Properties of water important for life

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Water is essential for life. It is the most abundant chemical and also the most abundant inorganic substance.

Main functions of water 

1. Water is the main component of the protoplasm (The  Living content of a cell that is surrounded by a plasma membrane)

2. Water is a reactant in man biochemical reactions e.g: Photosynthesis

3. Water is a good solvent. Therefore it is the medium for many biochemical reactions.

4. Water helps in maintaining turgidity in living organisms.

 In addition to these main functions

In plants water helps in :

1. Absorbing minerals and act as the medium of transport


2. Transporting organic food


3. Germinating seeds


4. Turgor movements  of stomata


5. Acting as a medium for fertilization


6. Medium for pollination


7.  Seed dispersal


8. Maintaining turgidity in herbaceous plants

In Animals water

1. Is the main component in body fluids


2.  Moistens the respiratory surfaces


3. Acts as a lubricant in joints


4. Cools the body surface by evaporation


5. Habitat for some organisms



Water has many important chemical and physical properties making it the main chemical found in living organisms.

chemical and physical properties of water

1. A liquid at room temperature- therefore water is the main medium of protoplasm


2. Polarity- water is a good solvent therefore


3. High surface tension-  small insects such as water skaters can live on the surface of water


4. High specific heat capacity-helps to maintain the body temperature without major fluctuations


5. High latent heat of vaporization-  cools body surfaces because a high heat is absorbed from body surfaces for evaporation


6. High latent heat of fusion- water doesn't freeze easily as a large amount of heat has to be dissipated from water to turn into ice


7. Anomalous expansion of water  when freezing- Due to this property density of water decreases when freezing. It makes ice float on water. Ice is a good insulator. theretofore liquid water remains at the bottom of water bodies without  freezing. Aquatic animals can survive in water dung winter season due to this.


8. Transparent- Water  is a transparent liquid. It allows penetration of light into deep water allowing the growth of aquatic plants and algae in a considerable depth


9. High adhesive and cohesive forces- transport of water in xylem is due to adhesive forces among water molecules and cohesive forces between water molecules and xylem capillary walls.

10. chemical property- water is a common reactant in biochemical reactions

Transition elements

Transition elements are the central block of elements in d- block of the periodic table. These metals are

• high in melting point
• high in density

e. g : Ti, V, Cr, Mn, Fe, Ni , Co

Transition elements are also having unique properties making their studies more interesting. Properties found in Transition elements

• has variable oxidation states

Mn Shows several oxidation numbers in differernt compounds ( +7 in KMnO4 ,  +2 in MnO2)

• forms colored compounds

KMnO4 ( Mn with oxidation number +7) has Purple color

K2Cr2O7 (Cr with oxidation number +6) has orange colour

Transition elements are also used as catalysts in several industries.

e.g: 

•  iron in the Haber process
• vanadium(V) oxide in the Contact process 
• nickel in the hydrogenation of alkenes

Advantage of using Catalysts in chemical industry:

•  lower energy demands and hence are economically advantageous 
•  help conserve energy sources

Group properties

Group I (Alkali metals)

Group I elements are metals having metallic properties. However they are soft and low densed elements.

These metals react with water rapidly. As the reactivity of the metals increases down the group, their reactivity with water is increased down the group. More vigorous reaction can be observed between cold water and potassium .   Reaction of Cesium with  water is even explosive. Reaction produces  hydroxide and hydrogen gas.

Group VII (the halogens)

halogens are non metals and all the elements exists as diatomic molecules. e.g Cl2

Their physical nature changes down the group. Fluorine  and Cl are gases, Br is a liquid and Iodine is a solid. Fluorine is a colourless gas, Chlorine is a gas with pale yellow color, Bromine is  brown color and iodine has a more dark color violet.

According to their reacivity decreases down the  group, they show a characteristic displacement reaction. That is the more reactive halogen is able to displace the less reactive halogen from its compound.

e.g : HCl

If Fluorine is added to HCl the followin reaction willl occur.

F2 + 2HCl   ---> 2HF  +Cl2

If Iodine was added instead of Chlorine, No reaction will occur as iodine is less reactive than chlorine.

Grop 0 ( the noble gases)

All the nobel gases has a fully filled outermost shell. Elements show reactivity to achieve fully filled outermost shells as it is the most stable state for elements. Nobel gases have fully filled outer most shell. Therefore they are already stable and are not reactive.

The lack of reactivity of the nobel gases are used where an inert atmosphere is necessary.

Next about Transition Elements

Periodic Trends

Periodic table can be used to predict patterns of properties of the elements. Lets consider the periodic table of S, and P groups mainly. (Group number I.....0)

1. Number of electrons in the outermost shell

Group number is equal to the number of electrons in the outermost shell of any element.
e.g: Na Group number I - number of electrons in the outer most shell= 1
   
Group number 0 is also referred as group number VIII. All the elements have 8 electrons in the outer shell But He having only 2 electrons.

