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Water & pH

Water & pH. A few more details…. Rain Water. Normal rain water is not pH 7 as you might expect…. Rain Water. …Instead, it is slightly acidic, usually around pH 5.6. Water vapor tends to combine with CO 2 in the atmosphere, forming carbonic acid: CO 2 + H 2 O  H 2 CO 3

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Water & pH

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  1. Water & pH A few more details…

  2. Rain Water • Normal rain water is not pH 7 as you might expect…

  3. Rain Water …Instead, it is slightly acidic, usually around pH 5.6. • Water vapor tends to combine with CO2 in the atmosphere, forming carbonic acid: CO2 + H2O  H2CO3 • But, carbonic acid is a weak acid, and partially dissociates: CO2 + H2O  H+ + HCO3-

  4. Acid Rain

  5. Acid Rain • Acid rain refers to rain water that has a pH below 5.6! • Water vapor in the atmosphere combines with pollutants like sulfur dioxide (SO2) to form Sulfurous Acid: SO2 + H2O  H2SO3 …Which can also dissociate: H2SO3 H+ + HSO3-

  6. Acid Rain • Also, sulfur dioxide in pollution can be oxidized into sulfur trioxide: 2SO2 + O2 2SO3 • Sulfur trioxide then reacts with water to form sulfuric acid: SO3 + H2O  H2SO4 …which can donate lots of H+ to rain water!

  7. Acid Rain • The same sorts of reactions can occur with other pollutants, like nitrogen oxide (NO2): 2NO2 + H2O  HNO2 + HNO3 …forming nitrous acid and nitric acid, both of which can further dissociate = more H+

  8. Acid Rain • The resulting low pH for rain water has many effects: • Increased leaching of important nutrients OUT of the soil. • Increased solubility of harmful metals (like aluminum) in soils. • Disrupted photosynthesis due to poor production of chlorophyll. • Killing of plants unable to secure nutrients. • Pollution of groundwater.

  9. Isn’t there only 1 kind of water?

  10. Tap Water • “Government-treated water”. • Contains many minerals, like Calcium & Magnesium. • Contains certain amounts of Chloride or Fluoride (for “sanitation”). • Often contains dissolved organic compounds. • Can contain metals.

  11. Spring Water • From a “Spring” – a point where groundwater meets the surface. • Minerals become dissolved in the water as it moves through underground rock. • Generally have high amounts of dissolved oxygen. • Have impurities.

  12. Distilled Water • Distilled water has gone through the distillation process in a still: • Water is boiled, and the re-condensed steam is collected as a liquid into a clean container • Most contaminants are left behind.

  13. Deionized Water • Water is purified by going through an ion exchange process, where the ionic impurities are removed. • Non-ionic impurities (like organic compounds) remain. • Certain ions remain (OH- and H3O+). What is this?

  14. pH • What we pictured happening: H2O H+ OH-

  15. H2O + H2O  H3O+ + OH- pH • What actually happens: • These Hydronium ions are VERY reactive, and THEY are technically what is measured by pH. Hydronium Ion

  16. Water

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