Question

Which is used as an acidic flux in metallurgy?
(A) $C{{O}_{2}}$
(B) graphite
(C) sand
(D) gas carbon

Answer 1

Hint: Acid flux is those compounds which are acidic in nature. Acids react with bases to give the neutralization reactions. This property of acid is used for the removal of basic impurities present in the metal ores. It is an effective method as the products formed are salts and water which do not harm the environment.

Complete step by step solution:
-Metal compounds found in nature are called minerals. Minerals from which we can extract metals conveniently as well as economically are called ores. It contains impurities which are called gangue.
-Extraction of metals from ores is called metallurgy. Metals are extracted from the earth’s surface and so along with the metals, certain impurities also appear with it which needs to be removed in order to increase the efficiency of the metals.
-The best way to extract the metal is to add oxygen to the ore so that all the impurities present in the metal react with oxygen to form the oxides. Once oxides are formed, they are removed easily as they are generally insoluble.
-The mixture of oxides with the impurities is called slag. It is present in the molten state along with the molten metal. The process by which this impurity containing slag is removed from the metal is called smelting.
Eg. $\begin{align}
& 2CuFe{{S}_{2}}+4{{O}_{2}}\to 2FeO+C{{u}_{2}}S+3S{{O}_{2}} \\
& FeO+C{{u}_{2}}S+Si{{O}_{2}}\to FeSi{{O}_{3}}\left( slag \right)+C{{u}_{2}}S \\
\end{align}$
-Impurities present in the metals can be acidic in nature or basic in nature. They are called acidic flux and basic flux respectively. Acidic flux refers to the acidic oxides which are formed generally by the reaction of non-metals with oxygen. Some of them are $Si{{O}_{2}},{{B}_{2}}{{O}_{3}},{{P}_{2}}{{O}_{5}}$. They are used to remove the basic impurities like CaO, MgO, FeO. This is because the acids and bases react easily with one another to form neutralization reactions. Here the acidic flux reacts with basic impurities to form slag.
-Basic impurities are called basic flux. They are generally the oxides of metals like $MgO$, $CaO$, $FeO$. They react with acidic oxides like $Si{{O}_{2}},{{B}_{2}}{{O}_{3}},{{P}_{2}}{{O}_{5}}$ and eliminate them by forming a slag.
-From all the given options, the best acidic oxide is formed by silicon which is silica and is referred to as sand. It forms silicon-dioxide which is acidic in nature and is used to remove the basic impurities. Its chemical formula for oxide is $Si{{O}_{2}}$.

Therefore the correct option is (C)- sand.

Note: Carbon-dioxide is also an acidic oxide formed by the reaction of a non-metal (carbon) with oxygen. But silica is preferred as acidic oxide as it is found as sand abundantly in nature. Also, it is more acidic than carbon-dioxide. The major reason is that carbon dioxide is a gas and silica is solid and can be brought at the place where slag formation has to occur.