biomedical science health and society, malmö university sergey shleev chemistry “acids, bases,...

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

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

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-

HCl NH4OH

White

smoke

HCl + NH3 = NH4Cl

?

HCl + NH4OH = NH4Cl + H2O

??Al(OH)3 or H3AlO3

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

electrical conductivity of melts?

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

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

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]

HA H+ + A-

HA+H2O H3O+ + A-

Arrhenius

Brønsted-Lowry

BH+ + OH- B + H2O

acid + base conjugate base + conjugate acid

Strong acid

Week acid

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

Mathematics

“Logarithms, exponents,and quadratic equations”

exponents

xay

xey

.........718.2e

y a xobserved variable constant controlled variable

Euler's number

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

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

pKa «acid dissociation constant»

pKb «base dissociation constant»

][]][[

HAHA

Ka

alogKpKa

][]][[

BOHBH

Kb

KbpKb log

Kw “self-ionization constant of water”

2H2O H3O+ + OH-

143 10]][[ OHOHKw

LmolOHH /10][][ 7

hydronium hydroxide

ba KKKw

pH «power of hydrogen» HapH log

HHCfa

HCpH log

pOH

OHOHCfa

OHapOH log

OHCpOH log

quadratic equations

x

Henderson–Hasselbalch equation

][

][log

HA

ApKpH a

][

][log

B

BHpKpOH b

)()(

pHdnd

BC

))(

][][

(3.2)(

)(2

HKKC

HHK

pHdnd

a

aAw

Buffer capacity

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

Asp ? 1.99 9.90

Lys ? 2.16 9.06

pI pK1 pK2pKs

3.90

10.54(9.6)

(2.8)

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