GENERAL DEFINITION
An acid is a substance which provides hydrogen (H+ ) ions in aqueous solution.
Example: HCl , HNO3 , H2SO4 etc.
DIFFERENT CONCEPTS OF ACID
ARRHENIUS CONCEPT OF ACID
According to Arrhenius, an acid is a substance, which provides H+ ions in aqueous solution.
Example:
HCl + H2O ⇋ H3O+ + Cl-
H2SO4 + H2O ⇋ H3O+ + HSO4-
LOWRY AND BRONSTED CONCEPT
According to Lowry & Bronsted concept, an acid is a compound or species which donates or tends to donate a proton .
CH3COOH + H2O⇋ H3O+ + CH3COO-
In this example acetic acid donates a proton to water.
LEWIS CONCEPT OF ACID
According to Lewis concept, "an acid is a compound or species that accepts a pair of electrons."
FeCl3, FeBr3, AlCl3 etc. (Lewis acid)
Br- + FeBr3 ➟ FeBr4-
BASE
GENERAL DEFINITION
A base is a substance which provides OH- ions in aqueous solution.
Example: NaOH, KOH, NH4OH etc.
DIFFERENT CONCEPTS OF BASE
ARRHENIUS CONCEPT OF BASE
According to Arrhenius a base is a substance which provides OH- ions in aqueous solution
NaOH ⇋ Na+ + OH-
KOH ⇋K+ + OH-
LOWRY AND BRONSTED CONCEPT OF BASE
According to Lowry& Bronsted concept a base is a substance or species, which accepts, tends to accept proton in aqueous solution.
LEWIS CONCEPT OF BASE
According to this concept "A base is compound or species that donate an pair of electron."
NH3, OH-, F- etc.
PHYSICAL PROPERTIES OF ACIDS
- It has a sour taste.
- It turns blue litmus to red.
- It turns methyl orange to red.
- Acids are electrolyte.
- Strong acids destroy fabric.
- Strong acids cause burn on skin.
CHEMICAL PROPERTIES OF ACIDS
NEUTRALIZATION
An acid when reacts with a base, salt & water are produced. This reaction is called neutralization
HCl + NaOH ➜ NaCl + H2O
HNO3 + NaOH ➜NaNO3 + H2O
HCl + KOH ➜ KCl + H2O
REACTION WITH CARBONATES
Acid and carbonates are combined to produce salt, water and carbon dioxide
MgCO3 + 2HCl ➜ MgCl2 + CO2 + H2O
CaCO3 + 2HCl ➜ CaCl2 + CO2 + H2O
Na2CO3 + H2SO4 ➜ Na2SO4 + CO2 + H2O
CaCO3 + H2SO4 ➜ CaSO4 + CO2 + H2O
REACTION WITH BICARBONATES
Acid and bicarbonates are combined to produce salt, water and carbon dioxide
NaHCO3 + HCl ➜ NaCl + CO2 + H2O
REACTION WITH METAL
With Zinc:
Zn + 2HCl ➜ ZnCl2 + H2
With Aluminum:
2Al + 6HCl ➜ 2AlCl3 + 3H2
Reaction with iron oxide:
6HCl + Fe2O3 ➜ 2FeCl3 + 3H2O
PHYSICAL PROPERTIES OF BASE
- They have a bitter taste.
- They have slippery touch.
- They conduct electrically.
- It turns red litmus to blue.
- It turns colorless phenolphthalein to pink
CHEMICAL PROPERTIES OF BASE
REACTION WITH ACIDS:
BASE + ACID ➜ SALT + WATER
KOH + HCl ➜ KCl + H2O
NaOH + HCl ➜ NaCl + H2O
REACTION WITH SALTS
FeCl3 + 3NaOH ➜ Fe(OH)3 + 3NaCl
2CrCl3 + 6NaOH ➜ 2Cr(OH)3 + 6NaCl
MgCl2 + 2NaOH ➜ Mg(OH)2 + 2NaCl
REACTION WITH METALS
2Al + 2NaOH + 2H2O ➜ 2NaAlO2 + 3H2
Zn + NaOH + H2O ➜ Na2ZnO2 + 2H2
Si + 2NaOH + H2O ➜ Na2SiO3 + 2H2
ELECTROPHILE
Any species, which accepts a pair of electrons, called electrophile
EXAMPLE: AlCl3, FeCl3, FeBr3
NUCLEOPHILE
Any species, which donates a pair of electron, is called Nucleophile
EXAMPLE: NH3, OH-
BASICITY
Basicity of acid is defined as the no of ionizable hydrogen (H+) ions present in one molecule of an acid is called basicity.
