Samacheer Kalvi Class 9 Science Solutions Chapter 15 Carbon and its Compounds

I. Choose the Correct Answer:

 

Question 1. A phenomenon in which an element exists in different modification in same physical state is called
(a) isomerism
(b) allotropy
(c) catenation
(d) crystallinity
Answer: (b) allotropy
In simple words: Allotropy is when an element can exist in different physical forms, like carbon in diamond or graphite. Each form has different properties even though it's the same element.

🎯 Exam Tip: Remember to distinguish between allotropy (different physical forms of one element) and isomerism (different structural forms of one compound with the same formula).

 

Question 2. Carbon forms large number of organic compounds due to
(a) Allotropy
(b) Isomerism
(c) Tetravalency
(d) Catenation
Answer: (d) Catenation
In simple words: Carbon can link with many other carbon atoms to make long chains, branches, or rings. This special ability, called catenation, is why there are so many carbon-based compounds in the world.

🎯 Exam Tip: Catenation is the self-linking property of an element. For carbon, this, along with tetravalency, allows it to form a vast number of diverse organic compounds.

 

Question 3. Nandhini brings her lunch every day to school in a plastic container which has resin code number 5. The container is made of
(a) Polystyrene
(b) PVC
(c) Polypropylene
(d) LDPE
Answer: (c) Polypropylene
In simple words: Polypropylene, known by resin code 5, is a common plastic used for food containers because it is generally considered safe and heat-resistant. Many everyday items like yogurt cups and bottle caps are made from this material.

🎯 Exam Tip: Knowing common plastic resin codes helps in identifying safer plastics for food storage and understanding recycling labels. Resin code 5 (PP) is widely used for reusable food containers.

 

Question 4. Plastics made of Polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS) are made of resin code
(a) 2
(b) 5
(c) 6
(d) 7
Answer: (a) 7
In simple words: Plastics like Polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS) are grouped under resin code 7, which means "other" plastics. This category includes various plastics not covered by codes 1-6, some of which may have specific concerns.

🎯 Exam Tip: Resin code 7 is a catch-all category for various plastics, including those like PC and ABS. It's often recommended to be cautious with these for food contact, especially with heat, due to potential chemical leaching.

 

Question 5. Graphene is one atom thick layer of carbon obtained from
(a) diamond
(b) fiillerene
(c) graphite
(d) gas carbon
Answer: (c) graphite
In simple words: Graphene is a super thin, one-atom-thick sheet of carbon, which is taken from graphite. Think of graphite as many layers of graphene stacked together, and graphene is just one of those very strong, conductive layers.

🎯 Exam Tip: Remember that graphite is made of many layers of graphene. Graphene is a 2D material with unique properties, making it very important in new technologies.

 

Question 6. The legal measures to prevent plastic pollution come under the Protection Act 1988.
(a) Forest
(b) Wildlife
(c) Environment
(d) Human rights
Answer: (c) Environment
In simple words: Laws to control plastic pollution are part of the Environment Protection Act of 1988. This act helps manage and reduce environmental issues, including pollution from plastics, to keep our surroundings healthy.

🎯 Exam Tip: Environmental protection laws are crucial for managing waste and pollution. Knowing specific acts helps understand the legal framework for environmental safety.

 

II. Fill in the Blanks:

 

Question 1. ............... named carbon.
Answer: Antoine Lavoisier
In simple words: Antoine Lavoisier was the scientist who first identified and named carbon as an element. He was a very important figure in early chemistry.

🎯 Exam Tip: Historical figures in science are often part of general knowledge questions. Remembering key scientists and their contributions can be helpful.

 

Question 2. Buckminster Fullerene contains .......................... carbon atoms.
Answer: 60
In simple words: Buckminsterfullerene, also called Buckyball, is a special carbon structure shaped like a soccer ball and is made of exactly 60 carbon atoms. It is a unique form of carbon.

🎯 Exam Tip: Fullerenes are a class of carbon allotropes. \( C_{60} \) Buckminsterfullerene is the most well-known example and has a distinct cage-like structure.

 

Question 3. Compounds with same molecular formula and different structural formula are known as ..........................
Answer: Isomers
In simple words: Isomers are different chemical compounds that have the exact same number and type of atoms, but these atoms are arranged in a different order. This difference in arrangement gives them different properties.

🎯 Exam Tip: Isomerism is a fundamental concept in organic chemistry. Be ready to give examples of isomers if asked, showing how the atoms are connected differently.

 

Question 4. .......................... is a suitable solven for Sulphur.
Answer: Allotropy
In simple words: Allotropy is a property of some elements where they can exist in different forms, each with unique physical characteristics. For example, carbon exists as diamond, graphite, and fullerene, which are all allotropes.

🎯 Exam Tip: Focus on the definition of allotropy as different structural forms of an *element*, not a compound, that exist in the same physical state.

 

Question 5. There are .......................... plastic resin codes.
Answer: seven
In simple words: There are seven common types of plastic, each with its own recycling code. These codes help us know what kind of plastic it is and how to recycle it properly.

🎯 Exam Tip: Familiarize yourself with the seven common plastic resin codes (1-7) to understand their uses and recycling guidelines. This knowledge is useful for environmental awareness.

 

III. Match the Following:

 

Question. Match the following.

Answer:
Alkyne - Triple bond
Andre Geim - Graphene
\( C_{60} \) - Bucky Ball
Thermocol - Polystyrene
Combustion - Oxidation
In simple words: We are matching specific chemical terms, names, and materials with their correct descriptions or related concepts. For example, an Alkyne is a type of hydrocarbon with a triple bond, and Andre Geim is a scientist known for his work on Graphene.

🎯 Exam Tip: For matching questions, link each item in the first column to its correct pair in the second. If unsure, match the most obvious pairs first to narrow down the remaining options.

 

IV. Answer in Briefly:

 

Question 1. Differentiate graphite and diamond.
Answer:

In simple words: Graphite and diamond are both made of carbon, but their atoms are arranged differently, giving them very different properties. Graphite is soft, slippery, and conducts electricity, while diamond is extremely hard, transparent, and does not conduct electricity. The way carbon atoms connect in each structure makes all the difference.

🎯 Exam Tip: When differentiating, always use a clear point-by-point comparison, highlighting contrasting properties for each feature. This shows a complete understanding of both substances.

 

Question 2. Write all possible isomers of \( C_4H_{10} \)
Answer:
For the molecular formula \( C_4H_{10} \), there are two possible isomers:
1. n-Butane: This is a straight-chain alkane. Its chemical structure is \( CH_3-CH_2-CH_2-CH_3 \).
2. Isobutane (or 2-Methylpropane): This is a branched-chain alkane. Its chemical structure is \( CH_3-CH(CH_3)-CH_3 \).
These two compounds have the same number of carbon and hydrogen atoms but differ in how these atoms are arranged, leading to different properties. For example, n-butane is a linear chain, while isobutane has a central carbon atom bonded to three other carbon atoms, creating a branched structure.

In simple words: For \( C_4H_{10} \), we can arrange the atoms in two main ways. One way makes a straight line of carbon atoms called n-Butane. The other way makes a branched shape, like a "T" with carbon atoms, called Isobutane. Both have the same chemical formula but different shapes.

🎯 Exam Tip: When drawing isomers, start with the longest possible carbon chain, then gradually shorten the chain and add branches. Ensure each carbon atom forms four bonds and each hydrogen atom forms one bond.

 

Question 3. Carbon forms only covalent compounds. Why?
Answer: Carbon forms only covalent compounds because it has four valence electrons. To achieve a stable octet, carbon needs to either gain four electrons or lose four electrons. However, gaining or losing four electrons requires a very large amount of energy. Instead, carbon atoms share their four valence electrons with other atoms, forming strong covalent bonds. This sharing allows carbon to create a vast array of stable compounds, which is why it is so versatile in chemistry.
In simple words: Carbon has four electrons in its outer shell. It is too hard for it to gain four more or lose all four. So, it shares its electrons with other atoms. This sharing creates strong connections called covalent bonds, making many different carbon compounds.

🎯 Exam Tip: The key to carbon's bonding is its tetravalency. Emphasize that it's the energy cost of forming ions that drives carbon to form covalent bonds through electron sharing.

 

Question 4. Define Allotropy.
Answer: Allotropy is a special property of certain chemical elements that allows them to exist in two or more different forms within the same physical state (solid, liquid, or gas). These different forms are called allotropes. Allotropes show different physical properties due to their distinct structural arrangements, even though they are chemically the same element. For example, carbon has allotropes like diamond, graphite, and fullerenes, all of which are pure carbon but look and behave very differently.
In simple words: Allotropy is when an element can show up in different physical forms, like solid carbon appearing as both a hard diamond and soft graphite. These different forms are called allotropes, and they have different physical looks and feels.

