HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

D1

Nov. 14,2018

Quantitative determination ofchloride ions in tap water

Environment
1. Abstract

Quantitative determination for chloride ions in tap water is stipulated in Standard Methods for theExamination of Water, and Standard Methods of Analysis for Hygienic Chemists, etc. A small amount ofchloride ion is contained in natural water, it is said to increase due to contamination of domestic drainage,
industrial drainage, and farming drainage, etc. Standard Methods for the Examination of Water adopts ion
exchange chromatograph method and Mohr method (titration method) as the chloride quantitative
determination method. The detection limit for ion exchange chromatograph method is 0.2 mg/L. Mohr method
is generally applied for samples including chloride ions in mg/L or more. This report introduces the Mohrmethod with precipitation titration, which quantifies chlorides by potentiometric titration with silver indicator
electrode instead of the color indicator titration described in Standard Methods for the Examination of Water.
100 mL of the sample water is collected and acidified with nitric acid for potentiometric titration withsilver nitrate titrant.

Cl-+AgNO3→AgCl↓+NO3-

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Hiranuma Automatic Titrator

COM Series

Electrode: Silver combination electrode

AGR-811Z (Double Junction Type)*The following electrodes are also usable.
・AGR-801Z (Silver reference combination electrode)・Combination of AG-311 (Silver indicator electrode) andMS-231Z (Silver reference electrode)・Combination of AG-311 and RE-241Z (Double junction type silver reference electrode)*RemarkThe general reference electrode (RE-201Z) cannot be used for this titration because KCl
inner solution might come out to sample solution and it causes measurement error.
The inner electrodes of AGR-801Z and MS-231Z contain mercury (I) sulfate. When theseelectrodes are disposed, please ask the specialized industrial waste disposal operator.

(2) Reagents
Titrant: 0.01 mol/L Silver nitrate standard solution

Additive solution: Diluted nitric acid (1:5, v/v)

3. Measurement procedure(1) Dispense 100 mL of sample into a 200 mL beaker with volumetric pipette.
(2) Add 1 ml of diluted nitric acid.
(3) Immerse electrode and start titration with 0.01 mol/L silver nitrate standard solution.

4. Measurement conditions and results
Example of titration condition
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto

12mV
500070
0.3
20sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
Factor
KL

1100
00.01
1.010
35.450Unit
FormulaDigits
Auto In Pram.

PPM(D-B)*K*F*M*1000/S3NonmL
mL
mol/L

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt SpeedPulse

805053240sec
mVsec
mV

Measurement results
Number ofSize

Titrant

Chloride ion

Measurement(mL)

Volume (mL)

(ppm)

1

100

4.739

16.968

2100

4.741

16.975

3100

4.737

16.961

Statistic
calculation

Avg.

16.97 ppm

SD0.0070 ppm

RSD

0.04 %

Example of titration curve

5. Note(1) Measurement
The chlorides in tap water was accurately determined by Mohr method with potentiometric titration
instead of color indicator titration.
(2) pH of sample
When the sample contains hydroxide ion or carbonate ion, they react with silver nitrate titrant andgenerate silver hydroxide or silver carbonate. It slightly causes positive error on titration for chloride ion.
Therefore this titration is generally performed at acidic pH adjusted to pH 2 ~ 3 by nitric acid.
Keywords: Tap water, Chloride ion, Precipitation titration, Silver electrode, Nitric acid*Some measurement would not be possible depending on optional configuration of system.