Chemical Reaction MCQ Quiz - Objective Question with Answer for Chemical Reaction - Download Free PDF

The correct answer is ​Black.

• The black coating on silver is an example of corrosion.

Key Points

• When a metal deteriorates due to its reaction with air present in the atmosphere, it can be said as corrosion.
• The process of corrosion takes place due to oxidation.
• Iron is rusted and silver is tarnished in the air when they are left free in the air.
• The metals need to be protected from corrosion.
• Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture.
• The beautiful blue-green color (patina) on copper after oxidation is the visible result of the metals losing electrons to the air.

Additional Information

• Many methods are developed via industrial research to protect a metal from corrosion.
• Except for gold and platinum, the corrosion of most of the metals is spontaneous.
• Anti-corrosive chemicals are used to prevent metal from corrosion.
• Iron can also be coated with tin to protect it from corrosion.
• Tin is less reactive and it will protect the iron.
• Cathodic protection, hot deep galvanization, alloyed steel, and barrier coatings are some other methods to protect a metal from corrosion.

The correct answer is gain of oxygen

Concept:

Chemical Reactions:

• A process in which one or more compounds are formed as products completely different from the reacting substances is known as a chemical reaction.
• There is generally a change in heat, colour, or appearance when a chemical reaction takes place.
• The evolution of gas may also occur.
• A chemical reaction may be reversible or irreversible in nature.

Oxidation reaction:

• Oxidation Reaction refers to a reaction in which either the addition of Oxygen takes place or the removal of Hydrogen takes place.
• It can also be said as the process of loss of one or more electrons by atoms or ions.
• Example is:

2Mg + O2 = 2MgO

Reduction Reaction:

• Reduction Reaction refers to a reaction in which either the addition of Hydrogen takes place or the removal of oxygen takes place.

• In the process of reduction, a chemical species also gains electrons.
• It is the reverse of the oxidation reaction.
• Example is:

H2 + F2 → 2HF

Explanation:

Oxidation is a chemical reaction that is characterized by 

• loss of electron
• addition of oxygen atom
• removal of the hydrogen atom 

The substance that undergoes oxidation is said to be oxidized.

The loss of electrons and an increase in the oxidation state are the characteristics of an oxidation reaction.

For example:

H2S + Cl2 → 2HCl + S

In this reaction, the chlorine is getting reduced to hydrochloric acid (HCl) on the addition of hydrogen provided by Hydrogen sulfide (H2S).

The correct answer is 0.

Key Points

• The oxidation number of an oxygen atom in the ozone is zero, just like in oxygen gas. 
• Oxygen being a reactive non-metal occurs in various forms, ozone is also one of the highly reactive gas made up of 3 oxygen atoms.
• Ozone is both natural and a man-made product that occurs in the earth’s upper
• As we know the molecular formula of ozone is O₃, which is 3 oxygen atoms, The atomic number of oxygen is 8 and its valency is -2, as it requires 2 electrons to complete its octet.

Additional Information

• The structure of ozone is

• Now, as we know, the oxidation number is the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. It is also known as the oxidation state.
• The oxidation number for elements in their natural forms is zero because these compounds are extremely stable.
• The oxidation number represents the number of electrons the element can give away (if positive) or lose (if negative). Such stable molecules have no electrons to lose or gain.
• The oxidation number for O₃ is zero despite being so reactive, which is kind of an exception for this general principle.

Concept:

• When an iron nail gets rusted, iron oxide (Fe2O3) also known as rust is formed.
• During the process of rusting, iron combines with the oxygen molecules from the atmosphere which adds to the weight of iron thus making it heavier.

4Fe + 3O2 → 2Fe2O3 (rust)

Explanation:

• When an iron nail gets rusted, the weight of the nail increases.
• It is because the layer of iron oxide is formed on the surface of the iron nail.
• This iron oxide layer is actually adding oxygen and hydrogen to the nail.

So, the weight of a rusty iron nail is more than the same nail without rusting.

