Inorganic Chemistry

What is the colour of the precipitate obtained by passing CO₂ gas through lime water ?

[amp_mcq option1=”Green” option2=”Blue” option3=”White” option4=”Brown” correct=”option3″]

Lime water is an aqueous solution of calcium hydroxide (Ca(OH)₂). When carbon dioxide (CO₂) gas is passed through lime water, it reacts with calcium hydroxide to form calcium carbonate (CaCO₃) and water. Calcium carbonate is insoluble in water and precipitates out as a fine suspension, which appears white.

– Reaction: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
– Calcium carbonate (CaCO₃) is the precipitate formed.
– Calcium carbonate is a white solid.

If CO₂ is passed through lime water for a prolonged period, the white precipitate of calcium carbonate dissolves as it reacts further with CO₂ and water to form soluble calcium bicarbonate (Ca(HCO₃)₂): CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq).

What is the number of water molecules present in a Ferrous Sulphate crystal ?

[amp_mcq option1=”1″ option2=”3″ option3=”5″ option4=”7″ correct=”option4″]

Ferrous Sulphate commonly exists as a hydrated salt known as green vitriol. The chemical formula for this hydrated form is FeSO₄·7H₂O. This indicates that each formula unit of ferrous sulphate is associated with 7 molecules of water of crystallization.

– Ferrous Sulphate forms hydrated crystals.
– The most common hydrate is the heptahydrate (FeSO₄·7H₂O).

Other less common hydrates of ferrous sulphate also exist, such as the monohydrate (FeSO₄·H₂O) and tetrahydrate (FeSO₄·4H₂O). However, unless otherwise specified, ferrous sulphate crystals usually refer to the heptahydrate.

Which one of the following compounds is used in ‘black and white’ photography ?

[amp_mcq option1=”AgF” option2=”AgBr” option3=”AgCl” option4=”Ag₂SO₄” correct=”option2″]

Silver halides are widely used in ‘black and white’ photography due to their sensitivity to light. When light strikes a silver halide crystal, it initiates a chemical change that can later be developed into a visible image. Silver bromide (AgBr) is the most common silver halide used in photographic films, although silver chloride (AgCl) and silver iodide (AgI) are also used, particularly in photographic papers. Among the options provided, AgBr is a standard compound used in black and white photography.

– Silver halides are photosensitive compounds.
– AgBr is widely used in photographic films.

The photographic process involves exposing the silver halide crystals on film or paper to light, creating a latent image. This image is then developed using chemical solutions which convert the exposed silver halide into metallic silver (appearing black). Unexposed silver halide is removed during fixing.

Chalk and marble are different forms of

[amp_mcq option1=”Calcium hydrogen carbonate” option2=”Calcium carbonate” option3=”Calcium acetate” option4=”Sodium carbonate” correct=”option2″]

Chalk and marble are both naturally occurring forms of calcium carbonate (CaCO₃).

– Calcium carbonate is a common substance found in rocks as the minerals calcite and aragonite.
– Marble is a metamorphic rock composed primarily of recrystallized carbonate minerals, most commonly calcite.
– Chalk is a soft, white, porous sedimentary rock, a form of limestone composed primarily of the mineral calcite.

– While chemically the same (CaCO₃), chalk, limestone, and marble differ in their crystal structure, formation process, and physical properties like hardness and texture.
– Calcium carbonate is also the main component of shells of marine organisms, snails, and eggshells.

Which one of the following is not a monatomic element ?

[amp_mcq option1=”Copper” option2=”Helium” option3=”Iodine” option4=”Barium” correct=”option3″]

The correct answer is C) Iodine.

A monatomic element is an element that exists stably as individual atoms rather than in molecules composed of two or more atoms. Helium (He) is a noble gas and exists as single atoms, making it monatomic. Copper (Cu) and Barium (Ba) are metals that exist as lattices of individual atoms in their solid state. Iodine (I) is a halogen that exists as a diatomic molecule ($I_2$) in its standard solid state and gaseous state (when it sublimes). Thus, Iodine is not a monatomic element; it is diatomic.

