Metals, Minerals, Ores: Properties, Uses

51. Which one of the following is not true for anodizing process?

Which one of the following is not true for anodizing process?

[amp_mcq option1=”It makes aluminium corrosion resistant.” option2=”Metals like aluminium, titanium and magnesium can be anodized.” option3=”Clean aluminium article is the anode and oxygen gas is evolved at the cathode.” option4=”It is used in aircraft industry.” correct=”option3″]

This question was previously asked in
UPSC CDS-1 – 2023
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Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
A) It makes aluminium corrosion resistant. This is true. The artificially thickened oxide layer is more robust and protective than the natural oxide layer, providing enhanced corrosion resistance.
B) Metals like aluminium, titanium and magnesium can be anodized. This is true. These are common metals that form stable oxide layers and are frequently anodized.
C) Clean aluminium article is the anode and oxygen gas is evolved at the cathode. In the anodizing process, the aluminium article to be anodized is made the anode (positive electrode). Oxidation occurs at the anode, forming the oxide layer on the aluminium surface. The cathode (negative electrode) is typically an inert material like graphite or lead. At the cathode, reduction occurs, which involves the reduction of water to hydrogen gas and hydroxide ions ($2H_2O + 2e^- \rightarrow H_2 + 2OH^-$) or the reduction of H⁺ ions to hydrogen gas ($2H^+ + 2e^- \rightarrow H_2$). Oxygen gas is evolved at the *anode* if the process involves the electrolysis of water ($2H_2O \rightarrow O_2 + 4H^+ + 4e^-$) as part of the overall reaction, which contributes to the oxide layer formation ($2Al + 3H_2O \rightarrow Al_2O_3 + 6H^+$). However, the primary anodic reaction is the formation of Al₂O₃. Oxygen gas evolution typically occurs at the cathode, especially if there are other species present, or as a side reaction. More accurately, hydrogen gas is evolved at the cathode. Therefore, the statement that oxygen gas is evolved at the cathode is *not* true.
D) It is used in aircraft industry. This is true. Anodizing is widely used in the aerospace industry to improve the corrosion resistance, wear resistance, and paint adhesion of aluminium alloys used in aircraft components.
The statement that is NOT true is C, specifically regarding oxygen evolution at the cathode.
– In anodizing, the metal article is the anode.
– Anodizing enhances corrosion resistance, wear resistance, and allows for dyeing.
– Hydrogen gas is typically evolved at the cathode during anodizing.
The electrolyte used in anodizing is typically an acidic solution (e.g., sulfuric acid, chromic acid, oxalic acid). The structure and properties of the anodic oxide layer depend on the type of electrolyte and process parameters. The porous nature of the oxide layer allows for subsequent dyeing if required.

52. Which one of the following substances do silver articles react with, t

Which one of the following substances do silver articles react with, that makes the silver articles black ?

[amp_mcq option1=”Sulphur” option2=”Oxygen” option3=”Carbon dioxide” option4=”Phosphorus” correct=”option1″]

This question was previously asked in
UPSC CDS-1 – 2021
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Silver articles become black due to their reaction with sulphur compounds present in the atmosphere, such as hydrogen sulphide (H₂S). This reaction forms a layer of black silver sulphide (Ag₂S) on the surface of the silver.
– The tarnishing of silver is primarily caused by the reaction with sulphur compounds, not oxygen or carbon dioxide under normal atmospheric conditions.
– The reaction is typically represented as: 2Ag(s) + H₂S(g) → Ag₂S(s) + H₂(g).
– While silver does react with oxygen at high temperatures, the common tarnishing phenomenon is due to sulfurization.
– Phosphorus is a reactive non-metal but does not cause silver tarnishing in this manner.

