Acids and Bases

Acids and Bases in the Oceans

Introduction to Acids and Bases

  • Acids are substances that can donate a proton (H+) to another substance in an aqueous solution.
  • Bases, on the other hand, are substances that can accept a proton from another substance in an aqueous solution.
  • A common example in the ocean system is carbonic acid (H2CO3) acting as an acid by donating a proton to form a bicarbonate ion (HCO3-).

pH and the Ocean Environment

  • The pH of a solution is a measure of its acidity or alkalinity, it is calculated as the negative logarithm of the hydrogen ion concentration.
  • Ocean water is slightly alkaline with a pH of about 8.1. However, increased carbon dioxide (CO2) absorption is causing ocean acidification.
  • When CO2 dissolves in the ocean it forms carbonic acid, which lowers the pH and increases the acidity of the water.
  • This increasing acidity can have significant effects on marine life, including impairing the ability of shell-forming marine organisms to form their shells.

Neutralisation Reactions

  • A neutralisation reaction occurs when an acid and a base react to form water and a salt.
  • In the ocean, bicarbonate ions derived from acids can react with cations (like Ca2+) in seawater to form insoluble carbonate minerals - a process helpful in the neutralisation of excess acid.

Buffer Systems in the Ocean

  • Buffer solutions can resist changes in pH upon addition of small amounts of acids or bases.
  • The carbonate buffer system helps maintain the pH of the ocean by shifting the bicarbonate and carbonate equilibria in response to changes in hydrogen ion concentration.
  • This mechanism helps to moderate the effects of acidification but its effectiveness may decrease due to continuing absorption of anthropogenic CO2.

Human Impacts on Ocean Chemistry

  • The burning of fossil fuels has led to a significant increase in atmospheric CO2, a large proportion of which is absorbed by the oceans resulting in their ongoing acidification.
  • Increasing ocean acidity reduces the availability of carbonate ions necessary for the formation of calcium carbonate shells and skeletons of marine organisms.
  • This has severe implications for marine ecosystems, including potentially catastrophic impacts on coral reefs, which provide habitat for a large proportion of marine biodiversity.
  • Understanding the chemistry of acids, bases and buffers in the marine environment is important for addressing these global climate change issues.