Comprehensive Study Notes on Hydrogen Gas: Preparation, Properties, Reactions, Uses, and Chemical Formulas

Overview and Historical Background of Hydrogen

• Scope of key atmospheric and laboratory gases:

  • Hydrogen gas ($H_2$)

  • Oxygen gas ($O_2$)

  • Nitrogen gas ($N_2$)

  • Ozone layer ($O_3$)

• Fundamental properties of Hydrogen:

  • Hydrogen is the lightest, simplest, and a highly reactive chemical element.

  • It was discovered by Henry Cavendish, a British scientist, in $1766\,\text{AD}$.

General Methods of Preparing Hydrogen Gas

• Preparation from Water:

  • Electrolysis of water: $2H_2O \xrightarrow{\text{Electricity}} 2H_2\uparrow + O_2\uparrow$

  • Reaction of active metals (such as sodium and potassium) with water at ordinary temperature: $2Na + 2H_2O \rightarrow 2NaOH + H_2\uparrow$ $2K + 2H_2O \rightarrow 2KOH + H_2\uparrow$

• Preparation from Acids:

  • Reaction of zinc with dilute sulphuric acid: $Zn + \text{dil. } H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow$

  • Reaction of magnesium with dilute hydrochloric acid: $Mg + \text{dil. } 2HCl \rightarrow MgCl_2 + H_2\uparrow$

• Preparation from Alkalis:

  • Active metals react with alkalis to liberate hydrogen gas: $Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2\uparrow$

  • The product $Na_2ZnO_2$ formed in the reaction above is sodium zincate. $2Al + 2NaOH + 6H_2O \rightarrow 2NaAlO_2 + 3H_2\uparrow$

Laboratory Preparation of Hydrogen Gas

• Chemical Principle:

  • In the laboratory, hydrogen gas is prepared by the chemical reaction of zinc granules with dilute hydrochloric acid ($\text{dil. } HCl$) or dilute sulphuric acid ($\text{dil. } H_2SO_4$).

• Reaction Equations:

  • Reaction with dilute hydrochloric acid: $\text{Zinc} + \text{Hydrochloric acid} \rightarrow \text{Zinc chloride} + \text{Hydrogen}$ $Zn + \text{dil. } 2HCl \rightarrow ZnCl_2 + H_2\uparrow$

  • Reaction with dilute sulphuric acid: $\text{Zinc} + \text{Sulphuric acid} \rightarrow \text{Zinc sulphate} + \text{Hydrogen}$ $Zn + \text{dil. } H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow$

• Selection of Impure Zinc Granules:

  • Impure zinc granules are intentionally used to prepare hydrogen gas in the laboratory instead of pure zinc.

  • If pure zinc is used, the chemical reaction occurs extremely slowly.

  • Impurities contained within the granulated zinc act as a catalyst and significantly accelerate the rate of the chemical reaction.

• Laboratory Apparatus Setup:

  • Woulfe's bottle

  • Thistle funnel

  • Corks

  • Delivery tube

  • Water trough

  • Beehive shelf

  • Gas jar

  • Granulated zinc and dilute acid ($HCl$ or $H_2SO_4$)

  • Water

• Detailed Laboratory Procedure:

  • Place a small quantity of impure granulated zinc into a clean Woulfe's bottle.

  • Insert a thistle funnel into one neck of the Woulfe's bottle and fit one end of a delivery tube into the second neck, securing both tightly using corks.

  • Submerge the opposite end of the delivery tube inside a water trough, placing it directly under the Beehive shelf.

  • Fill a gas jar completely with water and invert it over the opening of the Beehive shelf.

  • Pour dilute hydrochloric acid or dilute sulphuric acid carefully down through the thistle funnel until the bottom stem of the funnel is fully immersed below the liquid level.

  • Collect the evolving hydrogen gas inside the inverted gas jar via the downward displacement of water.

