Inorganic Chemistry Archives

11. Which one among the following is used in the manufacture of ultra-viol

Which one among the following is used in the manufacture of ultra-violet protective glasses ?

Aluminium oxide

Tungsten oxide

Molybdenum oxide

Cerium oxide

This question was previously asked in

UPSC CAPF – 2024

Download PDF Attempt Online

The correct option is D. Cerium oxide is commonly used as an additive in glass manufacturing to absorb ultraviolet radiation, thus producing ultra-violet protective glasses.

– Certain metal oxides, when added to glass, can impart specific optical properties, including the absorption of UV light.
– Cerium oxide (CeO₂) is particularly effective at absorbing UV radiation across the spectrum relevant for protecting eyes and materials from UV damage.

While other oxides can affect glass properties, cerium oxide is specifically known and widely used for its UV absorption capabilities in glasses for spectacles, laboratory ware, and architectural uses.

12. Which among the following are the main ingredients for manufacturing o

Which among the following are the main ingredients for manufacturing of glass ?

Silica, sodium carbonate, borax, alumina and cullets

Iron oxide, lead, sodium bicarbonate, alumina and cullets

Magnesium carbonate, alumina, silica and cullets

Iron oxide, sodium, alumina, silica and cullets

This question was previously asked in

UPSC CAPF – 2024

Download PDF Attempt Online

The correct option is A. The main ingredients for manufacturing common glass (soda-lime glass) are silica, sodium carbonate (soda ash), and calcium carbonate (limestone). Option A includes silica and sodium carbonate, along with other common additives and components used in glass manufacturing.

– Silica (sand) is the primary component, forming the glass structure.
– Sodium carbonate (soda ash) is added to lower the melting point of silica. It decomposes to sodium oxide (Na₂O) during heating.
– Calcium carbonate (limestone) is added to improve durability and prevent the glass from dissolving in water. It decomposes to calcium oxide (CaO) during heating.
– Alumina (aluminium oxide) is a common additive to increase strength, chemical resistance, and reduce devitrification.
– Borax (sodium borate) is used in the manufacture of borosilicate glass, which has high thermal resistance. Its presence in option A suggests a broader view of glass manufacturing ingredients beyond just standard soda-lime glass.
– Cullets are recycled glass added to the batch mixture. They act as a flux, reducing the melting temperature and saving energy.

While standard soda-lime glass primarily uses silica, sodium carbonate, and calcium carbonate, option A provides a list that includes key primary components and common additives like alumina and borax (for specific glass types), along with cullets which are universally used in modern glass production. Options B, C, and D contain inaccuracies like elemental sodium or less common primary components.

13. Which one of the following statements is not correct regarding the set

Which one of the following statements is not correct regarding the setting of cement?

The addition of a small percentage of gypsum (CaSO4) lengthens the setting period of cement.

According to the colloidal theory, gels of hydrated silicates are formed and when these gels harden, the set cement loses strength.

Tricalcium silicate is responsible for initial setting of cement.

Dicalcium silicate and tricalcium silicate are responsible for the final strength which occurs in about a year.

This question was previously asked in

UPSC CAPF – 2023

Download PDF Attempt Online

The incorrect statement is that according to the colloidal theory, gels harden and the set cement loses strength. When the gels formed during the hydration of cement silicates harden, they form a rigid structure that gives the set cement its strength. Therefore, hardening of gels leads to an *increase* in strength, not a loss.

The setting and hardening of cement are complex processes involving the hydration of its components. The colloidal theory describes the formation of hydration products as gels that eventually solidify. Gypsum (CaSO₄·2H₂O) is added to cement clinker to retard the setting time, preventing flash setting and allowing sufficient time for mixing, placing, and finishing. Tricalcium silicate (C₃S) hydrates relatively quickly and is primarily responsible for the initial set and early strength. Dicalcium silicate (C₂S) hydrates slowly and contributes significantly to the long-term strength gain of concrete.

The main components of Portland cement clinker are tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate (celite), and tetracalcium aluminoferrite (ferrite). The hydration reactions of these compounds produce hydrated calcium silicates (C-S-H gel) and calcium hydroxide, which are the main products responsible for binding the aggregates together and providing strength. The C-S-H gel is a colloidal substance that hardens over time.

