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

 Answer:
C) Mass of an atom compared to 1/12th of a carbon-12 atom

Key Points

• Atomic mass is a relative mass
• Compared to 1/12th of the mass of a carbon-12 atom
• Unit used: Unified Atomic Mass Unit (u)
• 1 u = 1.66 × 10⁻²⁷ kg
• Carbon-12 standard chosen for consistency and accuracy

Important Points

• Atomic mass helps compare heaviness of atoms
• Unified mass = standard reference unit
• Adopted by IUPAC as international standard

Additional Information

• Older systems used oxygen-16 as reference
• Modern chemistry uses carbon-12 for accuracy
• Atomic mass ≠ molar mass; molar mass is in g/mol

Key PointsRadium (Ra):

• Atomic Number: 88
• Group: Alkaline Earth Metal
• Highest Atomic Mass: Among the alkaline earth metals, radium has the highest atomic mass (approximately 226).
• Radioactive: Radium is a highly radioactive element, discovered in the late 19th century.
• Discovery:
• Discovered by Marie Curie and Pierre Curie in 1898.
• Discovery: They discovered radium while working with the mineral pitchblende, now known as uranyl.
• Nobel Prize: Marie Curie won the Nobel Prize in 1911 for her work on radioactivity, including radium.
• Properties:
• Radioactivity: Radium emits alpha, beta, and gamma radiation, which made it an essential part of early radiotherapy treatments.
• Glow: Radium glows faintly due to its radioactivity, a property that led to its use in luminous paints in early 20th century.
• Health Risks:
• Radium is highly toxic and radioactive, and prolonged exposure can cause serious health issues like radiation poisoning and increased risk of cancer.
• Radium Girls: A group of young women working with radium in the early 1900s unknowingly ingested the radioactive substance, resulting in radiation sickness and death. This led to significant public awareness of the dangers of radiation.

Important PointsAlkaline Earth Metal Group:

• Radium belongs to Group 2 of the periodic table (Alkaline Earth Metals).
• Alkaline Earth Metals include Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.
• These metals have two electrons in their outermost shell and are typically highly reactive, especially with water.
• Radioactive Decay:
• Radium is known for its radioactive decay process, which involves the emission of high-energy particles.
• It decays into other elements like Radon (Rn) and Polonium (Po).

Applications:

• Radium in medicine: Used historically in radiotherapy for cancer treatment before the development of modern radiation therapies.
• Radium in luminescent paints: Used in clocks, watches, and instrument dials, which glow in the dark. However, this application was discontinued due to health risks.
• Nuclear studies: Radium contributed to the study of nuclear chemistry and the understanding of radioactive decay.
• Marie Curie’s Contribution:
• Marie Curie, a pioneering physicist and chemist, is famous for discovering radium and polonium.
• She coined the term "radioactivity" and laid the foundation for future research in nuclear physics and medicine.

Additional InformationRadium’s History:

• The Curies’ discovery of radium in 1898 came after their discovery of polonium, and it revolutionized the scientific community's understanding of radiation.
• The discovery of radium played a key role in the development of nuclear science and led to the development of X-rays and later the use of radiation in cancer therapy.
• Radium’s Impact on Medicine:
• Before the dangers of radiation were fully understood, radium was used in radiotherapy for treating cancers and other ailments.
• Radium was also used in radium-infused water sold as a health tonic in the early 20th century, but these products were dangerous.
• Health Concerns and Regulation:
• Radium Girls: The tragedy of the Radium Girls led to greater regulation and awareness of the dangers of radioactive materials in the workplace.
• Today, radium is no longer used in commercial products due to the severe health risks associated with prolonged exposure to radiation.
• Legacy of the Curies:
• Marie Curie’s work with radium made her the first woman to win a Nobel Prize and the only person to win Nobel Prizes in two different fields (Physics in 1903 and Chemistry in 1911).
• Her work laid the foundation for the later development of nuclear medicine, which is still used today in cancer treatment.

Key PointsPVC (Polyvinyl chloride):

• Application: Manufacture of pipes, plastic furniture, coating of electric conductors, etc.
• Additional Info: PVC is one of the most widely used synthetic plastics. It can be made rigid (for pipes and doors) or flexible (for electrical insulation).
• Common Use: Construction (pipes), healthcare (medical tubing), electrical (cables), and packaging (films).

Polythene (Polyethylene):

• Application: Used in the manufacture of carry bags, tarpaulin sheets, and plastic containers.
• Additional Info: There are different types of polyethylene, such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), each used for different purposes.
• Common Use: Packaging (plastic bags, films), toys, containers, and more.

