Class 11 Chemistry MCQs | Chapter 9: Hydrogen – Part 2

Explanation: The standard laboratory preparation of hydrogen involves the reaction of zinc metal with dilute acids such as HCl or H₂SO₄:

$Zn + 2HCl \rightarrow ZnCl_2 + H_2\uparrow$.

This reaction proceeds smoothly at room temperature and produces pure hydrogen gas that is collected by the upward displacement of water. The gas is colorless, odorless, and highly inflammable.

Explanation: Zinc reacts with dilute acids at a moderate rate, producing hydrogen without excessive heat or explosion risk. Iron reacts more slowly, while magnesium reacts too vigorously, releasing heat that can cause safety hazards. Therefore, zinc provides an ideal balance for controlled hydrogen evolution in laboratory conditions.

Explanation: In the reaction $Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2$, zinc displaces hydrogen from the acid. Here, sulfuric acid acts as an oxidising agent by accepting electrons from zinc and releasing hydrogen gas. The reaction demonstrates the displacement of a less reactive element (hydrogen) by a more reactive metal (zinc).

Explanation: Concentrated nitric acid should not be used because it is a strong oxidising agent. Instead of liberating hydrogen, it oxidises the gas into water or nitrogen oxides:

$3H_2 + 2HNO_3 \rightarrow 2NO + 4H_2O$.

Hence, nitric acid destroys the hydrogen produced, making dilute HCl or H₂SO₄ the preferred acids for hydrogen generation.

Explanation: Hydrogen is collected by the upward displacement of water because it is lighter than air and only slightly soluble in water. The collection setup typically consists of a flask containing zinc and dilute acid, a thistle funnel for acid addition, and a delivery tube leading to a water trough with an inverted gas jar.

Explanation: During electrolysis of acidified water, reduction occurs at the cathode:

$2H^+ + 2e^- \rightarrow H_2\uparrow$.

Meanwhile, oxidation occurs at the anode:

$2H_2O \rightarrow O_2\uparrow + 4H^+ + 4e^-$.

Thus, hydrogen is released at the negative electrode (cathode), while oxygen is released at the positive electrode (anode).

Explanation: Pure water is a poor conductor of electricity due to its low ion concentration. A small amount of dilute sulfuric acid is added to increase the concentration of $H^+$ and $SO_4^{2-}$ ions, improving conductivity. This ensures efficient electrolysis, producing hydrogen at the cathode and oxygen at the anode in a 2:1 volume ratio.

Explanation: In the electrolysis process, the reaction $2H_2O \rightarrow 2H_2 + O_2$ shows that for every one molecule of oxygen, two molecules of hydrogen are produced. Therefore, the volume of hydrogen obtained is twice that of oxygen. This ratio is a clear confirmation of the molecular formula of water ($H_2O$).

Explanation: At the cathode, hydrogen ions ($H^+$) gain electrons to form hydrogen gas, while at the anode, water molecules lose electrons to form oxygen gas and hydrogen ions. This complementary redox process explains why the total number of atoms remains balanced, and the ratio of hydrogen to oxygen volume remains 2:1.

Explanation: Electrolysis of water yields 100% pure hydrogen and oxygen gases because no by-products or side reactions occur. Unlike acid-metal reactions, this method avoids contamination by acid vapors or metal oxides. Although it requires significant electrical energy, it is preferred when high-purity hydrogen is needed for industrial or laboratory purposes, such as in fuel cells and chemical synthesis.

Explanation: The Bosch process is a method for synthesizing methane from carbon monoxide and hydrogen. It involves the reaction of carbon monoxide with hydrogen in the presence of a catalyst at high temperature and pressure:

$$CO + 3H_2 \xrightarrow{catalyst} CH_4 + H_2O$$

This reaction is widely used for producing synthetic methane and in the manufacturing of synthetic fuels.

Explanation: In the Bosch process, carbon monoxide reacts with hydrogen to form methane and water, as shown in the equation:

$$CO + 3H_2 \rightarrow CH_4 + H_2O$$

This reaction occurs at high temperatures (300-400°C) and pressure (30-40 atm) in the presence of a catalyst, typically iron or nickel.

