Chapter 8: Chemistry for Technology

Chemistry explains the materials that engineers use, the processes that farmers and food technologists rely on, and the environmental effects of technology. This chapter covers the core ideas needed for both specialist subjects (Chang & Goldsby, 2016).

Matter, atoms, and the periodic table

Matter exists as solid, liquid, or gas; pure substances are elements or compounds, and mixtures can be separated by physical methods (filtration, evaporation, distillation, chromatography, magnetic separation). An atom has a nucleus of protons and neutrons surrounded by electrons. The atomic number is the number of protons; isotopes have different numbers of neutrons. The periodic table arranges elements by atomic number; elements in the same group have similar properties. Metals (left and centre) conduct heat and electricity and are malleable; non-metals (right) generally do not.

Bonding and structure

Ionic bonds form between metals and non-metals by electron transfer (NaCl); ionic solids have high melting points and conduct when molten or dissolved.

Covalent bonds form by electron sharing (H₂O, CO₂, CH₄); simple molecules have low melting points; giant covalent structures (diamond, silica) are very hard.

Metallic bonding gives conductivity and the ability to be shaped.

Formulae, equations, and the mole

A balanced equation shows that atoms are conserved: CH₄ + 2O₂ → CO₂ + 2H₂O. The mole is the amount of substance that contains entities; the molar mass links mass and moles, . Examples: 18 g of water (M = 18) is 1 mol. A solution made from 4 g of NaOH (M = 40) in 500 cm³ has mol and concentration . The mass percentage of nitrogen in urea, CO(NH₂)₂ (M = 60), is .

Acids, bases, and pH

Acids release H⁺ in water; bases release OH⁻. The pH scale is ; pH 7 is neutral, below 7 acidic, above 7 basic. Example: mol dm⁻³ gives pH 3. Acid + base → salt + water (neutralization). Indicators (litmus, universal indicator, phenolphthalein) show pH. Soil acidity, water quality, food preservation, and cleaning all depend on pH.

Redox, metals, and corrosion

Oxidation is loss of electrons; reduction is gain. Corrosion is the oxidation of metals: iron rusts when it is exposed to both oxygen and water, and the process is faster in salty conditions (a concern for coastal Sri Lanka). Prevention: painting, oiling, galvanizing (coating with zinc), plating, sacrificial anodes (a more reactive metal such as zinc or magnesium corrodes in place of the iron), and the use of stainless steel. Alloys are mixtures of metals with improved properties: steel (iron with a small percentage of carbon), brass (copper and zinc), bronze (copper and tin).

Organic chemistry and polymers

Hydrocarbons (alkanes, alkenes) are the basis of fuels and plastics. Alcohols (ethanol), carboxylic acids (ethanoic acid), and esters are common functional groups. Polymers are long chain molecules built from monomers: thermoplastics (polyethene, PVC, polystyrene) soften on heating and can be remoulded; thermosets (epoxy, Bakelite) set permanently. Plastics are strong, light, and cheap but cause serious waste and pollution, so reduce, reuse, recycle matters.

Fuels, energy, and combustion

Combustion releases energy: hydrocarbon + oxygen → carbon dioxide + water. Incomplete combustion produces carbon monoxide, a poisonous gas, which is why combustion appliances need ventilation. Renewable fuels include biogas and biofuels. The calorific value is the energy released per unit mass of fuel.

Fertilizers, soaps, and water

Fertilizers supply nitrogen (N), phosphorus (P), and potassium (K); labels give the NPK percentages. Soaps and detergents have molecules with a water-loving head and an oil-loving tail, which lets them lift grease into water. Hard water contains calcium and magnesium ions, which form scum with soap and scale in boilers. Water treatment usually involves coagulation, sedimentation, filtration, and disinfection (for example chlorination).

Environmental chemistry

The greenhouse effect (CO₂, CH₄ trapping heat) drives climate change; acid rain results from SO₂ and NOₓ; ozone depletion from CFCs; and water bodies suffer eutrophication from excess fertilizer nutrients. Technologists are expected to minimise waste, treat effluent, and follow environmental regulations.

Laboratory safety

Wear eye protection; never taste or sniff chemicals directly; add acid to water, not water to acid; handle flammable liquids away from flames; use the fume cupboard when required; label containers; dispose of waste as instructed.

Common mistakes

Forgetting to balance equations before calculating.

Using cm³ instead of dm³ for concentration.

Adding water to concentrated acid.

Practice questions

How many moles are in 4.4 g of CO₂ (M = 44)? [0.10 mol]

Find the molarity of a solution containing 5.85 g of NaCl (M = 58.5) in 250 cm³. [0.40 mol dm⁻³]

Find the pH of 0.01 mol dm⁻³ NaOH. [12]