All questions of Chemistry for Mechanical Engineering Exam

Answer :

Conversion of Chemical Energy into Electrical Energy in a Battery

The correct answer to the question is option 'C' - a battery. A battery is a device that converts chemical energy into electrical energy through a chemical reaction. It consists of one or more electrochemical cells, which are composed of two electrodes (a cathode and an anode) and an electrolyte.

Chemical Reactions in a Battery:

When a battery is connected to an external circuit, a chemical reaction occurs within the battery. This chemical reaction involves the transfer of electrons from the anode to the cathode through the external circuit. The chemical reaction is typically a redox reaction (oxidation-reduction reaction), where one electrode undergoes oxidation (loses electrons) and the other undergoes reduction (gains electrons).

Here is a breakdown of the chemical reactions that occur in a typical battery:

1. Anode Reaction: At the anode, oxidation takes place, and the anode material loses electrons. For example, in a typical alkaline battery, the anode reaction is:

Zn(s) -> Zn2+(aq) + 2e-

In this reaction, zinc metal (Zn) is oxidized to form zinc ions (Zn2+) and release two electrons (2e-).

2. Cathode Reaction: At the cathode, reduction takes place, and the cathode material gains electrons. For example, in a typical alkaline battery, the cathode reaction is:

2MnO2(s) + H2O(l) + 2e- -> Mn2O3(s) + 2OH-(aq)

In this reaction, manganese dioxide (MnO2) is reduced by gaining two electrons (2e-) and reacts with water (H2O) to form manganese(III) oxide (Mn2O3) and hydroxide ions (OH-).

3. Overall Reaction: The overall reaction in a battery is the sum of the anode and cathode reactions. In the case of an alkaline battery, the overall reaction is:

Zn(s) + 2MnO2(s) + H2O(l) -> Zn2+(aq) + Mn2O3(s) + 2OH-(aq)

This overall reaction releases energy in the form of electrical potential energy, which can be harnessed to do work in an external circuit.

Conversion of Chemical Energy to Electrical Energy:

The conversion of chemical energy into electrical energy occurs due to the movement of electrons from the anode to the cathode through the external circuit. This flow of electrons creates an electric current, which can be used to power various devices or perform work.

The chemical reactions in the battery result in a potential difference, or voltage, between the anode and cathode. This potential difference drives the movement of electrons, creating an electric current. The electrical energy produced can then be used to power devices such as flashlights, remote controls, smartphones, and many more.

In summary, a battery converts chemical energy into electrical energy through a redox reaction. The anode undergoes oxidation, losing electrons, while the cathode undergoes reduction, gaining electrons. The movement of electrons through the external circuit creates an electric current, which can be used to power various devices.

Understanding Detergents
Detergents are substances used for cleaning and they play a vital role in various cleaning applications. They can be categorized based on their chemical structure and the type of surfactants they contain.
Types of Detergents
- Sodium Salts of Fatty Acids: These are traditional soaps made from natural fats and oils. They work effectively in soft water but may not perform well in hard water. Thus, they are not classified as synthetic detergents.
- Sodium Salts of Sulphonic Acids: This is the correct answer. Synthetic detergents, commonly used in household and industrial cleaning products, are derived from petrochemicals and often take the form of sodium salts of sulfonic acids. These detergents are effective in hard water, provide better cleaning power, and are designed to work in a variety of conditions.
- Sodium Salt of Benzoic Acid: While this compound can serve as a preservative in food, it is not classified as a detergent. It does not possess the surfactant properties necessary for cleaning applications.
Conclusion
The correct classification of detergents is essential to understand their functionality and application. Sodium salts of sulfonic acids are designed to provide enhanced cleaning capabilities, making option 'B' the correct choice. Their effectiveness in hard water and ability to emulsify oils and dirt are what set them apart from traditional soap-based cleaners.

Gobar gas, also known as biogas, contains mainly methane (CH4) and carbon dioxide (CO2). Methane is the primary component of biogas and is responsible for its combustible properties. Carbon dioxide is a byproduct of the anaerobic digestion process that produces biogas. In addition to methane and carbon dioxide, small amounts of other gases such as hydrogen sulfide (H2S), nitrogen (N2), and trace amounts of various impurities may also be present in gobar gas.

Gas used to manufacture vanaspati from vegetable oil: Hydrogen

Explanation:
Vanaspati is a form of hydrogenated vegetable oil that is solid at room temperature. It is commonly used as a substitute for ghee (clarified butter) in cooking. The process of manufacturing vanaspati involves the use of hydrogen gas.