Explanation: The water-gas shift reaction is a critical process in hydrogen production, where carbon monoxide reacts with water to form carbon dioxide and hydrogen:

$$CO + H_2O \rightarrow CO_2 + H_2$$

This reaction is important in industrial processes like the production of hydrogen gas from synthesis gas (a mixture of CO and H₂) and is also used for CO removal from reformate gases in fuel processing.

Explanation: The water-gas shift reaction is catalyzed by iron oxide or copper-based catalysts, such as $Fe_2O_3$ or $CuO$. These catalysts facilitate the conversion of carbon monoxide and water into carbon dioxide and hydrogen, especially at temperatures of around 200–400°C.

Explanation: The water-gas shift reaction is used to increase the hydrogen yield from synthesis gas (CO and H₂). In many industrial hydrogen production methods, including steam reforming of methane, the water-gas shift reaction helps convert carbon monoxide into additional hydrogen and carbon dioxide. This is essential for producing high-purity hydrogen for fuel cells, ammonia production, and other applications.

Explanation: In the Bosch process, the catalyst, typically iron or nickel, accelerates the reaction between carbon monoxide and hydrogen to produce methane. The catalyst remains unchanged at the end of the reaction and can be reused for multiple cycles. This is a key feature of catalytic processes.

Explanation: The water-gas shift reaction plays a crucial role in the production of hydrogen gas by converting carbon monoxide into hydrogen and carbon dioxide. This reaction is commonly used in hydrogen production from synthesis gas, which is obtained from natural gas, coal, or biomass. The hydrogen produced is essential for various industrial applications such as in hydrogenation, fuel cells, and ammonia production.

Explanation: In industrial hydrogen production, the water-gas shift reaction is typically performed in two stages. First, the reaction occurs at high temperature (350–450°C) using an iron oxide catalyst (HTS), where a large portion of CO is converted. Then, the temperature is reduced to 180–250°C for a low-temperature shift (LTS), often using a copper-based catalyst to further convert CO and enhance hydrogen production.

Explanation: The primary reaction of the Bosch Process for industrial hydrogen production is the Water-Gas Shift Reaction (WGSR), which converts $\text{CO}$ to $\text{CO}_2$ and $\text{H}_2$. The correct reaction is D. $\text{CO} + \text{H}_2\text{O} \rightarrow \text{CO}_2 + \text{H}_2$. Option C is the methanation reaction used to remove traces of $\text{CO}$.

Explanation: The water-gas shift reaction is used to reduce the amount of carbon monoxide in hydrogen-rich gas streams. The reaction $CO + H_2O \rightarrow CO_2 + H_2$ converts carbon monoxide into carbon dioxide and hydrogen, effectively purifying the hydrogen for downstream applications such as fuel cells, refining, and ammonia production. This process is especially important after steam reforming or gasification of hydrocarbons.

Explanation: Hydrogen is used in fuel cells because it reacts with oxygen to produce only water and energy:

$$2H_2 + O_2 \rightarrow 2H_2O$$

This makes hydrogen a clean energy source, ideal for applications like electric vehicles and stationary power generation. The absence of harmful emissions such as CO₂ makes hydrogen fuel cells an environmentally friendly alternative to traditional fossil fuels.

Explanation: Oxyhydrogen welding uses a mixture of oxygen and hydrogen to produce a flame with a high temperature (around 3,200°C or 5,792°F). This high heat is used to melt and fuse metals, particularly for applications where precision and a clean welding environment are needed, such as in the repair of delicate equipment or fine jewelry.

Explanation: The Haber process is used to synthesize ammonia by reacting nitrogen ($N_2$) from the air with hydrogen ($H_2$) under high pressure and temperature (typically 400-500°C, 150-300 atm) in the presence of an iron catalyst:

$$N_2 + 3H_2 \rightleftharpoons 2NH_3$$

Ammonia is a key component of fertilizers, making hydrogen essential in the global agricultural industry.

Explanation: Hydrogenation is a process in which hydrogen is added to unsaturated fats (vegetable oils) to convert them into saturated fats. This reaction is done in the presence of a nickel catalyst and is commonly used to produce margarine from liquid vegetable oils. The hydrogenation process increases the melting point of the oils, turning them into a solid or semi-solid form suitable for spreads.

