Determination of Oxalic Acid with Potentiometric Methods

Determination of Oxalic Acid with Potentiometric Methods

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0232.100 combined pH glass electrode; input 1

Reagents
c(NaOH) = 0.1 mol/L; D0

Sample
2 mL c(C₂H₂O₄) = 0.1 mol/L; HOOC-COOH pK1 = 1.42, pK2 = 4.31
50 mL dist. water

Remarks

Calculations:

Oxalic=EP2*C01*C37/C02/C00;3;mol/L

Oxalic = concentration of oxalic acid in mol/L
C01 = concentration of titrating agent (0.1 mol/L)
C02 = factor for “normality“ (2)
C37 = titer of titrating agent (1.0013 common variable of “Tit.NaOH“)
Compare also titration in non aqueous medium, application No. 1-5
For pK determinations, the electrode should be calibrated.

Answer

Oxalic = 4.098 x 0.1 x 1.0013 / 2 / 2 = 0.103 mol/L

EP1 = 2.110 mL
EP2 = 4.098 mL
C00 = 2 mL

Literature
Metrohm’s Teachware on CD-ROM

Method documentation
'pa
751 GPD Titrino 15215 751.0010
DET pH Oxalic
parameters
>titration parameters
meas.pt.density ...4
min.incr. ...10.0 ml
dos.rate max.... ml/min
signal drift... 50 mV/min
equilibr.time... 26 s
start V: ...OFF
pause ...0 s
dos.element:... internal D0
meas.input:... 1
temperature... 25.0 °C
>stop conditions
stop V:... abs.
stop V ...6 ml
stop pH ...OFF
stop EP ...9
filling rate max. ...ml/min
>statistics
status:... OFF
>evaluation
EPC ...5
EP recognition:... all
fix EP1 at pH ...OFF
pK/HNP: ...ON
>preselections
req.ident:... OFF
req.smpl size: OFF
activate pulse: OFF
------------
'fm
751 GPD Titrino 15215 751.0010
DET pH Oxalic
>calculations
Oxalic=EP2*C01*C37/C02/C00;3;mol/l
C00= 2.00
C01= 0.1
C02= 2
C37= 1.0013
------------
'fr
751 GPD Titrino 15215 751.0010
pHc(init) ...2.41... DET pH Oxalic
smpl size ...2.00 ml
EP1 ...2.110 ml ...3.63...mV
EP2... 4.098 ml ...7.77...mV
pK1... 2.71
pK2... 4.17
Oxalic... 0.103 mol/l
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V ...0.000 ml ...DET pH Oxalic
2.0 ml/div ...dpH=2.0/div
============