Question

During the formation of slag by the reaction of flux and impurities which of the following is an example of acidic and basic flux?
\[\
  \left( i \right)FeO + Si{O_2} \to FeSi{O_3} \\
  \left( {ii} \right)Si{O_2} + MgO \to MgO \to MgSi{O_3} \\
\]
a.) $(i)Si{O_2}$ - Acidic Flux $\left( {ii} \right)MgO$ - Basic Flux
b.) $(i)Si{O_2}$ - Basic Flux $\left( {ii} \right)MgO$ - Acidic Flux
c.) $(i)Si{O_2}$ - Basic Flux $\left( {ii} \right)MgO$ - Basic Flux
d.) $(i)Si{O_2}$ - Acidic Flux $\left( {ii} \right)MgO$ - Acidic Flux

Answer 1

Hint: FeO is basic in nature and is a impurity and only acidic fluxes remove basic impurities by forming intermediate soluble compounds and in the other equation $Si{O_2}$is acidic in nature and only basic fluxes can remove basic impurities. Use this fact to dig further and reach the correct answer.

Complete step-by-step answer:
Flux is that substance which is added during the process of extraction of metals. On being subjected to heat it reacts with the earthy impurities i.e. (gangue) to form fusible (molten) mass which is known as slag. Flux can be of two types - acidic or basic in nature.
Flux is usually added to react with the charge, or a product of its reduction, and in metallurgy it is generally added to lower a melting point.
Acidic flux are those kinds of flux which are produced from substances like Lewis acid such as $SiO_2$, $H_3PO_4$, HCl etc. Acidic flux is usually used in metal welding or extractive metallurgy or Smelting. Silica ($SiO_2$) is used to eliminate the basic earthly impurities (gangue) such as lime (CaO) or MgO or FeO.
Basic flux is similar to Acidic flux but only differs in the fact that we take basic substances like CaO for welding process or extractive metallurgy or for the process of smelting.
Basic fluxes like lime (CaO), magnesium oxide (MgO) are used to eliminate acidic gangue and impurities such as $SiO_2$.
In the given reactions in the question we can see the first reaction as –
\[\left( i \right)FeO + Si{O_2} \to FeSi{O_3}\]
Clearly in this reaction FeO is the impurity and Silica i.e. $Si{O_2}$ is acting as an acidic flux as FeO is basic in nature and thus silica being an acidic flux is removing the basic impurity FeO by forming a soluble compound here which is $FeSi{O_3}$ .(Ferrosilite)
Looking at the second reaction we see that
\[\left( {ii} \right)Si{O_2} + MgO \to MgO \to MgSi{O_3}\]
Here as already established that $Si{O_2}$ is acidic in nature and here in this equation is serving as an acidic impurity, in order to remove it we make it react with the basic flux that is Magnesium Oxide (MgO) in this case which after the reaction gives Enstatite ie \[MgSi{O_3}\]as an intermediate composition.
Therefore the correct option for the above question is option (A) that is Silica ($Si{O_2}$) is acidic flux and (MgO) is the basic flux.

Note – Slag is a by-product formed in smelting, welding, and other metallurgical and combustion processes which is produced from impurities in the metals or ores being treated. Slag consists generally of the mixed oxides of elements like silicon, sulphur, phosphorus, and aluminium and ash and so the products formed in their reactions with furnace linings and fluxing substances such as limestone.