EXPT NO. 1
COLOUR, TURBIDITY, AND CONDUCTIVITY
DETERMINATION OF COLOUR, TURBIDITY, AND CONDUCTIVITY OF WATER
AIM
To analyse the physical characteristics viz. colour, turbidity, and conductivity of a given water sample and to
determine its suitability for drinking purposes.
1. DETERMINATION OF COLOUR
Objective
To determine the Colour of the given water sample using Platinum Cobalt (Visual Comparison) Method.
Introduction
Pure water should not pose any colour. Colour in water may result from the presence of natural metallic ions
(iron and manganese), humus and peat materials, plankton, weeds, and industrial wastes. Impurities in water
may exist either in the colloidal from or in suspended state. Colour caused by dissolved and colloidal substances
is referred as "true colour" and that caused by suspended matter, in addition to dissolved and colloidal matters,
is called "apparent colour" as it can be easily removed by filtration. Ground water may show colour due to the
presence of iron compounds. The colour value of water is extremely pH-dependent and invariably increases as
the pH of the water is raised. For this reason, recording pH along with colour is advised.
BIS requires drinking water to meet the "highest desirable" World Health Organisation (WHO) standards of less
than 5 colour units.
Environmental Significance
Though presence of colour in water is not always harmful to human but in most cases it is. Even if the water is
not harmful, aesthetically people do not prefer to use water with colour. Moreover, disinfection by chlorination
of water containing natural organics (which produces colour) results in the formation of tri-halomethanes
including chloroform and a range of other chlorinated organics leading to problems which is a major concern in
water treatment. So, it is important to limit the colour of water for domestic supplies.
Principle
Colour is measured by visual comparison of the sample with platinum – cobalt standards. One unit of colour is
that produced by 1 mg of platinum per litre in the form of chloroplatinate ion.
A small amount of cobalt may be added to aid in colour matching. The Hazen scale (platinum-cobalt units) is
usually satisfactory for most waters, but the hues and shades of some waters may not easily be compared with
standards. If the hue of the water does not compare with that of the standard, very little can be done except to
visually compare the absorbances of the sample and standard. Highly coloured waters should not be diluted
more than necessary because the colour of the diluted sample often is not proportional to the dilution.
Materials Required
Apparatus required
1. Nessler tube (50ml)
2. Reference standard solutions
Chemicals required
1. Standard chloroplatinate solution - Dissolve 1.246 g potassium chloroplatinate (K2PtCl6) (equivalent to
500 mg metallic platinum) and 1.00 g crystalline cobaltous chloride (CoCl2.6H2O) (equivalent to 250 mg
metallic cobalt) in distilled water containing 100 ml of concentrated hydrochloric acid. Dilute to 1000ml
with distilled water. This standard solution is equivalent to 500 colour units.
Procedure
Preparation of Standards
1. Prepare standards having colours units of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60 and 70 by diluting 0.5, 1.0,
1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0 and 7.0 mL standard chloroplatinate solution with distilled water to
50 ml.
2. Use distilled water as 0 unit standard.
3. Protect these standards against evaporation and contamination by use of clean inert stoppers. The
standards should also be protected against absorption of ammonia, which causes increase in
colour.
Apparent colour
1. Observe the colour of the sample by filling a matched Nessler cylinder to the 50 ml mark with water and
compare with standards.
DEPARTMENT OF CIVIL ENGINEERING, SNIT ADOOR
EXPT NO. 1
COLOUR, TURBIDITY, AND CONDUCTIVITY
2.
Compare by looking vertically downward through the cylinders towards a white surface placed at such an
angle that light is reflected upwards through the column of liquid.
3. If turbidity has not been removed, report the colour as ‘apparent colour’.
4. If the colour exceeds 70 units, dilute the sample with distilled water until the colour is in the range of the
standards.
True colour
1. Remove turbidity by centrifuging or filtering sample until the supernatant liquid is clear.
2. Compare the centrifuged or filtered sample with distilled water to ensure that turbidity has been removed.
3. If the sample is clear, then compare with the standards as given for apparent colour.
Observations
SAMPLE NO.
Volume of
Estimated
Colour Units
pH
sample
colour
1.
2.
Calculations
Calculate the colour units as follows:
Colour units =
50𝐴
𝑉
where
A = estimated colour of diluted sample, and
V = volume in ml of sample taken for dilution.
