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Hydrogen and Its Compounds
Chemical Properties
- Combustion: Burning hydrogen gas produces water.
- Fuel Property: Hydrogen gas is a very clean fuel, causing minimal air pollution compared to kerosene, coal, and diesel.
Reaction Stoichiometry
- Heat of Combustion: Burning one mole of hydrogen gas in excess oxygen releases 290 kJ of heat.
- Molar Mass: The molar mass of hydrogen gas (H₂) is 2 g/mol.
Forming Compounds
- An element with four valence electrons will form a compound with hydrogen with the formula XH₄ (e.g., Carbon forms CH₄, methane).
Composition of Water (H₂O)
- Molecular Formula: H₂O.
- Composition by Weight:
- Hydrogen constitutes approximately 11.11%.
- Oxygen constitutes the remaining 88.89%.
Water (H₂O)
Properties of Water
- pH Level: The pH of pure water is 7 (neutral).
- Solvent Properties:
- Water is an excellent solvent, capable of dissolving more substances than any other liquid.
- This property is due to its dipolar nature (high dipole moment).
- It is particularly effective at dissolving ionic salts.
- Purity and Forms:
- The purest form of water is distilled water.
- Rainwater is a relatively pure natural form.
Heavy Water (D₂O)
- Definition: A form of water where hydrogen atoms are replaced by the heavier isotope, deuterium (D).
- Formula: D₂O.
- Properties:
- Higher molecular weight (20) than ordinary water (18).
- Chemically similar to ordinary water but has different physical properties.
- Discovery: Discovered by H.C. Urey.
- Uses: Used as a moderator (to slow down neutrons) and a coolant in nuclear reactors.
Hard Water
- Definition: Water that contains dissolved minerals, specifically insoluble salts of calcium and magnesium.
- Problems and Unsuitability:
- Washing: Not suitable for washing with soap; it forms an insoluble scum, reducing lathering.
- Boilers: Not suitable for boilers; it causes scale formation, reducing efficiency and potentially causing damage.
- Drinking: Generally not considered suitable for drinking (context-dependent, often due to taste and scaling).
- Cause of Permanent Hardness: Caused by dissolved chlorides and sulfates of calcium and magnesium.
Water Purification Methods
Desalination (Removing Salt from Seawater)
- Purpose: Large-scale purification of seawater into drinking water.
- Common Process: Reverse osmosis.
- Other Method: Distillation.
General Purification Techniques
- Disinfection: Chlorine gas is used to kill microorganisms in drinking water.
- Demineralization: Ion-exchange processes are used to prepare large quantities of drinking water from impure water.
- Clarification: Alum is used to clean muddy water through coagulation, causing suspended particles to clump together and settle.
Related Chemistry (Hydrogenation)
- Process: Hydrogenation is the chemical process of adding hydrogen gas.
- Application: Used in the manufacture of Vanaspati Ghee from vegetable (Vanaspati) oil.
- Catalyst: A common catalyst for this reaction is Nickel.
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