Metals, Minerals, Ores: Properties, Uses

1. Which one among the following is the most reactive metal?

Which one among the following is the most reactive metal?

Na
K
Ca
Mg
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UPSC CISF-AC-EXE – 2023
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The reactivity of alkali metals increases down the group (K > Na) and alkali earth metals are generally less reactive than alkali metals. Comparing the given options, the standard reactivity series shows Potassium (K) is more reactive than Sodium (Na), which is more reactive than Calcium (Ca), which is more reactive than Magnesium (Mg). Therefore, Potassium (K) is the most reactive metal among the given choices.
– Reactivity of metals is related to their tendency to lose electrons (become oxidized).
– Alkali metals (Group 1) are generally more reactive than alkaline earth metals (Group 2).
– Within alkali metals, reactivity increases down the group.
– Within alkaline earth metals, reactivity generally increases down the group (though sometimes variations occur, but the general trend holds for Ca vs Mg).
– The order of reactivity for the given options is approximately K > Na > Ca > Mg.
Reactivity series can be determined experimentally (e.g., reaction with water, air, acids) or understood based on electronic configuration and ionization energies. Metals higher in the reactivity series can displace metals lower in the series from their compounds.

2. Manganese is extracted from Manganese dioxide by reaction with Alumini

Manganese is extracted from Manganese dioxide by reaction with Aluminium as described by the following unbalanced chemical equation :
MnO₂(s) + Al (s) → Mn (l) + Al₂O₃ (s)
The number of moles of Al (s) required to form one mole of Mn from its oxide is

1
0.75
1.33
2
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UPSC CISF-AC-EXE – 2020
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The unbalanced chemical equation is MnO₂(s) + Al (s) → Mn (l) + Al₂O₃ (s). To determine the moles of Al required to form one mole of Mn, we first need to balance the equation.
Balancing the oxygen atoms (2 on the left, 3 on the right), we find the least common multiple is 6. Multiply MnO₂ by 3 and Al₂O₃ by 2:
3 MnO₂(s) + Al (s) → Mn (l) + 2 Al₂O₃ (s)
Now, balance the aluminium atoms (1 on the left, 4 on the right). Multiply Al by 4:
3 MnO₂(s) + 4 Al (s) → Mn (l) + 2 Al₂O₃ (s)
Finally, balance the manganese atoms (3 on the left, 1 on the right). Multiply Mn by 3:
3 MnO₂(s) + 4 Al (s) → 3 Mn (l) + 2 Al₂O₃ (s)
The balanced equation is 3 MnO₂(s) + 4 Al (s) → 3 Mn (l) + 2 Al₂O₃ (s).
According to the balanced equation, 4 moles of Al react to produce 3 moles of Mn. To produce 1 mole of Mn, the number of moles of Al required is (4 moles Al / 3 moles Mn) * 1 mole Mn = 4/3 moles Al.
The question requires balancing the given chemical equation and then using stoichiometry to find the mole ratio between reactants and products. The ratio of Al to Mn in the balanced equation is 4:3.
This reaction is a type of redox reaction, specifically a thermite reaction where a metal oxide is reduced by a more reactive metal (Aluminium). Aluminium is a strong reducing agent. The value 4/3 is approximately 1.333…

3. Catalytic converter transforms waste gases from the engines of many ca

Catalytic converter transforms waste gases from the engines of many cars into carbon dioxide, nitrogen and water. The catalyst is made of

platinum and copper
molybdenum and copper
platinum and rhodium
rhodium and molybdenum
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UPSC CISF-AC-EXE – 2019
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Catalytic converters use precious metals like platinum, palladium, and rhodium as catalysts to convert harmful exhaust gases into less harmful substances.
Platinum and rhodium are commonly used together in catalytic converters, particularly in three-way converters, which target carbon monoxide (CO), unburnt hydrocarbons (HC), and nitrogen oxides (NOx).
Platinum is effective for oxidizing CO and HCs. Rhodium is effective for reducing NOx. Palladium is also used, often in conjunction with platinum, and is effective for oxidizing CO and HCs. Copper and molybdenum are not typically used as the primary catalysts in automotive catalytic converters.

