What is Hard Water?

The water which gives low or no froth with soap and detergent is known as hard water. Hard water is due to the presence of bicarbonates, sulphates, chlorides, nitrates of calcium and magnesium.

Hard water is of two types

Temporary hardness: Temporary hardness of water is due to the presence of bicarbonate of calcium and magnesium in the water. It can be easily removed by simply boiling water. Calcium bicarbonate and magnesium bicarbonates are converted into carbonate forms which settle down.

                Ca(HCO3)2 ———> CaCO3 ↓ + H2O + CO2

              Mg(HCO3)2 ————> MgCO3  +   H2O   +  CO2

Permanent hardness: Permanent hardness is due to the presence of sulphate, chlorides, nitrates of calcium and magnesium. Such water can’t be removed by boiling and advanced methods are applied. First of all total hardness of water is determined by titrating with EDTA and then permanent hardness is determined by the same method. Temporary hardness is determined by subtracting the amount of permanent hardness from total hardness.

Determination of total hardness

Both temporary and permanent hardness of water is determined by complexometric titration using EDTA (ethylene diamine tetraacetate) as a complexing agent in the presence of the solochrome black T indicator.

For total hardness: For determination of total hardness of water, a sample of 50 ml cold water is titrated with EDTA by using solo chrome black T prepared in the basic buffer solution till wine red color changes into clear blue color.

S.N Vol. of water Vol. of EDTA(Burrette reading Concurrent reading
Initial Final Different
1 50 ml        
2 50 ml        
3 50 ml        

Effect of hard water

  1. Soap and detergents do not give froth properly.
  2. It corrodes water pipe, metallic pots
  3. It fads the color of clothes, mats, etc.
  4. Also, it affects and can damage the human body parts such as the kidney, liver.
Effect of Hard Water on tap
Effect of Hard Water On Water Tap Surface

Also Read: Chemical Oxygen Demand (COD) AND Dissolved Oxygen (DO)


Air pollution

Air pollution is the addition of poisonous gases like CO,  NO, NO2, SO3, SO2, O3, H2S dust, smoke and unburnt hydrocarbons like CH4,C2H5, CFC,  etc. produced by either natural phenomena or human activities in Earth’s atmoshpher. These gases are continuously released to the atmosphere day by day due to which air pollution occurs.

The air pollutants present in the atmosphere disturb the dynamic equilibrium in the atmosphere and thereby affect the earth habitats and their environment.

Sources of air pollution

There are several sources of air pollution which may be either natural process or man made activities such as

  1. Burning of coal, wood, and Oils
  2. Internal combustion of engines of car, buses, trucks,  trains, etc
  3. Chemical industries: various poisonous gases like CO,  NO, NO2, SO3, SO, etc are released
  4. Dust produced from heavy traffic and crowded population
  5. Carbon monoxide by combustion hydrocarbon, fuels, etc.
  6. volcanic Eruption, Wars, agricultural activities, scientific experiments, rocket launching, etc

Effect of air pollution

  1. Human being suffers from diseases like heart failure, lungs disease, and high blood pressure.
  2. It increases tension makes fatigue and restless.
  3. It may cause blindness, skin disease.etc
  4. A man may become senseless.

Methods of control

The prevention of the production of air pollutants is the core of the control of air pollution.

It can be control by the following methods

  1. By minimizing the production of by adding tetra ethylene lead in petrol.
  2. It can be controlled by using alternative sources of energy instead of fossil fuels.
  3. By planting green trees in rural as well as urban areas.
  4. It can be controlled by make awareness of air pollution
  5. By banning the use of low-quality gasoline.
  6. It can be controlled for the long term by lunching international and national programs for the protection of the atmosphere.

Also Read This: Chemical Oxygen Demand (COD) AND Dissolved Oxygen (DO)



Alkalinity is the water quality parameter that determines the presence of dissolved hydroxide, carbonates and bicarbonates in the water. These may either be present alone or in the mixture form. Alkalinity also causes the hardness of water and increases turbidity of water. Such water can corrode water pipes, boilers, and can damage lever, kidney etc hoever it maintains PH value of water.

Determination of alkalinity

The extent of alkalinity present in the water is determined by volumetric titration of supplied water sample with standard acid using double indicator, first with phenolphthalein indicator and then second with methyl orange indicator.

In first titration, sample of water is taken in a conical flask and 2-3 drops of phenolphthalein is added as indicator. Then, it is titrated against standard acids solution taken in burette till pink color gets discharged. It is termed as phenolphthalein end point and volume consumed in the burette is noted. At this stage, hydroxides are completely neutralized and carbonate changes into bicarbonates as,

                    OH   +   H+   ——> H2O

                     CO3-2   +    H+ —— >HCO3

In second titration, methyl orange indicator is added and titration is further continued till the color of the solution changes from yellow to pink color. It is termed as methyl orange end point and volume is noted from beginning. At this stage, bicarbonate is completely neutralized to carbonic acid as,

                   HCO3   +   H+ ——–> H2CO3

Let,    x ml= volume of acid required up to phenolphthalein end point

       Y ml= vol. of acid required from beginning to methyl orange end point.