Explanation: Hydrogen is used as a reducing agent in the production of iron from its ore, reducing iron oxide ($Fe_2O_3$) into iron metal and releasing water as a byproduct:

$$Fe_2O_3 + 3H_2 \rightarrow 2Fe + 3H_2O$$

This process is being researched as an alternative to traditional blast furnace methods, which release carbon dioxide. Hydrogen-based reduction offers a cleaner, more sustainable way of producing iron, vital for reducing industrial CO₂ emissions.

Explanation: Hydrogen plays a key role in the production of methanol through the methanol synthesis process, where hydrogen reacts with carbon monoxide at high pressure and temperature to form methanol:

$$CO + 2H_2 \rightarrow CH_3OH$$

Methanol is an important feedstock for the chemical industry, used in producing formaldehyde, acetic acid, plastics, and as an alternative fuel.

Explanation: In the food industry, hydrogen is used for the hydrogenation of vegetable oils to produce solid fats such as margarine. This process involves adding hydrogen to unsaturated fats under controlled conditions using a catalyst, converting liquid oils into solids. This is commonly done to increase the shelf life and improve the texture of products like margarine, shortening, and some types of baked goods.

Explanation: In the electronics industry, hydrogen fluoride ($HF$) is used extensively for cleaning semiconductor wafers. The process involves the reaction of hydrogen with fluorine:

$$H_2 + F_2 \rightarrow 2HF$$

Hydrogen fluoride is essential for etching circuits on silicon wafers, a crucial step in semiconductor manufacturing.

Explanation: Hydrogen is used in hydrotreating processes to remove sulfur from crude oil, which helps reduce the sulfur content in gasoline and diesel fuels. This process improves the quality of fuel, minimizes sulfur dioxide emissions, and complies with environmental regulations. Hydrogen also plays a key role in the production of cleaner, more environmentally friendly fuels.

Explanation: While hydrogen is indeed used in the synthesis of methanol ($CH_3OH$), its single largest and most important industrial application is in the production of ammonia ($NH_3$) via the Haber Process. This process combines hydrogen with nitrogen ($N_2$) under high temperature and pressure to produce ammonia, which is essential for manufacturing fertilizers and other chemicals. The Haber Process is responsible for the majority of ammonia production worldwide, which is a critical component in agriculture.

Explanation: In the laboratory, hydrogen gas is most commonly prepared by reacting zinc metal with dilute sulfuric acid:

$$Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow$$

This method is simple, efficient, and widely used because it produces hydrogen in a controlled manner and can be done at room temperature. The gas is typically collected by upward displacement of water.

Explanation: Steam methane reforming (SMR) is the most common industrial method for producing hydrogen. It involves reacting methane ($CH_4$) with steam at high temperatures (700–1,000°C) and pressures to produce hydrogen and carbon monoxide:

$$CH_4 + H_2O \rightarrow CO + 3H_2$$

The hydrogen is then purified and separated for use in various applications, including ammonia synthesis, refining, and fuel cells.

Explanation: The water-gas shift reaction is used in the hydrogen production process to increase hydrogen yields by converting carbon monoxide and water into carbon dioxide and hydrogen:

$$CO + H_2O \rightarrow CO_2 + H_2$$

This reaction is important after steam methane reforming or gasification processes to convert carbon monoxide into hydrogen, improving the overall efficiency of hydrogen production.

Explanation: The Bosch process is used to produce methane from carbon monoxide and hydrogen. It involves reacting carbon monoxide with hydrogen at high temperatures and pressures, in the presence of a catalyst, to form methane ($CH_4$) and water:

$$CO + 3H_2 \rightarrow CH_4 + H_2O$$

This process is significant in the production of synthetic methane and hydrogen from synthesis gas (a mixture of CO and H₂).

Explanation: In the electrolysis of water, water is split into hydrogen and oxygen gases by passing an electric current through it. At the cathode (negative electrode), hydrogen ions ($H^+$) gain electrons to form hydrogen gas:

$$2H^+ + 2e^- \rightarrow H_2$$

At the anode (positive electrode), oxygen is formed:

$$2H_2O \rightarrow O_2 + 4H^+ + 4e^-$$

This reaction produces pure hydrogen and oxygen gases.

