ACIDS & BASES

ACIDS: 1.Have a sour taste

2. Contain H that can be exchanged for active metals with H2 release: 2HCl(aq)+Mg(s)H2+MgCl2(aq)

3. React with bases forming salt water(neutralization):HCl(aq)+KOH(aq)KCl(aq)+H2O

or with metal oxides: 2HCl(aq)+MgO(s) H2O+MgCl2(aq)

4. Change the color of some dyes: “acid-base indicators”

5. Acids are electrolytes: their solutions conduct electricalcurrent.

ARRHENIUS definition:

Acids are electrolytes that release H+ ions in the solution:

HCl(aq) H+(aq) + Cl-(aq)

All reactions are due to H+ can be presented as net ionic equations with these ions:

Neutralization: H+(aq)+OH-(aq)H2O

or: H+(aq)+MgO  H2O+Mg2+(aq)

reactions with metals:

Mg+2H+(aq) H2 +Mg2+(aq)

EQUILIBRIUM

Some rxn’s are irreversible, i.e. they can only go one direction A B, while some other are reversible, i.e. they can go both directions:

A B

If at the beginning only A is present, the forward rxn prevails.

As B is accumulated,the reverse rxn starts.

At some point the rate of forward rxn will be equal to the rate of the reverse rxn:

R = R

This is the state of

EQUILIBRIUM

We’ll apply this concept to electrolyte solutions:

Ionic compounds, when dissolve, completely dissociate into hydrated ions:

NaCl(s) Na+(aq) + Cl-(aq)

Ca(OH)2(s) Ca2+(aq) + 2OH-(aq)

CuSO4(s) Cu2+(aq) + SO42-(aq)

All ionic compounds are ELECTROLYTES

Because they completely dissociate into ions, they are
STRONG ELECTROLYTES

Many molecular compounds do not formions in solutions:

glucose C6H12O6, ethanol C2H5OH, acetone H3C-CO-CH3

They are non-electrolytes

Some molecular compounds, although they do not contain ions as pure substance, can form ions interacting with water.

Most important of those are ACIDS, which are IONIZED by water releasing H+

HCl(g) + H2O  H3O++ Cl-(aq)

acid ionization

in a simplified form (omitting H2O):

HCl(g)  H++ Cl-(aq)

There are acids that are completely ionized in water – they are

STRONG ACIDS

HCl, HBr, HI (but not HF !), HNO3, H2SO4, HClO4

H2SO4 H++ HSO4-

Other acids are ionized partially: their ionization is a reversible rxn.

There is an equilibrium between their ionsdissolved molecules:

H2CO3 H++ HCO3-

HClO  H++ ClO-

HCN H++ CN- H2SO3 H++ HSO3-



Acids with 1 displaceable H are monoprotic: HCl, HNO3

Acids with 2 displaceable H are diprotic

H2SO4 + Zn  ZnSO4 + H2

Acids with 3 displaceable H are triprotic

2H3PO4 + 3Ca  Ca3(PO4)2 + 3H2

Strong diprotic acids are completely ionized releasing 1 H+:

H2SO4 H+ +HSO4- ,

but further ionization is always reversible, with equilibrium shifted to the left:

HSO4-H+ +SO42-

Strong acids displace weak acids from their salts:

NaCN +HCl  NaCl + HCN

Strong Weak

or: CN- + H+ HCN

Arrhenius acids are

MOLECULAR ELECTROLYTES

i.e. they are ionized when interact with a solvent (solvated in general, hydrated in an aqueous solution).

The minimal solvated hydrogen ion is HYDRONIUM ION:
HCl(g)+H2O H3O+(aq)+Cl(aq) Naked proton does not exist in a solution

Arrhenius

BASE

Arrhenius BASES are electrolytes producing hydroxyde ion, OH-,

in a solution: KOH(s)K+(aq)+OH-(aq)

NH3(g)+H2O[NH4OH] NH4+ +OH-

Strong bases or alkali are solublemetal hydroxides(K2O + H2O2KOH)

KOH OH- + K+

Weak bases:

NH3(g) + H2O OH-+NH4+

Bases (when soluble) have bitter taste, feel slippery, color indicators differently from acids

Neutralization with acids:

KOH + HCl H2O + KCl

or with non-metal oxides:

KOH + CO2  KHCO3

Most of metal hydroxides are insoluble or low soluble, except:

Alkaline metal hydroxides, NH4+, alkaline earth metal hydroxides: Mg(OH)2, Ca(OH)2, Ba(OH)2

are soluble Be(OH)2 is insoluble

Bases are not only those electrolytes that release OH-, but any species that accepts H+:

NH3 + HCl NH4Cl or: NH3 + H+ NH4+

Bronsted-Lowry BASE: any acceptor of H+.

Bronsted-Lowry ACID: any donor of H+.

B-L bases have a highly electronegative element with a lone electron pair :NH3

LEWIS ACIDS & BASES


Acid –Base interaction is considered as electron pair transfer from one element, with lone el. pair(s) to another one, with an electron deficit or positive charge:

H H

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H – Cl: + :N – H  :Cl:- + H – N – H

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H H

BF3 + :NH3  F3B – NH3

Cu2+ + :NH3  Cu(NH3)2+

Light Dark

blue blue

COMMON ACIDS:

Strong acidsBinary acids

Aqueous solutions of hydrogen halides:

HCl(aq), HBr(aq), HI(aq).

Hydrochloric acid

HF(aq) is a weak acid!

Reason: H-bonds: H-F…H-F…HF…

Ternary compounds:

Oxygenic Acids

Nitric acid: HNO3  H++ NO3-

Chloric acid: HClO3 H++ClO3-

Perchloric acid:HClO4H+ +ClO4-

Sulfuric acid:

diprotic acid

H2SO4H++HSO4-2H++SO42-

Two-step ionization:

strong in first step, much weaker in second step.

Phosphoric acid:

triprotic acid

H3PO4H++H2PO4-2H++HPO42-3H++PO43-

Oxyacids may be considered as a combination of an non-metal oxide water:

SO3+ H2OH2SO4

P2O5+ 3H2O 2H3PO4

N2O5+ H2O 2HNO3
Weak acids:

Binary: HF  H+ + F-

Ternary: HCN  H+ + CN-

Weak Oxygenic Acids:

Acetic acid:

CH3COOH  CH3COO- + H+

Chlorous: HClO2H++ ClO2-

Nitrous:

HNO2H++ NO2-

SO2(g)+H2O H2SO3H+ + HSO3-

Sulfurous 

2H+ + SO32-

CO2(g)+H2OH2CO3H++HCO3-

Carbonic 

2H++CO32-

H2CO3 H2SO3are unstable acids: easily decompose to water (gaseous) acid anhydride: H2SO3 SO2(g)+H2O

H2CO3 CO2(g)+H2O

The only soluble but weak base in this course is ammonium hydroxide: NH3+ H3O NH4OH NH4++OH-