🎯 Exam Tip: When defining allotropy, always mention that it applies to *elements* and that the different forms have distinct *physical properties* but are *chemically similar*.

 

Question 5. Why are one-time use and throwaway plastics harmful?
Answer: One-time use and throwaway plastics are harmful for several reasons:
1. They cause significant short-term and long-term environmental damage by polluting land and water bodies.
2. A large portion of plastics produced today are for single-use items, which quickly turn into waste.
3. These plastics often block drains and pollute water bodies, harming aquatic life and urban infrastructure.
4. They can lead to health problems for humans, plants, and animals, as plastic breaks down into microplastics that enter the food chain and environment.
5. Common examples include plastic carry bags, cups, plates, straws, water pouches, cutlery, and sheets used for food wrapping, all of which contribute to plastic waste. This widespread use makes the problem much bigger.
In simple words: Single-use plastics harm the environment and living things. They pollute our land and water, block drains, and break into tiny pieces that can be dangerous. Many things we use every day, like plastic bags and cups, are thrown away after just one use, adding to the big problem of plastic waste.

🎯 Exam Tip: Focus on the environmental impact (pollution, drain blockage) and the health consequences (microplastics in food chain) when explaining why single-use plastics are harmful. Provide specific examples to support your points.

 

V. Answer in Detail:

 

Question 1. What is catenation? How does carbon form catenated compounds?
Answer: Catenation is the special property of an element to form bonds with atoms of the same element, creating long chains, branched chains, or ring structures. This self-linking ability happens through strong covalent bonds.

Carbon is the most common element that undergoes catenation, forming a huge variety of compounds. Here’s how carbon forms catenated compounds:

• Strong Carbon-Carbon Bonds: Carbon atoms can form very strong covalent bonds with other carbon atoms. This strength allows long and stable chains to be built.
• Tetravalency: Each carbon atom has a valency of four, meaning it can form four bonds. This allows carbon to link with multiple other carbon atoms and also with other elements like hydrogen, oxygen, nitrogen, and sulfur.
• Variety of Structures: Carbon atoms can link together repeatedly to form:
  - Linear chains (straight lines of carbon atoms).
  - Branched chains (carbon chains with side branches).
  - Ring structures (carbon atoms forming a closed loop).
  This diverse bonding capability creates a vast number of different organic compounds, from simple alkanes to complex proteins and DNA.
• Stability of Chains: The carbon-carbon bonds are stable enough to form long chains containing hundreds or even thousands of carbon atoms, as seen in polymers like starch and cellulose.

This unique ability makes carbon the backbone of organic chemistry. For instance, the structure of hydrocarbons varies greatly due to catenation, from methane to complex plastics.

In simple words: Catenation is when an element's atoms can connect to each other to make long chains, branched shapes, or closed rings. Carbon is very good at this because its atoms can form strong bonds with other carbon atoms and make four connections each. This helps create many different carbon compounds like straight chains, branched molecules, and ring structures, which are all very stable.

🎯 Exam Tip: When explaining catenation, clearly state the definition and then elaborate on *why* carbon is unique in this property (strong C-C bonds, tetravalency, and ability to form various chain types).

 

Question 2. What are the chemical reactions of carbon?
Answer: Carbon is a highly versatile element and undergoes various chemical reactions, especially at higher temperatures. Here are some of its key chemical reactions:

1. Reaction with Oxygen (Oxidation/Combustion):
Elemental carbon generally does not react at room temperature. However, when heated, carbon combines with oxygen to form its oxides, releasing heat. This process is called combustion.
For incomplete combustion (less oxygen), carbon monoxide is formed:
\( 2C_{(s)} + O_{2(g)} \longrightarrow 2CO_{(g)} + \text{heat} \)
For complete combustion (sufficient oxygen), carbon dioxide is formed:
\( C_{(s)} + O_{2(g)} \longrightarrow CO_{2(g)} + \text{heat} \)
Organic carbon compounds, like hydrocarbons, also undergo oxidation to form carbon oxides and steam, along with heat and flame, during combustion:
\( CH_{4(g)} + 2O_{2(g)} \longrightarrow CO_{2(g)} + 2H_2O_{(g)} + \text{heat} \)

2. Reaction with Steam:
At high temperatures, carbon reacts with steam (water vapor) to produce carbon monoxide and hydrogen gas. This mixture is known as water gas, which is an important industrial fuel.
\( C_{(s)} + H_2O_{(g)} \longrightarrow CO_{(g)} + H_{2(g)} \)

3. Reaction with Sulphur:
When carbon is heated with sulfur at high temperatures, it forms carbon disulfide.
\( C_{(s)} + S_{(g)} \longrightarrow CS_{2(g)} \)

4. Reaction with Metals (Carbide Formation):
At very high temperatures, carbon can react with certain metals, such as iron, tungsten, and titanium, to form carbides. Carbides are compounds where carbon is bonded to a metal, often having very hard properties.
\( W_{(s)} + C_{(g)} \longrightarrow WC_{(s)} \)
For instance, tungsten carbide (WC) is extremely hard and used in cutting tools. Carbon's ability to react with various substances highlights its chemical versatility and importance in many industrial processes.

In simple words: Carbon can react in several ways, mostly when it's hot. It burns with oxygen to make carbon dioxide or carbon monoxide, releasing heat. It can also react with steam to make "water gas," or with sulfur to make carbon disulfide. At very high temperatures, it can even join with metals to form new compounds called carbides.

🎯 Exam Tip: Remember the different conditions (e.g., presence of oxygen, steam, sulfur, or metals) and the main products formed in each reaction. Pay close attention to balancing the chemical equations.

 

Question 3. Name the three safer resin codes of plastics and describe their features.
Answer: Here are three commonly considered safer resin codes for plastics and their features:

In simple words: Plastics with resin codes 2, 4, and 5 are generally seen as safer for everyday use. Code 2 (HDPE) is strong and used for milk jugs, code 4 (LDPE) is flexible like plastic bags, and code 5 (PP) is tough for containers and bottle caps. These are good choices because they are stable and don't easily release harmful chemicals.

🎯 Exam Tip: When listing safer plastics, mention their resin codes, common uses, and key features like strength, flexibility, and recyclability. This demonstrates a practical understanding of plastic types.

 

VI. Higher Order Thinking Skills:

 

Question 1. Why do carbon exist mostly in combined state?
Answer: Carbon exists mostly in a combined state because of its unique bonding properties. Each carbon atom can form four chemical bonds with other atoms (tetravalency). This allows it to link with other carbon atoms in long chains, branched structures, or rings, and also to bond with many different elements like hydrogen, oxygen, and nitrogen. Because carbon atoms are also just the right size, they can fit comfortably into very large and complex molecules. This ability to form strong, stable, and diverse bonds with itself and other elements means carbon readily combines to create a huge variety of compounds, making it the fundamental element of all known life.
In simple words: Carbon loves to join with other atoms because it can make four strong connections. It can connect to other carbon atoms in many ways, forming long chains or rings. It can also connect to lots of other elements. This makes carbon very busy, so it is usually found combined with other atoms in many different compounds, rather than alone.

🎯 Exam Tip: Highlight carbon's tetravalency and its strong self-linking ability (catenation) as the primary reasons for its prevalence in combined states and the vast number of carbon compounds.

 

Question 2. When a carbon fuel burns in less aerated room, it is dangerous to stay there. Why?
Answer: When carbon fuel burns in a room with poor air supply (less oxygen), it is extremely dangerous to stay there because the fuel undergoes incomplete combustion. This process primarily produces carbon monoxide (CO), which is a highly toxic gas. Carbon monoxide is dangerous because:

• Formation of Carbon Monoxide: With limited oxygen, carbon fuel doesn't burn completely, leading to the formation of carbon monoxide instead of the less harmful carbon dioxide.
• Binding to Hemoglobin: When inhaled, carbon monoxide easily enters the human bloodstream and binds much more strongly to hemoglobin (the oxygen-carrying protein in red blood cells) than oxygen does.
• Oxygen Deprivation: This strong binding prevents hemoglobin from carrying oxygen to the body's cells and tissues.
• Health Effects: A lack of oxygen quickly affects vital functions, leading to symptoms like headache, dizziness, nausea, and confusion.
• Fatal Outcome: Prolonged exposure or high concentrations can rapidly lead to unconsciousness, brain damage, and even death due to suffocation at the cellular level. This is why carbon monoxide is often called a "silent killer" because it is colorless and odorless.

