Determination of Boric Acid with Potentiometric Method

Determination of Boric Acid with Potentiometric Method

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
5.00 mL c(H3BO3) = 0.1 mol/L
10 mL d-mannitol solution, saturated
40 mL dist. Water

Remarks

· Determination reaction:
Boric acid forms an ester with mannitol:
HO-CH HC-O O-CH -
H3BO3 + 2 → B H+ + 3 H2O
HO-CH HC-O O-CH

H3BO3+2H4C2O2 →( H4C4BO4 ) - H ++ 3 H2O

· Calculations:

Bor=EP1*C01*C02*C37/C00;1;mg/l

Bor = content of Bor in mg/L
C01 = bor equivalent (1.081 mg/mL titrating agent)
C02 = factor for the conversion mL Þ L (1000)
C37 = titer of titrating agent (1.0013)
· d-mannitol solution, saturated:
App. 200 g d-mannitol dissolved in dist. water.

. Answer

Bor = 4.719 x 1.081 x 1000 x 1.0013 / 5.0 = 1021.6 mg/L

EP1 = 4.719 mL
C00 = 5.0 mL

Literature
· Metrohm Application Bulletin No. 66: Potentiometric
determination of boric acid.

Method documentation
'pa
751 GPD Titrino 15215 751.0010
DET pH… Bor.Acid
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 …10 ml
stop pH …OFF
stop EP …9
filling rate max…. ml/min
>statistics
status: …OFF
>evaluation
EPC …5
EP recognition:… greatest
fix EP1 at pH… OFF
pK/HNP: …OFF
>preselections
req.ident: …OFF
req.smpl size:… OFF
activate pulse: …OFF
------------
'fm
751 GPD Titrino 15215 751.0010
DET pH …Bor.Acid
>calculations
Bor=EP1*C01*C02*C37/C00;1;mg/l
C00= 5.0
C01= 1.081
C02= 1000
C37= 1.0013
------------
'fr
751 GPD Titrino 15215 751.0010
pH(init)… 3.90 DET pH …Bor.Acid
smpl size …5.0 ml
EP1 …4.719 ml …8.66 mV
Bor….. 1021.6 mg/l
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET pH Bor.Acid
2.0 ml/div dpH=2.0/div
============