14. Consider the following redox reaction: 2Cu2O (s) + Cu2S (s) —— 6Cu (s)

Consider the following redox reaction:
2Cu2O (s) + Cu2S (s) —— 6Cu (s) + SO2 (g)
Identify the species among the following acting as oxidant and reductant, respectively:

Cu(I) and S of Cu2S

Cu and S of SO2

Cu and O of SO2

Cu(I) and O of SO2

This question was previously asked in

UPSC CAPF – 2023

Download PDF Attempt Online

In the reaction 2Cu₂O (s) + Cu₂S (s) → 6Cu (s) + SO₂ (g), the oxidation states are as follows:
In Cu₂O, Cu is +1, O is -2.
In Cu₂S, Cu is +1, S is -2.
In Cu, Cu is 0.
In SO₂, S is +4, O is -2.
Cu changes from +1 to 0, so it is reduced. The species causing reduction (oxidant) contains Cu(+1). Both Cu₂O and Cu₂S contain Cu(+1).
S changes from -2 (in Cu₂S) to +4 (in SO₂), so it is oxidized. The species causing oxidation (reductant) is Cu₂S, specifically the S atom within it.
Thus, Cu(I) acts as the oxidant and S of Cu₂S acts as the reductant.

An oxidant (oxidizing agent) is a substance that accepts electrons and is itself reduced. A reductant (reducing agent) is a substance that donates electrons and is itself oxidized. In this reaction, Cu(I) gains electrons to become Cu(0), hence Cu(I) is the oxidant. S(-2) loses electrons to become S(+4), hence S(-2) is the reductant.

This is a self-reduction reaction where the same element (Copper) is present in both reactants and is reduced, while another element (Sulfur) is oxidized. Specifically, Copper from both Cu₂O and Cu₂S is reduced. The sulfur from Cu₂S is oxidized. Therefore, Cu(I) collectively from the reactants acts as the oxidant, and S in Cu₂S acts as the reductant.

15. Borax is prepared from

Borax is prepared from

calcium carbonate

magnesium carbonate

potassium carbonate

sodium carbonate

This question was previously asked in

UPSC CAPF – 2022

Download PDF Attempt Online

Borax is sodium tetraborate decahydrate ($\text{Na}_2\text{B}_4\text{O}_7\cdot10\text{H}_2\text{O}$). It is a compound of sodium and boron. While industrially it is often extracted from naturally occurring borate minerals like kernite or colemanite, it can also be synthesized. One method of synthesizing borax in the lab involves reacting boric acid ($\text{H}_3\text{BO}_3$) with a sodium compound. Among the given options, sodium carbonate ($\text{Na}_2\text{CO}_3$) is a common reactant used in the preparation of borax from boric acid. The reaction is:
$4\text{H}_3\text{BO}_3 + \text{Na}_2\text{CO}_3 \rightarrow \text{Na}_2\text{B}_4\text{O}_7 + 6\text{H}_2\text{O} + \text{CO}_2$
This yields anhydrous sodium tetraborate, which can then be hydrated to form borax. Given the options, sodium carbonate is the most suitable precursor listed for the preparation of borax.

– Borax is a sodium borate compound.
– Its preparation often involves a sodium source and a boron source.
– Sodium carbonate is a common sodium source used in synthesizing borax from boric acid.

Other sodium compounds like sodium hydroxide ($\text{NaOH}$) can also be used to react with boric acid to produce borax, but $\text{Na}_2\text{CO}_3$ is explicitly listed as an option. Borax is an important boron compound used in various applications, including detergents, cosmetics, and as a flux in metallurgy.

16. Which one of the following metal oxides does not usually react with so

Which one of the following metal oxides does not usually react with sodium hydroxide?

Copper oxide

Aluminium oxide

Potassium oxide

Calcium oxide

This question was previously asked in

UPSC CAPF – 2021

Download PDF Attempt Online

The correct answer is A) Copper oxide.

Sodium hydroxide (NaOH) is a strong base. Basic metal oxides react with acids, and acidic oxides react with bases. Amphoteric oxides react with both acids and strong bases.
Aluminium oxide (Al₂O₃) is an amphoteric oxide and reacts with sodium hydroxide: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (at high temperature/concentration) or Al₂O₃ + 6NaOH + 3H₂O → 2Na₃[Al(OH)₆] (in aqueous solution).
Potassium oxide (K₂O) and Calcium oxide (CaO) are basic oxides. They react vigorously with water to form potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂), respectively, which are strong bases. Being bases, KOH and Ca(OH)₂ do not react with another base like NaOH.
Copper oxide (CuO) is also a basic oxide. It does not react with water and does not react with sodium hydroxide solution under usual conditions.
Among the given options, Aluminium oxide reacts with NaOH. Potassium oxide and Calcium oxide react with water to form hydroxides that do not react with NaOH. Copper oxide is a basic oxide that neither reacts significantly with water nor with NaOH solution under usual conditions. Therefore, Copper oxide is the one that does not usually react with sodium hydroxide.

