Water & pH

1. pH

2. Water & pH • H+can split off from H2O, leaving OH– • if [H+]= [-OH], water is neutral • if [H+]> [-OH], water is acidic • if [H+]< [-OH],water is basic • pH scale • how acidic or basic a solution is H2O  H+ + OH–

3. pH Scale Acids= compounds that donate H+ to a solution. Bases= compounds that accept H+ from a solution. They may also remove H+ from solutions by donating OH-.

4. 9 8 7 6 Buffering range 5 pH 4 3 2 1 0 0 1 2 3 4 5 Amount of base added Buffers & cellular regulation • pH of cells must be kept ~7 • pH affects shape of molecules • The shape of molecules affects their function • pH affects cellular function • Control pH by buffers • reservoir of H+ • donate H+ when [H+] falls • absorb H+ when [H+] rises

5. Figure 1: Average changes in the pH of water, buffer, and milk in response to incremental additions of HCL

6. Example: buffers in the blood • pH of human blood is 7.4 • Drops to 7.0 or increases to 7.8 are lethal after even a few minutes • Blood maintains pH using these compounds: Bicarbonate HCO3- accepts --> H2CO3 Carbonic acid H2CO3 donates --> HCO3-