4. Which one of the following metals does not react with oxygen directly?

Which one of the following metals does not react with oxygen directly?

Ti
Fe
Pt
Zn
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UPSC CAPF – 2023
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Platinum (Pt) is a noble metal known for its low reactivity. It does not react directly with oxygen under normal conditions (room temperature). While it can form oxides under extreme conditions or indirectly, direct oxidation like rusting of iron or tarnishing of silver does not occur easily.
Noble metals, such as Platinum, Gold (Au), and Silver (Ag), are resistant to oxidation and corrosion, which is why they are considered precious metals. Titanium (Ti), Iron (Fe), and Zinc (Zn) are reactive metals that readily react with oxygen to form stable oxides. Titanium forms a passive oxide layer that protects it from further corrosion, but the reaction with oxygen does occur. Iron readily forms rust (iron oxides/hydroxides). Zinc forms a protective layer of zinc oxide/carbonate.
The reactivity of metals with oxygen generally decreases across the periodic table from left to right and down within a group. Noble metals are found towards the right side of the d-block and have high ionization energies and positive standard electrode potentials, making them less likely to lose electrons and react with oxidizing agents like oxygen.

5. Cinnabar is an ore of

Cinnabar is an ore of

mercury
zinc
copper
lead
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UPSC CAPF – 2022
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Cinnabar is a mineral with the chemical formula $\text{HgS}$ (mercury(II) sulfide). It is the most common ore from which the element mercury ($\text{Hg}$) is extracted. Historically, it was mined extensively, and its red color made it a valuable pigment (vermilion). Roasting cinnabar in air converts the mercury(II) sulfide to elemental mercury and sulfur dioxide:
$\text{HgS(s)} + \text{O}_2\text{(g)} \rightarrow \text{Hg(g)} + \text{SO}_2\text{(g)}$
– Cinnabar is a mineral composed of mercury sulfide ($\text{HgS}$).
– An ore is a natural occurrence of a rock or sediment which contains sufficient minerals with economically important elements, metals or gems.
– Cinnabar is the primary ore for the extraction of mercury.
Other common ores of the metals listed are:
– Zinc: Sphalerite ($\text{ZnS}$), Calamine ($\text{ZnCO}_3$).
– Copper: Chalcopyrite ($\text{CuFeS}_2$), Malachite ($\text{Cu}_2(\text{CO}_3)(\text{OH})_2$), Azurite ($\text{Cu}_3(\text{CO}_3)_2(\text{OH})_2$).
– Lead: Galena ($\text{PbS}$).

6. Manganese is extracted by heating manganese dioxide with aluminium pow

Manganese is extracted by heating manganese dioxide with aluminium powder. Which one of the following statements with regard to the reaction is correct?

The reaction is exothermic.
The reaction is endothermic.
Manganese is produced as a solid.
Manganese is more reactive than aluminium.
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UPSC CAPF – 2021
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The reaction between manganese dioxide and aluminium powder is a type of thermite reaction. Thermite reactions are highly exothermic, releasing a significant amount of heat.
Thermite reactions involve the reduction of a metal oxide by a more reactive metal (typically aluminium). The general form is Metal Oxide A + Metal B → Metal A + Oxide of Metal B, where Metal B is more reactive than Metal A. These reactions are characterized by their high exothermicity, often producing molten metal.
In this specific reaction, Al is more reactive than Mn, displacing it from MnO2. The equation is 3MnO₂ + 4Al → 2Al₂O₃ + 3Mn + Heat. While Manganese is indeed produced as a solid at room temperature, during the reaction itself, the high temperature can cause the product metal (depending on its melting point and the reaction’s heat) to be in a molten state. However, the statement that the reaction is exothermic is a fundamental property of this reaction type.

7. Which one of the following metals produces hydrogen with cold water?

Which one of the following metals produces hydrogen with cold water?

