Acids and Bases are two classes of chemical Acids and Bases are two classes of chemical compounds that display generally opposite compounds that display generally opposite characteristics. characteristics.

When aqueous solution of an acid and a base are When aqueous solution of an acid and a base are combines, a neutralization reaction occurs.combines, a neutralization reaction occurs.

This reaction is very rapid and generally produces This reaction is very rapid and generally produces water and a salt. water and a salt.

HCl + NaOH NaCl + HHCl + NaOH NaCl + H22OO

Acids:----a)Turns blue litmus red,b)Has sour taste,c)Conducts electricity,d)Reacted with certain metals to give off hydrogen gas,e)Reacted with carbonates to evolve carbon dioxide gas, andf)Reacted with bases to neutralize them.

Bases:----a)Turns red litmus blue,b)Has bitter taste,c)Conducts electricity,d)Has a soapy, slippery touch, ande)Reacted with acids to neutralize them.

Arrhenius Concept of Acids & Bases

a) An acid is a substance which gives hydrogen ions, H+ when dissolved in water.

b) A base is a substance which gives hydroxyl ions, OH- when dissolved in water.

c) Neutralization is the combination of H+ ions from acid and OH- ions from the base forming H2O.

Acids HCl H+ + Cl- H2SO4 H+ + SO4

2-

HNO3 H+ + NO3-

CH3COOH H+ + CH3COO-

Bases NaOH Na+ + OH-

KOH K+ + OH-

Neutralization H+ + OH- H2O

Lewis Concept of Acids & Bases

a) An acid is an electron pair acceptor.

b) A base is an electron pair donor.

c) During neutralization, base donates an

electron pair to the acid forming a

co-ordinate bond.

Lewis Acids:----- BF3, AlCl3, SnCl4, H+

Lewis Bases:----- NH3, H2O, OH-

Neutralization:-----

B

F

F

F

N:

H

H

H

+ B

F

F

F

N

H

H

H

Strong acids: An acid which is completely ionized in water and thus produces a large number of hydrogen ions is called a strong acid.

“Strong” means “Degree of ionization”

HCl aq H+ aq

+ Cl- aq

H2SO4 aq H+ aq + SO4

2- aq

HNO3 aq H+ aq

+ NO3- aq

Weak acids: An acid which is partially ionized in water and thus produces a small number of hydrogen ions is called a weak acid.

HCN aq H+ aq

+ CN- aq

H3PO4 aq H+ aq + PO4

2- aq

CH3COOH aq H+ aq + CH3COO-

aq

Strong bases: A base which is completely ionized in water and thus produces a large number of hydroxide ions is called a strong base.

NaOHaq Na+ aq + OH-aq

KOH aq K+ aq + OH-aq

Weak bases: A base which is only partially ionized in water and thus produces a small number of hydroxide ions is called a weak base.

NH4OHaq NH4+ aq + OH-

aq

Mg(OH)2 aq Mg2+ aq + OH-aq

Ca(OH)2 aq Ca2+ aq + OH-aq

Basicity of an acid is the number of replaceable or ionisable hydrogen atoms present in a molecule of the acid.

HCl, HNO3, CH3COOH ……..Basicity = 1Simply……..Monobasic acids

H2SO4, H2CO3 ………Basicity = 2Simply……..Dibasic acids

H3PO4 ………..Basicity = 3Simply……..Tribasic acids

Acidity of the base is the number of replaceable or ionisable hydroxyl groups present in a molecule of the base.

NaOH, KOH ……..Acidity = 1Simply……..Monoacidic bases

Ca(OH)2, Mg(OH)2, ………Acidity = 2Simply……..Diacidic bases

Fe(OH)3, Al(OH)3………..Acidity = 3Simply……..Triacidic bases

Consider two reactions……………….

H2SO4 + 2NaOH Na2SO4 + 2H2O

HCl + NaOH NaCl + H2O

Examine the number of H+ needed to react with one molecule of base.

Get your answer…!

Consider two more reactions…………

2HCl + Ca(OH)2 CaCl2 + 2H2O

Examine the number of OH- or +ve ion needed to react with one molecule of acid.

2HCl + Na2CO3 2NaCl+ CO2 + H2O

Get your answer…!

Equivalent weight of an acid = Molecular weight

Basicity

Equivalent weight of a base = Molecular weight

Acidity

Acid/Base

Chemical Formula

Molecular weight

Acidity orBasicity

Eq. weight

Acid HCl 36.5 1 36.5

Acid HNO3 63 1 63

Acid H2SO4 98 2 49

Acid CH3COOH 60 1 60

Acid H2C2O4.2H2O 126 2 63

Base NaOH 40 1 40

Base KOH 56.1 1 56.1

Base Ca(OH)2 74 2 37

Base Mg(OH)2 58 2 29

Base Fe(OH)3 107 3 35.66

Base Al(OH)3 78 3 26

Base Na2CO3 106 2 53

Equivalent = Equal, Corresponding, Comparable, the same.

