ENGG CHEMISTRY
These are the topics from where most of the question come in exam.
- BOD and COD; -
Biochemical Oxygen Demand (BOD):
- Definition: BOD represents the amount of oxygen that microorganisms require to decompose organic matter under aerobic conditions.
- Measurement: It is determined by placing a sealed water sample under specific temperature conditions for five days.
- Purpose:
- BOD is used to assess waste loadings in treatment plants.
- It evaluates the efficiency of BOD removal in waste treatment facilities.
- It quantifies the amount of oxidizable pollutants present in water bodies.
- Provides insights into how an effluent will impact the receiving water body.
Chemical Oxygen Demand (COD):
- Definition: COD refers to the total amount of oxygen required to break down organic matter through chemical oxidation.
- Measurement: It is determined by placing a water sample with a strong oxidizing agent under specific temperature conditions for a short period.
- Comparison:
- COD values are higher than BOD values.
- Chemical oxidation is generally easier than biological oxidation.
- Application:
- COD helps quantify the oxidizable pollutants in water bodies.
In summary, BOD focuses on biological decomposition, while COD assesses chemical breakdown. Both parameters are crucial for understanding water quality and treatment processes.
- Natural and synthetic rubber: -
Natural Rubber:
- Source: Natural rubber is derived from the latex sap of rubber trees, primarily found in tropical regions. These trees belong to the species Hevea Brasiliense's.
- Composition: Natural rubber consists of polyisoprene, which is a long chain of linked isoprene molecules. Each isoprene molecule is a simple combination of 13 carbon and hydrogen atoms.
- Properties:
- Elasticity: Natural rubber exhibits excellent elasticity and can recover its shape after being stretched or distorted.
- Resilience: It can withstand repeated deformation without permanent damage.
- Low-Temperature Flexibility: Natural rubber remains flexible even at low temperatures.
- Preparation:
- Rubber Tapping: The milky white liquid latex is collected from rubber trees by making a slight V-cut on the tree bark. This latex is then washed, filtered, and reacted with acids to congeal the rubber particles.
- Mastication: The rubber obtained from tapping is brittle when cold and gluey when warmed up. It undergoes mastication (passing through rollers) to make it softer and more flexible.
- Calendaring: The rubber is shaped using rollers, and the final product is extruded into hollow tubes.
- Vulcanization: This process involves adding sulfur to rubber and heating it to improve its properties.
Synthetic Rubber:
- Source: Synthetic rubber is artificially produced through chemical processes. It is not derived from natural latex.
- Composition: Unlike natural rubber, synthetic rubbers are made from various molecular links, including atoms of fluorine, chlorine, silicon, nitrogen, oxygen, and sulfur.
- Advantages:
- Versatility: Synthetic rubber can be tailored for specific applications.
- Availability: It is not dependent on rubber trees and can be produced globally.
- Consistency: Synthetic rubber offers consistent properties.
- Disadvantages:
- Environmental Impact: The production of synthetic rubber involves petroleum and natural gas.
- Limited Renewable Aspect: Unlike natural rubber, it is not a renewable resource.
- Synthetic rubber is extensively utilized in the production of tires, gaskets, seals, hoses, footwear, and a variety of industrial applications.
In summary, natural rubber comes from trees, while synthetic rubber is artificially created. Both types have unique properties and find extensive applications in our daily lives.
- E-waste: - Certainly! Let’s delve into the fascinating world of Electronic Waste (E-waste):
Definition:
- E-waste, also known as waste electrical and electronic equipment (WEEE) or end-of-life (EOL) electronics, refers to discarded electrical or electronic devices.
- These devices have reached the end of their useful life and are either discarded, donated, or given to a recycler.
Scope of the Problem:
- E-waste is the fastest growing solid waste stream globally, increasing three times faster than the world’s population.
- Unfortunately, less than a quarter of the e-waste produced globally in 2019 was formally recycled.
- Despite containing valuable and finite resources, e-waste poses significant risks, especially in low- and middle-income countries (LMICs) where appropriate regulations, recycling infrastructure, and training are lacking.
- The transboundary movement of e-waste to LMICs continues, often illegally.
Hazards and Impact:
- E-waste is considered hazardous waste due to its toxic materials.
- When treated inappropriately, it can release as many as 1000 different chemical substances into the environment, including harmful neurotoxicants like lead.
- Pregnant women and children are particularly vulnerable due to their unique exposure pathways and developmental status.