In simple words: Burning carbon fuel in a room with little fresh air is risky because it makes a poisonous gas called carbon monoxide. This gas stops our blood from carrying oxygen to our body, which can make us sick very quickly and even cause death without us knowing, as it has no smell or color.

🎯 Exam Tip: Emphasize that incomplete combustion produces carbon monoxide (CO), not carbon dioxide. Crucially, explain *why* CO is dangerous: its strong affinity for hemoglobin, which prevents oxygen transport and leads to suffocation.

 

Question 3. Explain how dioxins are formed? Which plastic-type they are linked to and why they are harmful to humans?
Answer: Dioxins are highly toxic environmental pollutants that are generally not created on purpose but are formed as unwanted by-products of various human and natural activities.

Dioxin formation:

• Dioxin compounds are not intentionally produced but are formed inadvertently through certain processes.
• These activities include the combustion (burning) of waste, industrial incineration, forest fires, and specific chemical manufacturing processes.
• They can also be produced during the chlorine bleaching of pulp and paper, and from certain pesticide-treated wastes or polychlorinated biphenyls (PCBs).
• Cigarette smoke, some home heating systems, and vehicle exhaust (especially from leaded petrol or diesel fuels) also release small amounts of dioxins.

Their link with plastic:

• Dioxins are mainly linked with PVC (Polyvinyl Chloride) plastics.
• The most dangerous emissions of dioxins can occur when PVC plastics are burned, as the chlorine in PVC contributes to dioxin formation.

Harmful effects of Dioxins to humans:

• Dioxins are among the most toxic compounds for human organisms.
• They can cause cancer and disrupt the endocrine system, which regulates hormones.
• Exposure can lead to alterations in pituitary and thyroid gland functions, weaken the immune system, and cause neurobehavioral effects.
• They can also cause reproductive and developmental issues.
• Dioxins are carcinogenic (cancer-causing), persistent in the environment, and accumulate in body fat. This means mothers can pass them directly to their babies through the placenta.

In simple words: Dioxins are dangerous chemicals that form when things like waste or plastics are burned, especially plastics with chlorine like PVC. They are very bad for people because they can cause cancer, mess with our hormones, weaken our defense system, and harm babies. They stay in our bodies and the environment for a long time.

🎯 Exam Tip: When discussing dioxins, clearly explain their formation (often through combustion), their link to PVC plastics due to chlorine content, and their severe health impacts, especially on the endocrine and immune systems, and their carcinogenic nature.

 

Question 4. Yugaa wants to buy a plastic water bottle. She goes to the shop and sees four different kinds of plastic bottles with resin codes 1, 3, 5, and 7. Which one should she buy? Why?
Answer: Yugaa should buy a plastic water bottle with **Resin Code No. 5 (Polypropylene)**. This type of plastic is generally considered one of the safer plastics for food and beverage containers because it is robust, heat-resistant, and less likely to leach harmful chemicals.

Reasons to avoid resin codes 1, 3, and 7 for reusable water bottles:

• Resin Code 1 (PET or PETE - Polyethylene Terephthalate): This plastic is typically intended for single use. It can release a chemical additive called antimony, especially when exposed to heat or repeated use, which is not good for health.
• Resin Code 3 (PVC - Polyvinyl Chloride): PVC is often considered the most toxic plastic. It can contain harmful chemicals like phthalates and lead, which can leach into contents. It may also have a distinct chemical smell, often described as a "new shoe" smell, and should be avoided for food contact.
• Resin Code 7 (Others, including PC - Polycarbonate and ABS - Acrylonitrile Butadiene Styrene): This category includes various plastics, some of which, like polycarbonate (PC), may contain BPA (Bisphenol A). BPA is an endocrine disruptor and can leach into liquids, posing health risks. These plastics are generally considered unsafe and potentially toxic, especially when heated or scratched.

Therefore, Polypropylene (code 5) is the best choice for a reusable water bottle due to its chemical stability and low risk of leaching harmful substances, making it a safer option for daily hydration.

In simple words: Yugaa should choose a plastic bottle with Resin Code 5, which is Polypropylene. It's thought to be one of the safest plastics because it's strong and doesn't easily let out bad chemicals. Bottles with codes 1, 3, and 7 should be avoided. Code 1 is for one-time use and can release antimony. Code 3 (PVC) is very toxic. Code 7 can include plastics like Polycarbonate that might release BPA, which is harmful.

🎯 Exam Tip: When advising on plastic choices, clearly state the recommended resin code and provide specific reasons for avoiding others, mentioning the harmful chemicals associated with each. This shows a practical application of chemical knowledge.

 

Intext Activities

 

Activity -1

Question. With the help of your teacher, try to classify the following as organic and inorganic compounds.
HCN, \( CO_2 \), Propane, PVC, CO Kerosene, LPG, Coconut oil, Wood, Perfume, Alcohol, \( Na_2CO_3 \), \( CaCO_3 \). MgO, Cotton, Petrol.
Answer:

In simple words: We sort different compounds into two groups: organic and inorganic. Organic compounds mostly contain carbon and hydrogen, often forming complex structures (like propane, wood, or petrol). Inorganic compounds usually don't have carbon-hydrogen bonds and are simpler (like carbon dioxide, magnesium oxide, or common salts).

🎯 Exam Tip: Remember that organic compounds typically contain carbon-hydrogen bonds, while inorganic compounds usually do not. Some exceptions exist, like carbon monoxide and carbon dioxide, which are generally classified as inorganic.

 

Activity -2

Question. Take a football since it resembles Buckminsterfullerene. Count how many hexagonal and pentagonal panels are in it very corner is considered as one carbon. Compare your observation with fullerene and discuss with your friends.
Aim: To compare the structure of fullerene with football.
Materials required: Football
Procedure:
1. Take a football.
2. Count the hexagonal and pentagonal ring shapes on the football.
Observation:

Conclusion: The structure of a football is compared with fullerene.
In simple words: This activity shows how a football is like a C60 fullerene molecule. Both have 12 pentagonal (5-sided) and 20 hexagonal (6-sided) shapes, creating a closed, cage-like structure. Each corner of these shapes on the football can be thought of as a carbon atom in the fullerene.

🎯 Exam Tip: The football analogy is a great way to remember the structure of \( C_{60} \) fullerene. Focus on the numbers of pentagonal and hexagonal faces, as these are consistent in the \( C_{60} \) structure.

 

9th Science Guide Carbon and its Compounds Additional Questions and Answers

 

I. Choose the Correct Answer:

 

Question 1. Carbon is one of the most important ........................ element.
(a) Metallic
(b) Non-metallic
(c) Metalloid
(d) None of the options
Answer: (b) Non-metallic
In simple words: Carbon is a non-metallic element, meaning it does not have the properties of metals like being shiny, malleable, or a good conductor of heat and electricity in its elemental form (except graphite). It is crucial for all living things.

🎯 Exam Tip: Recall the basic properties of metals and non-metals. Carbon, despite its unique bonding abilities, falls under the category of non-metals.

 

Question 3. ................... is the first organic compound synthesized in the laboratory.
(a) Urea
(b) Acetic acid
(c) Methane
(d) Ethanol
Answer: (a) Urea
In simple words: Urea was the very first organic compound that scientists successfully made in a laboratory from non-living chemicals. This was a big step in chemistry.

🎯 Exam Tip: Remember important historical facts in chemistry, especially those that marked significant scientific breakthroughs or changed previous beliefs.

 

Question 4. The main component of water gas is ...................
(a) Carbon dioxide
(b) Carbon monoxide
(c) Calcium carbide
(d) Methane
Answer: (b) Carbon monoxide
In simple words: Water gas is a mixture of gases, and its main part is carbon monoxide. This gas is made when steam reacts with hot carbon.

🎯 Exam Tip: Familiarize yourself with common industrial gases and their main components, as this is a fundamental concept in applied chemistry.

 

Question 5. The ability of carbon to form ................... is the main reason for the formation of various classes of carbon compounds.
(a) Tetravalency
(b) Catenation
(c) Isomerism
(d) Multiple bonds
Answer: (b) Catenation
In simple words: Carbon can join with other carbon atoms to form long chains or rings. This special ability, called catenation, helps create many different types of carbon compounds.

🎯 Exam Tip: Understand catenation and tetravalency as the two primary reasons for carbon's unique ability to form millions of compounds.

 

Question 6. Arrangement of atoms in diamond is ...................
(a) Hexagonal
(b) Trigonal
(c) Tetrahedral
(d) Pentagonal
Answer: (c) Tetrahedral
In simple words: In a diamond, each carbon atom is connected to four other carbon atoms, forming a 3D shape like a small pyramid. This strong structure makes diamond very hard.

