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

Explanation:-

Energy Differences in Chemical Structures

• Resonance Energy: It is the difference in energy between the actual structure of a molecule and the lowest energy resonance structure. This energy represents the stabilization gained by the delocalization of electrons in the resonance hybrid.
• Electromeric Energy: It involves the temporary transfer of electrons due to an external factor such as the presence of a reagent.
• Ionization Energy: The energy required to remove an electron from an atom or ion in its gaseous state.
• Hyperconjugation Energy: Stabilization derived from the interaction of sigma bonds with an adjacent empty or partially filled p-orbital or a pi bond.

The resonance energy is defined as the difference in energy between the actual structure of a molecule (which is a resonance hybrid) and the most stable resonance structure.

The correct answer is Bromine.

Key Points

• Bromine is the only non-metal that is in a liquid state at room temperature.
• It is a halogen and is positioned in Group 17 of the periodic table.
• Its chemical symbol is Br and it has an atomic number of 35.
• Bromine has a red-brown color in its liquid form and emits a brownish vapor at room temperature.
• It is highly reactive and can cause burns upon contact with the skin.

Additional Information

• Chlorine
  • Chlorine is a non-metal that is a greenish-yellow gas at room temperature.
  • It is commonly used for water purification and in the production of various consumer products.
• Fluorine
  • Fluorine is the most reactive and electronegative element and exists as a pale yellow gas at room temperature.
  • It is used in toothpaste and in the manufacture of Teflon.
• Sulphur
  • Sulphur is a solid non-metal at room temperature, with a bright yellow appearance.
  • It is used in the production of sulfuric acid, fertilizers, and in vulcanization of rubber.

Explanation:

Rusting of iron:

Rusting is an oxidation reaction of iron. Iron reacts with oxygen and water to form rust which is iron oxide.

The process of rusting can be represented by the following equation as follows;

Iron (Fe) + Oxygen (O₂, from the air) + water (H₂O) → rust (iron oxide Fe₂O₃)

For rusting, the presence of both oxygen and water (or water vapour) is essential.

Opening of soda bottle: This is not an oxidation reaction. When a soda bottle is opened, the gas inside is released due to the decrease in pressure. There is no oxidation or reduction of any substance involved in this process.

Rancidity: Rancidity is a type of oxidation reaction that occurs in fats and oils. When fats and oils are exposed to air, the double bonds in the fatty acid molecules react with oxygen in the air to form peroxides, which further break down into aldehydes, ketones, and other compounds. These compounds have a rancid odor and taste.

Combustion: Combustion is a type of oxidation reaction in which a fuel reacts with oxygen to produce heat and light. Examples of combustion reactions include burning of wood, coal, and gasoline.

Therefore, the correct answer is Opening of soda bottle, which is not an oxidation reaction.

The correct answer is Argon.

Key Points

• Argon is a chemical element with the atomic number 18.
  • It is a Nobel gas.
  • It is in group 18 of the periodic table.
  • Argon is the third most abundant gas in the Earth's atmosphere (0.094%)
  • Uses: Fluorescent Lightning, Gas Discharge Tubes, Fluorescent Glow Starters.

Additional Information

• Xenon
  • Xenon(Xe) gas is also known as stranger gas.
  • It is called 'STRANGER GAS' because the word 'XENON' means 'STRANGE' in Greek.
  • The noble gas Xenon possesses the highest melting point.
  • It was discovered by William Ramsay and Morris Travers in 1898.
  • It is more than 4.5 times heavier than air.
  • xenon is colorless, odorless, and tasteless.
  • It is used in instruments for radiation detection.
• Radon
  • Group 18 consists of six elements: helium, neon, argon, krypton, xenon and radon.
  • All these are gases and chemically unreactive.
  • They form very few compounds.
  • Because of this they are termed noble gases.
  • All the noble gases except radon occur in the atmosphere.
  • Xenon and radon are the rarest elements of the group.
  • Radon is obtained as a decay product of 226Ra.
• Helium
  • Helium is the 2nd most abundant element available in the universe. 
  • Helium symbol (He) considered as noble gas having Atomic Number 2. 
  • It is colorless, odourless, tasteless and non toxic.
  • Helium gas is used to inflate party balloons, scientific balloons and blimps etc.
  • Atomic mass of Helium is 4.002602 u.
  • Boiling point of Helium is -268.9 °C.

The correct answer is two liquids.

Key Points

• An emulsion
  • It can be defined as a colloid consisting of two or more non-homogenous types of liquids wherein one of the liquids contains the dispersion of the different forms of liquids.
  • Emulsions are the mixtures of two or more types of liquids where, one is such as droplets, of tiny or even ultramicroscopic size, which are distributed throughout each other. Hence, Option 3 is correct.
  • These are usually formed from the component of liquids either in natural form or, more often, using mechanisms such as agitation, which is provided that these fluids mixed have no kind of mutual solubility.
  • Emulsions are said to be stabilized by some agents forming films at the surface of droplets or those which impart to them a kind of mechanical stability.
  • The unstable form of emulsions eventually separates into two forms of liquid layers.
  • The stable emulsions are destroyed by destroying or by deactivating the emulsifying agent—for example by the addition of appropriate third-party substances or even by the process of freezing or by heating.
  • Some common emulsions are milk (where the dispersion of fat molecules or droplets in the aqueous solution) and also butter (which is the dispersion of droplets of particles of an aqueous solution in the fat).

• Theories of Emulsification
  • Since there are different processes and mechanisms (both chemical and physical) involved in the process of emulsification, there are several theories that accompany it.
• Surface Tension Theory: This theory states or describes emulsification as a process that occurs by the reduction of interfacial tension between two phases.
• Repulsion Theory: With this theory, we learn that the emulsifying agent produces a film over one phase which further leads to the formation of globules. These compounds tend to repel each other and the repulsive force that exists between them helps them to remain suspended in the dispersion medium.

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 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 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 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 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 green.

Key Points 

• Barium Nitrate Ba(NO₃)₂ is an Oxidizer used to produce green colour in fireworks and fountains.
• This compound is also used in the production process of Barium Oxide in the vacuum tube industry.
• Barium is also used in medicine and oil and gas production.
• It is an inorganic compound that occurs with other elements like sulfur, oxygen, etc.
• Barium is found at 0.0425% on the earth’s crust, and 13 μg/L in seawater.
• It is a non-combustible compound but enhances the burning of combustible elements.
• The melting point of barium nitrate is 592 degrees Celcius.​

Additional Information

• 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.