Explanation: The most common industrial method for producing hydrogen is steam methane reforming (SMR), which involves reacting methane ($CH_4$) with steam at high temperatures (700–1,000°C) to produce hydrogen and carbon monoxide. This method is efficient and cost-effective, making it the dominant process used in hydrogen production worldwide.

Explanation: In the Bosch process, a catalyst such as iron is used to promote the reaction of carbon monoxide and hydrogen to form methane and water:

$$CO + 3H_2 \rightarrow CH_4 + H_2O$$

Iron or nickel catalysts are commonly employed to facilitate this reaction, which is performed under high temperature and pressure.

Explanation: Although electrolysis of water produces pure hydrogen, it requires a significant amount of electricity, making it an energy-intensive process. This limits its widespread use for hydrogen production unless the electricity comes from renewable sources, such as solar or wind, to reduce costs and environmental impact.

Explanation: In coal gasification, coal is reacted with oxygen and steam at high temperatures to produce synthesis gas (syngas), a mixture of carbon monoxide (CO) and hydrogen (H₂):

$$C + O_2 + H_2O \rightarrow CO + H_2$$

The syngas can then be further processed to produce hydrogen through the water-gas shift reaction or be used in other chemical processes like ammonia or methanol synthesis.

Explanation: In the laboratory preparation of hydrogen, zinc reacts with dilute sulfuric acid to release hydrogen gas. The sulfuric acid dissociates to produce hydrogen ions ($H^+$), which are reduced to form hydrogen gas at the surface of the zinc:

$$Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow$$

The acid provides the necessary ions for this reaction, allowing the metal to displace hydrogen from the acid.

Explanation: Hydrogen peroxide is a colorless, odorless, and tasteless liquid at room temperature. It is often used in diluted forms, primarily as a disinfectant, bleaching agent, and in various industrial applications. It has a slightly bitter taste when concentrated, but it is not volatile and does not have a strong odor.

Explanation: Hydrogen peroxide has a boiling point of 153.2°C. This relatively high boiling point is due to its ability to form hydrogen bonds, which require more energy to break compared to many other small molecules. Hydrogen bonding between molecules contributes to its unique physical properties.

Explanation: Hydrogen peroxide is highly soluble in water. It can form hydrogen bonds with water molecules, allowing it to dissolve in water in all proportions. In fact, it is commonly used in aqueous solutions with concentrations ranging from 3% (household solutions) to 90% (industrial applications).

Explanation: The chemical formula for hydrogen peroxide is $H_2O_2$, indicating it is made of two hydrogen atoms and two oxygen atoms. It is similar in structure to water ($H_2O$), but with an additional oxygen atom, making it a strong oxidizing agent due to the presence of the peroxide bond ($O-O$).

Explanation: Concentrated hydrogen peroxide (typically above 30%) appears as a yellowish, oily liquid. At lower concentrations (3–10%), it is typically colorless. The yellow color results from the formation of small amounts of decomposition products, and at higher concentrations, hydrogen peroxide becomes increasingly unstable.

Explanation: The decomposition of hydrogen peroxide into water and oxygen is catalyzed by various substances, with manganese dioxide being one of the most effective catalysts. The reaction is as follows:

$$2H_2O_2 \xrightarrow{MnO_2} 2H_2O + O_2$$

This decomposition reaction is exothermic and can be used to generate oxygen gas in laboratory settings.

Explanation: Hydrogen peroxide acts as an oxidizing agent that breaks down organic dyes and pigments, bleaching them to colorless compounds. This property makes it effective in the textile industry for bleaching fabrics, as well as in the paper and pulp industry for brightening products.

Explanation: Hydrogen peroxide can be prepared in the laboratory by reacting barium peroxide ($BaO_2$) with dilute sulfuric acid:

$$BaO_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O_2$$

This method produces hydrogen peroxide along with barium sulfate ($BaSO_4$) as a byproduct, which can be easily removed by filtration.