Report the results in whole numbers as follows:
Colour units
Record to nearest
1 to 50
1
51 to 100
5
101 to 250
10
251 to 500
20
Results
1) The colour of the given sample 1 = _______
2) The colour of the given sample 2 = _______
Inference
True colour is caused by dissolved compounds in water. It can be natural or anthropocentric. Dissolved and
suspended solids (together) cause apparent colour. For example, brown coloured water could be the result of
dissolved by-products of plant biodegradation (true colour) or suspended clay particles (apparent colour) or
both (also apparent colour). Colour is measured in Platinum-Cobalt units (Pt-Co). A Platinum-Cobalt solution
mimics natural water colour.
2. DETERMINATION OF TURBIDITY
Objective
To determine the turbidity of given water sample.
Introduction
Insoluble particles of soil, inorganic and organic materials and other micro-organisms impede (obstruct) passage
of light by scattering and absorbing the light rays. The interference to passage of light is turbidity. It is usually
caused by the finely dissolved and sometimes suspended particles of clay loam sand and microscopic organisms
all in suspension.Turbidity is measured photometrically by determining the quantity of light of given intensity
absorbed/ scattered.
Jackson turbidity meter and Nephlo turbidity meter in generally used to measure turbidity of water samples.
Jacksons turbidity meter in generally is based on light absorption and nephlo turbidity meter is based on intensity
of light scattered by the sample, taking a reference with standard turbidity meter suspensions.
Nephlometric turbidity meter is generally used for samples with low turbidity and expressed as NTU or mg/ltr.
For portable water allowable turbidity is between 5 to 10 mg/L.
Environmental Significance
Turbidity is objectionable because of aesthetic and engineering considerations. Disinfection of turbid water is
difficult because of adsorptive characteristics of some colloids and their tendency to solid organisms from the
disinfectant. In natural water bodies, turbidity interferes with light penetrations and pathogenic reactions of
DEPARTMENT OF CIVIL ENGINEERING, SNIT ADOOR
EXPT NO. 1
COLOUR, TURBIDITY, AND CONDUCTIVITY
aquatic plants. Turbidity measurements are useful to determine whether a supply requires special treatment by
chemical coagulation before public water supply. It is also used to determine the effectiveness of treatment
produced with different chemicals and dosage needful. Measurement of turbidity in settled water prior to
filtration is useful in controlling the chemical dosage so as to excessive loading of rapid sand filters. It is also
useful to determine the optimum dosage of coagulants and to evaluate the performance of water treatment
plants.
Principle
The method presented below is based on a comparison of the intensity of light scattered by the sample in specific
conditions with the intensity of light scattered by standard reference suspension under the same condition. The
higher the intensity of scattered lights, higher the turbidity. Formazine polymer, which has gained acceptance
as the turbidity standard reference suspension is used as a reference turbidity standard suspension for water. It
is easy to prepare and is more reproducible in its lights scattering properties than the clay or turbid natural water
standards previously used. The turbidity of a given concentration of formazine has an approximate turbidity of
100 NTU, when measured on candle turbidity meter. Nephelometric turbidity units based on formazine
preparation will have approximate units derived from Jackson candle turbidimeter but will not be identical to
them.
Materials Required
Apparatus Required
1. Nephlo turbidity meter
Sample Tubes
Chemicals Required
1. Hexamethylenetetramine
2. Hydrazine Sulphate
3. Distilled water
Procedure
Reagents Preparation
1. Dissolve 1.0gm Hydrazine sulphate and dilute to 100ml
2. Dissolve 10gm Hexamethylenetetramine and dilute in l00ml
3. 5ml of each of the above solution (1 and 2) in a l00ml volumetric flask and allow to stand for 24 hrs at
25±3°C and dilute to 1000ml. This solution has a turbidity of 40NTU.
Testing sample
1. The Nephelometer turbidimeter in switched on and waited for few minutes till it warms up.
2. The instrument is set up with a 4ONTU standard suspension
3. The sample is thoroughly shaked and kept it for sometimes so the air bubbles are eliminated
4. The sample is taken in Nephelometer sample tube and the sample is put in Sample chamber and the
reading is noted directly.
5. The sample is diluted with turbidity free water and again the turbidity is read.
Observations
Sample.
Temperature
Turbidity
No.
Results
The Turbidity of given sample 1 =
The Turbidity of given sample 2 =
The Turbidity of given sample 3 =
Inference
Turbidity is a measure of light transmission and indicates the presence of suspended material such as clay, silt,
finely divided organic material, plankton and other inorganic material. If turbidity is high, be aware of possible
bacterial contamination. Normally the groundwater may get contaminated by intrusion of domestic or industrial
wastewater causing turbidity of the sample. Turbidity in excess of 5NTU is usually objectionable for aesthetic
reasons. In case of freshwater lakes and ponds, due to contamination and algal growth the turbidity of these
water increases to very high levels. The clarity of seawater is very low because of huge amount of suspended
particles, thereby increasing the turbidity.
