Determination of p and m Value with Potentiometric Method

Determination of p and m Value with Potentiometric Method

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0239.100 combined pH glass electrode; input 2

Reagents
c(HCl) = 0.1 mol/L; D1

Sample
100 mL tap water

Remarks
· Values for the acid capacity of water.
p value = value of Phenolphthalein
m value = value of Methyl orange

· Calculations:

p value=EP1*C01;2;mmol/l
m value=EP2*C01;2;mmol/l

p value = p value in mmol/L (if 0.00 mmol/L, the water has an initial pH below 8.2)
m value = m value in mmol/L
C01= titer of titrating agent (1.0)

p value= 0.00 mmol/l
m value=5.653 x1.0 = 5.65 mmol/l

EP1 = 0.00 mL
EP2 = 5.653 mL

· The dosing unit is external D1. This method can therefore be used
directly in the TIP „Hardness“ (Application 2-4), an automated water
analysis method.
· Calibrate the electrode for the SET titration.
· For automatic curve output add in , >report “curve“.

Literature
· DIN 38 409, Teil 7 (19)

. Metrohm's teachware on CD-ROM

Method documentation

'pa
751 GPD Titrino 15215 751.0010
SET pH… p+m val.
parameters
>SET…1
EP at pH… 8.20
dynamics …2
max.rate ….10 ml/min
min.rate …5 ml/min
stop crit: …drift
stop drift …20 ml/min
>SET2
EP at pH …4.30
dynamics …3
max.rate …10 ml/min
min.rate …5 ml/min
stop crit:… drift
stop drift… 20 ml/min
>titration parameters
titr.direction:… auto
pause …1 0 s
start V: …OFF
pause …2 0 s
extr.time… 0 s
dos.element:… external D1
meas.input: …2
temperature …25.0 °C
time interval …2 s
>stop conditions
stop V: ….abs.
stop V ….99.99 ml
filling rate max. ml/min
>statistics
status: …OFF
>preselections
conditioning:… OFF
req.ident: …OFF
req.smpl size:… OFF
activate pulse: ….OFF
------------
'fm
751 GPD Titrino 15215 751.0010
SET pH ….p+m val.
>calculations

p value=EP1*C01;2;mmol/l
m value=EP2*C01;2;mmol/l

C01= 1.0
------------
'fr
751 GPD Titrino 15215 751.0010
pHc(init) …7.05 SET pH …p+m val.
smpl size …100 ml iTapWater
EP1 0.000 ml 7.05
EP2 5.653 ml 4.28
p value 0.00 mmol/l
m value 5.65 mmol/l
============
'cu
751 GPD Titrino 15215 751.0010
SET pH p+m val.
20.0 s/div dV=1.0 ml/div
============