Noble gases (He, Ne, Ar, Kr, Xe, Rn) are the most common examples of naturally occurring monatomic elements. While metals exist as individual atoms in their solid structure, the term “monatomic” is most frequently used to contrast with diatomic or polyatomic molecular elements like $O_2$, $N_2$, $S_8$, $P_4$, and halogens ($F_2$, $Cl_2$, $Br_2$, $I_2$). Among the given options, Iodine is the only one that exists as a diatomic molecule in its elemental form.

Which one of the following is termed as ‘Dry ice’ ?

[amp_mcq option1=”Ice present in ice-cream” option2=”Solid water at Antarctica” option3=”Solid state of carbon dioxide” option4=”Solid water of ionosphere” correct=”option3″]

‘Dry ice’ is the common name for solid carbon dioxide ($\text{CO}_2$). At standard atmospheric pressure, solid carbon dioxide does not melt into a liquid but instead undergoes sublimation, transitioning directly from the solid phase to the gaseous phase. This is why it is called “dry ice,” as it appears as ice but doesn’t produce liquid water upon warming.
A) Ice present in ice-cream is frozen water.
B) Solid water at Antarctica is frozen water (H₂O ice).
C) Solid state of carbon dioxide is indeed dry ice.
D) Solid water of ionosphere is not a recognized term for dry ice; the ionosphere is a layer of the atmosphere where water exists primarily as gas or plasma, not solid ice.

– Dry ice is solid $\text{CO}_2$.
– Dry ice sublimes (solid to gas transition) at atmospheric pressure.
– Common ice is frozen water (solid H₂O).

Dry ice is much colder than water ice, with a sublimation temperature of -78.5 °C (-109.3 °F) at atmospheric pressure. It is used for cooling, freezing, and fog effects (by causing water vapor in the air to condense).

The raw materials used for the manufacture of Portland cement are

[amp_mcq option1=”Lime, silica and sulphur dioxide” option2=”Lime, silica and carbon dioxide” option3=”Lime, silica and alumina” option4=”Lime, silica and boric acid” correct=”option3″]

The primary raw materials used for the manufacture of Portland cement clinker are calcium oxide (usually derived from limestone or chalk), silicon dioxide (silica, typically from clay or sand), and aluminium oxide (alumina, from clay or bauxite). These materials are mixed in specific proportions, heated in a kiln to high temperatures (calcination and clinkering), and then ground to produce cement. Option C lists lime, silica, and alumina, which are the essential components derived from these raw materials.

– The main chemical components of Portland cement are calcium silicates, calcium aluminates, and calcium ferroaluminates.
– These compounds are formed by heating a mixture of calcareous material (like limestone, source of CaO) and argillaceous material (like clay, source of SiO2 and Al2O3) in a kiln.
– Minor components like iron oxide and gypsum (added during grinding) are also involved but lime, silica, and alumina are the core raw material oxides.

– Limestone (CaCO3) is heated to produce lime (CaO) and carbon dioxide (CO2).
– Clay provides silica (SiO2), alumina (Al2O3), and iron(III) oxide (Fe2O3).
– Sulphur dioxide and boric acid are not standard raw materials for Portland cement. Carbon dioxide is a byproduct of the calcination process, not a raw material that is added.

Which one of the following statements about glass is not correct?

[amp_mcq option1=”Glass is often said to be a supercooled liquid.” option2=”Glass has no definite melting point.” option3=”Soda glass is harder than pyrex glass.” option4=”Boron is present in pyrex glass.” correct=”option3″]

The correct option is C) Soda glass is harder than pyrex glass. This statement is incorrect. Pyrex glass (borosilicate glass) is generally harder and more durable than soda-lime glass (soda glass).