Explanation: The anthraquinone process is the most widely used method for large-scale production of hydrogen peroxide. In this process, hydrogenation of anthraquinone is followed by oxidation, producing hydrogen peroxide. This method is efficient and allows for the continuous production of hydrogen peroxide with high yield.

Explanation: Hydrogen peroxide is commonly used in the medical field as an antiseptic to clean and disinfect wounds. It has mild antiseptic properties and helps remove dead tissue and bacteria. However, it is used in diluted forms (typically 3%) as higher concentrations can damage tissue.

Explanation: The structure of hydrogen peroxide (H₂O₂) is bent or V-shaped due to the presence of two lone pairs of electrons on each oxygen atom. The bond angle between the two O-H bonds is approximately 111.5°, which is slightly smaller than the typical 109.5° seen in tetrahedral structures, resulting in a non-linear geometry.

Explanation: In the structure of hydrogen peroxide, the bond angle between the O-H bonds is about 111.5°. This is because the oxygen atoms in hydrogen peroxide have two lone pairs of electrons each, causing repulsion and reducing the bond angle from the ideal tetrahedral angle of 109.5°.

Explanation: Hydrogen peroxide consists of two oxygen atoms bonded together by a single bond, with each oxygen atom bonded to a hydrogen atom. This gives the molecule the structure H-O-O-H, with oxygen as the central atom in the structure.

Explanation: In hydrogen peroxide (H₂O₂), the two oxygen atoms are connected by a single covalent bond. This single bond allows for the flexibility and reactivity of the molecule, which plays a significant role in its ability to act as an oxidizing agent.

Explanation: In the structure of hydrogen peroxide (H₂O₂), each oxygen atom is bonded to one hydrogen atom and the other oxygen atom. The structure can be written as H-O-O-H, where each oxygen has a single bond with a hydrogen atom and the other oxygen atom.

Explanation: The oxygen atoms in hydrogen peroxide are sp³ hybridized, meaning each oxygen has four regions of electron density: two bonding pairs with hydrogen atoms and two lone pairs. This hybridization leads to the bent shape of the molecule and the resulting bond angles being approximately 111.5°.

Explanation: The key difference between the structures of water (H₂O) and hydrogen peroxide (H₂O₂) is that water has a single oxygen atom bonded to two hydrogen atoms, while hydrogen peroxide has two oxygen atoms connected by a single bond, each bonded to a hydrogen atom. This gives hydrogen peroxide its unique open-book or “V-shaped” structure.

Explanation: In hydrogen peroxide, the oxidation state of each oxygen atom is -1. This is because hydrogen generally has an oxidation state of +1, and since there are two hydrogen atoms, the total positive charge is +2. The molecule must be neutral, so the two oxygen atoms must each have an oxidation state of -1 to balance the charge.

Explanation: The “open-book” structure of hydrogen peroxide refers to the bent or V-shaped arrangement of the molecule, with the oxygen-oxygen bond angle being about 111.5°. This flexibility is due to the lone pairs of electrons on each oxygen atom, which push the bonds apart, creating the non-linear shape.

Explanation: The lone pairs of electrons on the oxygen atoms in hydrogen peroxide cause electron-electron repulsion, which pushes the bonding pairs of electrons closer together. As a result, the bond angle is reduced to approximately 111.5°, which is smaller than the typical 109.5° seen in tetrahedral geometries, contributing to the V-shaped or “open-book” structure of the molecule.

Explanation: Hydrogen peroxide is a strong oxidizing agent due to the presence of the peroxide bond ($O-O$), which can easily break to release oxygen. In doing so, hydrogen peroxide can accept electrons from other substances, causing their oxidation while it gets reduced itself, typically to water or oxygen.

Explanation: In this reaction, hydrogen peroxide acts as a reducing agent by donating electrons and reducing to water. The reduction of hydrogen peroxide typically occurs in acidic conditions where it gains electrons and forms water, demonstrating its behavior as a reducing agent.

Explanation: Hydrogen peroxide’s strong oxidizing properties make it effective as a bleaching agent, especially in the textile and paper industries. It oxidizes colored compounds, breaking them down into colorless ones. For example, hydrogen peroxide is used to bleach hair and textiles, as it decomposes the pigment molecules into non-colored products.