Silver
Sodium
Copper
Iron
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UPSC CAPF – 2021
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Sodium is a highly reactive alkali metal. It reacts vigorously with cold water, producing hydrogen gas and sodium hydroxide.
The reactivity of metals with water varies. Very reactive metals (like Group 1 alkali metals) react with cold water. Less reactive metals (like zinc or iron) may react with steam but not cold water. Even less reactive metals (like copper, silver, gold) do not react with water at all.
The reaction of sodium with cold water is exothermic and can even ignite the hydrogen produced due to the heat generated. The general reaction is 2M + 2H₂O → 2MOH + H₂ (where M is an alkali metal). Other metals like Potassium and Calcium also react with cold water, while Iron reacts with steam to produce iron oxides and hydrogen.

8. Which one of the following metals does not react with oxygen, water or

Which one of the following metals does not react with oxygen, water or acids?

Na
Cu
Fe
Au
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UPSC CAPF – 2021
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Metals vary widely in their chemical reactivity. Some are highly reactive, readily reacting with oxygen, water, and acids, while others are much less reactive, sometimes referred to as noble metals.
Sodium (Na) is an alkali metal and is extremely reactive, reacting vigorously with oxygen, water, and acids. Copper (Cu) is moderately reactive; it reacts with oxygen to form oxides and with certain acids (like nitric acid or hot sulfuric acid) but is relatively stable in air and water compared to alkali metals. Iron (Fe) is also reactive; it rusts in moist air (reacts with oxygen and water) and reacts with acids. Gold (Au) is a noble metal, known for its low reactivity. It resists reaction with oxygen at normal temperatures, water, and most acids. It can only be dissolved by highly corrosive mixtures like aqua regia (a mixture of nitric acid and hydrochloric acid).
The reactivity series of metals ranks metals according to their reactivity. Gold is very low in the reactivity series, indicating its low tendency to participate in chemical reactions.

9. When calcium metal reacts with sulphuric acid, the reaction stops afte

When calcium metal reacts with sulphuric acid, the reaction stops after a short while. Why?

The reaction of calcium with sulphuric acid is not feasible at room temperature
Formed calcium sulphate is insoluble in water and covers the metal, preventing it from reacting any further
Formed calcium sulphate requires two molecules of water to crystallize as gypsum
Formed calcium sulphate is unstable
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UPSC CAPF – 2021
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The correct answer is B) Formed calcium sulphate is insoluble in water and covers the metal, preventing it from reacting any further.
Calcium is a relatively reactive metal that reacts with acids like sulfuric acid to produce hydrogen gas and a salt: Ca(s) + H₂SO₄(aq) → CaSO₄(s) + H₂(g). However, calcium sulfate (CaSO₄) is sparingly soluble in water, and its solubility is even lower in concentrated sulfuric acid. As the reaction proceeds, a layer of solid calcium sulfate forms on the surface of the calcium metal. This layer acts as a barrier, preventing the sulfuric acid from coming into contact with the underlying calcium metal, effectively stopping or significantly slowing down the reaction after a short while. This phenomenon is known as passivation.
Other metals that exhibit passivation with sulfuric acid include lead (forming insoluble PbSO₄) and barium (forming insoluble BaSO₄). With other acids like hydrochloric acid, calcium reacts vigorously because calcium chloride (CaCl₂) is soluble.

10. Which one of the following minerals is NOT a naturally occurring silic

Which one of the following minerals is NOT a naturally occurring silicate ?

Feldspar
Zeolite
Mica
Bauxite
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UPSC CAPF – 2020
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Bauxite is the principal ore of aluminium and is primarily composed of hydrated aluminium oxides and hydroxides, such as gibbsite, boehmite, and diaspore, often mixed with iron oxides, clay minerals, and quartz. It does not have the silicon-oxygen tetrahedral structure characteristic of silicate minerals. Feldspar, Zeolite, and Mica are all well-known families of naturally occurring silicate minerals.
Silicate minerals are composed of silicon and oxygen, often with other metals, forming structures based on the SiO₄⁴⁻ tetrahedron unit. Non-silicate minerals lack this fundamental structure.
Feldspars are tectosilicates, zeolites are porous tectosilicates, and micas are phyllosilicates (sheet silicates). Bauxite is classified as an oxide mineral.
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