The method includes analytical methods for total hardness and chloride content for soft water and de-ionized water analysis. Analytical tests in this method can be substituted by commercially available water test kits for the respective tests, selected for the appropriate specification levels and sensitivity. An analytical test method for free chlorine is D0005559
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Example water test kits - Hardness
Merck 114652, Chloride - Merck 111106, Free Chlorine - Merck 114670
Section A - Total hardness of water
section B - Determination of chloride
in water
Section C – Determination of Free
Chlorine
Section D - Conductivity of water
Total Hardness of Soft water
Total hardness - The hardness of water
is caused by the presence of alkaline earth, primarily calcium and magnesium.
Recently the statutory unit has been introduced for water hardness - "the
sum of the alkaline earth" - is expressed in mol/m3. The following
conversion table provides a summary of the international units used to assess
water hardness.
ANALYTICAL METHOD OF TOTAL HARDNESS
Principle
EDTA forms a chelated soluble complex
when added to a solution of certain metal cations. If a small amount of a dye
such as Eriochrome Black T is added to an aqueous solution containing calcium
and magnesium ions at a pH of about 10, the solution will become wine red. If
EDTA is then added as a titrant, the calcium and magnesium will be complexed.
After sufficient EDTA has been added to the complex all magnesium and calcium,
the solution will turn from wine red to blue. This is the endpoint of the
titration.
Reagents for total hardness
EDTA, sol 0.01 M - Weigh 3.7225 g of
Disodium EDTA dihydrate in 1000 ml of distilled water.
BUFFER SOLUTION pH 10 - Dissolve 54 g
of Ammonium Chloride in 350 ml of concentrated Ammonium Hydroxide. Dilute to
1000 ml with distilled water.
INDICATOR - Mix together 0.2 g of
Eriochrome Black T and 200 g of NaCl to prepare a dry powder mixture.
Total hardness test procedure
Read all safety data sheets and take
appropriate precautions as necessary. The aliquot of a sample taken for the
titration should require less than 15 ml of EDTA titrant. The duration of titration
should not exceed 5 minutes measured from the time of the buffer addition. Depending
on the water hardness, dilute a known volume of the sample (20-30 ml) to about
50 ml with distilled water in a 150 ml beaker. Add 1-2 ml of buffer solution
and an appropriate amount of powder indicator. Titrate with EDTA, under stirring,
until the last reddish tinge disappears from the solution.. The color of the
solution at the endpoint is blue under normal conditions.
Expression of
results/Calculation of hardness
Hardness as mg/l CaCO3 =V1 x A x 1000/
V2
Where
V1 = ml titration for sample
A = mg CaCO3 equivalent to 1.00 ml
EDTA titrant (1ml = 1mg CaCO3)
V2 = ml of the sample
Determination of Chloride content in water.
Principle
Read all safety data sheets and take
appropriate precautions as necessary.
This method determines the amount of
chloride by direct titration with silver nitrate and uses the secondary precipitate
of AgCrO4 as the indicator. It requires a neutral or nearly neutral solution.
Reagents
Calcium Carbonate (100%)
Dilute Acetic Acidc Acid to 100 ml
with distilled water
Potassium Chromate (5% aqueous) -- 5 grams potassium chromate to 100 ml with distilled water 0.02M Silver Nitrate solution
The procedure of chlorine content
Transfer 100 ml of the sample to a
conical flask.
Measure the pH of the sample using a
suitably calibrated pH meter. Record the value.
If the pH lies outside the range of 6.5
to 9.0, adjust with calcium carbonate or dilute acetic acid, measuring the
amounts added.
Add 1 ml of 5% w/v potassium chromate
solution and titrate with 0.02M silver nitrate solution to a reddish-brown
color.
Carry out a blank determination using
100 ml of distilled water, adding the same quantities of acetic acid or calcium
carbonate used in the sample.
Expression of results/ Calculation of Chlorine
Chloride, ppm as NaCl = (T - B) x
11.69
Where:
T = Volume of 0.02M silver nitrate
required by the sample
B = Volume of 0.02M silver nitrate
required by the blank
Free Chlorine test in water
Use an appropriate water test kit.
Alternatively use analytical test method for free chlorine is D0005559
What is conductivity of the water?
Principle
When all the ions have
been removed water has an extremely low conductance and ions such as Carbonate
ions, chloride ions, calcium, and sodium ions increase the conductance
depending on their concentration. Measuring the conductance gives a good
indication of the ion concentration as the higher the reading the more impure
is the water. Resistivity is the .reciprocal of conductivity.
Conductivity - micro
siemens Resistivity - mega ohms Approx. total dissolved solids -
Conductivity testing Procedure of water
Use a conductivity meter
with an appropriate range and sensitivity checking the calibration of the
instrument first. Ensure that the cell is thoroughly washed with boiled and cooled
de-ionized water before testing each sample.
Expression of results
Express results as micro siemens (conductivity) or mega Ohms (resistivity) as appropriate.
