WATER The Universal Solvent Introduction

INTRODUCTION 19.1 Water is colourless. Water has no smell. It is odourless. Water is tasteless . Water is shapeless . Water is the most common substance found on the Earth. About 3/4 th of the Earth is covered with water. Water can be found in ponds, rivers, lakes, oceans and seas. Water acquires certain properties when certain salts are dissolved in it .

In this chapter we will be learning about : Soft and Hard water Experiments with Hard Types of Hardness Disadvantages of Hardness Removal of Hardness Conservation of Water

Did you know ? Less than 1% of the water supply on earth can be used as drinking water. By the time a person feels thirsty, his or her body has lost over 1 percent of its total water amount When water contains a lot of calcium and magnesium, it is called hard water. Hard water is not suited for all purposes water is normally used for

HARD WATER AND SOFT WATER Soft water-Water that gives lather with soap easily and readily is called Soft water. Hard water- Hard water forms scum when it comes in contact with water.

IS RAIN WATER PURE?? No, Because Rain water dissolves small amount of atmospheric carbon dioxide in it to form a weak acid called carbonic acid .The other chemicals that are let into the atmosphere may also be dissolved.

HARD WATER Hardness of water is due to presence of dissolved salts such as bicarbonates, sulphates, chlorides of magnesium and calcium.

Let us consider how these salts render water hard..

RESULTS FOR TESTS ON HARD AND SOFT WATER

LETS SEE HOW THIS HAPPENS!! http://www.youtube.com/watch?feature=player_detailpage&v=41eBQ9_FFV4

SCUM FORMATION After ionization Mg++ and Ca++ cause hardness. These ions form an insoluble scum with soap. How?? Soap is a potassium stearate or sodium stearate these salts reacts with Mg++ and Ca++ to give Scum. scum

HARDNESS OF WATER PERMANENT HARDNESS: The hardness caused by dissolved Magnesium chloride, calcium chloride, magnesium sulphate or calcium sulphate is called permanent hardness.

TEMPORARY HARDNESS: The water that contains bicarbonate ions along with Mg++ and Ca++ ions could be softened by mere boiling. Hence, such water is called temporary hard water.

DISADVANTAGES OF HARD WATER

WHAT HAPPENS WHEN HARD WATER IS USED?? Makes the skin dry and leaves a whitish residue on the skin. The utensils lose shine and get stained when washed with hard water The utensils lose shine and get stained when washed with hard water

SCALE FORMATION: Hard water contains dissolved bicarbonates. The dissolved bicarbonates, on boiling, dissociate to form insoluble carbonates which go on depositing on the inner walls of the boiler. This results in “scaling”.

LETS SEE WHAT HAPPENS… WHEN SOAP SOLUTION IS ADDED TO HARD WATER.. Any guess..?? https://www.youtube.com/watch?feature=player_detailpage&v=zQjIr_jgqtE

WHAT COULD BE THE REMEDY?? THINK.. Converting hard water to soft water !!

Methods of Softening Hard Water Method of Removal of Temporary Hardness BOILING: When water is boiled, the bicarbonates that cause temporary hardness are converted into insoluble carbonates, leading to the removal of Ca++ and Mg++ from water. Calcium bicarbonate → Calcium carbonate ↓ + Water + carbon dioxide Ca(HCO3)2 → CaCO3↓ + H2O + CO2 (Aqueous) → (solid) (liquid) (gas)

Magnesium bicarbonate→ Magnesium carbonate↓ + Water + carbon dioxide Mg(HCO3)2 → MgCO3↓ + H2O + CO2 (Aqueous) (solid) (liquid) (gas) The precipitates that are formed are removed by filtering. Reasons to consider other methods of softening: Boiling is the easiest method of softening a small quantity of water. Softening a large quantity of water by boiling is highly expensive. The process is also time consuming. Temporary hardness is rare. Boiling removes the bicarbonate component only.

