Potentiometric Determination of Ca++ with Amalgamated Ag Electrode

Potentiometric Determination of Ca²⁺ with Amalgamated Ag Electrode

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0430.100 Ag Titrode amalgamated; input 1

Reagents
c(Na₂EDTA) = 0.1 mol/L; D0

Sample
2 mL c(CaCl₂) = 0.1 mol/L
10 mL buffer pH = 10
40 mL dist. Water

Remarks

· Calculations:

c(Ca++)=EP1*C01/C00;3;mol/l

Ca++ = concentration of Ca²⁺ in mol/L
C01 = concentration of titrating agent (0.1 mol/L)

. Answer

c(Ca++) = 2.043 x 0.1/2 = 0.102mol/L

EP1=2.043 mL
C00=2.000 mL

· Coating of Ag Titrode:
Clean Ag Titrode first by immersing it in conc. HNO₃, then immerse it shortly in Hg.

· Buffer pH = 10:
Dissolve 54 g NH₄Cl and 350 mL w(NH₃) = 0.25 (25%) in dist water and fill up of 1 liter.
· If several metal ions which form EDTA complexes are present, their sum is determined.
· For a greater break, add Hg-EDTA complex.

Literature
Metrohm’s Teachware on CD-ROM

Method documentation
'pa
751 GPD Titrino 15215 751.0010
MET U …Ca++
parameters
>titration parameters
V step …0.10 ml
dos.rate max…. ml/min
signal drift …OFF mV/min
equilibr.time …10 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 …3 ml
stop U …OFF mV
stop EP …9
filling rate max…. ml/min
>statistics
status: …OFF
>evaluation
EPC …30 mV
EP recognition:… all
fix EP1 at U …OFF mV
pK/HNP: …OFF
>preselections
req.ident: …OFF
req.smpl size:… OFF
activate pulse: …OFF
------------
'fm
751 GPD Titrino 15215 751.0010
MET U …Ca++
>calculations

c(Ca++)=EP1*C01/C00;3;mol/l

C00= 2.0
C01= 0.1
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -82 mV MET U... Ca++
smpl size …2.0 ml
EP1 …2.043 ml… -60 mV
c(Ca++) …0.102 mol/l
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml MET U Ca++
1.0 ml/div dU=10.0 mV/div
============