Inorganic Chemistry

Which one among the following oxides has the highest melting point ?

[amp_mcq option1=”Na₂O” option2=”MgO” option3=”Fe₂O₃” option4=”CuO” correct=”option2″]

Among the given options, Magnesium oxide (MgO) has the highest melting point.

Oxides of highly electropositive metals (like those in Group 1 and 2) and transition metals are generally ionic compounds with high melting points due to strong electrostatic forces in the crystal lattice. MgO is a Group 2 metal oxide with high lattice energy primarily due to the +2 and -2 charges of Mg²⁺ and O²⁻ ions and their relatively small ionic radii, resulting in a very high melting point (~2852 °C).

Comparing the options: Na₂O (~1132 °C), MgO (~2852 °C), Fe₂O₃ (~1565 °C, decomposes), CuO (~1326 °C, decomposes). MgO’s melting point is significantly higher than the others listed, making it a refractory material.

Which among the following is the correct composition of Borax ?

[amp_mcq option1=”Sodium, Boron, Magnesium and Hydrogen” option2=”Sodium, Boron, Oxygen and Hydrogen” option3=”Potassium, Boron, Oxygen and Hydrogen” option4=”Sodium, Boron, Nitrogen and Hydrogen” correct=”option2″]

The correct composition of Borax includes Sodium, Boron, Oxygen, and Hydrogen.

Borax is commonly found as the mineral sodium tetraborate decahydrate, with the chemical formula Na₂B₄O₇·10H₂O. This formula clearly shows the presence of Sodium (Na), Boron (B), Oxygen (O), and Hydrogen (H).

The B₄O₇²⁻ anion in borax is actually a complex polyborate ion, often more accurately represented as [B₄O₅(OH)₄]²⁻ in its hydrated forms. The decahydrate contains 10 water molecules of crystallization.

What is the coordination number of Na⁺ and Cl⁻ ions in NaCl lattice ?

[amp_mcq option1=”6, 1″ option2=”1, 6″ option3=”6, 6″ option4=”5, 5″ correct=”option3″]

In the NaCl crystal lattice, both Na⁺ and Cl⁻ ions have a coordination number of 6.

The NaCl crystal structure is a face-centered cubic (FCC) arrangement where each Na⁺ ion is octahedrally surrounded by six Cl⁻ ions, and similarly, each Cl⁻ ion is octahedrally surrounded by six Na⁺ ions.

The coordination number in an ionic lattice refers to the number of oppositely charged ions immediately surrounding a given ion. This coordination number is determined by the relative sizes of the ions and the need to maximize electrostatic attraction while minimizing repulsion.

Which among the following are essential constituents of Portland cement ?

[amp_mcq option1=”Sand, lime, clay” option2=”Silica, alumina, lime” option3=”Silica, lime, graphite powder” option4=”Sand, graphene, clay” correct=”option2″]

Portland cement is primarily made from materials containing calcium oxide (lime), silicon dioxide (silica), aluminum oxide (alumina), and iron oxide. The main raw materials are typically limestone (for lime) and clay or shale (for silica, alumina, and iron). These materials are heated in a kiln to produce clinker, which is then ground into fine powder with a small amount of gypsum added. Option B lists Silica, Alumina, and Lime, which are the essential oxide components derived from these raw materials, forming the bulk of the cement clinker.

The major chemical components of Portland cement clinker are tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate (celite), and tetracalcium aluminoferrite (ferrite). These are formed from the reaction of lime (CaO), silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3) during calcination.

Sand is commonly used as an aggregate in concrete (a mixture of cement, aggregates, and water), but it is not a constituent of cement itself. Graphite powder and graphene are forms of carbon and are not standard components of Portland cement. Clay is a raw material containing silica and alumina, used in cement production, but the essential *constituents* within the clinker are the oxides (silica, alumina, lime, etc.) derived from the raw materials.

Airbags work on the principle of a chemical reaction triggered by the impact producing a gaseous product that causes a sudden volume change. Which one among the following chemical conversions is responsible for this ?

[amp_mcq option1=”Sodium azide into nitrogen gas” option2=”Solid carbon dioxide into gaseous carbon dioxide” option3=”Carbon dioxide into carbon monoxide” option4=”Sudden conversion of gaseous carbon dioxide into carbon monoxide” correct=”option1″]

Modern automotive airbags typically rely on the rapid decomposition of sodium azide (NaN₃). Upon impact, a sensor triggers an electric current that ignites a small amount of a starter compound, which in turn initiates the decomposition of sodium azide. The chemical reaction is: 2 NaN₃(s) → 2 Na(s) + 3 N₂(g). The large volume of nitrogen gas (N₂) produced rapidly inflates the airbag. Potassium nitrate and silicon dioxide are often included to react with the highly reactive sodium metal produced.

The rapid inflation of an airbag is caused by the generation of a large volume of gas from a chemical reaction triggered by impact. Sodium azide decomposing to nitrogen gas is the basis of this process.

The complete reaction mixture in an airbag contains sodium azide, an oxidizer (like potassium nitrate) to react with the sodium produced, and a substance like silicon dioxide or aluminum oxide to react with the products to form harmless slag. This ensures that no harmful substances are released into the car cabin.

Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour ?

[amp_mcq option1=”Oxygen” option2=”Nitrogen” option3=”Water” option4=”Hydrogen” correct=”option3″]

Copper sulphate crystals available in the market are typically copper(II) sulphate pentahydrate (CuSO₄·5H₂O). The blue colour is due to the presence of water molecules coordinated to the copper ions in the crystal lattice. When heated, these crystals lose the water of crystallization, turning into anhydrous copper(II) sulphate (CuSO₄), which is white or off-white. The colour change is a classic demonstration of the role of water of crystallization.

