Water and Hardness Chemistry Notes

This flashcard set covers the properties, sources, uses, and treatment of water, as well as the causes and removal methods for water hardness.

Water

A colourless, odourless liquid consisting of hydrogen and oxygen in a ratio of $2:1$ that acts as a universal solvent.

Rain water

The purest form of natural water, described as a natural form of distilled water.

Distilled water

Chemically pure water prepared by condensing steam or passing water through an ion-exchange resin column, used in laboratories, drug preparation, and car batteries.

Hydrogen bonds

The molecular links responsible for water's unexpectedly high melting and boiling points, as well as its high surface tension.

Ice structure

An open hydrogen-bonded hexagonal lattice where each oxygen atom is surrounded tetrahedrally by four hydrogen atoms.

Heat capacity

The amount of heat required to raise the temperature of a substance by one degree; water has an unusually large capacity, making it an effective coolant.

Specific heat index

The property of water that helps regulate air temperature changes, ensuring seasonal transitions are gradual rather than sudden.

Anhydrous cobalt (II) chloride

A substance used to test for water that changes from blue to pink when hydrated ($CoCl_2 + 6H_2O \rightarrow CoCl_2 \cdot 6H_2O$).

Anhydrous copper (II) tetraoxosulphate (VI)

A white substance that turns blue in the presence of water to form a hydrate ($CuSO_4(s) + 5H_2O \rightarrow CuSO_4 \cdot 5H_2O$).

Coagulation

A water treatment process where lime and potash alum ($KAl(SO_4)_2$) or sodium aluminate (III) ($NaAlO_2$) are added to cause flocculation.

Disinfection (Water Treatment)

The addition of chemicals like chlorine to kill germs, iodine to prevent goitre, and fluorine to prevent tooth decay.

Hard water

Water that does not form lather readily with soap due to the presence of dissolved salts like $CaSO_4$, $MgSO_4$, or $Ca(HCO_3)_2$.

Scum

Unpleasant insoluble calcium or magnesium octadecanoate formed when soap reacts with the dissolved salts in hard water.

Temporary hardness

Hardness caused by dissolved $Ca(HCO_3)_2$ which can be removed by boiling or by adding slaked lime ($Ca(OH)_2$).

Permanent hardness

Hardness caused by calcium or magnesium ions in the form of tetraoxosulphates (VI) and chlorides, which can only be removed using chemicals.

Furring

The coating of the inner surface of kettles and boilers with a white layer of $CaCO_3$ resulting from the decomposition of temporarily hard water.

Stalactites and Stalagmites

Deposits of $CaCO_3$ formed on cave roofs and floors respectively from the decomposition of dripping temporarily hard water.

Washing soda ($Na_2CO_3$)

A soluble sodium compound added to hard water to remove permanent hardness by precipitating calcium and magnesium ions as insoluble carbonates.

Permutit (Zeolite)

An ion-exchange resin consisting of sodium aluminium trioxosilicate (IV) used to replace calcium and magnesium ions in hard water with sodium ions.

Regeneration (Permutit)

The process of restoring used-up zeolite by pouring a strong solution of common salt ($NaCl$) through the resin.