Water is the most important resource. Without water life is not possible.
From a chemical point of view, water, H2O, is a pure compound,
but in reality, you seldom drink, see, touch or use pure water. Water from
various sources contains dissolved gases, minerals, organic and inorganic
substances. This photograph of Guilin shows the beauty of natural water.
The rain curved an interesting landscape out of the lime stones in the area.
Natural waters are often important parts of wonders of the world.
The total water system surrounding the planet Earth is called the hydrosphere.
It includes freshwater systems, oceans, atmosphere vapour, and biological waters.
The Arctic, Atlantic, Indian, and Pacific oceans cover 71% of the
Earth surface, and contain 97% of all water. Less than 1% is
fresh water, and 2-3 % is ice caps and glaciers. The Antarctic
Ice Sheet is almost the size of North America continent.
These waters dominate our weather and climate, directly and indirectly
affecting our daily lives. They cover 3.35x108 km2.
The four oceans have a total volume of 1.35x109 km3.
The sunlight dims by 1/10 for every 75 m in the ocean, and humans barely see light below 500 m. The temperature of almost all of the deep ocean is 4°C (277 K).
The average ocean depth is 4 km, and the deepest point at the Mariana Trench is 10,912 m (35,802 ft), which compares to the height of 8.8 km for Mount Everest.
A Smithsonian Institution Traveling Exhibition is on view at Museum of Science Boston, Massachussetts October 10, 1998 to January 3, 1999. This web site takes you to the sight and sound of deep oceans almost just as good as the exhibits.
The distribution of water and other materials on Earth is given in Planetary Parameters. Many fact sheets are available in this link.
Among the planets, Earth is the only one in which there are solid, liquid and gaseous waters. These conditions are just right for life, for which water is a vital part. Water is the most abundant substance in the biosphere of Earth.
Groundwater is an important part of the water system. When vapor is cooled, clouds and rain develop. Some of the rain percolate through the soil and into the underlying rocks. The water in the rocks is groundwater, which moves slowly.
A body of rock, which contains appreciable quantities of water, is called an aquifier. Below the water table, the aquifier is filled (or saturated) with water. Above the water table is the unsaturated zone. Some regions have two or more water tables. These zones are usually separated by water-impermeable material such as boulder and clay.
Groundwater can be brought to the surface by drilling below the water table, and pumped out. The amount of water that can be pumped out depends on the structure of the aquifer. Little water is stored in tight granite layers, but large quantities of water are stored in limestone aquifier layers. In some areas, there are under ground rivers.
Fresh water is a commodity. As such, it is a focal point of trade between Canada and the United States.
| Ions in sea water | |
|---|---|
| Species | (mg/kg) |
| Cl- | 19,350 |
| Na+ | 10,760 |
| SO42- | 2,710 |
| Mg2+ | 1,290 |
| Ca2+ | 411 |
| K+ | 399 |
| HCO3- | 142 |
| Br- | 67 |
| Sr | 8 |
| BO43- | 4.5 |
| F- | 1.3 |
| H4SiO4 | 0.5-10 |
| H+ | 10-8.35 |
Hydrology is also the study of how solids and solute interact in, and with, water. In this link, the compositions of seawater, composition of the atmosphere, compositions of rain and snow, and compositions of river waters and lake waters are given in details.
A simplified table of the major ions present in seawater from the above link is given here. The composition does vary, depending on region, depth, latitude, and water temperature. Waters at the river mouths contain less salt. If the ions are utilized by living organism, its contents vary according to the populations of organisms.
Dust particles and ions present in the air are nucleation center of water drops. Thus, waters from rain and snow also contain such ions: Ca2+, Mg2+, Na+, K+, NH4+. These cations are balanced by anions, HCO3-, SO4-, NO2-, Cl-, and NO3-. The pH of rain is between 5.5 and 5.6.
Rain and snow waters eventually become river or lake waters. When the rain or snow waters fall, they interact with vegetation, top soil, bed rock, river bed and lake bed, dissolving whatever is soluble. Bacteria, algae, and water insects also thrive. Solubilities of inorganic salts are governed by the kinetics and equilibria of dissolution. The most common ions in lake and river waters are the same as those present in rainwater, but at higher concentrations. The pH of these waters depends on the river bed and lake bed. Natural waters contain dissolved minerals. Waters containing Ca2+ and Mg2+ ions are usually called hard water.
Minerals usually dissolve in natural water bodies such as lakes, rivers,
springs, and underground waterways (ground waters). These photographs
show crystals of typical
calcite, present abundantly in the Earth Crust.
Calcite is the
major mineral in limestones, marbles, and sea shells.
Calcium carbonate, CaCO3, is one of the most common inorganic compounds in the Earth crust. It is the ingradient for both calcite and aragonite. These two minerals have different crystal structures and appearance. This photograph shows crystals of typical Calcite.
Calcium-carbonate minerals dissolve in water, with a solubility product as shown below.
The carbon dioxide in natural water creates an interesting phenomenon.
Rainwater is saturated with CO2, and it dissolves limestones.