Explanation: Hydrogen peroxide decomposes into oxygen and water when heated, especially in the presence of a catalyst such as manganese dioxide ($MnO_2$):

$$2H_2O_2 \xrightarrow{MnO_2} 2H_2O + O_2$$

This reaction is exothermic and releases oxygen gas. It is used in laboratory settings to generate oxygen or in some cleaning applications.

Explanation: In the reaction of hydrogen peroxide with potassium iodide, hydrogen peroxide oxidizes iodide ions ($I^-$) to iodine ($I_2$), while it gets reduced to water. The reaction is as follows:

$$H_2O_2 + 2I^- + 2H^+ \rightarrow I_2 + 2H_2O$$

Here, hydrogen peroxide acts as the oxidizing agent, accepting electrons and causing the oxidation of iodide ions to iodine.

Explanation: Hydrogen peroxide is used in water treatment because of its powerful oxidizing properties. It helps to oxidize and remove impurities such as organic compounds, bacteria, and viruses, improving the quality of water. It also helps in breaking down pollutants and neutralizing odors by promoting the oxidation of harmful substances.

Explanation: In this reaction, hydrogen peroxide acts as an oxidizing agent by oxidizing iron(II) ions ($Fe^{2+}$) to iron(III) ions ($Fe^{3+}$), while it is reduced to hydroxide ions ($OH^-$). This demonstrates hydrogen peroxide’s ability to accept electrons and oxidize metal ions, a common feature of its oxidizing behavior.

Explanation: Hydrogen peroxide reacts with potassium permanganate ($KMnO_4$) in acidic or basic conditions to reduce the permanganate ion ($MnO_4^-$) to manganese dioxide ($MnO_2$) or manganese ions ($Mn^{2+}$), while it is oxidized to oxygen gas ($O_2$). This reaction demonstrates the strong oxidizing ability of hydrogen peroxide, and oxygen gas is released as a byproduct.

Explanation: In this reaction, hydrogen peroxide is reduced by gaining electrons to form hydroxide ions ($OH^-$). In this case, hydrogen peroxide acts as a reducing agent, donating electrons in certain reactions, which contrasts with its usual role as an oxidizing agent in other contexts.

Explanation: Hydrogen peroxide is widely used as a bleaching agent, especially in the cosmetic industry to lighten hair. It breaks down the pigment in the hair (melanin), lightening the hair color. It is commonly used in hair dyes and hair lightening products due to its effective oxidation of the color molecules.

Explanation: Hydrogen peroxide is widely used in the medical field as a disinfectant for cleaning wounds. It works by releasing oxygen, which helps to clean the wound by removing debris and bacteria. When applied to a wound, hydrogen peroxide foams, indicating the release of oxygen and the destruction of pathogens.

Explanation: Hydrogen peroxide is widely used as a bleaching agent in the textile and paper industries. It helps to whiten and brighten fabrics, paper, and wood pulp. Its oxidizing properties break down the color compounds in these materials, making it an environmentally friendly alternative to chlorine-based bleaches.

Explanation: Hydrogen peroxide is used in the environmental sector, particularly in wastewater treatment, to remove organic contaminants and to help purify water. It oxidizes pollutants in the water, breaking them down into harmless compounds, and is also used for decolorizing and disinfecting water.

Explanation: In the food industry, hydrogen peroxide is used as a bleaching agent for flour. It is used to whiten the flour, improve its texture, and increase shelf life. After use, hydrogen peroxide decomposes into water and oxygen, making it a safe option for food processing.

Explanation: In the cosmetic industry, hydrogen peroxide is used as a bleaching agent in hair lightening products. It is applied to lighten hair by breaking down the pigment (melanin) in the hair shaft. It is also used in some skin care products to help remove dead skin cells, although in lower concentrations.

Explanation: Hydrogen peroxide is commonly used in the textile industry for cleaning and bleaching fabrics. It is an effective agent for removing impurities and stains, and it is also used for bleaching natural and synthetic fibers. Unlike chlorine bleach, hydrogen peroxide is more environmentally friendly and does not leave harmful residues on fabrics.

