Buffering Capacity: Seawater CO 2 Chemistry Scripps Classroom Connectionhttp://earthref/SCC

Sand Dissolution Demo Materials Needed Calcium Carbonate Sand Two 100 mL beakers Distilled water Seawater pH Indicator (probe or dye) Stir plate & bars OR Spoon Scripps Classroom Connection

Where does sand come from? Riverine Runoff Weathering of Rocks Calcified parts of marine species Corals Foraminifera Scripps Classroom Connection

Chemistry of Sand Scripps Classroom Connection CaCO 3

CaCO 3 Minerals Calcite - rhombohedral Aragonite - orthorhombic Mg-Calcite – Mg 2+ replaces >4% of Ca 2+ in calcite Scripps Classroom Connection

Seawater Buffering Lab Materials Needed (per group) Two 50 mL beakers 1 beaker will have distilled water (DIW) 1 beaker will have seawater (SW) Universal Indicator HCl (strong acid) NaOH (strong base) Droppers Goggles (1 pair per student) Scripps Classroom Connection

Relation of carbonate chemistry and pH Scripps Classroom Connection

Seawater Buffering Capacity Alkalinity (TA or A T ) = excess bases over acids Scripps Classroom Connection

Modeling Seawater CO 2 Chemistry Scripps Classroom Connection CO 2 + H 2 O ↔ H 2 CO 3  HCO H + CO H + 

Modeling Seawater CO 2 Chemistry Scripps Classroom Connection COO CO 2 1. Dissolves in the ocean OHH H2OH2O COOOH HCO Reacts with water to form bicarbonate ion and hydrogen ion H+H+ COOO H+H+ 3. Most of that hydrogen ion reacts with carbonate ion to form more bicarbonate COOOH HCO 3 - CO 3 2-

The Need to Breathe Students hold breath as long as they can They should have felt the urge to take another breath This urge is due to increase of CO 2 beyond buffering capacity. Scripps Classroom Connection

Another Buffer: Blood

Conclusions Buffers combat pH change CO 2 chemistry buffers pH Seawater is a buffer Blood is a buffer Scripps Classroom Connection