- The informal recycling sector exposes millions of child laborers and women to e-waste risks.
Common E-waste Items:
- Computers, mobile phones, large household appliances, and medical equipment are common items found in e-waste streams.
- Millions of tons of e-waste are recycled using environmentally unsound techniques, stored in homes, dumped, exported, or recycled under inferior conditions.
Solutions:
- Proper e-waste management involves safe disposal, recycling, and reusing valuable components.
- Raising awareness, implementing regulations, and promoting responsible recycling practices are crucial steps in addressing this global challenge.
Remember, the responsible management of e-waste is crucial for environmental conservation and human health.
- Valency: -Certainly! Let’s explore the concept of valency:
Definition:
- Valency refers to the combining capacity of an atom in a molecule.
- It represents the number of chemical bonds an atom can form as part of a compound.
- Valency is determined by the number of electrons in the outermost shell (valence shell) of an atom.
Valence Electrons:
- Valence electrons are those present in the outermost orbit of an atom.
- When the outermost shell contains 8 electrons, the element is said to have a complete octet and is stable.
- The capacity of an atom is described by the total number of electrons lost, gained, or shared to complete its octet, which also determines its valency.
Finding Valency:
- For example:
- Hydrogen (H) has 1 valence electron, so its valency is 1 (it can easily lose 1 electron).
- Magnesium (Mg) has 2 valence electrons, so its valency is 2 (it can lose 2 electrons).
- Fluorine (F) has 7 valence electrons. It gains 1 electron to complete its octet, so its valency is 1.
- Elements in the same group of the periodic table have the same valency due to similar outer electron configurations.
- For example:
Difference from Oxidation Number:
- Valency has no sign, while the oxidation number can be positive or negative.
- For example, nitrogen’s valency is 3, but its oxidation numbers can range from -3 to +5.
- Quantum number: -
- Degree of ionization: - Certainly! Let’s explore the concept of Degree of Ionization:
Definition:
- The degree of ionization, also known as degree of dissociation, is a measure of the strength of an acid.
- It quantifies the extent to which an acid ionizes (breaks down into ions) when dissolved in water.
- The degree of ionization is represented by the Greek symbol α.
- It is defined as the ratio of the number of ionized molecules to the total number of molecules dissolved in water.
Significance:
- A higher degree of ionization indicates a stronger acid because more molecules dissociate into ions.
- Conversely, a lower degree of ionization corresponds to a weaker acid with fewer ionized molecules.
Example:
- Consider acetic acid ((CH_3COOH)):
- When acetic acid dissolves in water, it partially ionizes into acetate ions ((CH_3COO^-)) and hydrogen ions ((H^+)).
- The degree of ionization for acetic acid depends on its concentration and the specific conditions.
- Pollution and pollutants: -
Pollution:
- Definition: Pollution is the introduction of harmful materials into the environment.
- These harmful materials are called pollutants.
- Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light).
- It damages the quality of air, water, and land.
- Examples of pollution sources include factories, vehicles, and waste disposal.
Pollutants:
- Definition: Pollutants are the individual substances or energies that cause harm to the environment.
- They can be natural, such as volcanic ash, or created by human activity, such as trash or runoff produced by factories.
- Pollutants can damage the quality of air, water, and land.
- For instance, car exhaust, industrial emissions, and pesticides are common pollutants.
- Plastic and D/B Thermosetting and Thermoplastic plastic:-
Thermoplastic:
- Definition: Thermoplastics are plastic polymers that can be moulded or reshaped when heated and solidify upon cooling.
- Processability:
- Processed by methods such as injection moulding, extrusion, blow moulding, thermoforming, and rotational moulding.
- They have low melting points, allowing for easy remoulding or recycling.
- Bonding:
- Thermoplastics have secondary bonds between molecular chains.
- Properties:
- Low tensile strength due to their lower molecular weight.
- Examples include:
- Polystyrene
- Teflon
- Acrylic
- Nylon
Thermosetting:
- Definition: Thermosetting plastics are polymers that harden irreversibly when exposed to heat.
- Processability:
- Processed by methods like compression moulding and reaction injection moulding.
- They cannot be remoulded or reprocessed upon reheating.
- Bonding:
- Thermosetting plastics have primary bonds between molecular chains, held together by strong cross-links.
- Properties:
- High melting points and high tensile strength due to their higher molecular weight.
