HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

D2

Nov. 14,2018

Total hardness in tap water

Environment

1. Abstract
Hardness in water is total amount of calcium and magnesium ion in water converted to mg/L ofcomparable calcium carbonate. “Hardness” has the following types:(1) Total hardness

Total amount of calcium and magnesium ions(2) Calcium hardness

Calcium ion(3) Magnesium hardness(Total hardness) – (Calcium hardness)(4) Non-carbonate hardness (Permanent hardness)(5) Carbonate hardness (Temporary hardness)
These are stipulated in some applicable standard such as Standard Methods for the Examination of Water,
Standard Methods of Analysis for Hygienic Chemists, and JIS K0101 Testing methods for industrial water etc.
This report introduces an example for determination of total hardness in tap water with photometrictitration method using EDTA standard solution according to the Standard Methods for the Examination ofWater.
Take 100 mL of sample and add 1 mL of 0.01 mol/L magnesium chloride, 2 mL ammonia buffer, and 0.2
mL of EBT indicator. Titrate with 0.01 mol/L EDTA standard solution (red →blue color). Perform the sameprocedure for 100 mL of DI water instead of sample as blank measurement.

CaCO3
MgCO3++Na2EDTA →Na2EDTA →Ca-EDTA + Na2CO3
Mg-EDTA + Na2CO3

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

COM Series(M type photometric unit for photometric titration with 650 nm optical filter)(2) Reagents
Titrant: 0.01 mol/L EDTA standard solution

Additive solution: 0.01 ml/L Magnesium chloride solution

Buffer solution: Ammonium chloride-ammonia buffer solution (pH 10)
Dissolve 6.75 g of ammonium chloride in 30 mL of DI water, add 57 mL ofammonia solution, and dilute to 100 mL with DI water.

Indicator: EBT Indicator
Dissolve 0.5 g of eriochrome black T and 4.5 g of hydroxylammonium chloridein 100 mL of ethanol (95 % [v/v]).

3. Measurement procedure(1) Dispense 100 mL of sample into a 200 mL beaker with volumetric pipette.
(2) Add 1 mL of 0.01 mol/L magnesium chloride solution with volumetric pipette.
(3) Add 2 mL of ammonia buffer.
(4) Add 0.2 mL of EBT indicator.
(5) Immerse photometric probe and start titration with 0.01 mol/L EDTA standard solution.
(6) Perform the same procedure for 100 mL of DI water as blank measurement.

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

1
B cross

12T%
10000500
120sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

1000.01
1.001
00UnitFormulaDigits
Auto In Pram.

mL
D4Non

mL
mL
mol/L

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

805053240

sec
mV
sec
mV

Measurement of sample
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2
B cross

12T%
10000500
120sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
Factor
KL2100
1.040
0.01
1.001
1000Unit
FormulaDigitsAuto In Pram.

PPM(D-B)*K*F*M*1000/S
4NonmL
mL
mol/L

secmV
sec
mVMeasurement results
Measurement of blank
Number ofSize

Titrant

Measurement(mL)

Volume (mL)

1

1.041

2-

1.041

3

1.038

Statistic
calculation

Avg.

1.040 mLSD

0.0017 mL

RSD

0.17 %

Measurement of sample
Number of

Size

Titrant

Measurement(mL)

Volume (mL)

Totalhardness
(ppm)

1100

6.718

56.837

2100

6.745

57.107

3100

6.719

56.847

Statistic
calculation

Avg.

56.9 ppm

SD0.153 ppm

RSD

0.27 %

Examples of titration curves

5. Note(1) Measurement
The total hardness in tap water can accurately be determined by photometric titration method with EBT
indicator using photometric probe.
(2) End point detection“Method” on the condition parameter is set to “B cross” because the point where indicator color change iscompleted is detected as endpoint. When the concentration of total hardness is relatively high and muchtitrant volume is required, “ C.P. mL” function is useful. Titrant can be added at once by setting “C.P. mL”
to a few mL smaller than titrant volume at the endpoint, it can reduce measurement time.
Keywords: Tap water, Total hardness, Photometric titration, EDTA standard solution*Some measurement would not be possible depending on optional configuration of system.