Conditions(vol. in ml) CO3-2 HCO3 OH
If      X=0 ml Nil present nil
If      y=x  ml Nil nil present
If      X =1/2y Present nil nil
If      X>1/2y Present nil Present
If     X<1/2y Present present nil

Sample test

S.N. Vol.of water (ml)           Burette reading( HCl)
Initial reading(ml) phenolphthaleinendpoint(x) Methylorange end point (y)
1 50 0.0 5.2   5.0 19.8   20.0
2 50 0.0 5.0 20.0
3 50 0.0 5.0 20.0


Volume of HCl for phenolphthalein end point(x) =  5.0ml

Volume of HCl for methylorange end point(y) =   20.0 ml

condition   x>1/2y

since x>1/2y, therefore, water contains CO3-2 and HCO3 but not OH


Acid rain

Especially in the industrial areas, countries are suffered by the harmful acid rain. The atmosphere is polluted by different oxides of non metals like CO, CO2, NO, NO2, N2O5, SO2, SO3, P2O5, As2O3 etc produced from industries, factories. These non metallic oxides combine with water in the atmosphere to form acids and fall in the form of droplets on the earth surface which is called as acid rain.

Reactions of formation of acid rain from different non metallic oxides are

                      2NO + H2O→2HNO2 nitrous acid

                      2NO2   + H2O→HNO3   +  HNO2

                      SO2   + H2O→H2SO3 (sulphurous acid)

                       SO3  + H2O → H2SO4

                     P2O5  +  3H2O→2H3PO4 (ortho phosphoric acid)

                     CO2  + H2O → H2CO3 (carbonic acid)

 Effects of acid rain

 Acid raining is becoming more tremendous problem and challenge for coming generation. Developed industrial countries are affected badly till now but other countries will be victimized by acid rain very soon. Natural scenery, natural beauties, fertile lands, forests,grassy lands and artificial creations are going to be destroyed day by day.

Some of the adverse effects of acid rain are,

  1. It increases the acidity of soil which becomes unfit for crops production.
  2. It destroys forests, grassy lands and fertile lands.
  3. Causes stone leprosy.
  4. It destroys Buildings, marbles and wooden materials, statues and sculptures, Historical places etc.
  5. It corrodes metallic materials, pipes etc.
  6. Natural beauties like mountains, falls, rivers, coastal areas etc are destroyed.
  7. It disturbs the terrestrial, arboreal as well as aquatorial ecosystems.
  8. It causes sterility in animals, pieces, birds and retards production of vegetation.

  Control measures

  1. It can be controlled by applying alternative sources of energy instead of coal and gasoline.
  2. It can be controlled by banning of use of high fuel consuming vehicles, motor, lorry, vans.
  3. Can be controlled by removing old and low quality machine.
  4. It can be minimized by planting green trees on the road way sides and near industrial areas.
  5. It can be controlled by treating smoke of industries with suitable metals.
  6. World wide campaign of awareness must be run.

Chemical Oxygen Demand (COD) AND Dissolved Oxygen (DO)

Chemical   Oxygen Demand (COD)

The chemical oxygen demand is defined as the amount of oxygen expressed in gram per liter consumed under specified conditions in the oxidation of organic and oxidisable inorganic materials. It is quick method in comparison to BOD for the determining the total organic and oxidisable inorganic pollution in a sample of water.  Pollution like cellulose which are not measurable by BOD test since it can’t be bio-degraded by the oxygen dissolved in water; are easily measured by COD test. In COD test, acidified K2Cr2O7 is used instead of oxygen which is stronger oxidizing agent than oxygen.

The COD evaluation is carried out by adding a known excess of aq. Cr2O7-2 to the water sample and then estimating the unconsumed Cr2O7-2 by titrating it with Fe2+ solution [Mohr’s Salt Solution, FeSO 4(NH3)2SO4.6H2O].

When water sample is high polluted with organic wastes, the oxygen demand will exceed the maximum equilibrium solubility of O2 in water and such a water sample may not have any dissolved oxygen. The basic reaction involved in the COD test is

    Cr2O7-2 + 14H+ + 6e ———–> 2Cr3+ +   7H2O

    O2   +   4H+ + 4e —————-> 2H2O

From above reaction,

1 mol of Cr2O7-2 consumed = 6/4=1.5 moles of oxygen


Let amount of Cr2O7-2   initially taken = x mol

And amount of Cr2O7-2 left (unused) =y mol

Then   amount of Cr2O7-2 consumed = (x-y) mol

 x-y mol of Cr2O7-2  consumed =1.5 (x-y) mol oxygen

Dissolved Oxygen (DO)

The amount of oxygen dissolved in sample of water as uncombined form is known as dissolved oxygen. The fresh water has 5 to 7 mg per liter of dissolved oxygen. This level of DO is essential for supporting aquatic lives including micro organisms. The aerobic decay of organic waste matters by micro organisms keeps the water in fresh and clean condition.