Explanation: In the paper industry, hydrogen peroxide is used for whitening and bleaching paper. It oxidizes the lignin present in wood pulp, removing color and improving the brightness of the final paper product. It is an environmentally safer alternative to chlorine-based bleaching agents, which can release harmful byproducts.

Explanation: Hydrogen peroxide is used in the synthesis of peracetic acid, which is an effective disinfectant and bleaching agent. It is widely used in the food industry and as a sterilizing agent in water treatment. The reaction involves the oxidation of acetic acid by hydrogen peroxide:

$$CH_3COOH + H_2O_2 \rightarrow CH_3COOOH + H_2O$$

Explanation: Hydrogen peroxide is used as an oxidizing agent in the laboratory production of oxygen from potassium chlorate ($KClO_3$). The reaction is catalyzed by manganese dioxide, and hydrogen peroxide is added to release additional oxygen gas:

$$2KClO_3 \xrightarrow{MnO_2} 2KCl + 3O_2$$

Explanation: Hydrogen peroxide is commonly used in medicine as a disinfectant for treating minor cuts, wounds, and infections. Its antiseptic properties help to kill bacteria and clean the wound. It works by releasing oxygen when applied to the wound, which helps to flush out debris and bacteria. It is typically diluted before use to prevent tissue damage.

Explanation: Ionic hydrides, like sodium hydride (NaH) and calcium hydride (CaH₂), are formed when metals from the alkali and alkaline earth groups react with hydrogen. In these compounds, hydrogen exists as the hydride ion ($H^-$), which is bonded ionically to the metal cation. The metal donates an electron to hydrogen, resulting in the formation of a stable ionic lattice.

Explanation: Sodium hydride (NaH) is a classic example of a saline hydride, where sodium donates an electron to hydrogen, forming $Na^+$ and $H^-$. These ions then arrange in an ionic crystal lattice, similar to the structure of salts like sodium chloride (NaCl). The term “saline hydride” refers to ionic hydrides that resemble salts in their crystalline structure.

Explanation: Ionic hydrides like NaH and CaH₂ are reactive with water, releasing hydrogen gas and forming metal hydroxides. Additionally, when heated, they decompose to release hydrogen gas. For example, calcium hydride (CaH₂) reacts with water as follows:

$$CaH_2 + 2H_2O \rightarrow Ca(OH)_2 + 2H_2\uparrow$$

This decomposition and reactivity with water make ionic hydrides useful as reducing agents.

Explanation: Calcium hydride (CaH₂) reacts with water to form calcium hydroxide (Ca(OH)₂ and hydrogen gas ($H_2$). The reaction is exothermic and produces hydrogen gas, making CaH₂ a useful source of hydrogen in various industrial processes:

$$CaH_2 + 2H_2O \rightarrow Ca(OH)_2 + 2H_2\uparrow$$

Explanation: Sodium, an alkali metal, readily reacts with hydrogen to form sodium hydride (NaH), a typical ionic hydride. Sodium gives up an electron to hydrogen, forming $Na^+$ and $H^-$. This reaction is characteristic of alkali metals, which readily form ionic hydrides when reacting with hydrogen.

Explanation: In ionic hydrides like NaH and CaH₂, the bonding between metal and hydrogen is ionic. The metal (sodium or calcium) donates an electron to hydrogen, forming $H^-$ ions. The metal ions ($Na^+$ or $Ca^{2+}$) are held together by electrostatic forces with the hydride ions ($H^-$), forming a stable ionic structure.

Explanation: The hydride ion ($H^-$) in ionic hydrides acts as a reducing agent because it can donate electrons in reactions. For example, in the reaction of sodium hydride with water, the $H^-$ ion donates electrons to water, reducing it to hydrogen gas and oxidizing itself to form hydroxide ions ($OH^-$).

Explanation: Ionic hydrides such as NaH react with acids to form salt and hydrogen gas. For example, when sodium hydride reacts with hydrochloric acid, sodium chloride and hydrogen gas are produced:

$$NaH + HCl \rightarrow NaCl + H_2\uparrow$$

This is a typical reaction of ionic hydrides with acids, where the hydride ion ($H^-$) reacts with the proton ($H^+$) from the acid to form hydrogen gas.