2. Valency of the element

Valency is the number of electrons given, taken or shared in making bonds by the elements. It is important in writing the correct formula of a compound as well. General rule that  can be used to calculate the valency is as follows.

Valency of Groups I -IV

Equal to the group number

e.g : Mg= Group number II= valency= 2;


Valency of Groups IV- VII

equals to 8- group number

e.g: Cl group number 7= valency=( 8-7)= 1


Valency of Group number 0

equals to zero

3. Number of electronic shells

number of electronic shells is equal to the period number (horizontal raws) 

e.g Li is in period 2 = has 2 shells with electrons

4. Reactivity

Some of the metals in group I and II and also some elements in group number III are metals. All the other elements are non metals. The usual trend of reactivity

for  metals  : 

increases down the group. Na is more reactive than Li. K is more reactive than Na. The reason for this can be simply described as follows. Metals releases electrons to achieve the nobel gas configuration when making bonds. Releasing of electrons become more easy when the outer most shell electrons to be released is more distant from the nucleus.

for non metals

Decreases down the group. E.g Fluorine is more reactive than chlorine. Chlorine is more reactive than iodine.

Next about Group properties

Reversible reactions

Reactants becoming products is the usual type of reactions we are familiar with. If the products can again become reactants again it is called a reversible reaction.

e.g:  N2 (g) + 3H2 (g) 2NH3(g)

note the arrow that has been used to indicate a reversible reaction.

In this reaction, Nitrogen and hydrogen becoming ammonia is known as the forward reaction
Ammonia becoming nitrogen and hydrogen again is known as the backward reaction. In a reversible reaction both the forward and backward reaction takes place and after sometime they come to an equilibrium where rate of forward reaction and backward reaction become a constant.

This equilibrium can be altered by several factors so that forward or backward reaction is favored. This is important is several industries which make use of products made by reversible reactions such as the one given in the example , ammonia production.

Factors affecting the equilibrium of a reversible reaction

1. Pressure

If the pressure is increased in a reversible reaction of a gaseous system, the system tries to decrease the pressure by favoring the side of the reaction producing  less number of moles. According to the example reaction of producing ammonia, left hand side total number of moles (1+3 =4) and right hand side total number of moles=2.
If the pressure was increased, the forward reaction is favored which produces a less number of moles.

If the pressure was decreased, the backward reaction will be favored which produces more number of moles to the reaction.

2. Temperature

For the given example the forward reaction is exothermic. Which means if forward reaction takes place it produces heat for the system. In a reversible reaction if it is given that the forward reaction is exothermic, we can assume that the backward reaction is endothermic, the opposite. which means if the backward reaction takes place it will absorb heat from the system.

When the temperature is increased in a reversible system, the system tries to decrease the the temperature by altering the equilibrium to the side which will absorb the heat, the endothermic reaction. according to the ammonia example it would be the backward reaction.

When the temperature in decreased, the exothermic reaction will be favored.

3. Adding a reactant

If a reactant is added, the system tries to decrease the concentration of the added one by favoring the reaction that uses that reactant. for example in the above example if Nitrogen was added, the forward reaction is favored. If ammonia was added the backward reaction will be favored.

4. Removing a reactant

 If a reactant is removed, the system tries to produce more of the removed reactant. for example if nitrogen was removed, the backward reaction will be favored to produce more nitrogen from ammonia. If ammonia was removed the forward reaction is favored .

5. Adding a catalyst

Adding a catalyst does effect a reversible reaction  but not by favoring only one reaction as above. Adding a catalyst will faster both the forward reaction and the backward reaction making the time taken to reach the equilibrium faster. Iron fillings are used as the catalyst in the above reaction.

percentage yield and percentage purity

Chemical calculations are very useful for estimating the yield of a substance resulted from a chemical reaction.  e.g: mass of Fe that can be extracted from Iron (III) Oxide

In some cases  Due to impurities or imperfections in the extraction process amount of the product obtained can be less than the amount calculated. Percentage purity and percentage yield can be calculated to get an idea about the purity and the yield.

Percentage yield

Percentage Yield= obtained yield/ expected yield *100

e.g: 16 g of Fe2O3 was used to extract iron. 10 g of Pure iron was obtained from the process. what is the percentage purity of the iron ore?

Mr Fe2O3= 160

in 160g of Fe2O3 mass of Fe precent= 56*2= 112g
in 16g of Fe2O3 mass of Fe present=

112/160   *16
= 11.2 g (expected yield)

Percentage yield= obtained yield/ expected yield * 100
% yield= 10g/ 11.2g *100

= 89.286%

Percentage purity can be calculated the same way when the purity details are given.