If the DO decreases due to water pollution, then anaerobic decay may occurs which forms bad odor and indicates the polluted water.

When the water is polluted with large amounts of organic matter, a lot of dissolved oxygen would be rapidly consumed in the biological degradation. The decrease in the DO affect the aquatic life and may completely damage the ecosystem of the water.

DO is consumed by oxidation of organic substance in the presence of certain micro organisms or by reducing agent such as

  CH2O + O2 —————> CO2 + H2O

 2SO3-2 + O2  —————–> 2SO4-2


Determination of DO plays a key role in the control of the water pollution. It can be determined by iodometric titration method. In this method, dissolved oxygen is allowed to react with I solution to form I2 which is then titrated with standard Na2S2O3 solution (hypo solution).It is carried by addition of Mn+2salt in strongly alkaline medium. The basic reaction in the titration is,

Mn+2 + ½ O2 + 2OH ————> MnO2 ↓ + H2O

MnO2 + 2 I + 4H+ ———–> Mn+2 + I2   + 2H2O

I2 + 2S2O3-2 ————–> 2I–   + S4O6-2

From above,  2mol of S2O3-2= 1 mol I2 = ½ mol O2


Water Pollution ll Sources and control Measures of water pollution

The state of deviation from the pure condition of water due to the mixing of foreign substances whereby its normal functions and properties are affected is known as water pollution. Populated water is harmful to animals and plants as well as unfit for domestic, industrial and agricultural uses.

The domestic wastes from rural and urban areas, sewage and garbage from industries, hotels, chemicals, and sludge of hospitals, industries, and factories are the major factors for water pollution.

Polluted water has any one or more of the following signs

  1. It has a bad taste to drink.
  2. It has an offensive odor.
  3. Also, it has an unpleasant color.
  4. There is an unchecked growth of weeds.                     
  5. It may have oil or grease floating on the surface.

Sources of water pollution

The main sources that are responsible for water pollution are

  1. Sewage and domestic wastes: It includes excreta of animals and human, dead and decay parts of animals and plants, sewage, sludge, soap, detergents, untreated municipal sewage, etc. Most of the parts of the wastes come from the cooking room. These all pollutants mix directly or indirectly to the source of water.
  2. Industrial effluents: It contains toxic materials, chemicals and hazardous compounds like aldehyde, ketones, phenols, cyanides, oils grease, dyes, acids, alkalies corrosive metals like Pb, Hg, Sb, etc from industries, hospitals, auto-work shop, laboratories, etc.
  3. Agricultural discharges: The residues of chemical fertilizers, pesticides, insecticide, and herbicides retain on the soil surface and dissolve in water due to which uncontrolled growth of weed occurs and ponds, lakes, etc are converted into grassy lands. Mixing of the residue of pesticides, fertilizers, insecticides to drinkable water causes diseases like dysentery, cholera, typhoid, etc.
  4. Thermal pollutants: Coal-fired or nuclear fuel-fired steam power plants are the sources of thermal pollution in which only a fraction of the heat is converted into useful works and the rest is wasted. The condenser of power plants are drained to water sources like river or lakes at a high temperature which decreases the D.O. of water and it adversely affects aquatic life.
  5. Siltation: it is the process of mixing of soil and rock particles into water. It is a serious problem for the hilly region. It is mainly due to flooding and soil erosion.
  6. Radioactive materials:  Different human activities like mining and processing of ores to produce radioactive substances, uses of radioactive weapons, use of radioactive materials in power plants and uses of radioactive isotopes in medical, industries and research works are the main sources of radioactive materials.

What are the pollutants of water pollution ?

Types of water pollutants

According to nature and compositions, water pollutants are of following types

  1. Inorganic pollutants: It includes a broad range of pollutants such as acids and bases like HNO3, HCl, NaOH, Ca(OH)2, NH3, etc soluble salts like carbonates, acetates, nitrates, sulphates, bicarbonate, etc and inorganic pesticides.
  2. Organic pollutants: It includes oxygen demanding wastes, plant nutrients, sewage, synthetic organic compounds, fats, and oils.
  3. Sediments: They are the most extensive pollutants of surface water and are produced by soil erosion, flooding, agricultural and construction activity.
  4. Radioactive materials: Different human activities like mining and processing of ores to produce radioactive substances, uses of radioactive weapons, use of radioactive materials in power plants and uses of radioactive isotopes in medical, industries and research works are the main sources of radioactive materials.

