All questions of Nitrogen for SSS 2 Exam

HNO3, also known as Nitric Acid, is a highly corrosive and reactive compound that is commonly used in various industries and laboratory applications. In its gaseous state, the HNO3 molecule adopts a planar shape.

Explanation:
1. Molecular Formula:
- The molecular formula of Nitric Acid is HNO3.
- This means that the molecule consists of one hydrogen atom (H), one nitrogen atom (N), and three oxygen atoms (O).

2. Lewis Structure:
- To determine the shape of the molecule, we first need to draw the Lewis structure.
- The Lewis structure of HNO3 shows that the central nitrogen atom is bonded to three oxygen atoms.
- The nitrogen atom has a lone pair of electrons, and each oxygen atom has two lone pairs of electrons.
- The Lewis structure can be represented as follows:

O
//
H - N - O
\\
O

3. Electron Pair Arrangement:
- The electron pair arrangement for HNO3 is trigonal planar.
- This means that the three oxygen atoms and the lone pair of electrons on the nitrogen atom are arranged in a flat plane around the central nitrogen atom.

4. Molecular Geometry:
- The molecular geometry is determined by the arrangement of the bonded atoms.
- In HNO3, the three oxygen atoms are bonded to the nitrogen atom, resulting in a trigonal planar molecular geometry.
- The lone pair of electrons on the nitrogen atom also contributes to the overall shape of the molecule.

5. Conclusion:
- Based on the Lewis structure, electron pair arrangement, and molecular geometry, the HNO3 molecule adopts a planar shape in its gaseous state.
- This means that the three oxygen atoms and the lone pair of electrons on the nitrogen atom are arranged in a flat plane around the central nitrogen atom.

Selenium is the group 16 element that has 8 allotropic forms. Let's break down the answer and explain it in detail.

Allotropy refers to the existence of an element in two or more different physical forms, known as allotropes, in the same state. These allotropes have different molecular structures and properties.

Sulphur, oxygen, selenium, and polonium are all group 16 elements, also known as the chalcogens. Group 16 elements have six valence electrons and tend to form compounds with a -2 oxidation state.

Here's why selenium is the correct answer:

1. Sulphur:
Sulphur is well-known for its allotropes. It has several different forms, such as rhombic sulphur, monoclinic sulphur, and plastic sulphur. However, it does not have 8 allotropic forms, so it is not the correct answer.

2. Oxygen:
Oxygen is another group 16 element, but it primarily exists as a diatomic molecule (O2) in its most stable form. While it can form other compounds like ozone (O3), it does not have 8 allotropic forms, so it is not the correct answer.

3. Selenium:
Selenium is a semi-metal that has 8 known allotropic forms. These forms include gray selenium, red selenium, black selenium, vitreous selenium, crystalline selenium, metallic selenium, fibrous selenium, and amorphous selenium. Each form has a different molecular structure and physical properties.

4. Polonium:
Polonium is a radioactive element and is the heaviest of the group 16 elements. It is primarily known for its alpha particle emission and radioactive decay. However, it does not have 8 allotropic forms, so it is not the correct answer.

In conclusion, among the group 16 elements, selenium is the element that has 8 allotropic forms. These forms exhibit different molecular structures and properties, making selenium a fascinating element to study.

The correct order of reactivity of Group 16 elements is as follows:

1) Oxygen (O)
2) Sulfur (S)
3) Selenium (Se)
4) Tellurium (Te)
5) Polonium (Po)

This order is based on the ability of the elements to gain electrons and form stable anions. Oxygen is the most reactive element in Group 16 because it has the highest electronegativity and strongly attracts electrons. As you move down the group, the reactivity decreases because the atomic size increases and the attraction for electrons decreases.

Photosensitive elements are materials that exhibit a change in electrical resistance when exposed to light. They are commonly used in various applications such as photography, photodiodes, solar cells, and light sensors.

One example of a photosensitive element is Selenium (Se). Selenium is a nonmetal element that is often used in photocopiers and xerography machines. It is a semiconductor material with unique properties that make it suitable for photosensitive applications.

Here are some key points about Selenium as a photosensitive element:

1. Properties of Selenium:
- Selenium is a gray, brittle solid with a metallic luster.
- It has a high electrical conductivity in the dark, but its conductivity decreases significantly when exposed to light.
- The resistance of Selenium increases by several orders of magnitude when illuminated.

2. Working Principle:
- When light falls on Selenium, the energy from the photons is absorbed by the material.
- This absorption of energy excites the electrons in the Selenium atoms, causing them to move from the valence band to the conduction band.
- The movement of electrons reduces the number of charge carriers available for conduction, which leads to an increase in resistance.

3. Applications:
- Selenium is commonly used in photocopiers and xerography machines. In these devices, a photosensitive drum coated with Selenium is charged and exposed to light, creating an electrostatic image that is transferred onto paper.
- Selenium photodiodes are used in various electronic devices such as light meters, cameras, and optical sensors. These photodiodes convert light energy into electrical signals.

In conclusion, Selenium is a photosensitive element that exhibits a change in electrical resistance when exposed to light. Its unique properties make it suitable for various applications in the field of photography, photodiodes, solar cells, and light sensors.

The catalyst used for the oxidation of ammonia to produce nitric acid is the Platinum-Rhodium gauze.

The process of ammonia oxidation to nitric acid is known as the Ostwald process, and it involves several steps. The catalyst plays a crucial role in facilitating the reaction and increasing its efficiency.

Here is a detailed explanation of why the Platinum-Rhodium gauze is used as the catalyst for this reaction:

1. The Ostwald process:
- The Ostwald process is a multi-step chemical reaction that converts ammonia (NH3) to nitric acid (HNO3).
- The first step involves the oxidation of ammonia to nitric oxide (NO) and water (H2O).
- The second step is the oxidation of nitric oxide to nitrogen dioxide (NO2).
- The third step is the absorption of nitrogen dioxide in water to form nitric acid.

2. Catalyst requirements:
- The catalyst used in the ammonia oxidation process must have several key properties.
- It should promote the desired reaction while minimizing the formation of unwanted byproducts.
- It should have high activity and selectivity towards the desired reaction.
- It should be stable under the reaction conditions and resist deactivation.

3. Platinum-Rhodium gauze catalyst:
- The Platinum-Rhodium gauze is widely used as the catalyst in the Ostwald process.
- It is a mesh-like structure made of platinum and rhodium metals.
- The catalyst is typically supported on a ceramic or metal substrate.
- The Platinum-Rhodium gauze catalyst has several advantages for this reaction.

4. Advantages of Platinum-Rhodium gauze catalyst:
- High activity: Platinum and rhodium have high catalytic activity for the oxidation of ammonia.
- Selectivity: The catalyst promotes the desired oxidation reactions while minimizing side reactions.
- Resistance to deactivation: The Platinum-Rhodium gauze catalyst is stable under the reaction conditions and does not easily get deactivated.
- Surface area: The mesh-like structure of the catalyst provides a large surface area for the reactants to come into contact with the catalyst, enhancing the reaction rate.

In conclusion, the Platinum-Rhodium gauze catalyst is used for the oxidation of ammonia to produce nitric acid in the Ostwald process due to its high activity, selectivity, stability, and large surface area.

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