Chemistry · Rung 17 of 24

Air, water and soil

Three different things that always get confused. The greenhouse effect: sunlight comes in almost unhindered and warms the ground, the ground returns that heat as infrared, and CO₂ and methane absorb infrared and not visible light, so they let it in and do not let it out. Without them the Earth would be thirty degrees below zero; the problem is not that they exist but how many there are. Acid rain is another thing: it is caused by sulfur and nitrogen oxides from burning coal and oil, which dissolve in clouds and fall as dilute acid, eat limestone and acidify lakes. And bioaccumulation is a third: a toxin that is not excreted concentrates going up the food chain, so there is more mercury in a big tuna — which has eaten thousands of fish — than in the water it lives in. Making water drinkable runs the other way round: the big things first, the small things next, and the chemistry last.

Where this sits

Comes after
Solutions and gases
Opens up
Materials and their life cycle

Exercises from this rung

Generated by the app, from easiest to hardest

  1. What do greenhouse gases do?

    • They let light in and hold back the heat going out
    • They heat the air by reacting
    • They block sunlight
    • They make a hole in the ozone layer

    Why Sunlight comes in almost unhindered, warms the ground, and the ground returns that heat as infrared. CO₂ and methane absorb infrared and not visible light, so they let it in and do not let it out. Without them the Earth would be about thirty degrees below zero; the problem is not that they exist but how many there are.

    easier

  2. Put the steps of making water drinkable in order.

    Answer Branches and rubbish are caught by a grille, Small particles clump together and settle, The water passes through a bed of sand, Chlorine is added to kill bacteria

    Why From biggest to smallest, with the chemistry last. First what you can see, then what is suspended, then what is still floating, and only at the end the disinfection: putting chlorine in muddy water would spend it oxidising mud instead of killing bacteria.

    in between

  3. What causes acid rain?

    • Plastic in the sea
    • CO₂ in the air
    • Ozone in the stratosphere
    • Sulfur and nitrogen gases

    Why Sulfur and nitrogen oxides from burning coal and oil: they dissolve in cloud vapour and fall as dilute sulfuric and nitric acid. They eat the limestone of buildings and acidify whole lakes. It is a different thing from the greenhouse effect, which is caused by CO₂ and does not acidify rain appreciably.

    harder