Pearson Science Double Award Chemistry 2: Inorganic Chemistry

Inorganic chemistry uses group patterns, reactivity and analytical observations to predict behaviour. The Double Award boundary includes corrosion, acids, salts and qualitative tests, but not the broader separate-Chemistry extraction and transition-metal sections.

Group 1 and Group 7

Lithium, sodium and potassium are Group 1 alkali metals. Each reacts with water to form a metal hydroxide and hydrogen. Reactivity increases down the group: lithium fizzes, sodium reacts more vigorously, and potassium can ignite. Similar reactions reflect one outer electron; increasing reactivity reflects easier loss of that electron farther from the nucleus.

Chlorine is a pale green gas, bromine a red-brown liquid and iodine a grey solid at room temperature. Melting and boiling points increase down Group 7, while reactivity decreases. A more reactive halogen displaces a less reactive halide from solution. Chlorine therefore displaces bromide and iodide, but iodine displaces neither chloride nor bromide.

Atmosphere and combustion

Dry air contains about 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide by volume. Oxygen percentage can be estimated by reacting oxygen with a metal or non-metal in a closed measured volume and calculating the volume decrease.

Magnesium burns with a bright white flame to form magnesium oxide. Hydrogen burns to form water, and sulfur burns to form sulfur dioxide. Heating copper(II) carbonate forms copper(II) oxide and carbon dioxide. Carbon dioxide is a greenhouse gas, so increasing atmospheric concentration can contribute to climate change.

Reactivity, displacement and corrosion

The required metal order is potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver and gold. More reactive metals react more readily with water or dilute acid and displace less reactive metals from their oxides or salt solutions.

Oxidation is oxygen gain or electron loss. Reduction is oxygen loss or electron gain. A redox reaction contains both. The oxidising agent causes oxidation and is reduced; the reducing agent causes reduction and is oxidised.

Iron rusts when both oxygen and water are present. Barrier coatings exclude them. Galvanising coats iron with zinc, which also gives sacrificial protection if scratched because zinc oxidises more readily than iron. Sacrificial blocks must be more reactive than the protected metal.

Acids, bases and salts

Litmus, phenolphthalein and methyl orange distinguish acidic and alkaline solutions. Universal indicator estimates pH from 0 to 14. Acids supply hydrogen ions in water and donate protons; bases accept protons. Alkalis are soluble bases that supply hydroxide ions in water.

Acids react with metals to form a salt and hydrogen, with bases to form salt and water, and with metal carbonates to form salt, water and carbon dioxide. Nitric acid reactions with metals are excluded here.

To prepare a soluble salt from an insoluble reactant, warm acid gently, add excess solid until no more reacts, filter away excess, evaporate some water, cool to crystallise, then filter and dry the crystals. Excess solid ensures the acid is used up; it can be removed by filtration.