Important Points

• Rusting is an oxidation reaction.
• The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. 
• The oxidation process is the loss of electrons during a reaction by a molecule, atom, or ion.
• We can prevent rusting by following methods:
  • Painting
  • Keep moisture at Bay
  • Coat it with Oil, etc.

The correct answer is Corrosion.

Key Points

• Corrosion is when a refined metal is converted to a more stable form such as its oxide, hydroxide, or sulfide state this leads to deterioration of the material. It may be a result of some chemical process or it may occur naturally also. 
• Rust is a form of corrosion, but it specifically refers to the oxidation of iron or its alloys. Only metals with iron or its alloys can get rusted.
• Rust refers to the iron oxide that is produced in the process. For rusting to take place, there are certain necessary conditions. In the presence of oxygen and moisture or water, iron undergoes this reaction and form a series of iron oxide.
• The reddish-brown color compound, known as rust is formed. If rusting starts at one place, it will eventually spread, and the whole metal will eventually disintegrate.

Additional Information

• Corrosion in other metals:
  • Aluminum: Aluminum corrodes to form a thin layer of aluminum oxide forms over the surface of the metal, which acts as a protective barrier. This barrier doesn’t flake off like rust does, which prevents further corrosion of the aluminum in the future.
  • Copper: Copper corrodes to produces a green color compound known as patina. This patina is desirable as it not only forms a protective barrier to further corrosion but has a visual appeal that consumers like.

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 correct answer is Double displacement reaction.

Concept:

Chemical reaction:

• It is a process in which one or more substances, the reactants, are converted to one or more different substances, the products.
• A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Explanation:

• Double displacement reaction: 

• It is a chemical reaction in which two compounds react and exchange their ions forming new products. 
• This reaction often results in the formation of an insoluble compound called a precipitate. 
• Such reactions are represented by equations of the following form: A⁺B^- + C⁺D^- → A⁺D^- + B^-C⁺

​In the given chemical reaction: 

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

The reactants NaCl and AgNO₃ have exchanged their ions to form NaNO3  and AgCl. 

Thus, it is an example of a double displacement reaction.^​

^{Additional Information}

Types of Chemical Reactions:

Combination reaction:

• Two or more elements or compounds combine together to form a single compound.
• Such reactions are represented by equations of the following form:     A + B → AB.

Decomposition reaction:

• The opposite of a combination reaction, a complex molecule breaks down to make simpler ones.
• Such reactions are represented by equations of the following form: AB → A + B.

Displacement reaction:

• One element takes place with another element in the compound.
• Such reactions are represented by equations of the following form: A + BC → AC + B.

Redox reaction:

• It is a reaction in which one species is reduced and the other is oxidized. 
• Reduction means losing Oxygen or gaining hydrogen 
• Oxidation means gaining oxygen or losing hydrogen. 

The correct answer is CaSO4.1/2 H2O.

​EXPLANATION:

• Plaster of Paris (POP) is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry.
• It is also known as the Plaster of Paris because for the preparation of POP, the abundant gypsum was first found near the capital city of France i.e. Paris.
• The chemical formula of the Plaster of Paris is CaSO4.\(\frac{1}{2}\) H2O. Therefore option 3 is correct.
• Application of Plaster of Paris is as follows
  1. It is used as a building material as a protective coating on walls and ceilings.
  2. It is used as a moulding and vesting agent for decorative elements.
  3. It is also used for aesthetic touch to the construction elements.
  4. It is also used as plaster in orthopaedics and as a filling material by dentists, etc.

Mistake Points

\(\begin{array}{*{20}{c}} {CaS{O_{4.}} + \frac{1}{2}{H_2}O + 1\frac{1}{2}{H_2}O}\\ {\left( {Plaster\,Of\,Paris} \right)} \end{array} \to \begin{array}{*{20}{c}} {CaS{O_4}.2{H_2}O}\\ {\left( {Gypsum} \right)} \end{array}\)

• Gypsum is an ore of Calcium (Ca). The chemical formula of Gypsum is CaSO4. 2H2O.
• Gypsum is mainly used as a fertilizer, as the main constituent in plaster, chalk, etc.
• The plaster of Paris on mixing with water produces gypsum.
• Calcium Sulphate Hemihydrate (CaSO4·1/2 H2O) on hydration leads to the crystallization of gypsum calcium sulphate dihydrate (CaSO4·2H2O).

