Tie ocean acidification into your chemistry topics

Link UN sustainable development goal 14 to your teaching of dissolved ions, acids and the pH scale

A digital illustration of a swimming turtle with a 14 on its shell
Help your students see the impact that excess carbon dioxide has on the world’s oceans. Source: © hitandrun/Debut Art

Students at 14–16 will be familiar with the composition of the atmosphere and that carbon dioxide is one of the most significant greenhouse gases. The chemistry of the atmosphere and the impact of human activity on climate change is a key area of the 14–16 curriculum.

This article is part of the Sustainability in chemistry series, developed to help you integrate the UN’s sustainable development goals into your teaching of chemistry. It supports Goal 14: conserve and sustainably use the oceans, seas and marine resources.

The oceans play a vital role in atmospheric chemistry by ‘mopping up’ some of the excess carbon dioxide we produce. They cover 70% of the Earth’s surface and have absorbed about a third of the carbon dioxide emitted since the industrial revolution. This links with Goal 14: conserve and sustainably use the oceans, seas and marine resources.

Put it in context

Goal 14 is a good chance to introduce an important context when teaching about the atmosphere and climate change, because people tend to focus on the air around us. They’ll consider emissions from cars and factories and understand the importance of trees in the rainforest, but often ignore interactions between the atmosphere and oceans.

Student worksheet, for age range 14–16

Use this worksheet to explore and develop understanding of the pH scale and apply it in the context of ocean acidification. Extension questions provide more challenge and delve into other aspects of chemistry linked to ocean acidification, leading to a research task on the consequences for marine organisms.

Download the student worksheet as MS Word or pdf and the teacher notes (including answers) as MS Word or pdf.

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This goal also offers an interesting context when teaching students about dissolved ions and the pH scale. Carbon dioxide reacts with seawater to form carbonic acid, which dissociates. The resulting hydrogen ions can react with carbonate ions that would otherwise be used by marine organisms to build their shells and, if the pH gets too low, the shells themselves can even begin to dissolve.

Fish without shells can also be affected by carbonic acid from seawater. It changes the pH of their blood and they use energy to excrete the excess acid. This makes it more difficult to do other things, such as escaping predators, catching food or reproducing. Certain species might be better at adapting to these changes than others, changing the dominant fish species, which has a knock-on effect on fisheries.

Put it into practice

Carbonic acid is a weak acid, and this might be a suitable prompt to check if your students hold any of the common misconceptions around acids and the pH scale. Do they understand that the strength of an acid relates to the type of acid, not its concentration in solution, for example?

Niki Kaiser, Royal Society of Chemistry, 4 August 2021. Full article (registration required).

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