Reactivity of metal oxides with bases depends on their acidic, basic, or amphoteric nature. Oxides of highly electropositive metals (Group 1 & 2) are strongly basic. Oxides of transition metals can be basic, amphoteric, or even acidic depending on the oxidation state. Oxides of metalloids and non-metals are typically amphoteric or acidic.

17. If the formula of the sodium salt of an anion X is Na₂X, then the form

If the formula of the sodium salt of an anion X is Na₂X, then the formula of its aluminium salt would be

AlX

AlX₂

Al₂X₃

AlX₃

This question was previously asked in

UPSC CAPF – 2019

Download PDF Attempt Online

The correct answer is C, Al₂X₃.

The formula Na₂X indicates that the anion X has a charge of -2 (X²⁻) because sodium (Na) has a charge of +1, and there are two sodium ions balancing the charge of one X anion (2 * +1 + charge of X = 0, so charge of X = -2). Aluminium (Al) forms ions with a charge of +3 (Al³⁺).

To form a neutral compound between Al³⁺ and X²⁻, the total positive charge must equal the total negative charge. The least common multiple of the absolute charges (3 and 2) is 6. We need two Al³⁺ ions to get a total positive charge of +6 (2 * +3) and three X²⁻ ions to get a total negative charge of -6 (3 * -2). Therefore, the formula for the aluminium salt of anion X is Al₂X₃.

18. Which one of the following is used for water softening ?

Which one of the following is used for water softening ?

Mg(HCO3)2

Na3PO4

Na6P6O18

Na2HPO4

This question was previously asked in

UPSC CAPF – 2019

Download PDF Attempt Online

The correct answer is C, Na₆P₆O₁₈.

Na₆P₆O₁₈ is Sodium Hexametaphosphate, also known commercially as Calgon. It is a complex phosphate widely used as a water softening agent because it forms soluble complexes with calcium and magnesium ions, preventing them from precipitating and causing hardness.

Hard water contains high concentrations of dissolved minerals, particularly calcium (Ca²⁺) and magnesium (Mg²⁺) ions. Water softening aims to remove or neutralize these ions. Sodium salts like sodium hexametaphosphate sequester these ions, effectively “softening” the water. Sodium phosphate (Na₃PO₄) can also be used to precipitate hard ions, but hexametaphosphate is particularly effective due to its chelating ability.

19. Quartz is extensively used as a piezo electric material. It contains

Quartz is extensively used as a piezo electric material. It contains

This question was previously asked in

UPSC CAPF – 2019

Download PDF Attempt Online

The correct answer is B, Si.

Quartz is a crystalline mineral composed of silicon and oxygen atoms. Its chemical formula is SiO₂ (silicon dioxide). It is extensively used as a piezoelectric material due to its ability to generate an electrical charge when subjected to mechanical stress, and vice versa.

Piezoelectricity is a property of certain materials like quartz, where mechanical energy can be converted into electrical energy and vice versa. This property makes quartz useful in oscillators, sensors, and other electronic components.

20. Carborundum is used as an abrasive, because it

Carborundum is used as an abrasive, because it

has high thermal conductivity

has low coefficient of expansion

has high chemical stability

is extremely hard

This question was previously asked in

UPSC CAPF – 2017

Download PDF Attempt Online

The correct option is D.

Carborundum, also known as Silicon Carbide (SiC), is widely used as an abrasive primarily because it is extremely hard. Abrasive materials work by scratching or grinding away the surface of other materials, a process that requires the abrasive to be harder than the material being abraded. Carborundum is one of the hardest known materials, ranking high on the Mohs scale of hardness (around 9-9.5), making it effective for grinding and cutting hard substances.

While carborundum possesses other properties listed, such as high thermal conductivity (A) and high chemical stability (C), these properties are not the primary reason for its use as an abrasive. Low coefficient of expansion (B) contributes to its thermal shock resistance, useful in high-temperature applications, but is not the fundamental reason for its abrasiveness.