DEPARTMENT OF CIVIL ENGINEERING, SNIT ADOOR
EXPT NO. 1
COLOUR, TURBIDITY, AND CONDUCTIVITY
3. DETERMINATION OF CONDUCTIVITY
Objective
To determine the Conductivity of given water sample.
Introduction
Electrical conductivity (EC) is a measure of how conductive the water is to electrical current. Greater the ion
concentration, greater is the EC. Generally, higher the EC, higher is the total dissolved solids. Electrical
Conductivity is an indirect measure for finding the total dissolved solids in a water body. To convert the electrical
conductivity of a water sample (micro Siemens per cm, μS/cm) to the concentration of total dissolved solids
(ppm), the conductivity must be multiplied by a factor between 0.46 and 0.9 (depending on the unique mixture
of the dissolved materials). A widely accepted conversion factor is 0.67. TDS (ppm) = Conductivity {(μS/cm) x
0.67}. The instrument used for measuring conductivity is conductivity meter.
Environmental Significance
Electrical conductivity measurements are often employed to monitor desalination plants. It is useful to assess
the source of pollution. In coastal regions, conductivity data can be used to decide the extent of intrusion of sea
water into ground water. Conductivity data is useful in determining the suitability of water and wastewater for
disposal on land. Irrigation waters up to 2 millisiemens / cm conductance have been found to be suitable for
irrigation depending on soils and climatic characteristics. It is also used indirectly to fine out inorganic dissolved
solids.
Principle
Conductivity is measured with a probe and a meter. A voltage is applied between the two electrodes in the
probe immersed in the sample water. The drop in voltage caused by the resistance of the water is used to
calculate the conductivity per centimeter. Conductivity (G), the inverse of resistivity (R) is determined from the
voltage and current values according to Ohm’s law. i.e. R=V/I then, G=1/R=I/V. The meter converts the probe
measurement to micro mhos per centimeter and displays the result for the user.
Materials Required
Apparatus Required
1. Conductivity meter
Chemicals Required
1.
KCl
2.
Distilled water
Procedure
Preparation of reagents
Potassium Chloride Solution (0.1N):
1.
Measure 50 mL of distilled water and transfer it to the beaker.
2.
Weigh 0.7456g of Potassium chloride.
3.
Transfer the 0.7456g of potassium chloride to the beaker contains distilled water and mix it by the glass
rod until it dissolves thoroughly.
4.
Transfer the contents to the 100 mL standard flask.
5.
Make up the volume to 100 mL, by adding distilled water and shake the contents well. This solution is
used to calibrate the conductivity meter.
Testing the sample
1.
Connect the conductivity cell, temperature probe to the socket in the meter.
2.
Connect the meter to the power supply and switch on the supply.
3.
Allow the meter for few seconds.
4.
Dip the conductivity cell and temperature probe in standard KCl solution.
5.
Calibrate the instrument after placing the standard KCl solution.
6.
Remove the conductivity cell and temperature probe from the solution and rinse it with distilled water.
Wipe the conductivity cell and temperature probe with tissue paper.
7.
Dip the conductivity cell and temperature probe in water sample and note down the reading in the
display.
DEPARTMENT OF CIVIL ENGINEERING, SNIT ADOOR
EXPT NO. 1
COLOUR, TURBIDITY, AND CONDUCTIVITY
Observations
Sample no.
Temperature of
the sample (0C)
Conductity
(μmho)
1.
2.
3.
Results
The Conductivity of given sample 1 =
The Conductivity of given sample 2 =
The Conductivity of given sample 3 =
Inference
The conductivity value gives us a rapid and inexpensive way of determining the ionic strength of a solution. This
is an easy measurement to make and relates closely to the total dissolved solids content of water. The total
dissolved solids are about seventy percent of the conductivity. In the ground water, the ionisable salts are lesser
and thereby the conductivity is also lesser in nature. Water having a greater number of ionisable salts for
example sea water, is having high conductivity. The fresh water bodies only have a minimum amount of salts
and have moderate conductivity.
Solution
Conductivity
(μS/cm)
Totally pure water
0.055
Typical DI water
0.1
Distilled water
0.5
RO water
50-100
Domestic "tap" water
500-800
Potable water (max)
1055
Sea water
56,000
Brackish water
100,000
DEPARTMENT OF CIVIL ENGINEERING, SNIT ADOOR