Experiment No. 2
PHYSICAL PROPERTIES
Objectives:
To determine the temperature,
colour, turbidity, and pH of given sample water in the lab.
Apparatus Required:
·
Thermometer calibrated into .250ml beaker
·
Colour comparator or colorimeter
·
Hach turbidity meter of Nephelometer
·
Griffin pH meter
Chemical Required:
Introduction:
a) Temperature:
The temperature of water is measured by means of ordinary thermometers.
From the temperature the density, viscosity, vapour pressure and surface
tension as well as chemical, biochemical and biological activity are
determined. The temperature of surface water is generally at atmospheric
temperature while that of ground water may be more or less than atmospheric temperature.
The most desirable temperature for public supply is between 4.4°C to 10°C.
Temperatures above 26°C are
undesirable and above 35°C are
unfit for public supply.
b) Colour:
The colour of water is determined y comparing with standard colour solution or colour discs. The colour produced by one milligram of platinum in a litre of water has been fixed as the unit of colour. It is expressed as Hazen. It is due to organic matter in colloidal condition as well as mineral and dissolved organic impurities. The colour of water is not harmful but it is objectionable.
c) Turbidity:
Turbidity is a measure of the resistance of water to the passage of light through it. The turbidity is expressed in parts per million (ppm or mg/l). The turbidity produced by one milligram of silica in one litre of water is the unit of turbidity. Its unit is NTU (Nephelometer Turbidity Unit). It is due to presence of suspended and colloidal matter in the water. There are so many methods to determine the turbidity of water. Among which HACH Turbidity meter is one, which is used in the lab. The character and amount of turbidity depends on the type of soil over which water has moved.
d) pH-value:
The negative logarithm of Hydrogen ion concentration is known as pH-value. It indicates the concentration of Hydrogen ions in the water and it is measure of acidity or alkanity of substance. The pH-value is 7 for pure water. This value will increase if concentration of hydrogen ions decreases. If pH-value is more than 7, then the water is in alkaline range whereas if that is less than 7, then the water is in acidic range.
Mathematically, pH = -log [H⁺]
In lab, the pH-value of sample water is measured by Griffin pH meter.
Procedure:
a)
Temperature:
1. The sample
water of 200ml was poured into the beaker.
2. The
thermometer was dipped into the water.
3. It was to
be allowed enough time for the fluid in the thermometer to reach a steady
reading.
4. The
thermometer reading was observed and noted in degree centigrade.
b) Colour:
1. The
instrument was taken and its lid was opened at the top of instrument.
2. The colour
measurement disc (Hazen disc) was inserted and an empty glass tube was placed
in the left hand slot.
3. The other
tube was filled with the water sample and placed in the right hand slot.
4. The lid
was closed and the switch was on in the instrument.
5. The disc
was turned by looking through the eyepiece on the top of the instrument until
the colour on the disc matches the colour of the water.
6. The colour
value was read from the aperature and noted.
c)
Turbidity:
1. It was to
be allowed the instrument for stabilization for 10min after turning on it.
2. 100 NTU
standard cell was put into sample holder and the scale reading was adjusted
using standardizing knob.
3. The sample
cell was put by removing standard cell and cover with light shield.
4. The scale
reading was read and noted.
5. It was
cleaned the cells after use.
d)
pH-value:
1. The electrode
was connected to the meter and immersed in a buffer solution of know pH.
2. The meter
was turned on and adjusted to the zero.
3. The meter
was turned off and removed from the buffer solution and rinsed with deionised
water well.
4. It was
then immersed in the solution of unknown pH.
5. It was
turned on and the meter reading was noted.
Observation:
|
S.N. |
Characteristic |
Observed value |
|
1 |
Temperature |
16°C |
|
2 |
Colour |
40°H |
|
3 |
Turbidity |
40 NTU |
|
4 |
pH-value |
6.99 |
Conclusion:
In the lab, the temperature, colour, turbidity and pH-value of water sample are determined. According to WHO (World Health Organization), the highest desirable levels of colour, turbidity, and pH-value for drinking water standards are 5°H, 5 and 7-8 respectively. On the basis of these standards water sample used in lab is not suitable for drinking purpose. However, the colour, temperature and pH-value lie within maximum permissible value. The turbidity value doesn’t lie within permissible level. The maximum permissible level for colour, turbidity and pH are 50°H, 25 and min 6.5 respectively. The temperature above 26°C is undesirable and above 35°C is unsuitable for water supply.