- Examples include:
- Vulcanized rubber
- Bakelite
- Polyurethane
- Epoxy resin
- Electronic configuration (1 - 30): -
- Hydrogen (H): 1s1
- Helium (He): 1s2
- Lithium (Li): 1s2 2s1
- Beryllium (Be): 1s2 2s2
- Boron (B): 1s2 2s2 2p1
- Carbon ©: 1s2 2s2 2p2
- Nitrogen (N): 1s2 2s2 2p3
- Oxygen (O): 1s2 2s2 2p4
- Fluorine (F): 1s2 2s2 2p5
- Neon (Ne): 1s2 2s2 2p6
- Sodium (Na): 1s2 2s2 2p6 3s1
- Magnesium (Mg): 1s2 2s2 2p6 3s2
- Aluminum (Al): 1s2 2s2 2p6 3s2 3p1
- Silicon (Si): 1s2 2s2 2p6 3s2 3p2
- Phosphorus (P): 1s2 2s2 2p6 3s2 3p3
- Sulfur (S): 1s2 2s2 2p6 3s2 3p4
- Chlorine (Cl): 1s2 2s2 2p6 3s2 3p5
- Argon (Ar): 1s2 2s2 2p6 3s2 3p6
- Potassium (K): 1s2 2s2 2p6 3s2 3p6 4s1
- Calcium (Ca): 1s2 2s2 2p6 3s2 3p6 4s2
- Scandium (Sc): 1s2 2s2 2p6 3s2 3p6 4s2 3d1
- Titanium (Ti): 1s2 2s2 2p6 3s2 3p6 4s2 3d2
- Vanadium (V): 1s2 2s2 2p6 3s2 3p6 4s2 3d3
- Chromium (Cr): 1s2 2s2 2p6 3s2 3p6 4s2 3d4
- Manganese (Mn): 1s2 2s2 2p6 3s2 3p6 4s2 3d5
- Iron (Fe): 1s2 2s2 2p6 3s2 3p6 4s2 3d6
- Cobalt (Co): 1s2 2s2 2p6 3s2 3p6 4s2 3d7
- Nickel (Ni): 1s2 2s2 2p6 3s2 3p6 4s2 3d8
- Copper (Cu): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1
- Zinc (Zn): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2
- Arrhenius theory of ionization: -The Arrhenius theory of ionization, introduced by the Swedish scientist Svante Arrhenius in 1887, provides insights into the behavior of acids and bases in aqueous solutions. Here are the key points:
Acids:
- According to Arrhenius, acids are substances that dissociate in water to yield electrically charged atoms or molecules, called ions.
- One of these ions is a hydrogen ion (H+).
- Examples of well-known acids include sulfuric acid, hydrochloric acid, nitric acid, and acetic acid.
- Their acidic behavior is explained by their ability to yield hydrogen ions in solution.
Bases:
- Arrhenius also proposed that bases ionize in water to yield hydroxide ions (OH-).
- Bases are substances that can accept hydrogen ions.
- Examples of well-known bases include sodium hydroxide, potassium hydroxide, and calcium hydroxide.
- Their basic properties are explained by their ability to yield hydroxide ions in solution.
Hydronium Ion:
- It is now known that the hydrogen ion (H+) cannot exist alone in water solution.
- Instead, it exists in a combined state with a water molecule, forming the hydronium ion (H3O+).
- In practice, the hydronium ion is still customarily referred to as the hydrogen ion.
Neutralization Reaction:
- When an acid reacts with a base, it leads to the formation of a salt and water.
- The combination of a hydrogen ion and a hydroxide ion results in water.
- Faradays laws of electrolysis: -
Faraday’s First Law of Electrolysis:
- Statement: The amount of chemical reaction that occurs at any electrode during electrolysis is proportional to the quantity of electricity passed through the electrolyte.
- In other words, the mass of a substance deposited or liberated at an electrode is directly related to the charge (Q) flowing through the cell.
Faraday’s Second Law of Electrolysis:
- Statement: If the same amount of electricity is passed through different electrolytes, the masses of ions deposited at the electrodes are directly proportional to their chemical equivalents.
- The chemical equivalent is the mass of a substance that reacts with one mole of electrons during electrolysis.
Faraday Constant (F):
- The charge needed to deposit or liberate one mole of any substance during electrolysis is defined as one Faraday.
- The value of the Faraday constant is approximately 96,487 C/mol.
- It is denoted by the symbol (F)
- Greenhouse effect: -The greenhouse effect is a crucial natural process that plays a significant role in maintaining Earth’s temperature. Let’s explore it in more detail:
Definition:
- The greenhouse effect occurs when greenhouse gases in a planet’s atmosphere insulate the planet, preventing the escape of heat into space.
