Chemistry MCQs for NEET — Practice Questions with Answers

In the extraction of copper from its sulphide ore, when ore is subjected to roasting, some of it is oxidised to Cu₂O which reacts with the remaining Cu₂S (sulphide ore) to give copper metal.

Cu₂S + 2Cu₂O $\to$6Cu + SO₂ $\uparrow$

In this process Cu₂S behaves as reducing agent.

Pig iron contains about 4% carbon (major impurity) and other impurities (S, P, Si, Mn) in trace amounts.

Zr and Ti are purified by van Arkel method.

(c)Zn is extracted from its sulphide ore by roasting followed by carbon reduction

    Hg, Pb and Cu are extracted by self reduction from their sulphide ores.

(c) Cr metal is commercially extracted by Al-reduction method .

(a) Purification of Al metal : Hoop's method

Beayer's process is for extraction in which bauxite is converted into Al₂O₃

(a) When the impure metal has impurity of its own metal oxide, then the Poling process is used, e.g., impure Cu and Sn are purified by this method.

Poling is a [metallurgical] method employed in the purification of copper which contains copper oxide as an impurity and also in the purification of tin ("Sn") which contains tin oxide (stannic oxide or "SnO₂") as an impurity. The impure metal, usually in the form of molten blister copper, is placed in an anode furnace for two stages of refining.^[1]In the first stage, sulphur and iron are removed by gently blowing air through the molten metal to form iron oxides and sulfur dioxide.^[2] The iron oxides are skimmed or poured off the top of the copper and the gaseous sulfur dioxide exits the furnace via the off-gas system. Once the first oxidation stage is complete, the second stage (reduction or poling) begins. This involves using a reducing agent, normally natural gas or diesel (but ammonia,^[2] liquid petroleum gas,^[2] and naphtha^[3] can also be used), to react with the oxygen in the copper oxide to form copper metal. In the past, freshly cut ("green") trees were used as wooden poles.^[2][4] The sap in these poles acted as the reducing agent. The heat of the copper makes the pole emit wood gas(CO2 andH2) that reduces the cuprous oxide to copper.

It was the use of these greenwood poles gave rise to the term "poling."

Care must be taken to avoid removing too much of the oxygen from the anode copper, as this will cause other impurities to change from their oxide to metallic states and they will remain in solid solution in the copper, reduce its conductivity and change its physical properties. Also upper surface can be covered with coke to prevent reoxidation of metal.^[

(A) Randomness increases on changing the phase from soilid to liquid or from liquid to gas.

(A) $Au\left(S\right)\stackrel{O^2}{\to }A{u}^{+}\left(aq.\right)$

     $A{u}^{+}+2C{N}^{-}\left(aq.\right)\to {\left[Au{\left(CN\right)}_2\right]}^{-}$ soluble complex.

The partial hydrolysis of one mole of peroxodisulfuric acid (H₂S₂O₈) produces one mole of sulfuric acid (H₂SO₄) and one mole of peroxomonosulfuric acid (H₂SO₅). The reaction is: H₂S₂O₈ + H₂O → H₂SO₄ + H₂SO₅.