Process of manufacturing vanaspati:
1. Hydrogenation: The first step in manufacturing vanaspati is the hydrogenation of vegetable oil. This process involves the addition of hydrogen gas to vegetable oil under specific conditions of temperature and pressure.

2. Catalyst: The hydrogenation process is catalyzed by the presence of a catalyst, such as nickel or palladium. The catalyst helps in the breaking of double bonds present in the unsaturated fatty acids of vegetable oil and facilitates the addition of hydrogen atoms.

3. Saturation of fatty acids: During hydrogenation, the unsaturated fatty acids present in vegetable oil are saturated with hydrogen atoms. This process converts liquid vegetable oil into a solid form, which is characteristic of vanaspati.

4. Trans fatty acids: In the process of hydrogenation, some of the unsaturated fatty acids undergo a partial rearrangement, resulting in the formation of trans fatty acids. Trans fatty acids are known to have adverse health effects and are considered unhealthy when consumed in excessive amounts.

5. Deodorization and refining: After the hydrogenation process, the vanaspati undergoes further refining steps, including deodorization to remove any undesirable odors and impurities. This refining process helps in enhancing the quality and shelf life of vanaspati.

6. Addition of flavor and color: Finally, flavoring agents and food-grade colors may be added to the refined vanaspati to enhance its taste and appearance.

Conclusion:
Hydrogen gas is used in the manufacturing process of vanaspati from vegetable oil. The hydrogenation process involves saturating the unsaturated fatty acids in vegetable oil with hydrogen atoms, resulting in the solid form of vanaspati.

Understanding Corrosion in Steamboilers
Corrosion in steamboilers is a significant issue that can lead to operational failures, increased maintenance costs, and safety hazards. Among various salts, Magnesium Chloride is particularly corrosive.
Why Magnesium Chloride Causes Corrosion
- Chemical Properties: Magnesium Chloride (MgCl2) is highly soluble in water and dissociates into magnesium and chloride ions. The chloride ions are notorious for their aggressive nature in promoting corrosion.
- Electrochemical Reactions: When present in water, Magnesium Chloride can initiate electrochemical reactions on the metal surfaces of the boiler. These reactions accelerate the deterioration of metal, leading to pitting and general corrosion.
- Formation of Corrosive Compounds: The presence of magnesium ions can lead to the formation of corrosive compounds, which further exacerbate metal degradation. These compounds can create localized acidic environments that are detrimental to the integrity of the boiler materials.
Comparison with Other Salts
- Sodium Chloride: While it is also corrosive, Magnesium Chloride is more aggressive under certain operating conditions typically found in steamboilers.
- Calcium Bicarbonate & Potassium Bicarbonate: These salts are generally less corrosive compared to Magnesium Chloride. They can lead to scaling rather than direct corrosion, making them less harmful to the boiler's metal surfaces.
Conclusion
In summary, the presence of Magnesium Chloride in water is particularly harmful to steamboilers due to its chemical properties and the corrosive electrochemical reactions it can initiate. This understanding is crucial for maintaining boiler efficiency and longevity.

Understanding Chain Reactions in Nuclear Fission
During the fission of uranium, the most crucial particle for sustaining the chain reaction is the neutron. Here’s why:

Role of Neutrons in Fission
- **Initiation of Fission**: When a uranium nucleus absorbs a neutron, it becomes unstable and splits into two smaller nuclei, releasing a significant amount of energy and additional neutrons.
- **Sustaining the Chain Reaction**: The neutrons released can collide with other uranium nuclei, causing them to undergo fission as well. This process creates a self-sustaining chain reaction.

Why Not Other Particles?
- **Electrons**: While they are involved in atomic structure, they do not play a direct role in initiating or sustaining fission.
- **Protons**: These are positively charged particles found in the nucleus. They contribute to the identity of the element but do not initiate fission reactions.
- **Positrons**: These are the antimatter counterparts of electrons and are not involved in nuclear fission processes.

Conclusion
The neutron’s ability to induce and propagate fission makes it essential for the chain reaction. Without neutrons, the process cannot continue, highlighting their critical role in nuclear fission, particularly in reactors and atomic bombs. Thus, option 'C' – neutron, is indeed the correct answer.

Acetic Acid is the Chief Constituent of Vinegar
Acetic acid is the main component of vinegar, which gives it its characteristic sour taste and pungent smell. Let's delve into the details of why acetic acid is the chief constituent of vinegar:

Acetic Acid Content
- Acetic acid, with the chemical formula CH3COOH, is a weak acid that is produced through the fermentation of ethanol by acetic acid bacteria.
- It typically makes up around 4-8% of vinegar by volume, depending on the type of vinegar.

