Metals, Minerals, Ores: Properties, Uses

Which one among the following metals is not stored under oil ?

[amp_mcq option1=”Sodium” option2=”Rubidium” option3=”Potassium” option4=”Lithium” correct=”option4″]

Alkali metals (Group 1) are highly reactive and readily react with oxygen and moisture in the air. Sodium (Na), Potassium (K), and Rubidium (Rb) are particularly reactive and are stored under inert liquids like kerosene or mineral oil to prevent reactions with air and water. Lithium (Li), while also an alkali metal, is less reactive than Na, K, and Rb. It reacts readily with nitrogen in the air (unlike other alkali metals) but is less reactive with oxygen and water compared to the others. While it is often stored under oil or an inert atmosphere, it is sometimes the exception discussed when comparing storage methods due to its different reactivity profile. Among the given options, Lithium is the metal *least necessarily* stored under oil compared to the others, or has alternative common storage methods.

– Alkali metals are highly reactive.
– Storage under oil or inert atmosphere prevents reaction with air and moisture.
– Lithium’s reactivity and reaction products differ somewhat from heavier alkali metals.

The reactivity of alkali metals increases down the group. Potassium and Rubidium are more reactive than Sodium, which is more reactive than Lithium. Cesium (Cs) is even more reactive than Rubidium. These heavier alkali metals are often stored in evacuated glass ampoules or under inert gas rather than oil due to their extreme reactivity and lower melting points.

In the joining of railway tracks, iron oxide is made to react with

[amp_mcq option1=”Aluminium” option2=”Zinc” option3=”Copper” option4=”Tin” correct=”option1″]

In the joining of railway tracks, iron oxide (rust) is made to react with Aluminium powder. This reaction is the basis of thermite welding.

– The thermite reaction involves the reduction of a metal oxide by a more reactive metal, producing a large amount of heat and molten metal.
– The specific reaction used for rail welding is between iron(III) oxide (Fe₂O₃) and aluminium (Al): 2Al + Fe₂O₃ → Al₂O₃ + 2Fe + Heat.
– The molten iron produced at high temperature fills the gap between the rails, creating a weld.

The thermite process was discovered by Hans Goldschmidt in 1895 and is still used for various welding applications, particularly where electric welding is difficult or impractical, such as railway tracks.

Which one of the following is the correct reactivity order of metals reacting with dilute HCl?

[amp_mcq option1=”Mg > Al > Zn > Fe” option2=”Mg < Al < Zn < Fe" option3="Mg > Zn > Fe > Al” option4=”Fe > Mg > Al > Zn” correct=”option1″]

The reactivity of metals with dilute acids like HCl generally decreases down the reactivity series. Metals above hydrogen in the reactivity series can displace hydrogen from dilute acids. The correct order of reactivity for the given metals is Mg > Al > Zn > Fe. Magnesium is the most reactive among these, followed by Aluminum, then Zinc, and finally Iron.

The reactivity series of metals is determined by their tendency to lose electrons and form positive ions. Metals higher in the series are more reactive and can displace less reactive metals (or hydrogen from acids) from their compounds. The order of reactivity of these common metals is Mg > Al > Zn > Fe.

While this is the general order, the rate of reaction can sometimes be affected by factors like surface passivation (e.g., Aluminum forming a protective oxide layer), but the inherent reactivity order based on standard electrode potentials is Mg > Al > Zn > Fe.

What is the name of the process that converts sulphide ores into oxides by heating strongly in the presence of excess air ?

[amp_mcq option1=”Calcination” option2=”Roasting” option3=”Smelting” option4=”Incineration” correct=”option2″]

The process described involves heating a sulphide ore strongly in the presence of excess air to convert it into an oxide. This process is known as roasting. The general reaction is:
2MS(s) + 3O₂(g) → 2MO(s) + 2SO₂(g) (where M is the metal)
For example, roasting of zinc sulphide: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g).
Calcination involves heating a carbonate or hydroxide ore strongly in limited or no air to decompose it into an oxide.
Smelting is a process of using heat to extract a metal from its ore, often involving a reducing agent, and doesn’t specifically focus on converting sulphide to oxide in air.
Incineration is the burning of waste.
Therefore, roasting is the correct term for converting sulphide ores to oxides by heating in excess air.

– Roasting is specifically applied to sulphide ores.
– It requires heating in the presence of excess air.
– It converts the sulphide into a metal oxide and releases sulphur dioxide.

Oxide ores are generally easier to reduce to metals than sulphide ores. Hence, sulphide ores are often first converted to oxides by roasting before reduction processes are applied. Calcination is commonly used for carbonate ores (e.g., CaCO₃ to CaO).

When copper reacts with moist carbon dioxide (CO₂) in air, it forms a green coating of which one of the following compounds ?

[amp_mcq option1=”Cupric carbonate” option2=”Cuprous oxide” option3=”Cupric oxide” option4=”Copper sulphate” correct=”option1″]

When copper is exposed to the atmosphere, it reacts with components in the air, including moisture (H₂O), oxygen (O₂), and carbon dioxide (CO₂). This reaction leads to the formation of a green layer known as patina. The primary chemical compound responsible for this green colour is basic copper carbonate, with the formula generally represented as Cu₂(OH)₂CO₃ (malachite) or Cu₃(OH)₂(CO₃)₂ (azurite, blue, often found mixed with malachite) or a mixture of Cu(OH)₂ and CuCO₃. The term “cupric carbonate” refers to Copper(II) carbonate, CuCO₃. While the patina is technically *basic* copper carbonate, Cu₂(OH)₂CO₃, which is a compound containing both hydroxide and carbonate, among the given options, “Cupric carbonate” is the closest description of the carbonate component that gives the green colour, often formed via the reaction:
2Cu(s) + H₂O(g) + CO₂(g) + O₂(g) → Cu₂(OH)₂CO₃(s)
Cupric means Copper(II). Option A correctly identifies the compound as a form of copper carbonate.