Why to control water pollution?

Because of the following reasons, if you don’t aware and move forward to control it. Then one day you will be the victim of water pollution.

Water is the most interrelated substance with living things and humans. So its pollution can cause immense harm to public health. Some effects of water pollution are immediately recognized while others are only reflected after months or year later. Some effects of water pollutions are given here,

  1. Spread of infectious diseases: Water is the carrier of pathogenic micro-organisms and can cause adverse effects on public health. The water-borne diseases like typhoid, paratyphoid fever, dysentery, cholera, polio, etc. different skin diseases, poor blood circulation, etc are the main problem of polluted water.
  2.  Destroy of the aquatic ecosystem: sewage and runoff (fertilizers) from agricultural lands provide nutrients to the algae, weeds in the bottom of water sources and increase the overgrowth of the plants which cover the pond, lake and finally they turn in to grassy lands. The growth of plants in the water source causes the D.O.
  3. Destroy of aquatic life: Residue of pesticides, herbicides, toxic, oils, acid, and alkaline chemicals directly affect the aquatic life. It causes a decrease in D. O. Such pollutants to retard the breeding rates and damage the plants and animals.
  4. Damage of property of water: Pollutants destroy the natural properties of water. It causes acidity, turbidity, alkalinity and increases the temperature of the water.
  5. Contamination of marine food sources: Marine foodstuff is contaminated by polluted water which ultimately affects human health.

Control measures of Water Pollution

  1. The wastes from industries, factories, pharmaceuticals, and hospitals must be managed properly.
  2. Most of the wastes must be preceded for recycling.
  3. Sufficient and accessible dumping sites must be managed in rural and urban areas.
  4. Public awareness campaigned should be launched by central as well as local authorities.
  5. Sewage, industrial wastes should be preceded for aerobic and anaerobic treatment.

Soil Pollution and its effects

The contamination of soil with acid rain, fertilizer, insecticide and pesticide residue, metals like Pb from exhausted petrol, sulphate, nitrates, etc is known as soil pollution. Soil is the acceptor of large quantities of waste products that may be a domestic, human, animal, industrial and agricultural.

The combustion of sulphur containing fuels emits SO2 and finally leaves sulphate on the soil. Fertilizers, pesticides, insecticides, herbicides applied to the crops are largely retained by the soil. Industrial products such as plastics, rubbers, glasses, tin and similarly toxic wastes like waste oil, lubricants, acid tars, lacquers, etc are deposited on the soil. Such pollutants destroy soil quality.

Sources of soil pollution

  1. Industrial products: large percentage about 15.2% of pollutants includes from industrial productions like rubber, plastics, toxic substances, chemicals, sewage, glasses, dust, waste oil, paints, decay row materials, etc directly mix into sources of water and spread over fertile land through irrigation
  2. Agricultural: Residues of pesticides, herbicides and unconsumed fertilizers largely retained by the soil surface day by day due to their heavy use. After a certain year, fertile lands are converting into sterile and become bare land which causes land slide, flooding, soil erosion, etc.
  3. Domestic: It includes the garbage from houses and other premises such as un-degradable domestic wastes like containers, pieces of bottles, plastics, glasses, gasoline, polythene, etc. Such domestic pollutants take a large part in the pollution of soil in developing countries like Nepal. There are no safe and accessible dumping sites as well as strict rules-regulation by the government. So, domestics pollutant is not controlling and managed in our country due to which as a result soil is pollution is increasing rapidly. About 8.5% soil pollutants are from domestic and trade.
  4. Volcanic eruption: Metallic oxides, sulphate residues, and other tarry liquids. Solid tarry matters are spread over the soil surface and cover a large areas.
  5. Mining and quarrying: It contains about 67% soil pollutants like rock particles, heap of wastes from quarries and tarry liquids like seam of coal, acid tars, waste oil, etc from mining.
  6. Toxic substances: Tarry liquids, Pb containing gasoline sludge, water-kerosene mixture, acid tars, bases and cyanide wastes. Different organic solvent etc are toxic matters
  7. Construction: Various construction works such as the construction of roads, buildings, tunnels, bridges, etc are the sources of the soil pollutants. Construction work consists about 2% pollutants.

Effects of Soil Pollution

  1. It destroys the fertile land
  2. Affect the health of people through fruits ,vegetables and crops
  3. Decreases the production rate of crops, grains.
  4. It causes soil erosion and flooding.
  5. It direct effect habitats of human, forest, grassy lands and hilly regions.

Controls measure of soil pollution

  1. By replacing use of insecticides, fungicides by biological methods of control.
  2. Controlled by advising and applying manure rather the use of chemical fertilizers.
  3. By dumping domestic, industrial and chemicals.
  4. By advising to apply lead free gasoline
  5. Controlled by recycling the domestic materials.