Water

 

Water

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

• Drinking water is essential to human life
• In chemistry, it is a common polar solvent
• Ice is a key thermal absorption material

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 deposits
• 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

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
2. Boiling point
3. Melting point

Qualitative tests

1. Visual: Clear, colorless
2. Smell: None
3. Taste: Characteristic
4. Approximate Viscocity : Characteristic

Purification

Filtration

1. Passing water through clean, fine sand will remove some microorganisms.
2. Passing 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 (unpotable) water. It should still be boiled before drinking.

Distillation

Distilled water is water that has been condensed from a gas and stored in a clean container. Distilled water has no dissolved solids and is completely sterile.

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

Some contaminants form azeotropes with water (ammonia, ethanol, sulfuric acid, etc) and may not be easily removed 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