Chemistry: Water Hardness, Rusting, and Pollution

Educational flashcards covering water hardness types and removal, rust prevention mechanisms, soap chemistry, and water pollution concepts based on lecture notes.

Temporary hard water

Water containing dissolved calcium hydrogencarbonate $(Ca(HCO_{3})_{2})$ that can be removed by heating or boiling.

Permanent hard water

Water caused by dissolved calcium sulphate $(CaSO_{4})$ and magnesium sulphate $(MgSO_{4})$ that cannot be removed by boiling.

Clark's method

A cheap, large-scale water treatment process that uses the addition of $Ca(OH)_{2}(aq)$ to remove temporary hardness by converting $Ca^{2+}$ into insoluble $CaCO_{3}$.

Washing soda

Sodium carbonate $(Na_{2}CO_{3})$, a substance added to remove both temporary and permanent hardness by precipitating dissolved $Ca^{2+}(aq)$ ions as insoluble carbonates.

Ion exchange

A very convenient large-scale method for removing water hardness where water flows through a cation exchange to entirely remove ions responsible for hardness.

Rust

The product of the oxidation of iron in the presence of oxygen and water, chemically known as hydrated iron(III) oxide with the formula $2Fe_{2}O_{3} \cdot 2H_{2}O(s)$.

Galvanising

The process of preventing rust by coating iron with zinc, typically by dipping it into molten zinc or electroplating.

Sacrificial protection

A method of rust prevention where a more reactive metal like magnesium or zinc is attached to iron to corrode in its place by losing electrons.

Saponification

The soap-making process where oils and fats are broken down by boiling them with $KOH(aq)$ or $NaOH(aq)$ to form soap and glycerol.

Stearate ions

Also known as octadecanoate ions, these are the components in soap that react with $Mg^{2+}$ and $Ca^{2+}$ ions in hard water to form an insoluble precipitate.

Scum

An insoluble precipitate formed when the stearate ions in soap react with the calcium and magnesium ions found in hard water.

Hydrophobic tail

The water-hating, long-chained hydrocarbon part of a soap or detergent molecule that dissolves in grease and oil.

Hydrophilic head

The water-loving ionic group of a soap or detergent molecule that dissolves in water.

Biological Oxygen Demand (BOD)

A measure of the comparatively large amounts of oxygen needed for the natural oxidation of biodegradable waste materials by bacteria.

Nitrogen compounds

Water pollutants that contribute to high BOD because they are oxidized by bacteria into nitrates through steps involving oxygen uptake.