Question

The iron formed in the blast furnace is called:
A. Pig iron
B. Wrought iron
C. Steel
D. Cast iron

Answer 1

Hint: Blast furnace is used to form Iron from Iron ore at very high temperatures. Iron ore is obtained from the earth crust in which various kinds of impurities are present.

Complete answer:
The Blast Furnace is used to reduce the concentrated ore chemically to its liquid metal state. A blast furnace is a gigantic, steel stack lined with bricks where the concentrated iron ore, coke, and limestone are added from the top, and a blast of hot air is blown into the bottom. All the three components are crushed into small round pieces and mixed and put on a hopper which controls the input.
Hot air is blown from the bottom and burned to yield temperatures up to about 2200K. Burning coke gives the majority of the heat required for this process. At 2200K temperatures, Coke reacts with the oxygen in the presence of hot air to form Carbon Monoxide (CO). The CO and heat now move upwards and meet the raw material running down from the top. The temperature in the upper parts of the Blast Furnace is considerably lower than the 2200K at the bottom. In this part of the blast furnace Haematite and Magnetite are reduced to Ferrous Oxide (FeO).
Reactions occurs in the Blast furnace at 500 – 800 K, as follows
$3\text{F}{{\text{e}}_{2}}{{\text{O}}_{3}}+\text{CO}\to \text{2F}{{\text{e}}_{3}}{{\text{O}}_{4}}+\text{C}{{\text{O}}_{2}}$
$\text{F}{{\text{e}}_{3}}{{\text{O}}_{4}}+4\text{CO}\to \text{3Fe}+4\text{C}{{\text{O}}_{2}}$
$\text{F}{{\text{e}}_{2}}{{\text{O}}_{3}}+\text{CO}\to \text{2FeO}+\text{C}{{\text{O}}_{2}}$
 At 900 – 1500 K, In the lower sections of the furnace, reaction takes place between coke and carbon dioxide as
  $\text{C}+\text{C}{{\text{O}}_{2}}\to 2\text{CO}$
 $3\text{FeO}+\text{C}{{\text{O}}_{2}}\to \text{Fe}+\text{C}{{\text{O}}_{2}}$
The limestone also decomposes to calcium oxide (CaO) which removes the silicate impurity of the ore in the form of Slag. It can be easily separated easily from molten iron. The iron manufactured in Blast Furnaces contains about 3 – 4 % of Carbon and traces of many other impurities such as sulphur, Silicon, phosphorus etc. found .This is called Pig Iron. It is a hard but brittle metal and the impurities enhance its strength. Carbon seems to play a significant role in influencing the brittleness and hardness balance in iron. To further reduce the carbon content of pig iron, it is melted again with scraps of iron and coke and
subjected to the blast of hot air. This kind of iron is called Cast Iron and has a slightly lower carbon content 2 – 3 %. This is even harder than pig iron.
Option (A) is correct. Iron obtained from the blast furnace called pig iron.
So, the correct answer is “Option A”.

Note:
 The students should be aware about why blast furnaces are used i.e. to convert iron ore into iron. There are various kinds of iron ores present, for example, limonite, iron pyrites etc. The method of converting an ore into a metal is termed as metallurgy.
Further noted that Wrought iron is the purest form of iron and is prepared from cast iron by heating cast iron in a furnace with Haematite (Fe2O3). The Haematite reacts with Carbon in the cast iron to give pure iron and carbon monoxide gas evolves.
$\text{F}{{\text{e}}_{2}}{{\text{O}}_{3}}+3\text{C}+2\text{Fe}+3\text{CO}$
Limestone is then added as flux, and it creates the slag. Impurities such as S, Si, P etc. combined with the slag and the slag later can be easily separated to yield pure iron.