Ppt 1

CHEMISTRY

HARDNESS OF

WATER

HARD WATER• Hard water is water that has high mineral

content.

• Hard drinking water is generally not harmful to one's health, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water. In domestic settings, hard water is often indicated by a lack of suds formation when soap is agitated in water, and by the formation of limescale in kettles and water heaters. Wherever water hardness is a concern, water softening is commonly used

to reduce hard water's adverse effects.

SOURCE OF HARDNESS

• Water's hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are cations (positively charged metal complexes) with a charge greater than 1+. Usually, the cations have the charge of 2+. Common cations found in hard water include Ca2+ and Mg2+. These ions enter a water supply by leaching from minerals within an aquifer. Common calcium-containing minerals are calcite and gypsum. A common magnesium mineral is dolomite (which also contains calcium). Rainwater and distilled water are soft, because they contain few ions.

• The following equilibrium reaction describes the dissolving/formation of calcium carbonate scale:

• CaCO3 + CO2 + H2O ⇋ Ca2+ + 2HCO3−

• Calcium carbonate scale formed in water-heating systems is called limescale.

• Calcium and magnesium ions can sometimes be removed by water softeners.

TEMPORARY AND PERMANENT

• Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). When dissolved these minerals yield calcium and magnesium cations (Ca2+, Mg2+) and carbonate and bicarbonate anions (CO32-, HCO3-). The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulfate and chloride compounds, this "temporary" hardness can be reduced either by boiling the water, or by the addition of lime (calcium hydroxide) through the softening process of lime softening.

• Permanent hardness is hardness (mineral content) that cannot be removed by boiling. When this is the case, it is usually caused by the presence of calcium sulfate and/or magnesium sulfates in the water, which do not precipitate out as the temperature increases. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column

EFFECTS OF HARD WATER

• With hard water, soap solutions form a white precipitate (soap scum) instead of producing lather, because the 2+ ions destroy the surfactant properties of the soap by forming a solid precipitate (the soap scum). A major component of such scum is calcium stearate, which arises from sodium stearate, the main component of soap:

• 2 C17H35COO- + Ca2+ → (C17H35COO)2Ca

• Hardness can thus be defined as the soap-consuming capacity of a water sample, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap. Synthetic detergents do not form such scums.

• A portion of the ancient Roman Eifel aqueduct in Germany.

• Hard water also forms deposits that clog plumbing. These deposits, called "scale", are composed mainly of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2), and calcium sulfate (CaSO4). Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers. This precipitation (formation of an insoluble solid) is principally caused by thermal decomposition of bicarbonate ions but also happens to some extent even without such ions. The resulting build-up of scale restricts the flow of water in pipes.

PHYSICS

WATER AS AN ENERGY RESOURCE

INTRODUCTION

We have used running water as an energy source for thousands of years, mainly to grind corn.

The first house in the world to be lit by hydroelectricity was Cragside House, in Northumberland, England, in 1878.

In 1882 on the Fox river, in the USA, hydroelectricity produced enough power to light two paper mills and a house.

Nowadays there are many hydro-electric power stations, providing around 20% of the world's electricity.

The name comes from "hydro", the Greek word for water.

HOW IT WORKS

A dam is built to trap water, usually in a valley where there is an existing lake.

Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators.

Notice that the dam is much thicker at the bottom than at the top, because the pressure of the water increases with depth.

Hydro-electric power stations can produce a great deal of power very cheaply.

MORE…Gravitational potential energy is stored in the water

above the dam. Because of the great height of the water, it will arrive

at the turbines at high pressure, which means that we can extract a great deal of energy from it. The water then flows away downriver as normal.

In mountainous countries such as Switzerland and New Zealand, hydro-electric power provides more than half of the country's energy needs.

An alternative is to build the station next to a fast-flowing river. However with this arrangement the flow of the water cannot be controlled, and water cannot be stored for later use.

ADVANTAGES AND DISADVANTAGES

ADVANTAGES• Once the dam is built, the energy is virtually free. • No waste or pollution produced.• Much more reliable than wind, solar or wave power. • Water can be stored above the dam ready to cope with peaks in demand.• Hydro-electric power stations can increase to full power very quickly, unlike

other power stations. • Electricity can be generated constantly.

DISADVANTAGES• The dams are very expensive to build.

However, many dams are also used for flood control or irrigation, so building costs can be shared.

• Building a large dam will flood a very large area upstream, causing problems for animals that used to live there.

• Finding a suitable site can be difficult - the impact on residents and the environment may be unacceptable.

• Water quality and quantity downstream can be affected, which can have an impact on plant life.

WATERRECYCLING

WHAT IS WATER RECYCLING ?

The process in which waste water is treated to remove solids and certain impurities, and used in sustainable landscaping irrigation or to recharge groundwater aquifers is called water recycling. It basically means wastewater sent from a home or business through a pipeline system to a treatment facility, where it is treated to a level consistent with its intended use. The is then routed directly to a recycled water system for uses such as irrigation or industrial cooling.

HOW IS IT DONE?Treatment of wastewater is actually a remarkably simple process that utilizes very basic physical, biological and chemical principles to remove contaminants from water.The three steps involved in the treatment of wastewater are:-o Physical Systems- In physical processes raw sewage passes through bar screens and grit chamber. These physical processes remove approximately half of the contaminants in wastewater.o Biological Systems- It converts non-settleable solids to settleable solids which removes the rest of the contaminants from the wastewater.o Chemical System- Chemical system such as chlorine contact chambers are used to kill the remaining microorganisms not captured in final clarifiers. The point where treated water is discharged into a stream or body of water is called the outfall.

UTILIZATIONRecycled water can be used for various purposes.It can be used by agencies and businesses for:oIrrigationoCommercial processesoDecorative fountains and pondsoPressure washingoDust controloToilet flushingoGroundwater rechargeoStream flow and wetland enhancement