Ionization of Water

1. Ionization of Water • Water molecules have a tendency to “fall apart” or dissociate • “Dissociate” means to separate or disconnect from Two water molecules

2. Ionization of Water • This is usually written in a simplified version

3. Ionization of Water • This is usually written in a simplified chemical equation: H2O  OH- + H+ one water molecule Hydroxide ion Hydrogen ion

4. Ionization of Water How often does water disassociate to form ions? In pure water, about one water molecule in 550 million naturally dissociatesinto a Hydrogen Ion(H+)and a Hydroxide Ion(OH-)

5. Ionization of Water Because the number of positive hydrogen ions(H+)is equal to the number of negative hydroxide ions(OH-) produced, water is neutral.

6. Pop Quiz What is an ion? A polar molecule An atom with which gained or lost protons An atom with a + or – charge A molecule that loses an atom

7. Ionization of Water Onewater molecule in 550 million naturally dissociatesinto a Hydrogen Ion (H+) and a Hydroxide Ion(OH-) Hydrogen Hydroxide Ion Ion H2O  H+ + OH-

8. pH scale • Chemists created a measurement system called the pH scale to indicate the concentration of H+ ions in solution. • The pH scale measures the concentration of H+ ions in a solution. The scale ranges from 0 to 14. • Each unit is a 10x change in concentration • At pH 7, the concentration of H+ ions and OH- ions is equal. Thus, pH 7 is neutral.

9. ACIDS • Solutions with a pH below 7 are called acidic because they have more H+ ions than OH- ions. • Examples include lemon juice, stomach acid, aspirin, and coffee.

10. Acids • StrongAcids have a pH of 1-3 • Strong acids producelots of H+ ions

11. Bases • Solutions with a pH above 7 are called basic because they have more OH- ions than H+ ions. • Examples include soap, bleach, and seawater

12. Bases • Strong Bases have a pH of 11 to 14 • Containlots of OH-ions and fewer H+ ions

13. The pH Scale Review • Indicates the concentration of H+ ions • Ranges from 0 – 14 • pH of 7 is neutral • pH0 up to 7 is acid … H+ • pHabove 7 – 14 is basic… OH- • Each pH unit represents a factor of 10X change in concentration • pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6

14. A substance that eliminates large sudden changes in pH. Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life. Are combinations of H+ acceptors and donors forms in a solution of weak acids or bases Work by accepting H+ from solutions when they are in excess and by donating H+ when they have been depleted. Buffers

15. Why do we care about pH? • Living organisms are sensitive to pH levels and an imbalance in pH can lead to DEATH! • Organisms have developed ways of keeping pH within normal ranges using an acid-base buffering system • Buffer = substances that minimized change in pH

16. Biological pH • The pH of our stomachs are around 1-2, so that foods can be broken down • The optimal pH for healthy skin and scalp is around 5 slightly acidic for resistance to infection and diseases • Soaps and shampoos are basic and thus can cause drying of the skin and scalp • When you see a “pH-balanced” shampoo or soap, the manufacturer has lowered the pH so its closer to normal skin pH • Most organisms have an internal pH of

17. Acid Precipitation • Rain, snow or fog with more strongly acidic than pH of 5.6 • West Virginia has recorded 1.5 pH • East Tennessee reported 4.2 in 2000 • Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphere • Lowers pH of soil which affects mineral solubility – decline of forests • Lower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.

18. Acid Precipitation