The correct answer is carbon dioxide.

Key Points

• Urea is now prepared commercially from liquid ammonia and liquid carbon dioxide.
• The chemical name of urea is carbamide, the diamide of carbonic acid.
• Its formula is NH₂CONH₂.
• Urea has important uses as a fertilizer and feeds supplement.
• It is a colourless substance existing in the crystalline form, which melts at 132.7°C (271° F).
• Urea is a waste product in the body with no physiological function.
• It dissolves in the kidney and blood before it is excreted as urine.

Important Points

• Uses of Urea
  • It is mainly used as a nitrogen release fertilizer.
  • Urea is used as a stabilizer in most nitrocellulose explosive products.
  • It is used in manufacturing high explosive materials like urea nitrate (CH₅N₃O₄).
  • It is used as an important reagent in lanthanide chemistry.
  • It is used in creams/ointments that are used for rehydration.
  • It is used in hair removal creams and dish soaps.
  • It is used as a browning agent for pretzels.
  • It is used in manufacturing melamine.
  • It is used to detect the bacteria in the stomach through the urea breath test.

The correct answer is oxidizing.

Key Points

• Potassium permanganate (KMnO₄) is a strong oxidizing agent that oxidizes dissolved impurities from water such as iron, manganese, and hydrogen sulfide (H₂S) by converting them into solid particles.
• These impurities are then filtered out of the water.
• It is a salt consisting of K⁺ and MnO^{− 4} ions.
• It is a strong oxidizing agent.
• It is used as a medication for cleaning wounds and dermatitis.

Additional Information

• Some other chemical disinfectants used for water:
  • Hypochloride
  • Chlorine dioxide
  • Chlorine
  • Hydrogen peroxide
  • Potassium permanganate
  • Gamma rays
  • Ultraviolet light

The correct answer is a Combination Reaction.

Key Points 

• The combustion of coal is an example of Combination Reaction.
• A combination reaction is a reaction where two or more elements or compounds combine to form a single compound. Such reactions are represented by equations of the following form: X + Y → XY.
• The combination of two or more elements to form one compound is called a combination reaction.

​

Additional Information 

Other types of Chemical Reactions:

• Decomposition reaction:
  • The opposite of a combination reaction, a complex molecule breaks down to make simpler ones. Such reactions are represented by equations of the following form: AB → A + B.
• Precipitation reaction: 
  • Two solutions of soluble salts are mixed resulting in an insoluble solid (precipitate) forming. Such reactions are represented by equations of the following form: A + Soluble salt B  → Precipitate + soluble salt C.
• Neutralization reaction: 
  • An acid and a base react with each other. Generally, the product of this reaction is salt and water. Such reactions are represented by equations of the following form: Acid + Base → Salt + Water.
• Combustion reaction: 
  • Oxygen combines with a compound to form carbon dioxide and water. These reactions are exothermic, meaning they give off heat. Such reactions are represented by equations of the following form: A + O2 → H2O + CO2.
• Displacement reaction: 
  • One element takes place with another element in the compound. Such reactions are represented by equations of the following form: A + BC → AC + B.
• Double displacement reaction:
  •  Double displacement reactions occur when a part of two ionic compounds is exchanged and makes two new components.
  •  Double displacement reactions take place mostly in aqueous solutions wherein the ions precipitate and the exchange of ions takes place.                

The correct answer is Mg(s) + Cl2(g) → Mgcl2(s).