For example:
HCl (aq) ⇋ H+ + Cl- : Basicity = 1
H2SO4(aq) ⇋ 2H+ + HSO4- : Basicity = 2
ACID BASICITY
ACIDITY
- HCl, HNO3 1
- CH3COOH 1
- H2SO4 2
- Oxalic acid 2
Acidity of base is defined as the no of ionizable hydrogen ions (OH-) present in one molecule of a base is called acidity.
NaOH(aq)⇋ Na+ + OH- : Acidity = 1
Ca(OH)2(aq) ⇋Ca+2 + 2OH- : Acidity = 2
BASE ACIDITY
- NaOH 1
- Ca(OH)2 2
- KOH 1
PH SCALE
Meaning of pH:
The symbol pH stands for "power of hydrogen ion" .pH scale is used to describe the acidic or basic nature of a solution.
DEFINITION
pH is defined as "the negative logarithm to the base 10 of the molar concentration of hydrogen ions (H+).
Formula :
pH = -log [H+]
POH
Meaning of pOH:
The symbol POH stands for "power of hydroxyl ion"
DEFINITION
pOH is defined as "the negative logarithm to the base 10 of molar concentration of hydroxyl ions (OH-).
Formula :
pOH = -log [OH-]
IMPORTANT POINTS:
1. Values of pH scale ranges from zero to fourteen.
pH scale: 0(strong acidic)_ _ _ _ _ _ _7(neutral)_ _ _ _ _ _ _14 (strong alkaline)
2. If pH of a solution is less than ‘7’ then it is acidic.
3. If pH of a solution is greater than ‘7’ then it is alkaline.
4. If pH is ‘7’ then the solution is neutral.
5. The sum of pH & POH of a solution is equal to 14.
PH + POH = 14
PH OF DIFFERENT SUBSTANCES:
Apple : 2.9-3.3
pure water : 7
butter : 6.1-6.4
milk : 6.3-6.6
wheat flour : 5.5-6.5
cola : 3
dates : 6.2-6.4
tomato juice : 4.
STRONG ACID
An acid which ionize in aqueous solution to large extent is called "strong acid".
Example: HCl, H2SO4, HNO3
WEAK ACID
SALT - TITRATION An acid which ionizes in aqueous solution to smaller extent, is called "weak acid".
Example: CH3COOH, oxalic acid (COOH-COOH), formic acid (HCOOH).
HYDROLYSIS
Reaction of a substance with water in which pH of water is changed is called "Hydrolysis". In hydrolysis bond between H and O in water are broken down. Hydrolysis is reverse reaction of neutralization.
NH4Cl + H2O ➜ NH4OH + HCl
TYPES OF SALT
There are three types of salts
(1) Acidic salt.
(2) Basic salt.
(3) Neutral salt.
ACIDIC SALT
Salt formed by the reaction between strong acid and weak base is called "Acidic salt"
. Example: NH4Cl, CuSO4
weak base + strong acid ➜ acidic salt + water
NH4OH + HCl ➜ NH4Cl + H2O
BASIC SALT
Salt formed by the reaction between strong base and weak acid is called " basic salt".
. Example: CH3COONa, Na2S
strong base + weak acid ➜ basic salt + water
2NaOH + H2CO3 ➜ Na2CO3 + 2H2O
NEUTRAL SALT
Salt formed by the reaction between strong acid and strong base is called "neutral salt".
Example: NaCl, KNO3
strong base +strong acid ➜ neutral salt + water
NaOH + HCl ➜ NaCl + H2O
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