The blue colour of hydrated copper sulphate is caused by the presence of water molecules bound within the crystal structure.

The process of heating hydrated copper sulphate to remove water is an example of dehydration. The reverse process, adding water to anhydrous copper sulphate, will restore the blue colour and is often used as a test for the presence of water. Other metal salts also form coloured hydrates where water of crystallization affects the colour.

Which one of the following is not a pigment?

[amp_mcq option1=”Zinc oxide” option2=”Chalk” option3=”White lead” option4=”Silica” correct=”option4″]

The correct answer is Silica. While finely divided silica can appear white and contribute to opacity, it is not primarily classified or used as a pigment in the same way as Zinc oxide, Chalk, and White lead, which are well-established white pigments used for imparting colour (whiteness) and opacity.

– A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. Pigments are typically solid and ground into fine powder.
– Zinc oxide (ZnO) is a widely used white pigment known as Zinc White.
– Chalk is primarily Calcium carbonate (CaCO₃), which is used as a white pigment and filler.
– White lead (basic lead carbonate, (PbCO₃)₂·Pb(OH)₂) is a dense white pigment historically used in paints, although its use has declined due to toxicity.
– Silica (Silicon dioxide, SiO₂) occurs in many forms. While very fine forms like fumed silica can act as opacifiers and contribute to whiteness and are used as fillers in paints, its primary applications often lie outside of being a dedicated coloring pigment, such as abrasives, drying agents, fillers for controlling rheology or structure, and as a component of glass or ceramics. Compared to the others, its role as a pigment is less central.

The term “pigment” usually refers to a substance added to a material to change its color. While silica is white when powdered, its applications are broader than just coloration, and other options are classic examples of white pigments specifically used for their tinting strength and opacity.

Which one of the following is not an example of a redox reaction?

[amp_mcq option1=”AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl” option2=”2NaH → 2Na + H₂” option3=”4Fe + 3O₂ → 2Fe₂O₃” option4=”CuSO₄ + Zn → Cu + ZnSO₄” correct=”option1″]

The correct answer is A) AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl. This reaction is a double displacement (or hydrolysis) reaction, where no changes in oxidation states occur, unlike redox reactions.

– A redox reaction is a chemical reaction that involves the transfer of electrons, resulting in changes in the oxidation states of atoms.
– Oxidation is an increase in oxidation state (loss of electrons).
– Reduction is a decrease in oxidation state (gain of electrons).
– Let’s analyze the oxidation states in each reaction:
– A) AlCl₃ (+3, -1) + H₂O (+1, -2) → Al(OH)₃ (+3, -2, +1) + HCl (+1, -1). Oxidation states of all elements remain unchanged.
– B) 2NaH (+1, -1) → 2Na (0) + H₂ (0). Na changes from +1 to 0 (reduction), H changes from -1 to 0 (oxidation). Redox.
– C) 4Fe (0) + 3O₂ (0) → 2Fe₂O₃ (+3, -2). Fe changes from 0 to +3 (oxidation), O changes from 0 to -2 (reduction). Redox.
– D) CuSO₄ (+2, -2) + Zn (0) → Cu (0) + ZnSO₄ (+2, -2). Cu changes from +2 to 0 (reduction), Zn changes from 0 to +2 (oxidation). Redox.

Double displacement reactions, such as precipitation, neutralization, and some hydrolysis reactions, are typically non-redox reactions as they involve the exchange of ions without changes in oxidation states.

Which one of the following is a covalent compound?

[amp_mcq option1=”Calcium oxide” option2=”Sodium nitride” option3=”Silicon carbide” option4=”Zinc sulphide” correct=”option3″]

Among the given options, Silicon carbide (SiC) is predominantly a covalent compound.

Covalent compounds are formed by the sharing of electrons between atoms, typically non-metals or metalloids. Ionic compounds are formed by the transfer of electrons between a metal and a non-metal, resulting in the formation of ions held together by electrostatic attraction.

Calcium oxide (CaO), Sodium nitride (Na₃N), and Zinc sulphide (ZnS) are compounds formed between a metal and a non-metal. While ZnS has some covalent character, CaO and Na₃N are strongly ionic. SiC is a ceramic material where silicon and carbon atoms are bonded covalently in a crystal lattice structure, forming a giant covalent network.

Which one of the following is the correct molecular formula of ammonium carbonate if the valency of ammonium ion is (+1) and carbonate anion is (-2) ?

[amp_mcq option1=”(NH₄)₂CO₃” option2=”NH₄(CO₃)₂” option3=”(NH₃)₂CO₃” option4=”NH₄CO₃” correct=”option1″]

To form a neutral compound, the total positive charge from the cations must balance the total negative charge from the anions. Given the valencies, the correct ratio of ammonium ions to carbonate ions needs to be determined.

The valency (or charge) of the ammonium ion (NH₄⁺) is +1. The valency (or charge) of the carbonate anion (CO₃²⁻) is -2. To form a neutral compound, we need a total positive charge equal in magnitude to the total negative charge. If we take two ammonium ions, the total positive charge is 2 * (+1) = +2. If we take one carbonate ion, the total negative charge is 1 * (-2) = -2. The charges +2 and -2 balance to give a neutral compound. Therefore, the formula is (NH₄)₂CO₃, indicating two ammonium ions for every one carbonate ion.

When writing formulas for ionic compounds, the cation is written first, followed by the anion. Subscripts indicate the number of ions required to achieve charge neutrality. If the ion is polyatomic (like NH₄⁺ or CO₃²⁻) and more than one is needed, the ion formula is enclosed in parentheses before the subscript.