Key Points

• Magnesium (Mg) combines with chlorine (Cl2) to form a new product as magnesium chloride (Mgcl2). Therefore its a combination reaction and the balanced equation can be written as:
  • Mg(s) + Cl2(g) → Mgcl2(s)​

Additional Information

• A combination reaction is a reaction where two or more elements or compounds combine to form a single compound. Such reactions are represented by equations of the following form: X + Y → XY.
• The combination of two or more elements to form one compound is called a combination reaction.
• Other types of Chemical Reactions:
  • Decomposition reaction: The opposite of a combination reaction, a complex molecule breaks down to make simpler ones. Such reactions are represented by equations of the following form: AB → A + B.
  • Precipitation reaction: Two solutions of soluble salts are mixed resulting in an insoluble solid (precipitate) forming. Such reactions are represented by equations of the following form: A + Soluble salt B  → Precipitate + soluble salt C.
  • Neutralization reaction: An acid and a base react with each other. Generally, the product of this reaction is a salt and water. Such reactions are represented by equations of the following form: Acid + Base → Salt + Water.
  • Combustion reaction: Oxygen combines with a compound to form carbon dioxide and water. These reactions are exothermic, meaning they give off heat. Such reactions are represented by equations of the following form: A + O2 → H2O + CO2.
  • Displacement reaction: One element takes place with another element in the compound. Such reactions are represented by equations of the following form: A + BC → AC + B.

The correct answer is an Oxidation reaction.

Key Points

• Rancidity refers to the spoilage of food in such a way that it becomes undesirable for consumption. 
• It is caused by the oxidation of fats and oils present in food.
• It causes changes in the taste and smell of food.

Additional Information

•  Rancidity can be controlled by
  • Adding antioxidants to foods.
  • Keeping food items in a closed container.
  • Refrigerating food.
  • Replacing oxygen in the containers with another gas.

The correct answer is Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH₃

Key Points

• The Displacement reaction is a reaction in which a more reactive element displaces a less reactive element from its compound present in a dissolved state.
• In the Double displacement reaction, there is an exchange of ions between the reactants to give new substances.
• In BaCl2 + H2SO4 → BaSO4 + 2HCl, positive (Ba⁺) and negative(Cl^-) ions of the two reactants switch places forming two new compounds and so it is a double displacement reaction.
  • In this, Barium Chloride (BaCl2) reacts with Sulphuric acid (H2SO4) to form Barium Sulphate (BaSO4) and Hydrochloric acid (HCl).
• In CuSO4 + H2S → CuS + H2SO4, Hydrogen Sulphide (H2S) reacts with Copper (II) Sulphate (CuSO4) and gives Copper Sulphide (CuS) and Sulphuric acid (H2SO4).
  • Here, Cu⁺ and SO₄^- exchange their ions and so, this is a double displacement reaction. 
• In Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3, Magnesium nitride (Mg3N2) splits into two compounds namely Magnisium Hydroxide (3Mg(OH)2) and Ammonia (2NH3). 
  • A chemical reaction in which a single reactant or compound splits to form simpler products is called a Decomposition reaction.
  • So, this is not a Double displacement reaction, but a Decomposition reaction. Hence option 2 is correct.

Additional Information

• In NaOH + HCl → NaCl + H2O, Sodium (Na+) and OH- exchange ions and so this is a double displacement reaction.
  • This is also a Neutralization reaction because the acid and base reactants neutralize to become salt and water.
  • Sodium Hydroxide (NaOH) is a base and Hydrochloric acid (HCl) is an acid that combines to form a salt (NaCl) and release water (H2O).
• Magnesium nitride is a greenish-yellow colour that is commonly referred to as Trimagnisium dinitride.
  • ​It exists as a powder form at room temperature and normal pressure.
  • It can dissolve in acid and water as well but is slightly soluble in ethanol.
• Hydrogen Sulphide is a colourless chalcogen hydride poisonous and flammable gas with the foul smell of rotten eggs.
• Sulphuric acid also called the Oil of Vitriol has a strong acidic nature and is corrosive.
  • ​At high concentrations, it acts as an oxidizing agent and dehydrating agent.