b. Water Physical Properties

8/7/2019 b. Water Physical Properties

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ENVIRONMENTAL

TECHNOLOGY(CE20110)

PROPERTIES OFWATER


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Lesson Objectives Physical Properties:

State of water.

Density. Heat Capacity.

Conductivity.

Colour.

Solubility


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Introduction. Water is unique:

Earth is the only planet known to contain this

compound and present in all states.

About 71% of the earth is covered with water

and only 29% is landmass.

Life on earth is dependent on it.


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Introduction. Water is important:

For human consumption.

As a means of transport.

As an energy provider, e.g. hydroelectric

dams.


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1a. States of water 3 physical states of water:

Solid ice.

Liquid water.

Gaseous water (water vapor).

Unusualas it can exist as all 3 states in the

environment.


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1a. States of water


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1a. States of water

Solid Ice Liquid water

Gaseous water

Melting

Crystallising

Condensing

Boiling/

Evaporation


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1b. Density

Density is the mass (weight) per unit

volume.

Usually expressed in units ofg/cm3.

Relationship between mass and volume.

Mass (weight)

Density =

Volume


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1b. Density

Ex: A solid has a mass of 45 kg and

volume of3 m3. What is its density?

Density = m/v

= 45 kg/ 3 m3

= 15 kg/m3


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1b. Density

Density of liquid water = 1.0 g/cm3.

Density of solid ice = 0.92 g/cm3.

Results:

Ice floats on water.Freezing of pond or lake surfaces to

preserve life in winter.


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1b. Density Water expands when freezes.

Examples:

Keeping liquid water in a bottle and in the

freezer.

Bursting of pipes in cold weather.


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1c. Specific Heat Capacity Amount of heat needed to raise 1 gof

substance by 1C.

Units is J (joules)/ g- C.

For water it is 0.42 J/ g- C.


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1c. Specific Heat Capacity Ex: To heat 50 kg of water from 30 C to 70

DegC, the heat needed is:

Energy = mc

= 50kg x (70 30)C x 0.42J/g-C

= 840000 J


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1c. Heat Capacity Heat capacity is useful as:

It can be used to calculate the amount of

heat needed to heat up a given mass

To calculate the capacity of a heat

exchanger.


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1d. Colour of water Pure water (100%) is colourless.

(Not WHITE!)

Colour in water is due to:

Dissolved organic matter.

Silt (mud, sand).

Inorganic chemicals.


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1d. Colour of water Filtering can only remove suspended

matter (weeds, domestic waste etc.)

Other dissolved materials can only be

removed chemically.

Eg: RO, distillation,

Ion exchange


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1e. Solids in water

2 types of solids:

Suspended solids.

Dissolved solids.


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1e. Solids in water

Suspended solids:

Solids that can be removed by a standardfilter or settling.

Particle sizes varies a wide range.

Large particles form suspensions (e.g. sand inwater).

Fine particles form colloids (e.g. mud in

water).


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1e. Solids in water

Dissolved solids:

Examples: sugar, salt, etc. in water.

Notretained by standard filters.

Can only be removed by chemical means or by

evaporation.


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1e. Solids in water

Residue:

The solids (both dissolved and suspended)

that remains after the water is removed.

Total Solids (TS).

Unit is in mg/L orppm.


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1e. Solids in water

Turbidity:

Amount ofsuspendedsolids in a water

sample.

Measured using a nephelometer, by

measuring the amount of light scattered.


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1f. Temperature of water

Important as it affects other properties of

water.

Examples:

Reaction rates.

Solubility of gases.

Solubility of solids such as salt, sugar.


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1g. Electrical Conductivity It is the ability of water to conduct

electricity.

Pure water is a poor electrical conductor.

Conductivity improves when salts are

added.


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1g. Electrical Conductivity Electrical conductivity is expressed in micro-

siemens (mS).

Drinking water measures about 50 -1500 mS.

Industrial water measures more than10 000 mS.


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1g. Electrical Conductivity

Can be measured using a conductivity

meter(Lab Experiment).

Different concentrations of salts will give

different conductivity values.

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b. Water Physical Properties