Methods of removal of permanent hardness DISTILLATION: Principle: The condensation of water vapours produced on heating. This method removes both temporary and permanent hardness. Distilled water is both soft and pure. Youtube link: www.youtube.com/watch?v=xxNfJLMNS4E

DISTILLATION APPARATUS

SODA PROCESS: Both temporary hardness and permanent hardness of water can be removed by adding sodium carbonate. Sodium carbonate reacts with salts that cause hardness to give their respective carbonates. CaSO4 + Na2CO3 → CaCO3↓ + Na2SO4 MgSO4 + Na2CO3 → MgCO3↓ + Na2SO4 CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl MgCl2 + Na2CO3 → MgCO3↓ + 2NaCl Ca(HCO3)2 + Na2CO3 → CaCO3↓ + 2NaHC

The insoluble carbonates present in the softened water are removed by filtration. The water softened by this method contains salts such as sodium sulphate, sodium chloride and so on. These salts do not come in the way of formation of lather with soap.

PERMUTIT PROCESS: This method removes both temporary hardness and permanent hardness. Naturally occurring sodium aluminium silicate is called Zeolite. Artificially prepared sodium aluminium silicate is called permutit. Permutit is prepared by heating quartz, sand, china clay and sodium carbonate. Fusing sodium silicate and sodium aluminates is another method of preparing permutit. Permutit is in the form of a porous gel.

Principle: To convert the dissolved salts of calcium and magnesium into insoluble calcium and magnesium permutits, respectively. This is done by exchanging the base ion radicals such as Ca++ and Mg++ with the base ion Na+ of sodium aluminium silicate. Hence this process is also known as ‘base exchange process’. This is carried out by passing hard water through the layers of zeolite or permutit.

There will be a column in which gravel, sand and permutit are placed in alternate layers. Hard water is made to rise up through the various layers. As water passes through the permutit, the ions of calcium (Ca++) and magnesium (Mg++) which cause hardness are exchanged with the sodium ions of the permutit. Due to this exchange, the sodium ions of the permutit is changed eventually into calcium aluminium silicate and magnesium aluminium silicate. These are called calcium permutit and magnesium permutit respectively.

Sodium permutit + Calcium chloride → Calcium permutit + Sodium chloride Na2Pm + 2CaCl2  =  CaPm +NaCl Sodium permutit + Magnesium sulphate → Sodium sulphate+ Magnesium permutit Na2Pm + MgSO4 = Na2SO4 + MgPm The water softened by this method contains sodium ions. The presence of these ions will not make water hard. What we get through permutit process is only soft water and not pure water.

Advantages: Permutit process is an economical way of softening water Advantages: Permutit process is an economical way of softening water. The hardness is more or less completely removed by this method. Disadvantages: This method is not appropriate if the hard water contains sodium salts or suspended matter in large quantities. Lead. iron or manganese impurities.

9.6 CONSERVATION OF WATER

What is conservation of water? The effort made by the society towards the rational use, prevention of pollution and of water is called water conservation. Why do we need to conserve water? Water appears to be abundant source. This has led to abuse of water. Although more than 75% of the surface of the earth is covered with water, the water that is fit and available for our consumption is very much less. Therefore we need to conserve water. Let us study about distribution of water on earth

Distribution of water on earth Distribution of water on earth(in percentage) Ocean and salt lakes Ice Atmospheric vapour Rivers Ground water Ponds/lakes 97.3 2.0 0.7

97% of the earth’s water is salt water which is unfit to drink 2% is in the frozen form Only 1% is fresh water-fit to drink That needs to be enough for every one-all 7 billion of us 70% of all fresh water is in form of ice and snow, nearly 30% is in soil or underground. Rivers and lakes make up just 1% of all earth’s fresh water

There is serious water crisis in our world right now There is serious water crisis in our world right now. Nearly 1 billion people live without drinking water. 1 out of every 8 people on earth search for clean water every day. 1 in 6 has no access to toilet. Think about that. What would be your life like, if that were you? Every 20 sec a child die from water related disease. 4000 child die every day How much longer can we let this go,this can not last for ever.This needs a solution. SAVE water, CONSERVE water

There are many causes for the scarcity of water There are many causes for the scarcity of water. Some of these are listed below: Ever increasing population Unsatisfactory management of water Deforestation and soil erosion Inadequate storage facilities Pollution of water Growing crop-breeds that consume more water Overuse of ground water Wastage through leakage, absorption, and evaporation.

Lowering of the storage capacity of water bodies due to silt collection. Wasteful habits of using water. Click on link below http://www.youtube.com/watch?v=BCHhwxvQqxg http://www.youtube.com/watch?v=_9OGvcVA3Gw http://www.youtube.com/watch?v=GlWVDcdRVUA