Organic Chemistry MCQ Quiz - Objective Question with Answer for Organic Chemistry - Download Free PDF

CONCEPT:

Stability of Artificial Sweeteners at Cooking Temperature

• Artificial sweeteners are used as sugar substitutes in various food and beverage products. However, not all sweeteners are stable at high temperatures.
• Some sweeteners can break down or lose their sweetness when exposed to heat, making them unsuitable for cooking or baking.

EXPLANATION:

• Aspartame is an artificial sweetener that is known to be unstable at cooking temperatures.
  • When aspartame is heated, it can break down into its constituent components: aspartic acid, phenylalanine, and methanol.
  • This breakdown results in a loss of sweetness and can affect the flavor of the food.
• Other sweeteners like sucralose, alitame, and saccharin are more stable at higher temperatures and can be used in cooking and baking without significant loss of sweetness.
  • Sucralose is especially known for its high heat stability, making it suitable for a wide range of cooking applications.
  • Alitame and saccharin also maintain their sweetness when exposed to heat.

Therefore, the correct answer is option 2: Aspartame.

The Correct answer is Esters.

Key Points

• Esters are known for their fruity smell.
• They are commonly used in the production of flavors and fragrances.
• Esters are derived from carboxylic acids and alcohols through a process called esterification.
• Many natural esters are found in fruits, which is why they have a sweet and pleasant aroma.
• Examples include ethyl acetate (smells like pear), isoamyl acetate (smells like banana), and methyl butyrate (smells like apple).
• Esters are also used in the food industry to enhance the flavor of products such as candies and beverages.

 Additional Information

•  Alcohols
  • Alcohols generally have a sharp, pungent smell rather than a fruity one.
  • Examples include ethanol, which is used in alcoholic beverages, and methanol, which is toxic and used as an industrial solvent.
• Chloroform
  • Chloroform has a sweet but heavy and non-fruity odor.
  • It was historically used as an anesthetic but is now primarily used as a solvent in laboratories.
• Acid anhydride
  • Acid anhydrides generally have a strong, irritating smell and are used in the production of other chemicals.
  • An example is acetic anhydride, used in the production of aspirin.

The correct answer is Phosgene.

Key Points

• Chloroform, when exposed to air and light, is oxidized to form phosgene, a highly toxic gas.
• Phosgene is a colorless gas with a suffocating odor, resembling that of musty hay or green corn.
• It was used as a chemical weapon during World War I due to its lethal properties.
• Phosgene exposure can lead to severe respiratory damage and is potentially fatal even at low concentrations.

Additional Information

• Chloroform (CHCl₃)
  • A volatile, colorless liquid with a slightly sweet taste and odor.
  • Historically used as an anesthetic but discontinued due to its harmful effects on the liver and potential to cause cardiac arrhythmias.
• Oxidation Reaction
  • A chemical reaction where a substance loses electrons, often associated with the addition of oxygen or the loss of hydrogen.
  • In the case of chloroform, oxidation in the presence of light leads to the formation of phosgene.
• Chemical Weapons
  • Substances designed to cause death or harm through toxic properties.
  • Phosgene, being one of the first chemical warfare agents, caused significant casualties during World War I.
• Safety Precautions
  • Proper storage in dark, well-ventilated areas to minimize exposure to air and light.
  • Use of personal protective equipment (PPE) to avoid inhalation or skin contact.

The correct answer is Hydrocarbons.

Key Points

• Hydrocarbons are the principal constituents of petroleum and natural gas.
• They are organic compounds composed entirely of hydrogen and carbon atoms.
• Hydrocarbons are categorized into alkanes, alkenes, and alkynes based on the types of bonds between the carbon atoms.
• Petroleum is a complex mixture of hydrocarbons and other organic compounds, and it's found in geological formations beneath the Earth's surface.
• Natural gas primarily consists of methane (CH4), with smaller amounts of other hydrocarbons such as ethane, propane, and butane.

 Additional Information

• Allotropes
  • Allotropes are different forms of the same element, where the atoms are bonded together in different ways.
  • Examples include carbon allotropes like diamond, graphite, and graphene.
• Photolysis
  • Photolysis is a chemical process by which molecules are broken down into smaller units through the absorption of light energy.
  • It plays a significant role in processes like photosynthesis.
• Amorphous
  • The term amorphous refers to substances that lack a clearly defined crystalline structure.
  • Examples include glass and plastics.

CONCEPT:

Substitution Reaction

• A substitution reaction is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group.
• In organic chemistry, substitution reactions are common and are categorized as nucleophilic, electrophilic, or radical substitutions depending on the nature of the substituting species.

