Acids, bases and the environmentIB MYP Chemistry: Mind map

Exam questions on Acids, bases and the environment

1. Researchers in Sweden find that the pH of a lake has fallen from 6.8 to 4.9 over thirty years. Many of the fish have died and nearby trees are losing their leaves. A coal-burning power station, which has no gas filters on its chimney, operates 200 km upwind of the lake.
   Explain how burning coal can make the rain acidic.2 marks
2. A student in Cairo compares three antacid tablets, X, Y and Z, sold for indigestion. For each test she crushes one tablet, adds it to 25 cm³ of 0.10 mol dm⁻³ hydrochloric acid, which represents stomach acid, stirs for two minutes and measures the pH with a pH meter. The acid on its own has a pH of 1.0. After tablet X the pH is 3.2, after tablet Y it is 5.1 and after tablet Z it is 6.9. She concludes that tablet Z is the best antacid.
   Suggest one improvement to the method that would make the conclusion more reliable, and explain how it helps.2 marks
3. Marine scientists monitor the seawater around a coral reef in Australia. Over 40 years the average pH of the surface seawater has fallen from 8.11 to 8.04, while the amount of carbon dioxide in the air has risen. Corals and shellfish build their skeletons and shells from calcium carbonate.
   Explain how an increase in carbon dioxide in the air lowers the pH of seawater.3 marks