Role in Vinegar
- Acetic acid is responsible for the tangy flavor of vinegar and also acts as a natural preservative.
- It is commonly used in cooking, pickling, and as a condiment because of its distinctive taste.

Health Benefits
- Acetic acid has been linked to several health benefits, such as aiding in digestion, lowering blood sugar levels, and promoting weight loss.
- Some studies suggest that consuming small amounts of vinegar regularly may have positive effects on overall health.

Industrial Uses
- Acetic acid is not only found in vinegar but also has various industrial applications, such as in the production of plastics, synthetic fibers, and solvents.
- It is a versatile chemical that plays a crucial role in many industries.
In conclusion, acetic acid is the primary component of vinegar, contributing to its taste, preservation properties, and potential health benefits.

Discovery of the Atom Bomb
The atom bomb, also known as the atomic bomb, was discovered by Otto Hahn, a German chemist.

Background:
- Otto Hahn conducted groundbreaking research in nuclear chemistry and radiochemistry.
- He worked closely with Lise Meitner, an Austrian physicist, on nuclear fission experiments.

Discovery:
- In 1938, Otto Hahn and Fritz Strassmann, another chemist, conducted experiments in which they bombarded uranium with neutrons.
- This led to the splitting of the uranium atom, a process known as nuclear fission.
- This discovery laid the foundation for the development of the atom bomb.

Significance:
- The discovery of nuclear fission by Otto Hahn and Fritz Strassmann played a crucial role in the development of the atom bomb during World War II.
- Their work was instrumental in the Manhattan Project, a research and development project that produced the first atomic bombs.
In conclusion, Otto Hahn's discovery of nuclear fission was a pivotal moment in the history of science and technology, ultimately leading to the creation of the devastating atom bomb.

Understanding Glycogen
Glycogen is a crucial carbohydrate in biological systems, primarily functioning as an energy reserve.
Structure of Glycogen
- Glycogen is a multibranched polysaccharide composed of glucose units.
- Its structure allows for rapid release of glucose when energy is needed.
Function of Glycogen
- Energy Storage: Glycogen serves as a primary energy storage form in animals and fungi.
- Glucose Supply: During periods of increased energy demand, such as exercise or fasting, glycogen is broken down into glucose and released into the bloodstream.
Differences from Other Polysaccharides
- Cellulose: Contains linear chains of glucose and serves as a structural component in plant cell walls.
- Pectin: Found in plant cell walls, acts as a gelling agent, but does not serve as an energy reserve.
- Chitin: A structural polysaccharide found in the exoskeletons of arthropods and fungal cell walls, not involved in energy storage.
Importance of Glycogen
- Metabolic Role: Glycogen plays a vital role in glucose metabolism and maintaining blood sugar levels.
- Adaptation to Energy Needs: Its branched structure allows for quick mobilization of glucose, adapting to physiological demands.
In summary, glycogen is essential for energy storage and regulation in animals and fungi, distinguishing it from other polysaccharides like cellulose, pectin, and chitin.

Wrought iron is the purest form of iron among the given options.

Explanation:

Wrought iron is a form of iron that is almost entirely free from impurities and contains a very low percentage of carbon (less than 0.1%). It is characterized by its fibrous structure and is known for its high ductility and malleability.

Here are some key points that explain why wrought iron is considered the purest form of iron:

1. Carbon content:
- Wrought iron has the lowest carbon content among the given options. It contains less than 0.1% carbon, making it nearly pure iron.
- In comparison, steel contains a higher carbon content (up to 2%) which gives it greater strength but reduces its purity.
- Cast iron contains a higher carbon content (2-4%) and is known for its brittleness and inability to be forged.
- Pig iron is the crudest form of iron and has a high carbon content (3-4%). It is also brittle and cannot be used directly.

2. Impurities:
- Wrought iron is produced by a refining process known as puddling, which removes impurities such as sulfur and phosphorus.
- This process involves melting pig iron in a reverberatory furnace and stirring it to oxidize the impurities, which are then absorbed by the slag.
- The repeated stirring and oxidation help to purify the iron, resulting in wrought iron with minimal impurities.

3. Physical properties:
- Wrought iron is known for its fibrous structure, which is a result of the slag being worked into the iron during the refining process.
- This fibrous structure gives wrought iron its characteristic grainy appearance and enhances its mechanical properties, such as ductility and malleability.
- It can be easily forged, welded, and shaped into various forms without losing its strength.

In conclusion, wrought iron is considered the purest form of iron due to its low carbon content and the removal of impurities during the refining process. Its high ductility, malleability, and nearly pure iron composition make it suitable for various applications, including decorative ironwork, fencing, and historical artifacts.