EXPLANATION:

• In the chlorination of methane:

  CH₄ + Cl₂ → CH₃Cl + HCl

  • Methane (CH₄) reacts with chlorine (Cl₂).
  • One hydrogen atom in methane is replaced by a chlorine atom, forming chloromethane (CH₃Cl) and hydrochloric acid (HCl).
• This reaction involves the substitution of a hydrogen atom in methane with a chlorine atom, making it a substitution reaction.

Therefore, the chlorination of methane is an example of a substitution reaction.

• According to the law of Dobereiner’s triads, the atomic mass of the middle element of the triad is the arithmetic mean of the atomic masses of the other two elements.
• If A, B, and C are elements in Dobereiner’s triads, then the atomic mass of B will be equal to the arithmetic mean of the atomic mass of A and C.

Therefore, the atomic mass of element B is 88.

The correct answer is Nitrogen.

Important Points

​Amines:

• An amine is a functional group with a nitrogen atom having a lone pair.
• Basically, Amines are derived from ammonia (NH₃).
• Nitrogen has a valency of 5, that's why it makes a trivalent with a lone pair.

Uses:

• ​ Amines are used in water purification, medicine manufacturing, and insecticides, and pesticides.
• These are also used in the production of Amino acids.
• It is also used in pain-relieving medicines. 

Types:

• Amines are generally of four types:

1. Primary Amines
2. Secondary Amines
3. Tertiary Amines
4. Cyclic Amines

• Amines can be obtained from Halogen alkanes.

Biogas is produced from biomass by Anaerobic fermentation.

• The element carbon is available abundantly in nature and occurs in free as well as in the combined state.
• Carbon in Free State is found as diamond and graphite.
• In the Combined State, it is found in the following compounds:

The correct answer is Sodium benzoate.

Key PointsSodium benzoate is the sodium compound most commonly used as a preservative in items such as sauces, salad dressings, and beverages. Its excellent antimicrobial characteristics help extend the shelf life of foods and beverages.

 Additional Information

• Sodium bicarbonate - Commonly known as baking soda, is primarily used in baking as a leavening agent.
• Sodium fluoride - It's widely used in toothpaste and drinking water to prevent tooth decay.
• Sodium hypochlorite - This is the active ingredient in bleach and is commonly used for disinfection and water treatment.

The correct answer is Rayon

• Rayon is obtained from the wood pulp.
• Rayon is a regenerated cellulose fiber.
• It is made from natural sources such as wood and agricultural products.
• There are two types of man-made fibers.
  • Synthetic fibers: Synthetic fibers are made only from polymers found in natural gas and the by-products of petroleum. Examples: Nylon, Acrylics, Polyurethane, and Polypropylene
  • Regenerated fibers: Regenerated fibers are made from cellulose polymers that occur naturally in plants such as cotton, wool, hemp, and flax.  Examples: Rayon and Acetate.

Methane is the lightest hydrocarbon having one carbon and four hydrogen atoms. Its molecular weight is 16. It is also a fuel gas commonly called marsh gas because it is produced from marshy lands. Some facts about it: 

• Methane is produced when vegetation decomposes naturally within some geographical marshes, swamps.
• The main process behind the production of methane is anaerobic digestion.
• Biogas or Gobar gas also contains 60-70% of methane. 
• Methane is one of the greenhouse gases. Other greenhouse gases are- carbon dioxide, water vapour, nitrous oxide and ozone.
• Methane is produced in the soil during microbial decomposition of organic matter and reduction of CO2 under strictly anaerobic conditions. 

Hence, we conclude that Methane is known as Marsh gas.

Concept:

The compounds having a triple bond between carbon atoms are called Alkynes.

General Formula for various hydrocarbons groups are:

Alkane: C_nH_{2n + 2}

Alkene: C_nH_2n

Alkyne: C_nH_{2n - 2}

Application:

C₃H₄ follows the general formula for a compound for n = 3

Hence C₃H₄  belongs to the alkyne family.

The correct answer is Lexan.Key Points

• Lexan is a type of polycarbonate i.e., thermosetting polymers composed of carbonate groups. They are hard and are observably .
• They are strong, tough materials, and are optically . This is why a laminated polycarbonate (Lexan) is used to make bulletproof glass.

Important Points

• Kevlar is a heat-resistant and strong synthetic fiber.
• Usage of other polymers:

• Propanal is an example of an aldehyde  functional group.
• R−CHO is a general structural formula for Aldehyde.