Storing carbon dioxide Learning objectives:  Describe the factors determining the relative solubility of a solute in aqueous and non aqueous solvents.  Discuss the global influence of the processes occurring when carbon dioxide dissolves in water

Storing carbon dioxide Solubility of gases decreases as temperature increases, just as increases in pressure can cause gases to be more soluble

Storing carbon dioxide Carbon dioxide dissolves in the oceans, which takes the gas out of the atmosphere and helps to maintain a stable environment on Earth. This exchange takes place very quickly

Storing carbon dioxide The uptake of carbon dioxide by the oceans is further speeded up by the action of marine life. CO 2 is taken up by phytoplankton during photosynthesis. Chemical Ideas Dissolving of carbon dioxide in the oceans

Storing carbon dioxide Why is CO 2 soluble? CO 2 molecules contain polar C=O bonds which can form hydrogen bonds with water molecules. CO 2 (g) ↔ CO 2 (g) Also, some of the CO 2 molecules react chemically with water and are removed from the equilibrium. More CO 2 dissolves to maintain the equilibrium position.

Storing carbon dioxide CO 2 (aq) + H 2 O (l) ↔ H + (aq) + HCO 3 - (aq) HCO 3 - (aq) ↔ H + (aq) + CO 3 2- (aq) The reaction with water produces a mixture which contains mainly hydrogencarbonate ions (HCO 3 - ) and H + ions together with some carbonate ions (CO 3 2- ) Chemical Ideas 7.2 – Equilibrium constants

Storing carbon dioxide CO 2 (g) + H 2 O (l) ↔ 2H + (aq) + CO 3 2- (aq) Le Chatelier’s principle tells us that any way of removing H + or CO 3 2- ions from solution will cause more CO 2 to dissolve. Removing H + ions by adding a base is one way of doing this – CO 2 is an acidic gas and it dissolves well in alkaline solutions. Chemical Ideas 8.1 – revise ideas on acids, bases and alkalis

Storing carbon dioxide Many marine organisms build protective shells composed of insoluble calcium carbonate using CO 3 2- ions in the sea water. Another way of mopping up CO 2

Storing carbon dioxide Saying something is soluble or insoluble is often an oversimplification. CaCO 3(s) ↔ Ca 2+ (aq) + CO 3 2- (aq) The dissolving is controlled by equilibria, where the position of the equilibrium is determined by an equilibrium constant.. Solubility products.PPT

Storing carbon dioxide A saturated solution is a solution of a solute into which no more of that solute will dissolve at that temperature. The solubility product has the symbol K sp. It represents the conditions for equilibrium between a sparingly soluble solid and its saturated solution. Chemical Ideas 7.7 – Solubility products