Analysis of the Nitrating Acid with Potentiometric Method

Analysis of the Nitrating Acid with Potentiometric Method



Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0133.100 pH glass electrode; input 1
6.0726.100 Ag/AgCl double junction reference electrode
(c(LiClO4) = 1 mol/L in acetic acid)

Reagents
c(Cyclohexylamine) = 0.5 mol/L; D0

Sample
3 mL nitrating acid
25 mL methanol

Remarks
Nitrating acid:
1 mL H2SO4 ( 96 %, Den = 1.84 g/L)
1 mL HNO3 (app. 65 %)
20 mL dist. water
fill up with methanol to 100 mL
1st break: HNO3 + H2SO4 + 2 CHA → NO3 - + HSO4- + 2 HCHA+
2nd break: HSO4- + CHA → SO4-- + HCHA+
CHA = Cyclohexylamine

Calculations:

H2SO4=(EP2-EP1)*C01*C02/C00;2;g/l
HNO3=(EP1-(EP2-EP1))*C01*C03/C00;2;g/l

H2SO4 = sulphuric acid in g/L of nitrating acid
HNO3 = nitric acid in g/L of nitrating acid
C01 = concentration of titrating agent (0.5 mol/L)
C02 = molecular mass of H2SO4 (98.08 g/mol)
C03 = molecular mass of HNO3 (63.01 g/mol)

Answer

H2SO4= (3.113-1.965) x 0.5 x 98.08 / 3.0 = 18.77 g/L
HNO3= (1.965-1.148) x 0.5 x 63.01 / 3.0 = 8.58 g/L

EP1 = 1.965 mL
EP2 = 3.113 mL
C00 = 3.000 mL

Literature
Metrohm Application Bulletin No. 39: Potentiometric analysis of
nitrating acid

Method documentation
'pa
751 GPD Titrino 15215 751.0010
DET U NitrAcid
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 U… OFF mV
stop EP 9
filling rate max…. ml/min
>statistics
status: …OFF
>evaluation
EPC …5
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
DET U NitrAcid
>calculations
H2SO4=(EP2-EP1)*C01*C02/C00;2;g/l
HNO3=(EP1-(EP2-EP1))*C01*C03/C00;2;g/l
C00= 3.0
C01= 0.5
C02= 98.08
C03= 63.01
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) 463 mV DET U NitrAcid
smpl size… 3.0 ml
EP1 ….1.965 ml…. 349 mV
EP2 3….113 ml… 96 mV
H2SO4 ….18.77 g/l
HNO3 …8.58 g/l
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U NitrAcid
1.0 ml/div dU=100.0 mV/div