🎯 Exam Tip: Distinguish between the atomic arrangements of different carbon allotropes (diamond, graphite, fullerene) as this explains their varied properties.

 

Question 7. The amorphous allotropic carbon used for making electrodes in dry cell
(a) Coke
(b) Charcoal
(c) Lampblack
(d) Gas carbon
Answer: (d) Gas carbon
In simple words: Gas carbon is a form of carbon that doesn't have a clear crystal shape. It's often used to make the parts of batteries that conduct electricity.

🎯 Exam Tip: Be aware of the different uses of various carbon allotropes, both crystalline and amorphous, based on their properties.

 

Question 8. Elemental carbon undergoes ................... reaction at room temperature.
(a) Oxidation
(b) Reduction
(c) Free radical
(d) no.
Answer: (d) no
In simple words: Pure carbon, like graphite or diamond, usually does not react with other things when it's just at normal room temperature. It needs heat to start reacting.

🎯 Exam Tip: Understand that elemental carbon is generally unreactive at room temperature but becomes highly reactive at elevated temperatures.

 

Question 9. Amorphous forms of carbon and graphite are almost ............... in colour.
(a) Grey
(b) brownish
(c) black
(d) dirty white
Answer: (c) black
In simple words: Most forms of carbon that are not clear like diamond, such as coal, charcoal, or even the common pencil lead (graphite), appear black in color.

🎯 Exam Tip: Learn the basic physical properties, like color, of common allotropes of carbon to easily identify them.

 

Question 10. Carbon monoxide displaces ................... from hemoglobin.
(a) nitrogen
(b) oxygen
(c) hydrogen
(d) carbon dioxide
Answer: (b) oxygen
In simple words: Carbon monoxide is very dangerous because it attaches to hemoglobin in your blood much more easily than oxygen. This stops oxygen from reaching your body's cells.

🎯 Exam Tip: Understand the physiological effects of toxic gases, especially how carbon monoxide interferes with oxygen transport in the body.

 

Question 11. Burning of PVC releases
(a) Dioxins
(b) Carbon monoxide
(c) Sulphur dioxide
(d) Chlorine
Answer: (a) Dioxins
In simple words: When PVC plastic is burned, it can create very harmful chemicals called dioxins. These chemicals are highly toxic and bad for health.

🎯 Exam Tip: Be aware of the environmental and health impacts of burning different types of plastics, particularly those that release toxic substances.

 

Question 12. Which among the following plastics release antimony when we reuse.
(a) PVC
(b) HDPE
(c) PP
(d) PET
Answer: (d) PET
In simple words: When plastic bottles made of PET are reused many times, they can sometimes release tiny amounts of a chemical called antimony. This is why it's better to use these bottles for a limited time.

🎯 Exam Tip: Know which chemicals are associated with different plastic types and the potential risks of reusing certain plastics, especially for food and drink.

 

Question 13. According to the Octet rule, carbon requires ................... electrons to attain the nearest noble gas.
(a) One
(b) two
(c) Three
(d) Four
Answer: (d) Four
In simple words: The octet rule says atoms want to have eight electrons in their outermost shell. Carbon has four, so it needs four more electrons to become stable like a noble gas.

🎯 Exam Tip: Remember the octet rule and how it applies to carbon's bonding behavior, which involves sharing four electrons (tetravalency).

 

Question 14. Most one-time use plates are made from ...................
(a) Polypropylene
(b) Polystyrene
(c) Polyethylene
(d) Polyvinylchloride
Answer: (b) Polystyrene
In simple words: Many plates designed to be used just once, like disposable foam plates, are made from polystyrene. This material is cheap to produce but not good for the environment.

🎯 Exam Tip: Learn about common plastics used in everyday items, especially single-use plastics, and their environmental implications.

 

Question 15. Which among the following compound is soluble in water?
(a) Methane
(b) Ethylene
(c) Ethanol
(d) Phenol
Answer: (c) Ethanol
In simple words: Ethanol, which is alcohol, can easily mix and dissolve in water. The other options, like methane, do not mix well with water.

🎯 Exam Tip: Understand the factors that affect solubility, such as polarity and hydrogen bonding, which explain why ethanol dissolves in water but methane does not.

 

Question 16. The number of free electrons in each carbon of diamond is
(a) Zero
(b) One
(c) Two
(d) None of these
Answer: (a) Zero
In simple words: In a diamond, every carbon atom uses all its outer electrons to form strong bonds with four other carbon atoms. Because all electrons are used in bonding, there are no free electrons to move around.

🎯 Exam Tip: Remember that the absence of free electrons is why diamond is a poor conductor of electricity, unlike graphite which has delocalized electrons.

 

Question 17. The carbon atoms in Graphene are arranged in
(a) Hexagon
(b) Pentagon
(c) octagon
(d) Tetragon
Answer: (a) Hexagon
In simple words: Graphene is made of carbon atoms joined together in flat layers, and these atoms are always arranged in a repeating pattern of six-sided rings, like a honeycomb.

🎯 Exam Tip: Visualize the structure of graphene as a single layer of graphite, characterized by its hexagonal lattice arrangement.

 

Question 18. Resin Code" represents the type of ............ used to make the plastic.
(a) Polymer
(b) Rubber
(c) monomer
(d) Polymerisation
Answer: (a) Polymer
In simple words: A plastic resin code tells us what kind of polymer was used to make that specific plastic item. Polymers are large molecules made of many smaller repeating units.

🎯 Exam Tip: Connect the concept of "resin code" to the underlying chemical structure of plastics, which are primarily polymers.

 

Question 19. Diamond is not a good conductor of electricity because
(a) it is very hard
(b) it has no free electron
(c) its structure is uniform
(d) it is insoluble in water
Answer: (b) it has no free electron
In simple words: Diamond cannot carry electricity because all its electrons are locked in strong bonds between carbon atoms. There are no loose electrons that can move and conduct electricity.

🎯 Exam Tip: A key principle in electrical conductivity is the presence of mobile charge carriers, such as free electrons. Diamond lacks these.

 

Question 20. Which of the following is highly toxic?
(a) Carbon dioxide
(b) Carbon monoxide
(c) Calcium carbonate
(d) Sodium bicarbonate
Answer: (b) Carbon monoxide
In simple words: Carbon monoxide is very harmful and poisonous, even in small amounts, because it stops your blood from carrying oxygen to your body. The other options are much less toxic.

🎯 Exam Tip: Distinguish between carbon dioxide, which is a greenhouse gas, and carbon monoxide, which is a lethal poison due to its effect on hemoglobin.

 

Question 21. Which of the following plastic items are banned by the Government of Tamil Nadu as of 1st January 2019?
(a) Plastic sheets
(b) Plastic teacups
(c) Plastic water packet
(d) All of the options
Answer: (d) All of the options
In simple words: The government of Tamil Nadu banned several single-use plastic items, including plastic sheets, teacups, and water packets, starting in 2019 to help reduce pollution.

🎯 Exam Tip: Be aware of environmental regulations and bans related to plastics, as they are often aimed at reducing pollution from single-use items.

 

Question 22. Graphite is used as a lubricant in machines because
(a) it is a good conductor of electricity
(b) it is made of slippery layers and has a high melting point
(c) it has a high density
(d) it is strong and soft
Answer: (b) it is made of slippery layers and has a high melting point
In simple words: Graphite's atoms are arranged in layers that can slide over each other easily, making it slippery. This property, combined with its high melting point, makes it perfect for lubricating machines.

🎯 Exam Tip: Understand how the layered structure of graphite contributes to its softness and lubricating properties, making it useful in various applications.

 

Question 23. Plastic resin codes are shown as three chasing arrows in a ................... with a number in the middle or letters (an acronym of that plastic type).
(a) Logo
(b) Recycling Symbol
(c) Square
(d) Triangle
Answer: (b) Recycling Symbol
In simple words: The symbol with three arrows chasing each other, along with a number or letters inside, is a universal sign that tells you if a plastic item can be recycled and what type of plastic it is.

🎯 Exam Tip: Recognize the recycling symbol and understand that the number inside it indicates the type of plastic, which is crucial for proper waste segregation.

 

II. Fill in the blanks :

 

Question 1. ............... is the main constituent of coal.
Answer: Carbon
In simple words: Coal is mostly made up of carbon. This carbon comes from ancient plants that were buried and changed over a very long time.

🎯 Exam Tip: Remember that coal is a fossil fuel primarily composed of carbon, formed from the decomposition of plant matter.

 

Question 2. Carbon chemistry is also called as ...................
Answer: Living chemistry
In simple words: The study of carbon compounds is often called living chemistry because carbon is the main element in all living things, and its compounds are fundamental to life.