- These greenhouse gases allow sunlight to pass through the atmosphere and heat the planet’s surface.
- However, they also absorb and redirect some of the longwave radiation (heat) emitted by the planet.
How It Works:
- The Sun emits shortwave radiation (sunlight) that passes through greenhouse gases and heats Earth’s surface.
- In response, Earth’s surface emits longwave radiation (heat) primarily in the infrared wavelengths.
- Greenhouse gases, such as carbon dioxide, methane, and water vapor, absorb this longwave radiation, preventing it from escaping into space.
- As a result, the surface temperatures rise, making Earth habitable.
Impact:
- Without the greenhouse effect, Earth’s average surface temperature would be much colder (around -18°C or -0.4°F) compared to the current average of about 14°C (57°F).
- Human activities, such as burning fossil fuels, have increased greenhouse gases like carbon dioxide, contributing to global warming.
Global Warming:
- Since the Industrial Revolution, global warming has led to an increase in Earth’s average surface temperature (about 1.2°C or 2.2°F).
- The greenhouse effect, while essential for life, has been intensified by human actions.
- Electrolysis: -Electrolysis is a fascinating process that utilizes direct electric current (DC) to drive otherwise non-spontaneous chemical reactions. Let’s explore it further:
Definition:
- Electrolysis involves passing an electric current through a substance (usually an electrolyte) to bring about a chemical change.
- During electrolysis, ions in the electrolyte migrate towards the electrodes, where they either gain or lose electrons.
- This process allows for the separation of elements from naturally occurring sources, such as ores.
Key Points:
- Electrolyte: An electrolyte is a substance that can conduct electricity when dissolved in water or melted.
- Electrolytic Cell: The setup used for electrolysis consists of an electrolytic cell, which contains the electrolyte and two electrodes (anode and cathode).
- Anode: The positive electrode where oxidation occurs (loss of electrons).
- Cathode: The negative electrode where reduction occurs (gain of electrons).
Applications:
- Electroplating: Electrolysis is used for coating objects with a layer of metal (e.g., gold-plated jewelry).
- Extraction of Metals: It plays a crucial role in extracting reactive metals (such as aluminum, sodium, and potassium) from their ores.
- Electrolytic Refining: Used to purify metals (e.g., refining copper).
- Electrolysis of Water: Splitting water into hydrogen and oxygen gases.
Faraday’s Laws:
- Faraday’s First Law: The amount of substance deposited or liberated during electrolysis is directly proportional to the quantity of electricity passed through the cell.
- Faraday’s Second Law: If the same amount of electricity passes through different electrolytes, the masses of ions deposited are directly proportional to their chemical equivalents.
- Bohr's Model: -Bohr’s model of the atom, proposed by the Danish physicist Niels Bohr in 1913, revolutionized our understanding of atomic structure. Let’s explore its key features:
Background:
- Prior to Bohr’s model, the Rutherford model described the atom as a tiny, dense nucleus (positively charged) surrounded by electrons.
- However, the Rutherford model couldn’t explain the stability of electrons or their energy levels.
Bohr’s Postulates:
- Quantized Energy Levels:
- Bohr proposed that electrons move in fixed orbits (also called shells or energy levels) around the nucleus.
- Each orbit has a specific energy associated with it.
- Electrons can jump from one orbit to another by absorbing or emitting energy.
- Angular Momentum Quantization:
- Bohr introduced the concept of quantized angular momentum.
- The angular momentum of an electron is an integer multiple of Planck’s constant divided by 2Ï€.
- Radiation and Stability:
- Electrons in stable orbits do not emit radiation.
- Only when an electron transitions between orbits does it emit or absorb energy in the form of photons.
- Quantized Energy Levels:
Energy Levels:
- The first energy level (K) is closest to the nucleus, followed by L, M, and so on.
- Electrons in the innermost K shell have the lowest energy.
- Electrons in higher shells have progressively higher energies.
Limitations:
- While Bohr’s model explained the spectral lines of hydrogen, it had limitations:
- It couldn’t explain spectra of other elements.
- It didn’t account for electron spin.
- Bohr’s model paved the way for more advanced quantum mechanical models.
- While Bohr’s model explained the spectral lines of hydrogen, it had limitations:
- Isotopes and isobars: -Let’s explore the differences between isotopes and isobars:
Isotopes:
- Definition: Isotopes are atoms of the same element with the same atomic number (same number of protons) but different mass numbers (different number of neutrons).