A) Glass is an amorphous solid, lacking a long-range ordered crystalline structure. Its structure is similar to a liquid’s, and it becomes increasingly viscous as it cools, without a sharp transition like freezing. Hence, it is often described as a supercooled liquid or an amorphous solid. This statement is generally considered correct.
B) Due to its amorphous nature, glass does not have a specific melting point. It softens gradually over a range of temperatures. This statement is correct.
C) Soda-lime glass (soda glass) is the most common type of glass (window panes, bottles). Pyrex is a brand of borosilicate glass, which contains boron oxide (B₂O₃) in addition to silica. The addition of boron oxide significantly changes the properties, making it more resistant to thermal shock and chemical corrosion, and generally harder and more resistant to scratches compared to soda-lime glass. Therefore, soda glass is *not* harder than pyrex glass; it is softer.
D) Pyrex glass is a type of borosilicate glass, meaning it contains boron (specifically in the form of boron oxide). This statement is correct.

The composition differences between soda-lime glass and borosilicate glass lead to their different properties. Soda-lime glass typically contains silicon dioxide (silica, ~70%), sodium oxide (soda), and calcium oxide (lime). Borosilicate glass typically contains silica (~80%), boron oxide (~13%), and smaller amounts of sodium oxide and aluminium oxide. The higher silica and boron content contribute to the superior properties of borosilicate glass.

Which one of the following compounds does not exhibit a different oxidation number of the same element?

[amp_mcq option1=”Pb₃O₄” option2=”Fe₃O₄” option3=”Fe₂O₃” option4=”Mn₃O₄” correct=”option3″]

The correct option is C) Fe₂O₃. In Fe₂O₃, iron exists in only one oxidation state.

We need to determine the oxidation state of the metal element in each compound:
A) Pb₃O₄ is a mixed oxide, often written as 2PbO·PbO₂. In PbO, O is -2, so Pb is +2. In PbO₂, O is -2 (total -4 for 2 O atoms), so Pb is +4. Lead has oxidation states +2 and +4 in Pb₃O₄.
B) Fe₃O₄ is a mixed oxide, FeO·Fe₂O₃. In FeO, O is -2, so Fe is +2. In Fe₂O₃, O is -2 (total -6 for 3 O atoms), so 2 Fe atoms are +6, meaning each Fe is +3. Iron has oxidation states +2 and +3 in Fe₃O₄.
C) Fe₂O₃: Assuming oxygen is -2, the total charge from 3 oxygen atoms is 3 * (-2) = -6. For the compound to be neutral, the total charge from 2 iron atoms must be +6. Thus, the oxidation state of each Fe atom is +6 / 2 = +3. All iron atoms in Fe₂O₃ are in the +3 oxidation state.
D) Mn₃O₄ is a mixed oxide, MnO·Mn₂O₃. In MnO, O is -2, so Mn is +2. In Mn₂O₃, O is -2 (total -6 for 3 O atoms), so 2 Mn atoms are +6, meaning each Mn is +3. Manganese has oxidation states +2 and +3 in Mn₃O₄.

Mixed oxides like Pb₃O₄, Fe₃O₄, and Mn₃O₄ contain the metal element in more than one oxidation state combined within the same compound structure. Simple binary oxides like Fe₂O₃ (or FeO, FeO₂, etc.) typically have the metal in a single oxidation state throughout the compound.

Which one of the following is the chemical formula of gypsum?

[amp_mcq option1=”CaSO₄·2H₂O” option2=”Ca₂SiO₄” option3=”2CaSO₄·H₂O” option4=”CaSO₄” correct=”option1″]

Gypsum is a mineral commonly found in evaporite deposits. Its chemical composition is calcium sulfate dihydrate, meaning it contains calcium sulfate (CaSO₄) and two molecules of water of crystallization per formula unit. The chemical formula for gypsum is CaSO₄·2H₂O.

The degree of hydration of calcium sulfate determines whether it is gypsum (dihydrate), plaster of Paris (hemihydrate), or anhydrite (anhydrous).

When gypsum (CaSO₄·2H₂O) is heated, it loses water to form calcium sulfate hemihydrate (CaSO₄·½H₂O), which is commonly known as Plaster of Paris. Further heating removes all water, resulting in anhydrous calcium sulfate (CaSO₄), or anhydrite. Gypsum is widely used in plaster, drywall (gypsum board), cement production, and as a soil conditioner.