– The green coating on copper exposed to air is called patina.
– Patina is formed by the reaction of copper with moisture, oxygen, and carbon dioxide.
– The main component of green patina is basic copper carbonate.

Other compounds listed: Cuprous oxide (Cu₂O) is reddish-brown. Cupric oxide (CuO) is black. Copper sulphate (CuSO₄) is a blue crystalline solid or white powder and is soluble in water; it wouldn’t typically form a persistent green coating from atmospheric exposure alone unless sulphur dioxide is also present, forming basic copper sulfate.

Which one of the following does not form oxide on reaction with oxygen?

[amp_mcq option1=”Magnesium” option2=”Lead” option3=”Tin” option4=”Silver” correct=”option4″]

Silver (Ag) is a noble metal and is relatively unreactive. While many metals readily react with oxygen to form oxides, silver does not easily form an oxide when exposed to oxygen in the air under normal conditions.

Reactivity with oxygen varies among metals. Highly reactive metals like Magnesium react readily, forming stable oxides. Lead and Tin are less reactive than Magnesium but still form oxides. Silver is one of the least reactive metals and does not readily oxidize.

Silver tarnishes when exposed to sulfur compounds in the air, forming silver sulfide (Ag₂S), which appears as a black layer. Direct reaction with oxygen to form silver oxide (Ag₂O) requires specific conditions, such as heating at lower temperatures (around 160-200°C) and the oxide decomposes at higher temperatures.

Silver articles turn black when kept in the open for longer time due to the formation of

[amp_mcq option1=”H₂S” option2=”AgS” option3=”AgSO₄” option4=”Ag₂S” correct=”option4″]

Silver articles tarnish and turn black when exposed to the air for a prolonged period. This tarnishing is primarily due to the reaction of silver (Ag) with hydrogen sulfide (H₂S) gas present in the atmosphere (often produced by the decomposition of organic matter or industrial pollution). This reaction forms a layer of black silver sulfide (Ag₂S) on the surface of the silver article. The overall reaction is 2Ag + H₂S → Ag₂S + H₂.

Silver tarnish is caused by the formation of silver sulfide (Ag₂S) through the reaction of silver with hydrogen sulfide in the air.

H₂S is the reactant from the air. AgS is not the correct chemical formula for silver sulfide (silver has a +1 charge, sulfide has a -2 charge, so Ag₂S is formed). AgSO₄ is silver sulfate, which would typically be formed by a reaction with sulfuric acid or sulfates, not the common cause of black tarnish in air. The black deposit is definitively silver sulfide (Ag₂S).

Which one of the following is the correct order of reactivity of Mg, Al, Zn and Fe with HCl?

[amp_mcq option1=”Mg > Al > Zn > Fe” option2=”Mg > Al > Fe > Zn” option3=”Zn > Fe > Mg > Al” option4=”Fe > Al > Zn > Mg” correct=”option1″]

The reactivity of metals with dilute acids like HCl to displace hydrogen depends on the position of the metal in the reactivity series. Metals higher in the series are more reactive.

The standard reactivity series (based on standard electrode potentials) places these metals in the order of decreasing reactivity as Mg > Al > Zn > Fe > H. Therefore, their reactivity with HCl follows the same order: Mg > Al > Zn > Fe.

While Aluminium is theoretically more reactive than Zinc, its reaction with acids can sometimes be slower than expected due to the formation of a protective oxide layer on its surface. However, the fundamental order of reactivity based on standard potentials remains Mg > Al > Zn > Fe.

Which of the following statements are true for the reaction of Fe₂O₃ with aluminium?

• 1. It is known as the ‘thermite reaction’.
• 2. The heat evolved is used for welding purpose.
• 3. Aluminium metal acts as an oxidizing agent.
• 4. Molten Fe and Al are formed at the end of the reaction.

Select the correct answer using the code given below.

[amp_mcq option1=”1 and 2″ option2=”1 and 3″ option3=”2 and 4″ option4=”1 and 4″ correct=”option1″]

The reaction of Fe₂O₃ with aluminium is a highly exothermic displacement reaction where aluminium, being more reactive than iron, reduces iron(III) oxide to molten iron. The balanced chemical equation is 2Al + Fe₂O₃ → Al₂O₃ + 2Fe + Heat.

– Statement 1 is correct: This reaction is famously known as the thermite reaction.
– Statement 2 is correct: The large amount of heat produced in the thermite reaction results in molten iron, which is used for welding broken railway tracks or cracked machine parts (thermite welding).
– Statement 3 is incorrect: Aluminium acts as a reducing agent because it removes oxygen from Fe₂O₃. Iron(III) oxide (Fe₂O₃) acts as the oxidizing agent.
– Statement 4 is incorrect: Molten iron (Fe) is formed at the end of the reaction. Aluminium is converted to aluminium oxide (Al₂O₃), not molten aluminium metal.

The thermite reaction involves a redox process. Aluminium is oxidized (gains oxygen), and iron is reduced (loses oxygen). The reaction produces a significant amount of heat, reaching temperatures up to 2500°C, which is why the iron is produced in a molten state.