Explanation: The crystal structure of sodium hydride (NaH) is similar to that of sodium chloride (NaCl). In both structures, sodium ions ($Na^+$) are arranged in a face-centered cubic lattice, with the hydride ions ($H^-$) in sodium hydride and chloride ions ($Cl^-$) in sodium chloride occupying the interstitial spaces. This similarity is due to the ionic nature of both compounds.

Explanation: Calcium hydride (CaH₂) is primarily used as a reducing agent in organic and inorganic chemical reactions. It is used in the reduction of various compounds, including the reduction of metal halides to metals. In addition, it is used in laboratories to produce hydrogen gas by reacting with water, making it an important chemical in hydrogenation processes.

Explanation: Methane (CH₄) is a covalent hydride where the hydrogen atoms are bonded to carbon by covalent bonds. Unlike ionic hydrides, where the bonding is ionic, covalent hydrides like methane share electrons between atoms, resulting in the formation of stable molecules. Methane is a common example of a covalent hydride with carbon forming four covalent bonds with hydrogen.

Explanation: Ammonia (NH₃) is a covalent hydride where nitrogen shares electrons with three hydrogen atoms. Each nitrogen-hydrogen bond is covalent, with the nitrogen atom forming a pair of electrons with each hydrogen atom. The molecule has a trigonal pyramidal shape due to the lone pair of electrons on nitrogen, and it exhibits strong intermolecular hydrogen bonding in the liquid state.

Explanation: Methane (CH₄) is commonly used as a rocket fuel, particularly in liquid propulsion systems. It has a high energy density, is easy to store, and can be efficiently combusted with oxidizers such as liquid oxygen (LOX). Methane’s low molecular weight and high combustion efficiency make it ideal for use in rocketry.

Explanation: The molecular geometry of water (H₂O) is bent (V-shaped) due to the presence of two lone pairs of electrons on the oxygen atom. These lone pairs cause electron-electron repulsion, which pushes the hydrogen atoms closer together. The bond angle in water is approximately 104.5°, smaller than the ideal tetrahedral angle of 109.5°.

Explanation: Hydrogen chloride (HCl) is a covalent hydride formed by the sharing of electrons between hydrogen and chlorine. In HCl, the hydrogen atom forms a covalent bond with chlorine, with the electron density shifted toward chlorine due to its higher electronegativity. HCl is a gas at room temperature and forms hydrochloric acid when dissolved in water.

Explanation: Covalent hydrides such as methane (CH₄), ammonia (NH₃), and water (H₂O) are poor conductors of electricity because they do not contain free ions or electrons capable of conducting an electric current. These compounds consist of molecules held together by covalent bonds, which do not dissociate into ions in solution.

Explanation: Methane (CH₄), ammonia (NH₃), and hydrogen chloride (HCl) are examples of covalent hydrides, but only HCl is truly polar due to the large electronegativity difference between hydrogen and chlorine. Ammonia is polar because of its trigonal pyramidal structure and lone pair on nitrogen, and methane is generally considered nonpolar, although slight polarity exists due to the distribution of electrons.

Explanation: The boiling points of covalent hydrides generally increase with molecular size. For example, methane (CH₄) has a very low boiling point of -161.5°C, while ammonia (NH₃) has a higher boiling point of -33.3°C due to its hydrogen bonding. Water (H₂O) has an even higher boiling point of 100°C due to the strong hydrogen bonds between water molecules.

Explanation: Ammonia (NH₃) exhibits hydrogen bonding due to the electronegativity of nitrogen and the presence of lone pairs of electrons on the nitrogen atom. This allows ammonia molecules to form hydrogen bonds with one another, which gives ammonia its relatively high boiling point compared to other covalent hydrides like methane or hydrogen chloride.

Explanation: Methane (CH₄) exhibits a tetrahedral geometry because the central carbon atom forms four bonds with hydrogen atoms. The bond angles in methane are approximately 109.5°, characteristic of a tetrahedral structure. This geometry minimizes electron-pair repulsion and allows methane to be a stable molecule in nature.