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

Sulfuric acid

Sulphuric Acid is a strong acid and used for several chemical industries as well.

Uses of sulphuric acid

• manufacture of detergents 
• manufacture of fertilisers
• as a battery acid

Manufacture of sulfuric acid from Contact Process

Raw materials used:

• Sulfur
• Air
• Water

The process of producing Sulfuric acid is as follows

1. Burning Sulfur in air

S(s) +O2 (g) -> SO2 (g)

2. Reacting Sulfur dioxide with air

This is a reversible reaction

2SO2 (g) + O2 (g)  ⇌ 2SO3 (g)

Conditions used and Explanation:

• Temperature 450 °C 
• Pressure 2 atm
• Vanadium (V) Oxide as the Catalyst

Temperature:

The forward reaction is exothermic in this reaction. In order to achieve a high yield of Sulfur trioxide, using lower temperatures is likely. Under lower temperatures the forward reaction will be favored but the kinetic energy of the particles will be less to achieve a high rate. A moderate temperature is used.

Pressure:

High pressures results in favoring the forward reaction producing less number of moles. According to the equilibrium forward reaction is favored even at the room temperature. A very high pressure is not economically advantageous. Therefore a small increase in the pressure is used for the process.

Catalyst:

Catalyst reduces the activation energy for the reaction to occur.

3. Sulphur troxide is absorbed to concentrated sulfuric acid

Sulfur trioxide when dissolved in water produces sulfuric acid. This reaction is exothermic and produces a huge amount of heat enough to evaporate sulfuric acid. Therefore it is first absorbed to sulfuric acid producing the product H2S2O7

4. Dissolve in water

Produced  H2S2O7  is dissolved in water to produce sulfuric acid as the final step.

Sulfur dioxide used in this process has many uses

1. as a bleach.

2. in the manufacture of wood pulp for paper. 

3. as a food preservative (by killing bacteria).

Properties and uses of ammonia

Ammonia is a widely used chemical having characteristic properties.

Properties of ammonia

• is a gas having a characteristic pungent smell

• is alkaline - turns wet red litmus paper blue

• lighter than air - can be collected via upward delivery

• highly soluble in water - turns water alkaline

Preparation of Ammonia

Ammonia preparation involves a reversible reaction starting from hydrogen and Nitrogen

         3H2 (g) +2N2  (g) ⇌  2NH3 (g)

for the industrial preparation of ammonia 

• Nitrogen is obtained by fractional distillation of atmospheric air
• Hydrogen is obtained by cracking oil

Essential conditions for the manufacture of ammonia by the Haber process

The process of preparing ammonia is also referred as Haber process

Conditions used in haber process

• Temperature 450 °C
• Pressure 200 atm
• Iron fillings as the catalyst

Reasons for using the above conditions can be explained by their effect on obtaining higher yields of ammonia by the reversible reaction of preparing ammonia.

refer about reversible reactions

Temperature:

The forward reaction is an exothermic reaction for the preparation of ammonia. If the temperature was increased, it will favor the backward reaction. However lower temperatures , even favoring the forward reaction,  does not provide enough activation energy for the reaction to take place. The yield of ammonia will be less due to lack of collisions between the reactant particles.  Therefore the temperature used in haber process is said to be a moderate temperature.

Pressure:

High pressures always favor the reaction producing less number of moles in a reversible reaction. Therefore a high temperature as 200atm is used in haber process for a higher yield of ammonia.

Catalyst:

A catalyst favors both forward reaction and  the backward reaction in a reversible reaction making the time taken to reach the equilibrium reducing the activation energy of the reaction. Iron fillings is used as the catalyst in the haber process.

Uses of ammonia

One of the main uses of ammonia in industry is producing nitrogenous fertilizers.  Nitrogenous fertilizers contain soluble nitrogen salts promoting plant growth.

Effect of adding Calcium hydroxide to soil with added nitrogenous fertilizers

Soil pH is a very important factor considered in plant growth. Soil pH requirement is different from one crop to another. Less soil pH or high acidity in soil is a problem faced by maney farmers which can be treated by adding alkalies like Ca(OH)2

However when alkalies are added, it causes loss of nitrogen from the soil by the added nitrogenous fertilizers.

e.g: 

2NH4NO3 (s) + Ca(OH)2  (aq)->  Ca(NO3)2 (aq)  + 2NH3 (g) +2 H2O (l)

According to the reaction  Ammonia gas is produced by the reaction. As Ammonia is a gas it will cause the loss of nitrogen from soil.