Water and it's properties including hydrophobicity, hydrogen bonding and others

1. Water and its Properties
Bhanu Krishan

2. INDEX
S.no Topic Slide
Number
1) Introduction to water 3
2) Structure of water 4
3) Properties of water 5 - 9
4) Dissociation of water 10 - 12
5) Water as an Universal Solvent 13 - 14
6) References 15
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3. INTRODUCTION TO WATER (H₂O)
•Water is a transparent and nearly colorless chemical substance
that is the main constituent of Earth’s, streams, lakes and oceans
and the fluids of the most living organisms.
•It’s chemical formula is H₂O.
3

4. STRUCTURE OF WATER
• Water is a covalent structure: H – O – H. Oxygen bonded with two
hydrogen molecules.
• The water molecule itself is bent, with an angle of 104.5° between the
hydrogen (compare to 109.5° for sp³ tetrahedron.
4

5. PHYSICAL PROPERTIES OF WATER
 The physical properties of water differ usually from those of other
solvents. For example:
Water as a hydride of oxygen has a higher melting point, boiling
point, heat of vaporization and surface tension than do the
comparable hydrides of sulphur and nitrogen and most other common
liquids.
5

6.  Expansion on freezing: Most substances decreases in volume
(and hence increase in density) as their temperature decreases. But in
case of water there is temperature at which its density exceeds that at
higher or lower temperature. This temperature is 4°C.
Uniquely high surface tension: Water has the highest surface
tension (of 72.8) of any known liquid and it is the reason why water rises
to unusually high levels in narrow capillary tubes. This has great
significance in physiology.
Uniquely high heat capacity: There occurs a smaller
temperature rise in water as compared to most substances, when a given
amount of heat is applied. Thus water act as a temperature buffer. It
maintains its temperature more successfully than most other substances.
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7. High solvent power: Water is a solvent for a great number of
molecules which forms ionized solutions in water. It may thus, be
called a universal solvent which facilitates chemical reactions both
outside of and within biological systems.
Cohesion: Cohesion among water molecules allows water striders
to skate across the surface of still waters.
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8. CHEMICAL PROPERTIES OF WATER
Hydrogen Bonds: Molecules and ions with water forms hydrogen
bonds (such as NaCl) are hydrophilic. On the other hand, ions and
molecules that do not form hydrogen bonds with water are
hydrophobic.
Liquidity at Room Temperature: At room temperature, most
compounds with low molecular weights takes gaseous forms. With
water, however, hydrogen bonding helps to keep it a liquid at room
temperature 8

9. Chemical reaction: Once ionic compounds are dissolve, there
anions and cations circulates through the water allowing further
reactions to occur. Thus water also sponsors and facilitates chemical
reactions.
Stable temperature: Water takes more heat to raise its
temperature than other common compounds, since much of that heat
is required to first break the hydrogen bonds.
Freezing point: At 32°F (or 0°C) and below, water molecules form
hydrogen bonds in a crystalline lattice structure. This bonding spaces
the molecules a bit, farther apart than usual, causing water to expands
when it freezes. This results in ice being less dense than the liquid
water, which is why ice floats. 9

10. DISSOCIATION OF WATER
Pure water is not really pure. The purest water contains some hydronium ions and hydroxide ions.
These two are formed by the self-ionization of two water molecules. This happens rarely.
The process is an equilibrium where the reactants, intact water molecules, dominate the mixture.
At equilibrium the molarities for the hydronium ion and hydroxide ion are equal. [H3O1+] = [OH1-]
10

11. The equation is
H2O + H2O <---> H3O1+ + OH1-
The equilibrium expression is the normal products over reactants.
K = [H3O1+] [OH1-] / [H2O] [H2O]
The morality for the water is a constant at any specific
temperature. This means the equation can be rewritten as
K[H2O] [H2O] = [H3O1+] [OH1-]
11

12. The quantity on the right hand side of the equation " K[H2O]
[H2O] = Kw " is formally defined as Kw. The numerical value
for Kw is different at different temperatures.
At 25oC Kw = 1.0 x 10-14
Kw = K[H2O] [H2O]
Kw = [H3O1+] [OH1-] = 1.0 x 10-14
12

13. Water as a Universal Solvent
Water is capable of dissolving a variety of different substances, which
is why it is such a good solvent and water is called the “universal
solvent” because it dissolves more substances than other liquid.
This is important to every living thing on earth. It means that wherever
water goes, either through the ground or through our bodies, it takes
along valuable chemicals ,minerals and nutrients.
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14.  It is water’s chemical composition and physical attributes that
make it such an excellent solvent.
 Water molecules have a polar arrangement of the oxygen and
hydrogen atoms, - one side (hydrogen) has a positive electrical
charge and the other side, (oxygen) had a negative charge. This
allows the water molecule to become attracted to many other
different types of molecules.
Water can become so heavily attracted to a different molecules
like salt(NaCl), that it can disrupt the attractive forces that
hold the Sodium and Chloride in the salt molecule together and
thus dissolve it.
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15. REFERENCES
• https://water.usgs.gov/edu/qa-solvent.html
• http://www.800mainstreet.com/acid_base/dissociation_of_water.
html
• https://en.wikipedia.org/wiki/Water
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