Gas Testing and Collection Mechanisms

• Experimental Test for Hydrogen Gas:

  • Introduce a burning matchstick into the mouth of a gas jar containing the produced gas.

  • If the gas is hydrogen, it burns with a pale-blue flame, and the matchstick flame gets extinguished with a distinct "pop" sound.

• Collection Mechanism:

  • Hydrogen gas and oxygen gas are both collected using the downward displacement of water (water displacement method).

  • Hydrogen is lighter than water and virtually insoluble / slightly soluble in water, making water displacement the effective method for gas collection.

Industrial Manufacture of Hydrogen Gas

• Methane-Steam Reaction (Steam Reforming):

  • Methane gas reacts with steam under elevated temperature and pressure conditions: $CH_4 + H_2O \xrightarrow{1200\,^\circ\text{C} \,/\, 30\,\text{atm}} CO + 3H_2\uparrow$

• Electrolysis of Acidulated Water:

  • Water combined with dilute sulphuric acid ($\text{dil. } H_2SO_4$) undergoes decomposition via electrical power: $2H_2O \xrightarrow{\text{Electricity}} 2H_2 + O_2$

Physical Properties of Hydrogen Gas

• Color, Odor, and Taste:

  • Hydrogen gas is completely colourless, odourless, and tasteless.

• Density:

  • It is the lightest gas known and is lighter than atmospheric air.

• Chemical Neutrality and Solubility:

  • It is neutral to indicators and does not alter the color of blue or red litmus paper.

  • It is slightly soluble in water.

• Phase Change Critical Temperatures:

  • Liquefaction point: Converts to liquid at $-253\,^\circ\text{C}$ (also recorded as $-258\,^\circ\text{C}$).

  • Solidification point: Freezes into solid form at $-259\,^\circ\text{C}$.

Chemical Properties of Hydrogen Gas

• Reaction with Air / Oxygen:

  • Hydrogen combusts in the presence of oxygen or air to yield water: $2H_2 + O_2 \xrightarrow{\text{burn}} 2H_2O$

• Reaction with Active Metals:

  • Reacts directly with alkali and alkaline earth metals at $300\,^\circ\text{C}$ to form metal hydrides: $2Na + H_2 \xrightarrow{300\,^\circ\text{C}} 2NaH$

  • Product name: Sodium hydride. $2K + H_2 \xrightarrow{300\,^\circ\text{C}} 2KH$

  • Product name: Potassium hydride. $Ca + H_2 \xrightarrow{300\,^\circ\text{C}} CaH_2$

  • Product name: Calcium hydride.

• Reaction with Halogens:

  • Combines with halogens under specified light and thermal conditions to yield hydrogen halides: $H_2 + F_2 \xrightarrow{\text{In dark}} 2HF$

  • Product name: Hydrofluoric acid. $H_2 + Cl_2 \xrightarrow{\text{In light}} 2HCl$

  • Product name: Hydrochloric acid. $H_2 + Br_2 \xrightarrow{400\,^\circ\text{C}} 2HBr$

  • Product name: Hydrobromic acid. $H_2 + I_2 \xrightarrow{440\,^\circ\text{C}} 2HI$

  • Product name: Hydrogen iodide.

• Reaction with Metallic Oxides (Reduction Process):

  • Functions as a strong reducing agent by stripping oxygen from heated metallic oxides: $CuO + H_2 \xrightarrow{\Delta} Cu + H_2O$ $PbO + H_2 \xrightarrow{\Delta} Pb + H_2O$ $2Fe_2O_3 + 6H_2 \xrightarrow{\Delta} 4Fe + 6H_2O$ $Fe_3O_4 + 4H_2 \xrightarrow{\Delta} 3Fe + 4H_2O$ $2ZnO + H_2 \xrightarrow{\Delta} 2Zn + H_2O$

• Reaction with Non-Metals:

  • Direct combination with carbon: $2H_2 + C \rightarrow CH_4$

  • Product name: Methane.

