(c) gases in the atmosphere

four most abundant gases in dry air (2.9)

nitrogen (N₂) - 78.1%

oxygen (O₂) - 21.0%

argon (Ar) - 0.9%

carbon dioxide (CO₂) - 0.04%

how to determine the percentage by volume of oxygen in the air using experiments involving the reactions of copper (2.10)

the copper is in excess and uses up the oxygen to form copper oxide (CuO)

copper + oxygen → copper oxide

2Cu + O₂ → 2CuO

all the oxygen in the air is therefore used up, so the volume of the air decreases by about 20%

how to determine the percentage by volume of oxygen in the air using experiments involving the reactions of iron (2.10)

the iron reacts with the oxygen in the air (rusting). as long as both the iron and water are in excess, the total volume of air enclosed by the apparatus decreases by around 20% over several days.

iron + oxygen + water → hydrated iron(III) oxide (aka rust)

4Fe + 3O₂ + nH₂O → 2Fe₂O₃.nH₂O

how to determine the percentage by volume of oxygen in the air using experiments involving the reactions of phosphorus (2.10)

the phosphorus is lit with a hot wire, reacting with the oxygen in the air and causing the water level in the bell jar to rise by about 20%

phosphorus + oxygen → phosphorus oxide

4P + 5O₂ → 1P₄O₁₀

combustion of magnesium in oxygen (2.11)

when magnesium reacts with oxygen, a bright white flame is produce, leaving behind a white ash of magnesium oxide

magnesium + oxygen → magnesium oxide

2Mg _(s) + O₂ → 2MgO

combustion of hydrogen in oxygen (2.11)

hydrogen reacts with oxygen explosively. this is the basis of the ‘squeaky pop’ test (where a lit split is held into a test tube. if a ‘squeaky pop’ sound is heard, hydrogen is present in the test tube) this can be dangerous when larger quantities of hydrogen are present

hydrogen + oxygen → water

2H_{2 (s)} + O₂ → 2H₂O _(l)

combustion of sulfur in oxygen (2.11)

when sulfur reacts with oxygen, it produces a blue flame.

sulfur + oxygen → sulfur dioxide

S _(s) + O_{2 (g)} → SO_{2 (g)}

when sulfur dioxide dissolves in water, it forms an acidic solution of sulfurous acid

sulfur dioxide + water → sulfurous acid

SO_{2 (g)} + H₂O _(l) → H₂SO_{3 (aq)}

describe the formation of carbon dioxide from the thermal decomposition of metal carbonates (2.12)

thermal decomposition is the process of breaking something down by heating it

upon heating, metal carbonates thermally decompose into metal oxides and carbon dioxide

e.g.

copper carbonate → copper oxide + carbon dioxide

CuCO₃ → CuO + CO₂

carbon dioxide is..? (2.13)

a greenhouse gas. increasing amounts of greenhouse gases in the atmosphere may contribute to a climate change due to their ability to absorb infrared radiation, therefore warming the atmosphere

determine the approximate percentage by volume of oxygen in air using a metal or a non-metal (2.14)

see point 2.10