53. Aluminium is manufactured from

Aluminium is manufactured from

[amp_mcq option1=”Copper ore” option2=”Bauxite ore” option3=”Mica ore” option4=”Manganese ore” correct=”option2″]

This question was previously asked in
UPSC CDS-1 – 2021
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The correct answer is B) Bauxite ore. Aluminium is primarily manufactured from bauxite, which is an aluminium ore rich in aluminium oxides. The process involves refining bauxite into alumina (aluminium oxide) and then smelting alumina using electrolysis (Hall-Héroult process) to produce aluminium metal.
Bauxite is the principal ore from which aluminium is extracted globally.
India has significant reserves of bauxite, mainly found in Odisha, Gujarat, Jharkhand, Maharashtra, and Chhattisgarh. Other ores listed (Copper ore, Mica ore, Manganese ore) are sources for Copper, Mica, and Manganese respectively, not Aluminium.

54. Silver articles become black after some time when exposed to air

Silver articles become black after some time when exposed to air because

[amp_mcq option1=”silver gets oxidized to silver oxide” option2=”silver reacts with moist carbon dioxide in the air to form silver carbonate” option3=”silver reacts with sulphur in the air to form a coating of silver sulphide” option4=”silver reacts with nitrogen oxides in the air to form silver nitrate” correct=”option3″]

This question was previously asked in
UPSC CDS-1 – 2020
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Silver articles tarnish and become black when exposed to air primarily due to a reaction with small amounts of sulfur compounds (like hydrogen sulfide, H₂S) present in the atmosphere. This reaction forms a thin layer of silver sulfide (Ag₂S) on the surface, which is black.
– Silver reacts with sulfur compounds in the air.
– The reaction produces silver sulfide (Ag₂S).
– Silver sulfide is black, causing the tarnish.
While silver can react with oxygen at high temperatures to form silver oxide, the black tarnish at room temperature is predominantly due to the formation of silver sulfide. Sources of hydrogen sulfide in the air include pollution, volcanic activity, and the decomposition of organic matter.

55. Which one of the following chemical reactions is not feasible?

Which one of the following chemical reactions is not feasible?

[amp_mcq option1=”Fe + CuSO₄ → FeSO₄ + Cu” option2=”Zn + CuSO₄ → ZnSO₄ + Cu” option3=”Cu + PbCl₂ → CuCl₂ + Pb” option4=”Mg + CuSO₄ → MgSO₄ + Cu” correct=”option3″]

This question was previously asked in
UPSC CDS-1 – 2020
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A chemical reaction where a metal displaces another metal from its salt solution is feasible only if the displacing metal is more reactive than the metal being displaced. The reactivity series of metals dictates this.
Comparing the reactivity of the metals involved: Magnesium (Mg) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > Copper (Cu).
– A) Fe + CuSO₄: Fe is more reactive than Cu. Fe displaces Cu. Feasible.
– B) Zn + CuSO₄: Zn is more reactive than Cu. Zn displaces Cu. Feasible.
– C) Cu + PbCl₂: Cu is less reactive than Pb. Cu cannot displace Pb. Not feasible.
– D) Mg + CuSO₄: Mg is more reactive than Cu. Mg displaces Cu. Feasible.
The reactivity series is determined experimentally and shows the relative tendency of metals to lose electrons and form positive ions. More reactive metals are higher in the series.

56. Which one of the following metals is kept immersed in Kerosene oil to

Which one of the following metals is kept immersed in Kerosene oil to protect it and to prevent accidental fire ?

[amp_mcq option1=”Calcium” option2=”Sodium” option3=”Vanadium” option4=”Magnesium” correct=”option2″]

This question was previously asked in
UPSC CDS-1 – 2021
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Sodium (Na) is a highly reactive alkali metal. It reacts vigorously with moisture and oxygen in the air, which can lead to ignition. To prevent this, sodium is typically stored immersed in kerosene oil, which prevents it from coming into contact with air and water.
– Alkali metals like sodium and potassium are very reactive due to their low ionization energies.
– Kerosene is a non-polar hydrocarbon that does not react with sodium and acts as a barrier against air and moisture.
– Calcium and Magnesium are alkaline earth metals (Group 2) and are less reactive than alkali metals. They react with water but do not require storage in kerosene.
– Vanadium is a transition metal and is much less reactive than the alkali metals.
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