- Characteristics:
- Isotopes have identical chemical properties because they have the same number of electrons and therefore interact similarly in chemical reactions.
- Their physical properties, such as density and melting point, may vary due to differences in mass.
- Examples include carbon-12 (12C) and carbon-14 (14C).
Isobars:
- Definition: Isobars are atoms of different elements that have the same mass number (sum of protons and neutrons) but different atomic numbers (different number of protons).
- Characteristics:
- Isobars have different chemical properties because they belong to different elements with distinct electron configurations.
- Despite different chemical behavior, they share the same mass number.
- An example of isobars is calcium-40 (40Ca) and potassium-40 (40K).
Summary:
- In brief:
- Isotopes: Same atomic number, different mass number.
- Isobars: Different atomic number, same mass number.
- Air pollution: -Air pollution refers to the contamination of air due to the presence of substances called pollutants in the atmosphere. These pollutants can be harmful to the health of humans and other living beings, or they may cause damage to the climate or materials. Air pollution can occur both outdoors and indoors and has wide-ranging effects on our environment and well-being.
Here are some key points about air pollution:
Types of Pollutants:
- Gases: Examples include carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), methane (CH4), and chlorofluorocarbons (CFCs).
- Particulates: These are tiny solid or liquid particles suspended in the air, such as dust, smoke, and pollen.
- Biological Molecules: These include allergens, bacteria, and viruses.
- Effects: Air pollution can cause diseases, allergies, and even death in humans. It also harms animals, crops, and the natural environment.
Sources of Air Pollution:
- Human Activities: Burning fossil fuels (such as coal, oil, and gasoline), industrial processes, and transportation.
- Natural Phenomena: Volcanic eruptions, wildfires, and dust storms.
Health Impacts:
- Air pollution is a significant risk factor for various diseases, including respiratory infections, heart disease, stroke, and lung cancer.
- Exposure to poor air quality can also affect cognition, mental health, and perinatal health.
Global Impact:
- Air quality is closely related to the Earth’s climate and ecosystems.
- Many air pollutants are also sources of greenhouse emissions, contributing to climate change.
- Aufbau principle and Hund rule: -Let’s explore the Aufbau principle and Hund’s rule, two fundamental concepts related to electron configurations in atoms:
Aufbau Principle:
- The Aufbau principle (from the German word “aufbauen,” meaning “to build up”) describes the order in which electrons fill atomic orbitals.
- According to this principle:
- Electrons fill the lowest energy orbitals first before moving to higher energy levels.
- The main energy level (given by the principal quantum number, (n)) increases as we move down the periodic table.
- Within the same principal level, orbitals with a lower value of (l) (azimuthal quantum number) have lower energy and are filled first.
- The order of filling electrons based on energy levels and orbitals can be summarized as follows:
- 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < …
Hund’s Rule:
- Hund’s rule states that:
- When filling degenerate (equal-energy) orbitals (such as the three 2p orbitals), electrons will occupy separate orbitals with parallel spins (spin-up and spin-down) before pairing up.
- In other words, electrons prefer to occupy different orbitals within the same subshell rather than pairing up in the same orbital.
- This rule ensures that the total electron spin is maximized, leading to greater.
- Hund’s rule states that:
- Electrovalent and covalent: -Aufbau principle and Hund’s rule, two fundamental concepts related to electron configurations in atoms:
Aufbau Principle:
- The Aufbau principle (from the German word “aufbauen,” meaning “to build up”) describes the order in which electrons fill atomic orbitals.
- According to this principle:
- Electrons fill the lowest energy orbitals first before moving to higher energy levels.
- The main energy level (given by the principal quantum number, (n)) increases as we move down the periodic table.
- Within the same principal level, orbitals with a lower value of (l) (azimuthal quantum number) have lower energy and are filled first.
- The order of filling electrons based on energy levels and orbitals can be summarized as follows:
- 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < …
Hund’s Rule:
- Hund’s rule states that:
- When filling degenerate (equal-energy) orbitals (such as the three 2p orbitals), electrons will occupy separate orbitals with parallel spins (spin-up and spin-down) before pairing up.
- In other words, electrons prefer to occupy different orbitals within the same subshell rather than pairing up in the same orbital.
- This rule ensures that the total electron spin is maximized, leading to greater stability.
- Hund’s rule states that:
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