🎯 Exam Tip: Understand that organic chemistry, the study of carbon compounds, is essentially the chemistry of life, hence the term "living chemistry."

 

Question 3. Graphene has a thickness of just ................... atom.
Answer: One
In simple words: Graphene is incredibly thin, made up of only a single layer of carbon atoms arranged in a hexagon pattern. This makes it the thinnest material known.

🎯 Exam Tip: Highlight graphene's unique property of being a single-atom-thick material, which contributes to its exceptional strength and conductivity.

 

Question 4. ................... is the Father of Modern Organic Chemistry
Answer: Friedrich Wohler
In simple words: Friedrich Wohler is known as the "Father of Modern Organic Chemistry" because he was the first person to make an organic compound (urea) from inorganic chemicals in a lab.

🎯 Exam Tip: Associate key scientists with their groundbreaking contributions, like Wohler's synthesis of urea which challenged the vital force theory.

 

Question 5. The inorganic carbon compound that takes part in photosynthesis is ...................
Answer: Carbon dioxide
In simple words: During photosynthesis, plants use carbon dioxide from the air as a key ingredient, along with sunlight and water, to make their own food and release oxygen.

🎯 Exam Tip: Recall the essential role of carbon dioxide in photosynthesis, where it is converted into organic compounds by plants.

 

Question 6. The carbon cycle is the ................... cycle.
Answer: Biogeochemical
In simple words: The carbon cycle is called a biogeochemical cycle because it involves the movement of carbon through living things, Earth's rocks and soil, water, and the air.

🎯 Exam Tip: Understand the term "biogeochemical" as it signifies the involvement of biological, geological, and chemical processes in nutrient cycles.

 

Question 7. ................... structure accountable for hardness and rigidity of diamond.
Answer: Three dimensional
In simple words: Diamond's strong, rigid, and very hard nature comes from its atoms being linked together in a complex, three-dimensional network. This structure makes it very tough.

🎯 Exam Tip: Connect the macroscopic properties of materials, such as hardness, to their microscopic atomic arrangements and bonding patterns.

 

Question 8. Hexagonal layers in Graphite are held together by ...................
Answer: weak VanderWaals forces
In simple words: In graphite, the flat layers of carbon atoms are held together by very weak forces. These weak connections allow the layers to slide over each other easily.

🎯 Exam Tip: Remember that the weak Van der Waals forces between graphite layers are responsible for its soft, slippery nature and lubricating properties.

 

Question 9. Pet name for Buckminster Fullerene is ...................
Answer: Bucky ball
In simple words: Buckminsterfullerene, which looks like a tiny soccer ball, is often called a "bucky ball" for short. It's a unique form of carbon with 60 atoms.

🎯 Exam Tip: Familiarize yourself with common informal names for scientific compounds, such as "bucky ball" for Buckminsterfullerene.

 

Question 10. A large family of fullerene exists, starting at ................... and reaching upto .
Answer: C20, C540
In simple words: Fullerenes are a group of carbon molecules that can have many different numbers of carbon atoms, starting from as few as 20 and going up to over 500 atoms in a cage-like structure.

🎯 Exam Tip: Understand that fullerenes are a diverse class of carbon allotropes, not just C60, with various cage-like structures.

 

Question 11. Graphene is ................... shaped hexagonal ring
Answer: Honeycomb
In simple words: Graphene's structure is like a flat sheet of carbon atoms connected in repeating six-sided rings, which looks very much like a honeycomb pattern.

🎯 Exam Tip: Visualize the distinctive two-dimensional honeycomb lattice of graphene as fundamental to its extraordinary properties.

 

Question 12. Cigarette smoking is a source of ...................
Answer: Carbon Monoxide
In simple words: When a cigarette burns, it creates carbon monoxide gas. This harmful gas is breathed in by smokers and can cause serious health problems.

🎯 Exam Tip: Be aware of the harmful byproducts of combustion, such as carbon monoxide, and their health consequences.

 

Question 13. Carbon monoxide enters into human body through ...................
Answer: breathing
In simple words: Carbon monoxide enters the human body when someone breathes in air that contains this gas. It then quickly travels into the bloodstream through the lungs.

🎯 Exam Tip: Understand the primary route of entry for airborne toxins into the human body, which is typically through the respiratory system.

 

Question 14. Do not use ................... for school projects.
Answer: Thermocol
In simple words: Thermocol, which is a type of polystyrene foam, should not be used for school projects because it is not environmentally friendly and can be hard to dispose of.

🎯 Exam Tip: Advocate for eco-friendly practices by avoiding non-biodegradable materials like thermocol in projects and daily life.

 

Question 15. Polycarbonate (PC) plastic contains ...................
Answer: Bisphenol A
In simple words: Polycarbonate plastics often contain a chemical called Bisphenol A, also known as BPA. Some people worry about its health effects, especially when used in food containers.

🎯 Exam Tip: Be informed about chemicals like Bisphenol A (BPA) found in certain plastics and their potential health implications, leading to choices like "BPA-free" products.

 

III. Match the following :

 

(I)

Answer: 1-c, 2-d, 3-a, 4-b
In simple words: Graphite has a hexagonal arrangement. Fullerene often has a dome-shaped structure, like a soccer ball. Graphene is a single layer with a honeycomb pattern. Diamond has a tetrahedral network.

🎯 Exam Tip: When matching, clearly understand the characteristic structures of each carbon allotrope (e.g., hexagonal layers for graphite/graphene, tetrahedral for diamond, cage-like for fullerene).

 

(II)

Answer: 1-b, 2-c, 3-a, 4-d
In simple words: Resin code 2 is for High Density Polyethylene. Resin code 5 is Polypropylene. Resin code 4 is for Low Density Polyethylene. Resin code 1 is for Polyester (often PET).

🎯 Exam Tip: Memorize the common plastic resin codes (1-7) and their corresponding plastic names, as this is crucial for understanding recycling and plastic properties.

 

(III)

Answer: 1-c, 2-a, 3-b, 4-c
In simple words: Resin code 3 means PVC (Polyvinyl Chloride). Resin code 6 stands for PS (Polystyrene). Resin code 7 refers to Other plastics, often including ABS. Resin code 4 is for LDPE, but in this matching, it's mapped to PVC according to the source.

🎯 Exam Tip: Pay close attention to the specific options provided in matching questions, even if some mappings seem unusual or potentially incorrect based on general knowledge.

 

IV. True or False :

 

Question 1. About 18% of the weight of the human body is carbon.
Answer: True.
In simple words: Carbon is a very important element in our bodies, making up almost one-fifth of our total weight. It forms the backbone of all organic molecules like proteins and DNA.

🎯 Exam Tip: Remember the significant percentage of carbon in the human body, highlighting its role as a fundamental building block of life.

 

Question 2. There is more abundance of carbon in the earth
Answer: False.
Correct statement: There is less abundance of carbon in the earth.
In simple words: Carbon is not the most common element on Earth. While important, it is less abundant compared to elements like oxygen, silicon, or iron in the Earth's crust.

🎯 Exam Tip: When a True/False statement is false, always be prepared to provide the corrected statement to demonstrate complete understanding.

 

Question 3. Carbon has the tendency to lose its four electrons with that of other atoms to complete its octet.
Answer: False.
Correct statement: Carbon has the tendency to share its four electrons with that of other atoms to complete its octet
In simple words: Carbon does not usually lose or gain four electrons because it takes too much energy. Instead, it prefers to share its four outermost electrons with other atoms to become stable.

🎯 Exam Tip: Emphasize that carbon primarily forms covalent bonds by sharing electrons, rather than ionic bonds by losing or gaining them, due to its tetravalency.

 

Question 4. All the allotropic forms of carbon are solids.
Answer: True.
In simple words: Different forms of carbon, like diamond, graphite, and fullerenes, all exist as solid materials at room temperature. They are simply arranged differently.

🎯 Exam Tip: Recognize that allotropy refers to different structural forms of an element in the same physical state, which for carbon is solid.

 

Question 5. Carbon's amorphous forms have high melting and boiling poult compared to crystalline forms.
Answer: False.
Correct statement: Carbon's amorphous forms have low melting and boiling point compared to crystalline forms.
In simple words: Amorphous carbon, like charcoal, has a less organized structure, which generally means it melts and boils at lower temperatures than highly structured crystalline forms like diamond or graphite.

🎯 Exam Tip: Remember that crystalline structures, with their ordered and strong bonding networks, typically have higher melting and boiling points than amorphous forms.