Natural Rubber:

• Application: Primarily used in the manufacture of tyres and various other rubber products.
• Additional Info: Derived from the latex of rubber trees, natural rubber is used in manufacturing items that require elasticity and durability.
• Common Use: Tyres, footwear, seals, gaskets, and medical products.

Teflon (Polytetrafluoroethylene - PTFE):

• Application: Most commonly used for coating of the inner surface of non-stick cookware.
• Additional Info: Teflon is known for its non-stick properties, electrical insulation, and resistance to heat and chemicals.
• Common Use: Non-stick cookware, pipe linings, electrical insulation, and lubricants.

Important Points

• PVC is one of the most versatile polymers, used in a variety of applications due to its durability, cost-effectiveness, and ease of manufacturing.
• Polythene is primarily used for packaging materials like bags, films, and containers due to its strength and moisture resistance.
• Natural rubber is key to the automotive industry, particularly in the production of tyres, due to its high elasticity and strength.
• Teflon is widely recognized for its use in non-stick cookware, but it is also used in many industrial applications such as cable insulation and gaskets because of its chemical and heat resistance.

Additional Information

• PVC: In addition to being used for plumbing and electrical insulation, it is also used in medical devices, such as blood bags and tubing, because of its ability to be sterilized.
• Polythene: HDPE is used for strong, impact-resistant applications such as storage tanks, while LDPE is used for flexible, low-density applications like plastic bags and wraps.
• Natural Rubber: Synthetic rubber, made from petroleum-based sources, is an alternative to natural rubber. However, natural rubber is still preferred in many high-performance applications, such as in tyres and seals.
• Teflon: Teflon’s ability to resist chemical corrosion makes it suitable for use in chemical processing industries, as well as for medical devices like catheters and surgical implants.

Answer:
Correct Answer: 3) I, II and III

Key Points-OH Group and Methanol: The -OH (hydroxyl) group in the carbon chain indeed influences the characteristic properties of methanol, such as its solubility in water and its ability to form hydrogen bonds.

Alcohols: Aliphatic hydrocarbons with an -OH group are classified as alcohols, a group of organic compounds that include methanol, ethanol, etc.

IUPAC Nomenclature: According to IUPAC rules, alcohols are named by replacing the 'e' in the alkane name with 'ol'. For example, methane becomes methanol, and ethane becomes ethanol.

Important PointsFunctional Group: The -OH group is the functional group in alcohols, and its presence makes alcohols different from alkanes and other hydrocarbons.

Naming Alcohols: The IUPAC naming system helps standardize the names of organic compounds, making it easier to identify the structure and class of the compound.

Additional InformationProperties of Alcohols: Alcohols are generally polar due to the hydroxyl group, and they often have higher boiling points than hydrocarbons due to hydrogen bonding.

Alcohol Applications: Alcohols, particularly methanol and ethanol, are used as solvents, fuels, and in chemical manufacturing.

Answer:
Correct Answer: 3) I, II and III

Key PointsAlkyl Group: An alkyl group is indeed formed when a hydrogen atom is removed from a carbon atom in a saturated hydrocarbon, typically by breaking a C-H bond.

CH₃ Molecule: When a hydrogen atom is removed from a CH₃ group, the result is the -CH₂ group, which is a common alkyl group. 

Alkyl Groups in Organic Molecules: Alkyl groups are derived by removing a hydrogen atom from saturated hydrocarbons, and they are fundamental components of organic molecules.

Important PointsSaturated Hydrocarbons: Saturated hydrocarbons are hydrocarbons in which all carbon atoms are connected by single bonds, and they are often referred to as alkanes.

Alkyl Group Function: Alkyl groups are important because they modify the chemical properties of larger organic molecules and can act as substituents in chemical reactions.

Additional InformationExamples of Alkyl Groups: Examples of alkyl groups include methyl (-CH₃), ethyl (-C₂H₅), propyl (-C₃H₇), etc., which are all derived from their respective hydrocarbons by removing a hydrogen atom.

Hydrocarbon Derivatives: The removal of a hydrogen atom from any saturated hydrocarbon results in the creation of an alkyl group, which can then form more complex molecules through bonding with other atoms or groups.

The correct answer is Sodium carbonate.

Explanation:

• Washing soda is a chemical compound with the formula Na2CO3, known as sodium carbonate, and it's a salt of carbonic acid.
• Properties of a Washing soda:
  • It is a transparent crystalline solid.
  • It is one of the few metal carbonates which are soluble in water.
  • It is alkaline with a pH level of 11, it turns red litmus to blue.
  • It has detergent properties or cleansing properties because it can remove dirt and grease from dirty clothes, etc.
  • It attacks dirt and grease to form water-soluble products, which are then washed away on rinsing with water.

