Using resources flashcards

Topic 10: Using resources

Sustainable development

Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.

Potable water vs pure water

Potable: safe to drink, with low levels of dissolved salts and microbes. Pure: only water molecules, no dissolved substances.

How is potable water produced from fresh water in the UK?

Choose a suitable source (ground water, lakes, rivers), pass it through filter beds to remove solids, then sterilise with chlorine, ozone or ultraviolet light.

Desalination: two methods and their drawback

Distillation or reverse osmosis. Both need large amounts of energy.

Stages of sewage treatment, in order

Screening and grit removal → sedimentation (sludge and effluent) → anaerobic digestion of the sludge → aerobic biological treatment of the effluent.

Phytomining and bioleachingHigher

Phytomining: plants absorb metal compounds, are harvested and burned; the ash contains metal compounds. Bioleaching: bacteria produce leachate solutions containing metal compounds. The metal is then obtained by displacement with scrap iron or electrolysis.

Stages of a life cycle assessment (LCA), and why it is not fully objective

Raw materials → manufacture and packaging → use → disposal (with transport throughout). Pollutant effects are hard to quantify and need value judgements.

What does rusting need, and how does galvanising protect iron?

Both air (oxygen) and water. Galvanising coats iron with zinc: a barrier, plus sacrificial protection, because zinc is more reactive and corrodes instead of the iron, even when scratched.

Percentage of gold in 18 carat gold

% gold = carat ÷ 24 × 100 = 18 ÷ 24 × 100 = 75%. (24 carat is 100% gold.)

Thermosoftening vs thermosetting polymers

Thermosoftening: no cross-links, weak forces between chains, so they melt on heating. Thermosetting: cross-links between chains, so they do not melt.

Haber process: equation, raw materials and conditions

N₂ + 3H₂ ⇌ 2NH₃. Nitrogen from the air, hydrogen from natural gas. Iron catalyst, about 450 °C, about 200 atmospheres. Ammonia is removed by cooling (it liquefies); unreacted gases are recycled.

Why are 450 °C and 200 atmospheres compromise conditions in the Haber process?Higher

Forward reaction exothermic: a lower temperature gives a higher yield but a slower rate. 4 gas molecules → 2: higher pressure gives a higher yield and faster rate, but costs more in equipment and energy.