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| Last Updated:06/01/2014

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Water water everywhere

SUDHAMAHI REGUNATHAN, The Hindu, 03 January, 2014


INTERNET A closer look at that common but vital molecule that matters so much to human life. SUDHAMAHI REGUNATHAN


The second commonest molecule in the world is water, the first being Hydrogen. Even though it is so common and vital to our life, we know precious little about it. There may be some amongst us who know more than the rest of us, like it covers 70% of the universe, we are surrounded by more than 330 cubic miles of it, it is one of the simplest but also one of the most intriguing molecules, it dissolves more substances than any other liquid, there are at least 15 different types of ice, Lavoisier found the composition of water as H20, Lavoisier named Hydrogen which means the water maker element and that Cavendish found Hydrogen and even used oxygen to show combustion.


Andrea Sella, a Professor of chemistry in London says, “The first thing which makes water so unique is that water is able to store enormous amount of energy and that is why we are able to use it in heating systems. The second thing is as we cool water down, it does something very very peculiar. Till it touches 4 degrees it contracts but below that it expands and its density actually reduces and by the time it actually freezes you have a substance that is less dense than in its liquid state. There is no other, molecular material which will actually float in its liquid form. Its boiling point is completely anomalous…all of them boil at minus 20, minus 40 or minus 200 and water boils at 100 degrees…Finally, you might think that the sun may boil the water away. The light of the sun does not divide the molecules of water because the atmosphere has some molecules which deter that and protect water.”


Professor of History and Philosophy Science, Hasok Chang says, “Alexander Williamson, in the middle of nineteenth century was able to show that water is actually a parent to a whole class of molecules. If you think of water as HOH and if you replace one H with carbon then you get alcohol and if you replace the other hydrogen then you get an ether... in many ways that cemented water with organic chemistry.”


Patricia Hunt describes the molecule of water as a triangle with oxygen at the apex and the hydrogen atoms at the base. “Alongside the hydrogen atoms are rabbit ear like electrons which are perpendicular to the position of hydrogens. This makes the local environment around the oxygen atom tetrahedral. The bunny ears are negatively charged and so hydrogen gets a positive charge. This complex structure is what makes water form a network and boil at a higher temperature. The density of ice is less because when water turns into ice more of the hydrogen bonds form and push the water a little bit to make space. This reduces its density. Water forms very quickly… the hydrogen bonds so quickly that it cannot be seen and so we have to use quantum mechanics to understand the process.”


The element next to oxygen is sulphur and that too forms hydrogen bonds but not half as strong.Chang adds,“Hydrgen bonds makes water sticky…this means the water molecules are attracting each other with this additional force that you can imagine and so you have to give it extra heat to break apart…that is why water boils at a higher temperature. “


Sella adds another dimension. He says water molecules are not just sticky towards each other ( hydrogen is positive and oxygen negative)… For example if your finger touches the table it is not really your finger but the water molecules on your finger that is touching the water molecules on the table. That creates enormous problems for chemists…water is extremely reactive…one of the consequences is that chemists have to go to great lengths to keep water out of chemical reactions.”


Many more amazing scientific facts emerge…sodium chloride melts at 800 degrees but if you dissolve it into water, it does not fizz…that is because water is able to absorb that energy. Oil does not dissolve in water…so you can have a membrane with water. Your blood is carrying around lots of things in your body…so you need to have a fluidity that water has. Water regulates our body temperature and also helps us hold our heat. This is the single property that makes it essential for life…its property of being a good solvent…that is why it is in your blood…regulating heat, carrying material which dissolve in it, helping protein form…”