Important Points

Some common chemical compounds with their common names are:

K2CO3 or potassium carbonate is known as pearl ash.

• Pearl ash, in ancient times, was created by baking potash in a kiln in order to remove impurities. The remaining fine, white powder was pearl ash.
• Potassium carbonate is an inorganic compound and a white salt which is soluble in water.
• It is mainly used in the production of glass and soap.

Additional Information

The correct answer is increases.

Important Points

• In normal cases, the volume of substances increases on heating and decreases while cooling.
• When 1 litre of water is cooled from 4°C to 0°C volume of water will start increasing this due to water's unique property known as 'Anomalous Expansion of Water'.
• Anomalous Expansion of Water occurs between 4°C to 0°C.
• The density of water is a maximum at 4 °C.
• When water is cooled from 4°C to 0°C, its density decreases.
• The anomalous expansion of water helps preserve aquatic life during very cold weather.

Explanation:

• When water reaches 4°C the molecules have been pushed as close to one another as possible and the density of water becomes precisely 1.00 g/cm³
• When water freezes at 0°C due to the crystal structure the molecules arranged in some structured fashion so a little far apart ended up less dense - 0.93 g/cm³  - and so floats due to buoyancy.

As density decreases the volume increases.

Volume = mass /density.

The correct answer is Methanoic acid.

Key Points

• Nettle is an herbaceous plant that grows in the wild.
• Nettle leaves have stinging hair, which causes painful stings when touched accidentally. 
• This is due to the methanoic acid secreted by them. 
• A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle.

Additional Information

• The word ‘atom’ is coined by Democritus.
• He suggested that if we go on dividing matter at a certain point the atom becomes indivisible or cannot be divided further.
• He called these particles as atoms (Indivisible).

Explanation:

• Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
• Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
• When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
• In the chemical reaction it can be shown as :

\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" id="MathJax-Element-1-Frame" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2

• However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">​\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)​\(\rm \underset{Lime\ water}{Ca CO_3} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{Ca(HCO_3)_2 \ (g)}\)Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate\(\rm \underset{Calcium\ Carbonate}{Ca CO_3} \ \ +H_2O+ \ \underset{Carbon \ Dioxide}{CO_2 \ (g) } \ \longrightarrow \ \underset{Calcium \ bi\ Carbonate}{Ca(HCO_3)_2 \ (g)}\)

Additional Information Reaction involved-

CaCO₃ + 2HCl →  CaCl₂ + CO₂ + H₂O

• The evolved gas is carbon dioxide which then passes through lime water and turns it milky.

Ca(OH)₂ + CO₂ → H₂O + CaCO₃  

• Due to formation of these compounds
• when excess CO₂ is passed

CaCO₃ + H₂O + CO₂ →  Ca(HCO₃)₂ 

• Bicarbonate is formed which again clears the solution

Mistake Points

•  Do not confuse Calcium carbonate and calcium bicarbonate.
• One produces white colour while the other makes it colourless.

The correct answer is option 1, i.e  Alkali Metals.

EXPLANATION:

• The elements in the first group of s-block are also known as Alkali Metals. These have only one electron in their outermost shell and hence are quite reactive as they easily lose their electron to form bonds with non-metals.

• The elements in the second group of s-block are also known as Alkaline Earth Metals. These have two electrons in their outermost shell and are less reactive than Alkali metals.
• Halogens are the group 17 elements and are placed in the p-block.
• Noble gases are the group 18 elements and are placed in the p-block. These are the least reactive amongst all the elements found in the periodic table as they have a stable configuration.

The correct answer is Lactic Acid.

Key Points

• Lactic acid is present in Sour milk or curd.
• The sourness of the milk is due to the presence of lactic acid.
• Human beings feel tired due to the accumulation of lactic acid in the muscles.​

Additional Information

The correct answer is The acid present in tomatoes.

Key Points

• Oxalic acid is a chemical compound that occurs naturally in almost every plant to some degree, including fruit, vegetable and grain plants. 
• Tomato contains more than 10 types of acids such as citric acid, malic acid, ascorbic acid, oxalic acid etc. 
• The oxalic acid content of tomatoes is about 50 mg per 100 g serving. 

Additional Information 

• Some natural sources of acid:

• The number of water molecules present is washing soda is 10.
• We know the molecular formula for Washing Soda is Na₂CO₃.10H₂O.
• Recrystallisation of Sodium Carbonate (Na₂CO₃) gives washing soda.
• In a Washing soda, water is present in the form of crystals.