ph and acid based

1. CONCEPT Of pH
Definition:-
1. The pH of a solution may be defined as the negative logarithm of the reciprocal of the
hydrogen ion concentration.
pH = - log10[H+
] where, [H+
] = concentration of hydrogen ions.
Or
2. pH is a measurement of hydrogen ion concentration also a measurement of acidity or
alkalinity of a solution.
 The pH scale is a series of numbers, which express the degree of acidity or alkalinity of the
solution.
 The minimum value of pH is 0(zero) and the maximum value is 14(fourteen). The pH range
between 0 and 7 indicates acidic nature of the solution while between 7 and 14 indicates alkaline
nature of the solution. pH 7 indicates neutral solution.
 The concept of pH was introduced by Sorensen (1909), a Danish Biochemist.
 Unknown definition of p is given by many scientists. Where p is equal to power and we refer
it as power of hydrogen ions. Some scientists refer it to potenz (german word). Potenz means
power again. Jens Norby said that p is the constant and stands for negative logarithm. This
definition of p is widely accepted at international level.
 pH of solution is temperature dependent. As temperature of solution is change the pH of
solution is change.
 Importance of pH measurement is in medicine / pharma industries, food science (agro
processing industries), environmental science, oceanography etc.
 We can measure pH of solution by pH meter and pH strips. Litmus paper is also used to
check that the solution is acid or base. By using pH strips, we get rough idea about pH of
solution. pH meter gave us exact number of pH of solution.
Electrodes of pH meter:-
Glass and quinhydrone electrodes are used in conjunction with saturated calomel electrode to
measure the pH of solution.
It is necessary to standardize pH meter prior to use because of the time and temperature
dependent of asymmetric potential of the glass electrode. For the standardization of pH meter buffer
solutions are used frequently.
Buffer solutions :-
The solutions which resist change in pH on dilution or with the addition or small amounts of
acid or alkali are called Buffer solutions.
A mixture of acetic acid and sodium acetate acts as buffer solution around pH 4.75 and a
mixture of ammonium chloride(NH4Cl) and ammonium hydroxide/ammonia (NH3[aq]) acts as a
buffer around pH 9.25. Now, a days tablets are available in market which we can dissolve in some
amount of water we get a pH 4, 7, 9.25 as per our requirement.
pOH:-
pH is used for the measurement of hydrogen ions. Same way, pOH is used for the measurement
of hydroxyl ions (OH-
) or alkaliny of solutions.
pOH is not measured directly but is derived from pH.
pH + pOH = 14
_____________________________________________________________________
CALCULATE THE EXAMPLES: (for practice purpose only)
1. If the pH of basic solution is 8.23 than what is the pOH of that solution?
2. If the pH of acidic solution is 6.15 than what is the pOH of that solution?
3. If the pH of acidic solution is 2.22 than what is the pOH of that solution?
4. If the pH of acidic solution is 3.65 than what is the pOH of that solution?
5. If the pH of basic solution is 12.11 than what is the pOH of that solution?
.

2. Acid-Base Concept
Robert Boyle, some three hundred years back, was first to pronounce that a
reaction between an acid and base will result in formation of salt and water.
Based upon this, the properties of acids and bases were described for the firs
time. They are as under :
 Acids and Bases described by three leading and useful theories:
i) Arrhenius Acid-Base Principle.
ii) Lowry-Bronsted Acid-Base Principle.
iii) Lewis Acid-Base Principle.
Arrhenius Acid-Base Principle.
Arrhenius defined acids as substances that produce hydrogen ions when
dissolved in water and bases as those which produced hydroxyl ions.
Thus, H+
were considered responsible for acidic properties of HCl and OH-
ions
responsible for basic properties of NaOH.
Arrhenius definition laid down the bases for understanding the acid base
reactions.
Some limitations also found in Arrhenius acid-base principle.
a) The nature of H+
(proton) in aqueous solution can’t be explained.
b) Some compounds behave as bases even when they do not have
OH-
hydroxyl ions, for eg. NH3, NH2CO3.
c) This principle does not explain the role of water, even though
water is essential for acid base reactions.
Lowry-Bronsted Acid-Base Principle:
Lowry and Bronsted in 1923, gave a wider definition of the acids and bases than
the Arrhenius theory.
According to them acids are substances that are capable of loosing a proton and
bases are substances that are capable of accepting a proton. According to this principle
acid-base reaction is a proton transfer reaction.
Lewis Acid-Base Principle:
Lewis further extended the principle of acid-base in 1923, in which the basic
requirement of proton transfer was given up and called this process as electron
transfer process.
A base is a compound that donates a pair of electrons and acid is compound that
accepts a pair of electrons in an acid-base reaction.
Acid Properties Base
Sour TASTE Bitter
Turn blue litmus
paper into red
EFFECT ON
LITMUS
PAPER
Turn red litmus
paper into blue
When react with
base the result is
neautralisation.
REACTION When react with
acid the result is
neautralisation.
0-7 pH Scale 7-14
Acid donate the
hydrogen ions
HYDROGEN
IONS
Base accept the
hydrogen ions.