Arrhenius

Brønsted-Lowry

BH+ + OH- B + H2O

acid + base conjugate base + conjugate acid

Page 10: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Strong acid

Week acid

Page 11: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Dissociation of an acid can be written in several possible ways:

HA+ <=> A + H+

HA <=> A- + H+

HA- <=> A2- + H+

Note that in some cases the conjugate base (A, A-, or A2-) has a negative charge and in other cases it does not,

but in all cases it has one less positive charge than the acid.

For convenience, we will always write such reactions asHA <=>H+ + A-

The equilibrium constant (Ka) for the dissociation of a weak acid (often called the dissociation constant):

][]][[

HAHA

Ka

Page 12: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Mathematics

“Logarithms, exponents,and quadratic equations”

Page 13: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

exponents

xay

xey

.........718.2e

y a xobserved variable constant controlled variable

Euler's number

Page 14: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Arrhenius law(equation)

RT

Ea

eAk

k A Ea

R T

activation energy(T independent constant; (kJ mol-1)

frequency or pre-exponential factor

temperatue(K)

gas constant(8.3155 J K-1 mol-1)

rate constant ofchemical reaction

Page 15: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Logarithms

Natural logarithm ln(x) – the inverse function to exponential (ex)

log(x) – the inverse function to 10x

So…

xey xy ln

xy 10 xy log

Page 16: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

pKa «acid dissociation constant»

pKb «base dissociation constant»

][]][[

HAHA

Ka

alogKpKa

][]][[

BOHBH

Kb

KbpKb log

Page 17: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Kw “self-ionization constant of water”

2H2O H3O+ + OH-

143 10]][[ OHOHKw

LmolOHH /10][][ 7

hydronium hydroxide

ba KKKw

Page 18: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

pH «power of hydrogen» HapH log

HHCfa

HCpH log

pOH

OHOHCfa

OHapOH log

OHCpOH log

Page 19: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

quadratic equations

x

Page 20: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Henderson–Hasselbalch equation

][

][log

HA

ApKpH a

][

][log

B

BHpKpOH b

Page 21: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

)()(

pHdnd

BC

))(

][][

(3.2)(

)(2

HKKC

HHK

pHdnd

a

aAw

Buffer capacity

Page 22: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

pI «isoelectic point» the pH at which a particular molecule or surface carries no net electrical charge

For glycine, an amino acid with only one amine and one carboxyl group

221 pKpK

pI

6.06 2.35 9.78

Page 23: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

Asp ? 1.99 9.90

Lys ? 2.16 9.06

pI pK1 pK2pKs

3.90

10.54(9.6)

(2.8)

Page 24: Biomedical Science Health and Society, Malmö University Sergey Shleev Chemistry “Acids, bases, pH, pK, pI”

The relative concentrations of the three forms of glycineas a function of pH