water

**Water (H2O)** is also known as the "universal solvent." Water is a chemical compound composed of two hydrogen atoms covalently bonded to one oxygen atom. It has a bent molecular geometry due to the two lone pairs on oxygen, resulting in an angle of approximately 104.5 degrees. This structure gives water unique properties, including strong hydrogen bonding capabilities, which contribute to its high specific heat, boiling point, and unusual density behavior when it freezes (ice is less dense than liquid water). Water's hydrogen bonds are responsible for many of its distinctive properties, such as its surface tension, ability to dissolve many substances (hence "universal solvent"), and its role as a medium for various chemical reactions. In addition to being essential for life, water participates in numerous chemical reactions, such as the water-gas shift reaction, and forms complexes with metal ions.

### Repeated Clues for Water (H2O)

1. **Universal Solvent**: Many question stems refer to water as the "universal solvent," highlighting its ability to dissolve a wide range of substances due to its polarity and hydrogen bonding. This phrase underscores water's critical role in both biological and chemical processes.

2. **Hydrogen Bonding**: Several questions mention water's high boiling point, specific heat, or surface tension due to extensive hydrogen bonding. Hydrogen bonds between water molecules make it unique among small molecules, particularly in terms of its phase behavior and heat-related properties.

3. **Bent Molecular Geometry**: Water's molecular geometry is commonly noted, with a bond angle of about 104.5 degrees, caused by the two lone pairs on the oxygen atom. This shape is a critical feature of its molecular structure, affecting its polarity and ability to form hydrogen bonds.

4. **Phase Diagram Negative Slope**: Water is noted for its unusual solid-liquid equilibrium line, which has a negative slope in its phase diagram. This property means that ice is less dense than liquid water, allowing ice to float—a phenomenon that has ecological significance.

5. **Autoionization/Conductivity**: Questions reference the autoionization of water, a process in which water molecules spontaneously dissociate into hydronium (H3O+) and hydroxide (OH-) ions. This process is foundational to acid-base chemistry and explains water's slight conductivity.

6. **Temperature and Density Anomalies**: Water's maximum density at 4°C is frequently mentioned, emphasizing how it becomes less dense upon freezing. This density anomaly has significant implications for aquatic life, as ice floats on liquid water.

7. **Clathrates and Hydrates**: Water forms structures called clathrates, where water molecules form cage-like structures around other molecules, like methane. Water also acts as a ligand in hydrates, binding to metal ions in crystalline forms.

### Related Quizbowl Facts That Appeared in More Than One Toss-up on qbreader.org

1. The "universal ___1___ " is a title given to water due to its ability to dissolve a wide range of substances.

2. Water's high specific heat and boiling point are due to its extensive ___2___ bonding network, which stabilizes its molecules.

3. Water molecules exhibit a ___3___ geometry with a bond angle of around 104.5 degrees, due to the lone pairs on the oxygen atom.

4. The ___4___ slope in water's solid-liquid boundary on a phase diagram is unusual, as it results in ice being less dense than liquid water.

5. Autoionization describes how water molecules dissociate into ___5___ and hydroxide ions, which explains water's slight conductivity.

6. Water reaches its maximum density at ___6___ degrees Celsius, a property that impacts aquatic environments.

7. Water can form clathrates, where it traps ___7___ molecules in a cage-like structure, or hydrates by coordinating with metal ions in crystals.

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1. Solvent

2. Hydrogen

3. Bent

4. Negative

5. Hydronium

6. Four

7. Methane

1. **Water as the universal solvent** - 17 occurrences  

   - Water’s polarity allows it to dissolve a wide range of substances, earning it the title of the “universal solvent.” This property is essential for biochemical reactions in living organisms and environmental processes.

2. **Hydrogen bonding** - 12 occurrences  

   - Hydrogen bonds between water molecules give rise to its high cohesion, surface tension, and other unique properties. Hydrogen bonding is also crucial for water’s high boiling point relative to its molecular weight.

3. **Combustion reaction producing water and carbon dioxide** - 9 occurrences  

   - Combustion of hydrocarbons yields water and CO₂, central to energy production and metabolism. This reaction is a fundamental example of an exothermic process and is essential in cellular respiration.

4. **Water's high specific heat capacity** - 8 occurrences  

   - Water’s ability to absorb heat with minimal temperature change stabilizes environments, contributing to temperature regulation in ecosystems and within organisms.

5. **Clathrate formation involving water** - 7 occurrences  

   - Clathrates are ice-like structures where water forms a lattice trapping gas molecules, such as methane. They are significant in fields like natural gas storage and understanding potential energy sources.

6. **104.5-degree bond angle** - 6 occurrences  

   - Water’s bent geometry, with a 104.5° bond angle, creates a dipole moment, contributing to its polarity. This angle results from the tetrahedral arrangement of electron pairs around oxygen.

7. **Grotthuss mechanism** - 5 occurrences  

   - The Grotthuss mechanism describes proton transfer through a hydrogen-bond network in water, explaining how protons move efficiently, essential in acid-base chemistry and biological processes.

8. **Autoionization of water forming hydronium and hydroxide ions** - 5 occurrences  

   - Water autoionizes into hydronium and hydroxide ions, giving it a slight conductivity and defining its pH of 7. This process is central to acid-base chemistry.

9. **Maximum density of water at 4 degrees Celsius** - 4 occurrences  

   - Water reaches maximum density at 4°C, causing ice to float. This property is ecologically important, as it allows aquatic life to survive in cold environments.

10. **Pourbaix diagram (related to water stability)** - 4 occurrences  

    - Pourbaix diagrams plot the stability of water across pH and potential ranges, indicating conditions where water will oxidize or reduce, crucial in electrochemistry and corrosion studies.