The weight of the The weight of the acid acid which contains one which contains one part by weight of part by weight of replaceable replaceable hydrogen atom.hydrogen atom.

The weight of The weight of the basethe basewhich neutralizes which neutralizes one equivalent of one equivalent of an acid.an acid.

How Much You Have Followed ?

Electronic Concept

According to electronic Concept…….

Oxidation means Loss of electrons

M M+ + e-

Reduction means Gain of electrons

M + e- M-

During Redox reaction,

Oxidation and reduction will take place together.An oxidising agent will get reduced and reducing agent will get oxidised.

Understand…….oxidising agent……reducing agent……

Oxidation NumberOxidation Number

Oxidation number or oxidation state is Oxidation number or oxidation state is defined by the total number of electrons defined by the total number of electrons that an atom either gains or loses in order that an atom either gains or loses in order to form a chemical bond with another to form a chemical bond with another atom. atom.

Make it by heart……..!

Rules for assigning oxidation numberRules for assigning oxidation number1 The algebraic sum of the oxidation numbers of all atoms in a compound is

zero.

2 Oxidation number of an element in its elementary state is zero.

3 Oxidation number of all metals in all compounds is positive.

4 Oxidation number of all non-metals in all compounds is negative.

5 Oxidation number of hydrogen is +1, but in hydrides it is -1. (NaH, MgH2)

6 Oxidation number of oxygen is -2, but in peroxides it is -1 and in OF2 it is +2.

7 Oxidation number of first group element is is +1 and that of second group element it is +2.

8 The oxidation number of the elements in their molecules like H2, N2, Cl2, Br2, O2 etc is zero.

9 The oxidation number of a simple ion is equal to the charge on the ion.

Find the oxidation numbers of S in i) H2SO4 ii) Na2SO4 iii) H2S

O N of H = +1, O = -2…….So O N of S = X In H2SO4, 1x2 + X + -2x4 = 2+X-8 = 0X-6 = 0, ie, X = 6

O N of Na = +1, O = -2…….So O N of S = X In Na2SO4, 1x2 + X + -2x4 = 2+X-8 = 0X-6 = 0, ie, X = 6

O N of H = +1, …….So O N of S = X In H2S, 1x2 + X = 2+X = 0 ie, X = -2

Do the problems from text book….

+-battery

Na (l)

electrode half-cell

electrode half-cell

Na+

Cl-

Cl- Na+

Na+

Na+ + e- Na 2Cl- Cl2 + 2e-

Cl2 (g) escapes

Observe the reactions at the electrodesObserve the reactions at the electrodes

NaCl (l)

(-)

Cl-

(+)

Commercial form of Daniel CellCommercial form of Daniel Cell

Cu

1.0 M CuSO4

Zn

1.0 M ZnSO4

Salt bridge – KCl in agarProvides conduction between half-cells

CellConstruction

Observe the electrodes to see what is occurring.

Cu

1.0 M CuSO4

Zn

1.0 M ZnSO4

Cu deposits on electrode

Zn electrode erodes or dissolves

cathode half-cellCu+2 + 2e- Cu

anode half-cellZn Zn+2 + 2e-

-+

What about half-cell reactions?

What about the sign of the electrodes?

What happened at each electrode?

Why?

Definitions:Definitions:

CATHODE

REDUCTION occurs at this electrode

ANODE

OXIDATION occurs at this electrode

Anode

Cathode

Zinc plate is eaten away and Copper deposits on the copper plate. Electrons produced at the zinc anode flow through the outer circuit to the copper cathode.

Electric Current is assumed to flow from copper to zinc, ie, from positive terminal to negative terminal.

Zn Zn+2 + 2e-

Cu+2 + 2e- Cu

Electricity can be produced by connecting two different metals in solutions of their metal ions.

ACopper

Zinc

Copper sulphate solution Zinc sulphate solution

Ion/salt bridge

e-e-

The purpose of the “ion bridge” (“salt bridge”) is to complete the circuit.

ACopper

Zinc

Copper sulphate solution Zinc sulphate solution

Ion/salt bridge

e-e-

Parts of Daniel cellParts of Daniel cell

1.Two half cells, namely zinc half cell and copper half cell. In the former is a zinc rod dipped in a ZnSO4 solution and the latter is a copper rod dipped in a CuSO4 solution. The two metallic rods are called electrodes.

2. The two half cells are connected externally by a metallic wire to a galvanometer through a key and internally by a salt bridge.

3. The salt bridge is an inverted U-tube containing an arouse solution of an inert salt like KCl, KNO3, NH4NO3 to which some agar-agar or gelatin has been added to convert it into a semi solid, ie gel. The ends of the U-tube are plugged with glass wool.

1.Permits the passage of electric current internally,2.Maintains the electrical neutrality of the solution,3.Prevents intermixing of the solutions,4.It does not take part in cell reaction.

ZnZn(s)(s) / Zn / Zn2+2+(aq)(aq) // Cu // Cu2+2+

(aq)(aq)/Cu/Cu(s)(s)

Representation of Daniel Cell