JAGDALPUR BASTAR
YEAR-2012
SEMINAR - II
TOPIC- pH METER
JAIRAM DAS
M.Sc.ZOOLOGY
SEMESTER I (2012)
GOVT.K.P.G. COLLEGE, JAGDALPUR
1.INTRODUCTION
2. DISCOVERY
3. MEASURING AND CALIBARATION
OF PH
4. TYPES OF pH METER
(i) Cambridge pH meter
(ii) Cambridge direct reading pH meter
(iii) Backmann pH meter
5. APPURATUS
(i) Glass electrode
(ii) The calomel electrode
6. DETERMINATION OF PH
(i) colorimetric method
(ii) henderson hasselbalch equation
7. pH SCALE
8. USE & PRECAUTION
9. CONCLUSION
10. REFERENCE
1.INTRODUCTION:A pH meter is a electronic
device used for measuring the PH ( acidity or
alkalinity ) of a liquid (through specil probrs are
some solid substance) .
A Typical PH meter cousist of a special
measuring Probe (a glass electrode ) connected
to an electronic meter that measurs and
displays the PH reading .
2.DISCOVERY: Sren Peder Lauritz Srensen introduced the
pH-scale as a simple way of expressing it in
1909.
First commercial PH meter is called radio meter
and it is discovered by Arroid bachman. In 1970
Joanco electronics of Tanwan manufactured The
first problem digital PH meter.
3.MEASURING AND CALIBRATION OF pH :The PH probe mearures PH as the activity
of the hydrogen cataions surrounding a thin walled glass bulb at its tip . the
probe produces a small voltage (about 0.06volt per PH unit ) that is
measured and displayed as PH units by the meter for more information
about PH probes see glass electrode for very prices.
Work the PH meter should be calibrated before each measurement for
normal use calibration should be performed at the beginning of each day.
The reason for this the glass electrode does not give a reproducible e.m.f.
over longer periods of time calibration should be performed with at least
two standard buffer solutions that span a rang of PH buffers at PH 4 and
PH 10 are acceptable.
The PH meter has one control so set the meter reading equal to the value
of the first standerd buffer and a second control with is used to adjust the
meter reading to the value of the second buffer. A third control allows the
tem to be set standerd buffer sachet .
Which can be obtained from a variety of suppliers usally state how to
buffer value changer with three buffer solutions calibrations is preferred.
As PH 7 is essentialy a 2eao point .
4. TYPES OF pH METER :These are different types PH meter available now
these days out of those three of them or of prime importance the are :(i)Cambridge PH meter :-
Glass electrode is used in this type of elect rode (diptype of calomel
electrode ) whose PH (rang) from 0 to 14 its unite is measured in 0.02
galvano meter works as a null point detecter . inter alia is used to
detected the temperature of test solution .
Cell is also used in some instruments some times circuit
Also to be used to obtained the value of PH.
Each of the division represented as 2 milivolt and whose
Total rang tends from o to 14 milivolts.(0-1400milivolts)
(ii) Cambridge direct reading PH meter :It is a very heavy type of (Robust ) instreument. Glass
electrode is also used in this instruments whose PH ranges from 0-14 .
it is mainly study from only 0.1 PH TO 0.5 PH it is standerdised by
buffer solution. Dial also been given in front of the electrode.system
for restoring the temperature.
(iii )Backman PH meter:Dial ranges from 0-13 PH it is
indicates its measurements.it is graduated on 0.1PH(units) .
It is studied only 0.02PH which is fixed .
Switch helps to studied (meter scale) (milivolt) this is why the PH
of scale limited to 0-13 PH rather than 0-1300 milivolts.
Switch capable the polarity in opposite direction.thats why its
maximum capability ranges from -1300 to +1300 milivolts.
PH meter can be stenderdised by any kinds of buffer solution.
Generally 0.05M of (potassium,hydrogen phthalate) PH 4.00;20*
or 0.05M of( sodium borate) PH9.18 20*) is used.
0.01M of aquaeous solution of acetate buffer (acetic acid) or 0.1M
aquaeous (solution of sodium acetate at 4.64 PH on 20*
centigrade)
Also considerd to be the best buffer this buffer of 200ml. M
(sodium hydroxide) as well as 1liter of distilled water.
5.APPURATUS:(i)The glass electrode
The mesurment of PH by
glass electrodes in values the use of two reference
electrodes. Separated by a glass membrare whose
function function is to establish an electrical potivity of
the solution being tested.
The design of the glass electrodes is enormously
variably but a basic construction is shown in figure.
It consign of a high rasistance glass tube with a thin
low resistance glass buld fused at the bottom.
The bulb is responsible for the PH sensitivity: the
8rest of the electrode un unsensitivity to [H+] the tube
is field up with 0.1N solution of HCL. Deeping in this
solution is a silver \ silver chloride electrode. The
other reference electrode might
bea colomel
electrode but in most current instruments this
electrode also is an also Ag/ Agcl electrode when
both electrodes are dipped in to a simple the resulting
e.m.f. gives the PH the solution.
The glass electrode
(ii).The calomel electrode:The desing of
calomel electrode various for different
application but a general parpose calomel
electrode can be illustrated as in figure.
The electrode consist of a strip of platinum
sealed into glass and allowed to dip into
mercury.
A past of calomel ( Hg2 cl2 , 0.1) is held
against the mercury by means of a sintered
glass plug or cotton wool . The whole
electrode is filled with saturated KCL.
Contact with saturated is maintained
Through a porous ceramic plug.
The calomel electrode
6.DETERMINATION OF pH:pH can be determined either by calorimetric
methods or E.M.F. methods or handerson equation .
(a)Calorimetric method
As soon as when the medium of pH becomes
different then some organic compounds changes its colours.
If undicator is added on the the series of known PH value of buffer
solution than the colouring for pH forms the standard series.
pH us to be determined by adding unknown solution in in
an indicator.
Than colour is to compared from the stanrdard pH indicator of pH is
limited. In the way various set of standards is to be prepared in all of
them indicatior is different.
By this pH can be found out after comparing the colour.
(Electrometer method) is not suitable for this determination.
(B)Henderson hasselbalch equation:For weak electrolytyes with wich
the physiolongic chemistry is concerned this may be calculated by the law of
mass action let us consider HA a weak acid that ionize as follows.
Ka [H+]+ [A]-/[HA] { ka= [ dissocation constant]
[H+] = Ka X [HA] / [A-]
LOG[H+] = LOG Ka +log[HA/A-] ( Taking log on both side )
Log [H+]= - Log Ka Log [HA/A-] (Changing side on both side)
PH = pka + Log [A-]/[HA]
PH = Pka + log [salt ]/[Acid]
[ -log [H+] = pH and log ka =pak]
7.pH SCALE :Hydrogen consantration us actually meant for the regulation of acid base
blance in the body fluid by the calculation of fluid scientist SORESON used one
scale thet is callad as PH scale.
8.USE AND PRECAUTION:Use (I) By PH meter we can calculet PH value of organic compounds.
(ii) It is also Important of medical Therapy.
(iii) Also absorve the PH value of body fluieds.
Precaution(i)PH meter must be standredized before every measurement.
(ii)When not in use use the referenced in water so that PH sensitive membrane
does not become dehydrated.
9.CONCLUSIONA typical PH meter consist of a special measuring
probe (a glass electrode)
Connected on a electronic meter that mesures and
displays
the PH meter.
It is also important of medical therapy. By PH meter we
can calculate PH value of organic compounds.
10.REFERENCE:1.Advanced cellbiology.
By SEWARTS
2.Bio physical chaemistry.
By- Upadhaya & Nath