 

Question 6. Used plate is easy to recycle.
Answer: False.
Correct statement: Used plate difficult to recycle.
In simple words: Many used plastic plates are difficult to recycle because they are often contaminated with food waste or made from mixed materials, making the recycling process complicated and costly.

🎯 Exam Tip: Understand the practical challenges in recycling, such as contamination and material sorting, which make certain used items hard to process.

 

Question 7. Do not eat hot food items in plastic containers.
Answer: True.
In simple words: It's best not to put hot food in plastic containers because the heat can make harmful chemicals from the plastic leak into your food.

🎯 Exam Tip: Be aware of the potential for chemical leaching from plastics into food, especially when exposed to heat, and choose safer alternatives for hot meals.

 

V. Assertion and Reason type questions :

 

Question 1. Assertion (A) : The number of carbon compounds alone is more than the number of compounds of all the elements taken together. Reason (R) : Carbon has some unique properties such as 1) Catenation, 2) Tetravalency, 3) Multiple bonds, 4) Allotropy, 5) Isomerism.
Answer: (a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
The assertion is true because carbon's special properties, like forming many bonds and linking to itself (catenation), allow it to create a huge variety of compounds. The reason correctly lists these properties, explaining why the assertion is true. Carbon's ability to form stable bonds with itself and other elements in diverse arrangements is unmatched.
In simple words: Carbon can make many, many different kinds of compounds because it has special skills like linking up with itself and making four bonds. This is why there are more carbon compounds than all other elements combined.

🎯 Exam Tip: For Assertion-Reason questions, first check if both statements are individually true, then determine if the reason directly explains the assertion's truth.

 

Question 2. Assertion (A): There are various classes of carbon compounds formed. Reason (R) : The property of Isomerism is the main reason.
Answer: (c) If Assertion is true but the reason is false
Reason: The ability to form multiple bonds is the main reason.
The assertion is true because carbon forms a vast number of compounds. However, isomerism (where compounds have the same formula but different structures) is just one contributing factor. The primary reasons for carbon's diversity are its tetravalency and catenation, allowing it to form stable single, double, and triple bonds. The ability to form multiple bonds is key to structural variety.
In simple words: Carbon does make many kinds of compounds (Assertion is true). But, the reason why it makes so many is not just about isomers. It's more about carbon being able to make four strong bonds and link up with itself (catenation).

🎯 Exam Tip: Differentiate between primary reasons (like tetravalency and catenation) and secondary factors (like isomerism) when explaining the diversity of carbon compounds.

 

Question 3. Assertion (A) : Carbon monoxide is a toxic gas of carbon. Reason (R): smoking is a source of carbon monoxide.
Answer: (b) If both assertion and reason are true but the reason is not the correct explanation for assertion
Both statements are true: carbon monoxide is indeed a toxic gas, and smoking is a source of it. However, smoking being a source does not explain *why* carbon monoxide is toxic. Its toxicity comes from its ability to bind to hemoglobin, not from where it originates. Carbon monoxide is toxic regardless of its source.
In simple words: Carbon monoxide is a poisonous gas (true). Also, smoking makes carbon monoxide (true). But, smoking being a source doesn't explain *why* the gas is poisonous. The gas is poisonous because it harms your blood.

🎯 Exam Tip: For Assertion-Reason questions, ensure the reason provides a direct causal explanation for the assertion, not just another true statement related to it.

 

Question 4. Assertion (A): PVC is an unsafe plastic. Reason (R)Burning PVC releases dioxins, a most toxic chemical.
Answer: (a) If both Assertion and Reason are true and Reason is the correct explanation for Assertion
The assertion that PVC is unsafe is true. The reason provides a direct explanation: burning PVC releases dioxins, which are highly toxic chemicals. This chemical release is a significant factor contributing to PVC's classification as an unsafe plastic. Dioxins are known carcinogens and environmental pollutants.
In simple words: PVC plastic is unsafe (true), and this is because when you burn it, very harmful chemicals called dioxins are released (true and explains why it's unsafe).

🎯 Exam Tip: Link the properties of specific plastics to their chemical composition and the potential environmental and health hazards associated with their disposal.

 

VI. Answer the following by rearranging the jumbled letters :

 

Question 1. It is the hardest allotrope of carbon mnodaid
Answer: Diamond
In simple words: The jumbled letters "mnodaid" spell out "Diamond." Diamond is known as the hardest natural material on Earth.

🎯 Exam Tip: Use the clue provided in the question ("hardest allotrope of carbon") to help deduce the jumbled word, rather than solely relying on letter rearrangement.

 

Question 2. Organic compounds having a double bond between carbon atoms are knelaes
Answer: (jumbled letters decoded as) Alkenes
In simple words: These are hydrocarbons that have at least one carbon-carbon double bond. These compounds are often used as building blocks in making plastics and other chemicals.

🎯 Exam Tip: Identifying the number of carbon atoms and the presence of double or triple bonds is crucial for naming organic compounds.

 

Question 3. Reaction of carbon with oxygen gives osdiex
Answer: (jumbled letters decoded as) Oxides
In simple words: These are compounds that form when oxygen reacts with another element, like carbon. Carbon dioxide, a common carbon oxide, is a gas vital for plant photosynthesis.

🎯 Exam Tip: Remember that carbon forms both carbon monoxide (CO) and carbon dioxide (CO2) when reacting with oxygen, depending on the oxygen supply.

 

Question 4. In this molecule, carbon is attached to four hydrogen atoms. emathen
Answer: (jumbled letters decoded as) Methane
In simple words: It's a gas where one carbon atom is joined to four hydrogen atoms. Methane is the main component of natural gas, a common fuel.

🎯 Exam Tip: Methane is the simplest alkane and a powerful greenhouse gas, important in both natural gas and environmental studies.

 

Question 5. Carbon combines with other elements through the ______ bond. Inaocvet
Answer: (jumbled letters decoded as) Covalent
In simple words: This is a type of bond where atoms share electrons with each other. Covalent bonds are very strong, allowing carbon to form many stable compounds.

🎯 Exam Tip: Carbon's ability to form four strong covalent bonds is the basis for the vast number of organic compounds.

 

Question 6. Plastics made of ______ are represented by resin code #6. sytlopynere
Answer: (jumbled letters decoded as) Polystyrene
In simple words: This is a type of plastic often used for foam cups and food containers, and it has the resin code number 6. Polystyrene foam is known for its excellent insulation properties, keeping things hot or cold.

🎯 Exam Tip: Knowing plastic resin codes helps in proper recycling and making informed choices about plastic use.

 

Question 7. One-time use plastics are also known as ______ plastics. áwyrhotwa
Answer: (jumbled letters decoded as) throwaway
In simple words: These are plastics meant to be used just once and then thrown away. Such plastics contribute significantly to waste generation and environmental pollution.

🎯 Exam Tip: Always be aware of single-use plastics and look for reusable alternatives to reduce waste.

 

Question 8. One-time use plastics cause ______ damage. trnvomenialne
Answer: (jumbled letters decoded as) Environmental
In simple words: These plastics harm nature, like animals and oceans. This damage includes harming wildlife, polluting water, and creating large amounts of waste that lasts a long time.

🎯 Exam Tip: Emphasize the long-term impact of plastic waste, particularly on marine life and ecosystems.

 

Question 9. Expanded polystyrene is commercially known as ______ mthreolco
Answer: (jumbled letters decoded as) Thermocol
In simple words: This is a light, white foam plastic, often used for packaging. It is widely used in packaging to protect fragile items during shipping because of its shock-absorbing qualities.

🎯 Exam Tip: While useful for insulation and packaging, thermocol is difficult to recycle and often contributes to landfill waste.

VII. Very Short Answer Questions:

 

Question 1. How can graphite be transformed to diamond?
Answer: Graphite can be changed into diamond by applying very high temperatures and intense pressure. This process mimics the natural conditions deep within the Earth where diamonds form. This transformation involves reorganizing the carbon atoms from a layered structure to a compact, tetrahedral lattice.
In simple words: To make diamond from graphite, you need to use extreme heat and squeeze it with a lot of force.

🎯 Exam Tip: Remember that both graphite and diamond are allotropes of carbon, meaning they are made of the same element but have different atomic arrangements.

 

Question 2. How did the ancients obtain charcoal?
Answer: Ancient people made charcoal by burning organic materials like wood in a limited supply of oxygen. This slow burning removed water and other volatile compounds, leaving behind almost pure carbon. Charcoal was highly valued as a fuel for metallurgy and cooking because it burned hotter and cleaner than wood.
In simple words: People long ago made charcoal by burning wood or plants very slowly, without much air.

🎯 Exam Tip: The process of making charcoal is a form of pyrolysis, where organic materials are decomposed by heat in the absence of oxygen.

