Dr Sharipah Ruzaina Syed Aris

Water is the ubiquitous chemical substance, composed of hydrogen and oxygen.

Liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam.

Electrolysis of water: 2H2O(l) → 2H2(g) + O2(g)

Hard water Soft water

Water that has high mineral contents (Ca2+ and Mg2+ ions) also bicarbonate and sulfates.

Calcium usually enters the water as either CaCO3, in the form of limestone and chalk, or calcium sulfate (CaSO4).

Hard water is generally not harmful to one's health.

Water that contain few or no calcium or magnesium metal cations.

Temporary hard water Permanent hard water

is caused by a combination of calcium ions and bicarbonate ions in the water.

It can be removed by boiling the water or by the addition of lime (calcium hydroxide).

Mineral cannot be removed upon heating.

It is usually caused by the presence of calcium and magnesium sulfates and/or chlorides in the water, which become more soluble as the temperature rises.

1. Distillation (temporary) : Method in preparing pure water/distill water. The water is boiled and the vapour produced then flowing through condenser to condense back the vapor to water.

2. Boiling (temporary)3. lime-soda ash treatment : involves the

addition of slaked lime (calcium hydroxide — Ca(OH)2) to a hard water supply to convert the hydrogen carbonate hardness to carbonate, which precipitates and can be removed by filtration:

Ca(HCO3)2 + Ca(OH)2 → 2CaC03 + 2H20

4. ion-exchange Uses sodium chloride (table salt) to recharge

beads made of ion exchange resin that exchange hardness minerals for sodium.

Artificial or natural zeolites can also be used. As the hard water passes through and around the beads, the hardness mineral ions attach themselves to it, dislodging the sodium ions.

When the bead or sodium zeolite has no sodium ions left, it is exhausted, and can no longer soften water. The resin is recharged by flushing (often back-flushing) with saltwater. The high excess of sodium ions force the hardness ions off the resin beads. The excess sodium is rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many, many time before the resin loses its ability to react to these forces.

Advantages Disadvantages

Contains a lot of Ca and good for our bones and teeth.

High mineral

Lime scale furring of kettles and pipes. The fur is the insoluble carbonate formed which can cause blockage.

Soap is wasted because more soap is required for washing.

The range of materials found in the building such as wood, stone, metal, plaster and brick will face serious problem like deterioration when exposed to water.

Effect of humidityEffervescence of building

material

Most building materials surface has a attraction force to water vapour to stick onto their surface.

Causing wall to wet and mold to grow.

Effervescence is the escape/liberation of gas from a liquid solution.

Exp: the reaction between CaCO3 and HCl which produced CO2 (given off as bubbles).

Cement in sandstones will also effervesce.