Water

 

Water
aka distilled water, ice

Chemical formula	H2O
OTP appearance	clear liquid
Index of refraction	1.333
Molar Mass(g/mol)	18
Enthalpy of Formation(kJ/mol)	−187.80
Density(g/cc)	1
Melting Point(°C)	0.1
Boiling Point(°C)	100
Solubility in ethanol(g/L)	misc
NFPA 704	0 0 0

Water, in the English language, is an inexact term. This article deals with the chemical compound H₂O: pure water.

Uses

Primary

• Water is essential to human life
• In chemistry, it is a common polar solvent
• Ice is a key thermal absorption material
• Triple point is key in thermal measurement and calibration of thermometers.

Secondary

• Expansion on freezing is a key mechanic in early stone splitting

Natural occurrence

• Water occurs naturally
  • as fresh water (ultimately derived from rain)
    • Rain
    • Springs
    • Rivers
    • Lakes
  • and salt water from
    • Oceans
    • Seas
    • Salt lakes
    • Brine pools
• Structural water occurs in many minerals
• Many plants contain an abundance of water

Hazards

• Drowning
• Overconsumption (≥2L/hr for multiple hours when normally hydrated) can lead to hyponatremia

Character

• Boiling point_°C = 65.8 + 0.045P_mmHg
  • Inside the "normal" atmospheric pressure range (750-770) the boiling point of water remains within 100±0.5°C.
  • To get down to a boiling point of 99°C, you would need a pressure below 738 (mmHg)
  • To get up to a boiling point of 101°C, you would need a pressure above 782 (mmHg)
• Resistivity ρ_cm@25°C = 18.18 MΩ
  • 0.055 micro-siemens/cm

Production

Extraction

• Pure water can be extracted from fresh water and salt water by distillation.

Synthesis

from hydrogen gas

1. Burn hydrogen in air, directing the combustion products to a condenser

   2 H₂ + O₂

   {

   →

   combustion}

   H₂O(v)

2. Condense the water formed

As a side product

Many chemical reactions, particularly acid/base reactions (e.g. acetic acid and calcium hydroxide), produce water as a side product.

2 CHCOOH + Ca(OH)₂ → Ca(CH₃COO)₂ + 2 H₂O // acetic acid and calcium hydroxide produce calcium acetate and water

Testing

Quantitative tests

1. Density 1.0
2. Triple point 0.01°C
3. Boiling point 100°C
4. pH 7.0
5. Resistivity 18MΩ/cm

Qualitative tests

1. Visual: Clear, colorless
   • Adding a few drops of silver nitrate will show chlorides, carbonates, hydroxides, and sulfates as insoluble precipitates
2. Smell: None
3. Taste: Characteristic
4. Approximate Viscocity : Characteristic

Purification

Filtration

1. Filtering water through clean, fine sand will remove some microorganisms.
2. Filtering water through charcoal or activated charcoal will remove toxins such as cyanide.

Arranging a filter with layers of sand and charcoal is an effective way to produce relatively clean water. It should still be boiled before drinking.

Boiling

Boiling fresh or salt water will render it relatively safe to drink as far as monad pathogens go. This will not, generally, remove or change and dissolved compounds, so the salt in salt water, or other potentially harmful materials, will remain.

Distillation

Main Article: Distillation

Distilled water is water that has been condensed from a pure water vapor. In simple cases this will render it both completely free of contaminants and totally sterile.

1. distil water
2. discard residue
3. distillate is distilled water

NB: Some contaminants form fixed gaseous mixtures with water. (e.g. ethanol, sulfuric acid) These are not easily removed by simple distillation.

Other

• The mineral witherite is sometimes used for the removal of calcium and magnesium sulfates from water via precipitation

  2 BaCO₃(s) + CaSO₄(aq) + MgSO₄(aq) → CaCO₃(s) + MgCO₃(s) + BaSO₄(s)

Storage

Store in watertight containers.

Disposal

Water can be safely discarded into the environment

See Also

• Fresh water vs salt water