 

Question 3. Which theory was challenged by the synthetic preparation of Urea?
Answer: The theory challenged by the creation of urea in a lab was the 'Vital Force Theory'. This theory stated that organic compounds could only be made by living organisms, not by artificial means. Friedrich Wöhler's synthesis of urea from inorganic compounds in 1828 marked a significant turning point in the history of chemistry.
In simple words: Making urea in a lab showed that the idea of 'vital force' was wrong. This theory said only living things could make organic stuff.

🎯 Exam Tip: Wöhler's synthesis of urea is considered a milestone, leading to the rise of modern organic chemistry as a distinct field of study.

 

Question 4. Name two inorganic carbon compounds which are used as an antacid?
Answer: Two inorganic carbon compounds used as an antacid are calcium carbonate \( CaCO_3 \) and sodium bicarbonate \( NaHCO_3 \). These compounds help to neutralize excess stomach acid. Antacids work by reacting with hydrochloric acid in the stomach to raise the pH and relieve symptoms of heartburn.
In simple words: Two carbon compounds used as antacids are calcium carbonate and sodium bicarbonate. They help calm an upset stomach.

🎯 Exam Tip: Remember that antacids are bases that react with the acidic environment of the stomach to provide relief.

 

Question 5. What is tetravalency?
Answer: Tetravalency is the special ability of a carbon atom to form four chemical bonds by sharing its four valence electrons with other atoms. This allows it to achieve a stable outer shell with eight electrons, known as an octet. This unique property enables carbon to form a vast array of complex and diverse organic compounds.
In simple words: Tetravalency means carbon can make four connections with other atoms by sharing its electrons. This makes it very stable.

🎯 Exam Tip: Carbon's tetravalency is fundamental to understanding the structure and reactivity of all organic molecules.

 

Question 6. Name the primary factor that determines the physical and chemical properties of compounds.
Answer: The most important factor that decides how a compound behaves, both physically and chemically, is the nature of the chemical bonds within it. These bonds dictate how atoms interact and the overall structure of the molecule. For example, strong covalent bonds lead to high melting points, while weaker intermolecular forces result in lower melting points.
In simple words: The type of chemical bond in a compound is what mainly decides its physical and chemical features.

🎯 Exam Tip: Understanding bonding, such as ionic, covalent, or metallic, is key to predicting a compound's properties.

 

Question 7. Why do elements show allotropy?
Answer: Elements show allotropy because they can exist in different structural forms. These different arrangements of atoms lead to various physical and chemical properties for the same element, even in the same physical state. Allotropy occurs due to different ways atoms are bonded or arranged within the substance.
In simple words: Elements show allotropy because their atoms can arrange themselves in different ways, creating different forms of the same element.

🎯 Exam Tip: Common examples of allotropy include carbon (diamond, graphite) and oxygen (O2, O3).

 

Question 8. Why is graphite softer than a diamond?
Answer: Graphite is much softer than diamond because of its atomic structure. In graphite, carbon atoms are arranged in flat hexagonal layers that are stacked on top of each other. These layers are held together by weak forces called van der Waals forces, allowing them to slide past each other easily. This layered structure also makes graphite an excellent lubricant and a conductor of electricity.
In simple words: Graphite is soft because its carbon atoms are in layers that slide easily, held by weak forces. Diamond is hard because its atoms are strongly locked together.

🎯 Exam Tip: Remember the key difference: strong covalent bonds throughout the diamond lattice versus weak intermolecular forces between layers in graphite.

 

Question 9. What are Polymer resins?
Answer: Polymer resins are essentially plastics, which are large molecules made up of many small repeating units linked together to form long chains. These long-chain organic compounds give plastics their unique properties. These materials can be molded into various shapes when soft and then hardened, making them useful for countless products.
In simple words: Polymer resins are materials like plastic, made from many small parts joined into long chains.

🎯 Exam Tip: The term 'polymer' comes from Greek, meaning 'many parts,' highlighting the repeating unit structure.

 

Question 10. List the three unsafe plastics.
Answer: The three resin codes generally considered unsafe are numbers 3, 6, and 7. These codes represent plastics that may leach harmful chemicals into food or liquids. Many countries are now working to reduce the use of these particular plastics due to health and environmental concerns.
In simple words: PVC (Polyvinyl Chloride), Polystyrene (like Thermocol), and Polycarbonates (type 7) are three plastics that are not very safe.

🎯 Exam Tip: Familiarize yourself with the seven plastic resin codes, especially those to avoid for food contact.

 

Question 11. How many valence electrons are there in carbon?
Answer: Carbon has 4 valence electrons. These are the electrons in the outermost shell that are available for forming chemical bonds, even though carbon has a total of 6 electrons. Having four valence electrons allows carbon to form four stable bonds, which is fundamental to organic chemistry.
In simple words: Carbon has 4 electrons in its outer shell. These are the ones it uses to make connections with other atoms.

🎯 Exam Tip: The number of valence electrons determines an element's bonding capacity and chemical reactivity.

 

Question 12. Who is called 'Father of Modern Organic Chemistry'?
Answer: Friedrich Wöhler is known as the 'Father of Modern Organic Chemistry'. He earned this title after synthesizing urea from inorganic compounds in 1828. His groundbreaking work disproved the vital force theory, opening new avenues for the study of carbon compounds.
In simple words: Friedrich Wöhler is called the father of modern organic chemistry. He was famous for making urea in a lab.

🎯 Exam Tip: Be sure to correctly spell "Friedrich Wöhler" and remember the year 1828 as a key historical date in chemistry.

 

Question 13. Which three resin codes are unsafe?
Answer: The three resin codes generally considered unsafe are numbers 3, 6, and 7. These codes represent plastics that may leach harmful chemicals into food or liquids. Code 3 is PVC, Code 6 is polystyrene, and Code 7 includes various other plastics like polycarbonates.
In simple words: Plastic codes 3, 6, and 7 are usually not safe to use for food or drinks.

🎯 Exam Tip: Advise students to look for resin codes 1, 2, 4, and 5 for safer plastic choices, especially for food and beverage containers.

VIII. Short Answer Questions:

 

Question 1. Prove that a diamond is a pure form of carbon?
Answer: Diamond is proven to be a pure form of carbon because when equal amounts of both diamond and charcoal (another form of carbon) are burned completely, they both produce the exact same amount of carbon dioxide. This shows that, like charcoal, diamond is composed solely of carbon atoms. This experiment demonstrates the law of conservation of mass and the elemental purity of diamond.
In simple words: If you burn diamond and charcoal, they both make the same amount of carbon dioxide. This shows diamond is pure carbon, just like charcoal.

🎯 Exam Tip: This experiment is a classic example of proving elemental composition through combustion analysis, leading to carbon dioxide as the sole product.

 

Question 2. Write the classification of carbon compounds.
Answer: Carbon compounds are broadly classified into two main types: Organic Carbon Compounds and Inorganic Carbon Compounds. This classification helps us understand their different origins and properties.

In simple words: Carbon compounds are divided into organic (from living things) and inorganic (from non-living things).

🎯 Exam Tip: While organic compounds are primarily based on carbon, some simple carbon compounds like carbonates and oxides are traditionally classified as inorganic.

 

Question 3. Write short notes on the carbon cycle.
Answer: The carbon cycle describes how carbon moves through different parts of Earth's systems. It is a biogeochemical cycle where carbon is exchanged between living things (biosphere), rocks and soil (geosphere), water bodies (hydrosphere), and the air (atmosphere). Carbon is vital as it forms the backbone of all biological compounds and is also a key part of many minerals, such as limestone. This cycle helps regulate Earth's climate and the availability of carbon for life processes.
In simple words: The carbon cycle shows how carbon moves around the Earth. It goes from living things, rocks, water, and the air. Carbon is important for all life and for many rocks.

🎯 Exam Tip: Emphasize the interconnectedness of the biosphere, geosphere, hydrosphere, and atmosphere in the carbon cycle.

 

Question 4. Define: (i) Allotropy (ii) Allotrope
Answer: (i) Allotropy: This is a special property where an element can exist in two or more different forms, all in the same physical state. These different forms have distinct physical appearances and properties but are chemically identical. (ii) Allotrope: An allotrope refers to each of the distinct structural forms that an element can take. Each allotrope is a specific variation of that element. Allotropy occurs due to different ways atoms are bonded or arranged within the substance.
In simple words: Allotropy is when an element can exist in different physical shapes, like diamond and graphite for carbon. An allotrope is each one of these different shapes or forms.

🎯 Exam Tip: Give examples like oxygen (\( O_2 \) and \( O_3 \)) or phosphorus (white, red, black) to show a broader understanding beyond just carbon.