When CO2 is lost due to temperature changes or escaping from
water drops, the reverse reaction takes place. The solid formed, however,
may be a less stable phase called aragonite, which has the same chemical
formula as, but a different crystal structure than that of calcite.
The photograph here shows aragonite and calcite. A common progression from aragonite due to evaporative enrichment is seen this photograph, where a nodular mass of calcite popcorn is tipped by sprays of aragonite needles.
The rain dissolves calcium carbonate by the two reactions shown above. The water carries the ions with it, sips through the crack of the rocks. When it reached the ceiling of a cave, the drop dangles there for a long time before fallen. During this time, the carbon dioxide escapes and the pH of the water increases. Calcium carbonate crystals begin to appear. Calcite, aragonite, stalactite, and stalagmite are four common solids found in the formation of caves.
Natural waters contain metal ions. Water containing calcium, magnesium and their counter anions are called hard waters. Hard waters need to be treated for the following applications.
After boiling, metal ions remain due to presence of chloride ions, sulfate ions, nitrate ions, and a rather high solubility of MgCO3. Amount of metal ions that can not be removed by boiling is called permanent hardness. Total hardness is the sum of temperary hardness and permanent hardness. Hardness is often expressed as equivalence of amount of calcium ions in the solution.
Thus, water conditioning is an important topic. The value of water treatment market has been estimated to be worth $30 billion.
Lime-soda softening is the removal of temporary hardness by adding a calculated amount of hydrated lime, Ca(OH)2:
Zeolites are a group of hydrated crystalline
aluminosilicates found in certain volcanic rocks.
The tetrahedrally coordinated aluminum and silicon atoms form
AlO4 and SiO4 tetrahedral groups.
They interconnect to each other sharing oxygen atoms forming cage-type
structures as shown on the right. This diagram and the next structural
diagram are taken from
an introduction to zeolites
There are many kinds of zeolites, some newly synthesized.
Whatever kind, the crystal structure of zeolites contains large cages. The cages are connected to each other forming a framework with many cavities and channels. Both positive and negative ions can be trapped in these cavities and channels as shown below.
For each oxygen that is not shared in the AlO4 and SiO4 tetrahedral groups, a negative charge is left on the group. These negative charges are balanced by trapping alkali metal and alkaline earth metal ions. When more cations are trapped, hydroxide and chloride ions will remain in the cavities and channels of the zeolites.
To prepare a zeolite for water treatment, they are soaked in concentrated NaCl solution. The cavities trap as many sodium ions as they can accommodate. After the treatment, the zeolite is designated as Na-zeolite. Then the salt solution is drained, and the zeolite is washed with water to eliminate the extra salt. When hard water flow through them, calcium and magnesium ions will be trapped by the Na-zeolite. For every Ca2+ or Mg2+ trapped, two Na+ ions are released. The treated water contains a rather high concentration of Na+ ions, but low concentrations of Mg2+ and Ca2+. Thus, zeolite ion exchange convert hard water into soft water.
Bayer markets
LEWATIT
ion exchange resins for water treatment.
Anderson has its
own brand, but the type of resin is not specified in their web site.
DongDa
markets Strongly Acidic Styrene Type Cation Exchange Resin series,
Strongly Basic Styrene Type Anion Exchange Resin series, Macroporous
Weakly Basic Styrene Type Anion Exchange Resin series, Macroporous Weakly
Acidic Acrylic Acid Type Cation Exchange Resin series, and more than 30
types Ion Exchange Resin. All ion exchange resins are almost spherical
beads as shown in the picture (from DongDa).
In most cases, the resins are polystyrene with functional -SO3H groups attached to the polymer chain for cation exchange resin, and with functional group -N(CH3)3+ attached to the chain for anion exchange resin.
To prepare the resin for making pure or deionized water, the cation resin is regenerated with HCl so that the groups are really -SO3H. The anion resin is regenerated with NaOH, so that the functional groups are -N(CH3)3(OH). When water containing any metal ion M+ and anion A- passes through the ion exchange resins in two stages, the following reactions take place,
The following is a list of companies selling magnetic devices for magnetic water treatment. All devices are based on results of some ressearch indicating that when water runs through a magnetic field, the calcium carbonate will precipitate as aragonite rather than the usual calcite. For example, K.J. Kronenberg has published an article in IEEE Transactions on Magnetics, (Vol. Mag-21, No. 5, September 1985, pages 2059-2061). and stated the following:
In any case, their web sites are well made, and they are listed here for you to scrutinize. Listing their web sites is not a recommandation of their devices. Any independent testing result is welcome.
Example 1
Solution
Discussion
There may be other ions present in the system and other equilibria conditions
in addition to the equilibrium mentioned here. Problems are more complexed
in the real world.
Skill -
Analyze water by chemical method.
High Field Magnet Laboratory provides high magent field for material research, but not water scale remover.
MarSolve is a non-toxic, non-corrosive, non-flammable, non-injurious tar oil base solvent, heavily fortified with wetting and penetrating agent. It is used for the rapid removal of water scale, lime and rust deposits found on the water side of any equipment that is water cooled, water heated or water operated, in any manner. An Material Safety Data Sheet (MSDS) is given.
Rydlyme is a liquid water scale solvent, almost the same as MarSolve.