  • Direct combination with heated sulfur: $H_2 + S \xrightarrow{\Delta} H_2S$

  • Product name: Hydrogen sulphide.

• Reaction with Nitrogen:

  • Synthesizes ammonia gas under high pressure and temperature: $3H_2 + N_2 \xrightarrow{500\,^\circ\text{C} \,/\, 200\,\text{atm}} 2NH_3$

• Reaction with Unsaturated Hydrocarbons:

  • Addition reaction converting ethene to ethane over a nickel catalyst: $C_2H_4 + H_2 \xrightarrow{\text{Ni} \,/\, 477\,\text{K}} C_2H_6$

• Hydrogenation of Vegetable Oils:

  • Converts liquid vegetable oil into solid vegetable ghee: $H_2 + \text{Vegetable Oil} \xrightarrow{\text{Ni} \,/\, 200\,^\circ\text{C} \,/\, 8\text{--}10\,\text{atm}} \text{Vegetable Ghee}$

Practical Applications and Uses of Hydrogen Gas

• Manufacturing of Edible Fats:

  • Used extensively in the manufacture of vegetable ghee from vegetable oil via the hydrogenation process.

• Aerospace Propellants:

  • Utilized as high-efficiency liquid fuel in space rockets.

• Chemical Synthesis:

  • Essential raw material in the industrial synthesis of ammonia gas ($NH_3$) and chemical nitrogenous fertilizers.

• Metallurgy and Metal Work:

  • Acts as an effective reducing agent in extraction and chemical processes.

  • Combined with oxygen to generate oxyhydrogen flames used for cutting and welding metals.

Important Chemical Formulas and Molecular Nomenclature

• Acidic Compounds:

  • Hydrochloric acid: $HCl$

  • Sulfuric acid: $H_2SO_4$

  • Nitric acid: $HNO_3$

  • Carbonic acid: $H_2CO_3$

  • Acetic acid: $CH_3COOH$

  • Phosphoric acid: $H_3PO_4$

• Hydrides, Oxides, and Hydroxides:

  • Potassium hydride: $KH$

  • Calcium hydride: $CaH_2$

  • Hydrogen peroxide: $H_2O_2$

  • Potassium hydroxide: $KOH$

  • Magnesium hydroxide: $Mg(OH)_2$

  • Calcium hydroxide: $Ca(OH)_2$

  • Magnesium oxide: $MgO$

  • Calcium oxide: $CaO$

  • Sodium oxide: $Na_2O$

  • Potassium oxide: $K_2O$

  • Aluminium oxide: $Al_2O_3$

  • Zinc oxide: $ZnO$

• Inorganic Salts:

  • Magnesium chloride: $MgCl_2$

  • Calcium carbonate: $CaCO_3$

  • Sodium bicarbonate: $NaHCO_3$

  • Iron (II) sulfate: $FeSO_4$

  • Copper sulfate: $CuSO_4$

  • Sodium chloride: $NaCl$

  • Sodium carbonate: $Na_2CO_3$

  • Sodium nitrate: $NaNO_3$

• Molecular Gases and Organic Compounds:

  • Ozone: $O_3$

  • Sulfur dioxide: $SO_2$

  • Sulfur trioxide: $SO_3$

  • Carbon dioxide: $CO_2$

  • Methane: $CH_4$

  • Ammonia: $NH_3$

  • Glucose: $C_6H_{12}O_6$

Environmental and Atmospheric Phenomena

• Function of the Ozone Layer:

  • The Ozone layer ($O_3$) serves as a protective atmospheric layer shielding Earth from harmful solar ultraviolet (UV) radiation.

• Glacial and Ice Sheet Depletion:

  • The melting rate of mountain ice and glaciers is accelerating.

  • This acceleration is caused by the ongoing depletion of the ozone layer and the associated rise in global surface temperatures.