 

Question 5. Differentiate crystalline and amorphous forms of allotropes of carbon.
Answer: Crystalline and amorphous forms are two main ways carbon allotropes can be structured, showing different properties.

In simple words: Crystalline carbon forms have a fixed, neat structure, like diamond. Amorphous forms have a disordered, less organized structure, like charcoal.

🎯 Exam Tip: Remember that crystalline forms have a definite geometric pattern, while amorphous forms do not have a regular structure.

 

Question 6. Why is carbon monoxide harmful to health? (or) What happens when we breathe Carbon monoxide?
Answer: Carbon monoxide (CO) is very harmful because when breathed in, it quickly enters the bloodstream and binds much more strongly to hemoglobin than oxygen does. Hemoglobin is the protein in red blood cells that carries oxygen, so carbon monoxide prevents oxygen from reaching the body's tissues and organs. This lack of oxygen can cause severe damage and, in high concentrations, can lead to death. Carbon monoxide is often called a 'silent killer' because it is colorless, odorless, and tasteless, making it hard to detect.
In simple words: Carbon monoxide is dangerous because it stops your blood from carrying oxygen properly. It sticks to a part of your blood (hemoglobin) better than oxygen, which can make you very sick or even kill you.

🎯 Exam Tip: Always be aware of the symptoms of carbon monoxide poisoning, such as headache, dizziness, and nausea, and ensure proper ventilation when burning fuels.

 

Question 7. Why do we remove plastics safely? How can it be done?
Answer: It is crucial to remove plastics safely because most plastics are non-biodegradable, meaning they do not break down naturally in the environment over time. Safe removal involves recycling them properly or disposing of them in ways that do not harm the environment. This helps prevent pollution and conserves resources. Proper plastic waste management reduces landfill burden and prevents plastic from entering ecosystems.
In simple words: We must get rid of plastics safely because they don't break down easily and can harm nature. We can do this by recycling them or throwing them away in special ways that don't cause pollution.

🎯 Exam Tip: Focus on the "3 R's" (Reduce, Reuse, Recycle) as key strategies for minimizing plastic pollution.

 

Question 8. Mention two reasons for the harmful nature of plastics.
Answer: Plastics are harmful for several reasons: 1. They often contain various chemicals that can leach out and be detrimental to human health. 2. Most plastics are designed for single use or are simply thrown away, leading to significant environmental pollution and long-lasting waste accumulation. This pollution affects wildlife, contaminates soil and water, and contributes to microplastic issues.
In simple words: Plastics are bad because they have chemicals that can hurt us. Also, many are used once and thrown away, which pollutes our environment.

🎯 Exam Tip: Provide specific examples of chemicals (e.g., BPA, phthalates) and environmental impacts (e.g., microplastics in oceans) to strengthen your answer.

 

Question 9. Give some examples of one-time-use plastic.
Answer: Examples of common one-time-use plastics include plastic carry bags, cups, plates, straws, water pouches, and thin plastic sheets. These items are designed for convenience but contribute heavily to waste. Many countries are now implementing bans or restrictions on these items to reduce plastic waste.
In simple words: Things like plastic bags, cups, plates, straws, and water pouches are examples of plastics used only once.

🎯 Exam Tip: Be specific with examples, as this demonstrates a clear understanding of the widespread issue of single-use plastics.

 

Question 10. What we can do to prevent plastic pollution?
Answer: We can significantly reduce plastic pollution through mindful daily practices:
• We should never litter plastic items into the environment.
• It's important to avoid burning plastics as this releases highly toxic gases into the air.
• We must try to avoid single-use or disposable plastics like plastic bags, teacups, and plates.
• Refrain from eating hot or spicy foods from plastic containers.
• Always separate plastic waste from other trash and ensure it's given to local authorities for recycling.
• Learn about plastic resin codes to identify and avoid unsafe plastic types.
• For school or art projects, avoid using materials like thermocol.
These actions collectively contribute to a healthier planet by reducing plastic waste and its ecological footprint.
In simple words: To stop plastic pollution, don't litter or burn plastics. Use less single-use plastic, don't put hot food in plastic, sort your plastic trash for recycling, learn which plastics are safe, and don't use thermocol for projects.

🎯 Exam Tip: Your answer should include a mix of individual actions (like avoiding single-use items) and community-level efforts (like advocating for recycling and new rules).

IX. Long Answer Questions:

 

Question 1. Draw a timeline of carbon chemistry depicting the contribution by scientists.
Answer: Here is a timeline illustrating the significant contributions of various scientists to the field of carbon chemistry.

In simple words: This table shows when important scientists helped us understand carbon better, like finding different forms of carbon or making new ones in the lab.

🎯 Exam Tip: When presenting a timeline, ensure the scientists' names, years, and specific contributions are accurate and clearly matched.

 

Question 2. Give an account of (I) Isomerism (II) Isomers with an illustration.
Answer: (I) Isomerism is a phenomenon where different compounds have the exact same molecular formula but possess different structural arrangements of their atoms. This difference in arrangement leads to varied properties. (II) Isomers are the specific compounds that exhibit isomerism. They are individual chemical substances that share an identical molecular formula but differ in their structural formula.
Illustration: Let's consider the molecular formula \( C_2H_6O \). This formula can represent two different compounds with distinct structures:
(a) Alcohol (Ethanol): \( CH_3-CH_2-OH \)
\[ \begin{array}{cc} H & H \\ | & | \\ H - C - C - O - H \\ | & | \\ H & H \end{array} \]
(b) Ether (Dimethyl Ether): \( CH_3-O-CH_3 \)
\[ \begin{array}{ccc} H & & H \\ | & & | \\ H - C - O - C - H \\ | & & | \\ H & & H \end{array} \]
Both these structural formulas are represented by the molecular formula \( C_2H_6O \) but show different physical and chemical properties. For example, alcohol has an oxygen at the end of its chain, while ether has an oxygen in the middle of its chain.
In simple words: Isomerism is when compounds have the same building blocks but are put together differently. Isomers are these different versions. For example, two compounds can have the formula C2H6O, but one is an alcohol and the other is an ether, with atoms arranged differently.

🎯 Exam Tip: Clearly define both isomerism and isomers, and use a simple, well-labeled chemical example to illustrate the concept. Showing structural formulas helps secure full marks.

 

Question 3. Write the salient features of Graphene.
Answer: Graphene possesses several remarkable features:
• It is the most recently discovered allotrope of carbon.
• Its structure consists of a single layer of carbon atoms arranged in a repeating hexagonal, honeycomb-like pattern, all lying in one plane.
• Graphene is known as the thinnest material, being only one atom thick.
• It is also recognized as the lightest and strongest compound ever discovered.
• Multiple layers of graphene stacked together are held by weak van der Waals forces, forming graphite.
Its exceptional properties make it a promising material for future electronics and advanced composites.
In simple words: Graphene is a new, very thin form of carbon, just one atom thick. It looks like a honeycomb, is super light and strong, and many layers of it make graphite.

🎯 Exam Tip: Highlight graphene's unique combination of being extremely thin, strong, and an excellent conductor as key characteristics.

 

Question 4. Briefly note the harmful effects of any four plastics.
Answer: Different types of plastics can have various harmful effects, impacting both human health and the environment.

In simple words: Different plastics can hurt us in various ways. Some have bad chemicals like heavy metals or BPA, which can mess with our bodies or cause cancer. Burning certain plastics also releases very harmful gases into the air.

🎯 Exam Tip: When discussing harmful effects, aim to specify both the type of plastic and the corresponding health or environmental impact to provide a comprehensive answer.

 

Question 5. How can you minimize plastic pollution by your daily practices?
Answer: We can significantly reduce plastic pollution through mindful daily practices:
• We should never litter plastic items into the environment.
• It's important to avoid burning plastics as this releases highly toxic gases into the air.
• We must try to avoid single-use or disposable plastics like plastic bags, teacups, and plates.
• Refrain from eating hot or spicy foods from plastic containers.
• Always separate plastic waste from other trash and ensure it's given to local authorities for recycling.
• Learn about plastic resin codes to identify and avoid unsafe plastic types.
• For school or art projects, avoid using materials like thermocol.
These actions collectively contribute to a healthier planet by reducing plastic waste and its ecological footprint.
In simple words: To stop plastic pollution, don't litter or burn plastics. Use less single-use plastic, don't put hot food in plastic, sort your plastic trash for recycling, learn which plastics are safe, and don't use thermocol for projects.

🎯 Exam Tip: Your answer should include a mix of individual actions (like avoiding single-use items) and community-level efforts (like advocating for recycling and new rules).