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Water And Soil


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Water And Soil

  1. 1. Water and Soil E7 + E12
  2. 2. Glossary! <ul><li>Soil pollution </li></ul><ul><ul><li>Any sort of chemicals or harmful gases that pollute the soil </li></ul></ul><ul><ul><li>Industrial waste from tankers and used engine oil </li></ul></ul><ul><ul><li>Pesticides and fertilizers disrupt food chains and affect soil </li></ul></ul>
  3. 3. <ul><li>Soil degradation </li></ul><ul><ul><li>Soil quality is lowered due to acid soils, contamination, erosion, dry soil and sea water. </li></ul></ul><ul><ul><li>Also by human activities such as logging, industry waste and grazing </li></ul></ul><ul><ul><li>Results in reduced crop production </li></ul></ul>
  4. 4. <ul><li>Salinization </li></ul><ul><ul><li>Caused by excess irrigation (supplying land with water or wastewater) </li></ul></ul><ul><ul><li>When water evaporates, salt is accumulated </li></ul></ul><ul><ul><li>Roots of plants can’t take root on salty soil </li></ul></ul><ul><ul><li>High level of salt is also toxic to plants </li></ul></ul>
  5. 5. <ul><li>Nutrient Depletion </li></ul><ul><ul><li>Plants take out nutrients out of soil </li></ul></ul><ul><ul><li>Nutrient level in soil reduces </li></ul></ul><ul><ul><li>Levels should be replenished so crops can grow healthily </li></ul></ul><ul><ul><li>Done by adding manure or planting clovers and legumes </li></ul></ul>
  6. 6. Soil Organic Matter (SOM) <ul><li>Organic chemicals in the soil </li></ul><ul><ul><li>Such as plant and material waste </li></ul></ul><ul><li>Decomposition of these waste material creates high molecular mass molecules and smaller molecular mass molecules, these are called Humus (IMPORTANTE!) </li></ul>
  7. 7. Functions of Humus
  8. 8. Organic Soil Pollutants Organic Soil Pollutants Source Hydro Carbons Transport, solvents VOCS, SVOCS (semi/volatile organic compounds) Transport, solvents Agrichemicals Pesticides, fungicides, herbicides Polyaromatic hydrocarbons Incomplete combustion Polychlorinated biphenyls (PCBs) Fridges, capacitors, transformers Organotin compounds Bactericides, fungicides
  9. 9. Removal by chemical Precipitation <ul><li>Removing heavy metals ions, phosphates and nitrates from water/sewage can be done by chemical precipitation </li></ul><ul><ul><li>Hg (aq) 2+ + S (aq) 2- = HgS (S) </li></ul></ul><ul><ul><li>Cu (aq) 2+ + OH (aq) 2- = Cu(OH) 2(S) </li></ul></ul>
  10. 10. Calculations <ul><li>Solubility product K sp is measure of solubility </li></ul><ul><li>K sp =[A][B] </li></ul><ul><ul><li>E.g. find K sp of PbS (S) </li></ul></ul><ul><ul><li>Pb (aq) 2+ + S (aq) 2- = PbS (S)   </li></ul></ul><ul><ul><li>K sp = [Pb (aq) 2+ ][ S (aq) 2- ] </li></ul></ul>
  11. 11. Solubility Product K sp <ul><li>K sp is temperature dependent. </li></ul><ul><li>Precipitation will only form when the product of the ions exceeds the numerical value of K sp at that temperature </li></ul><ul><ul><li>[A][B] > K sp </li></ul></ul><ul><ul><li>E.g. [Pb (aq) 2+ ][ S (aq) 2- ] > K sp </li></ul></ul>
  12. 12. How to solve problems of solubility <ul><li>Three types of questions for solubility </li></ul><ul><ul><li>Determine Molar Solubility </li></ul></ul><ul><ul><li>Determining if precipitate is formed </li></ul></ul><ul><ul><li>Find minimum concentration of one ion </li></ul></ul><ul><li>Molar Solubility </li></ul><ul><ul><li>Write out ionic equation of problem </li></ul></ul><ul><ul><li>Substitute K sp value </li></ul></ul><ul><ul><li>Calculate molar solubility by square root of K sp </li></ul></ul>
  13. 13. <ul><li>Determining if precipitate forms </li></ul><ul><ul><li>Write out ionic equation of problem </li></ul></ul><ul><ul><li>Determine if forms precipitate by finding product of concentration of ions </li></ul></ul><ul><ul><li>If products of concentration of ions greater than K sp then precipitate forms </li></ul></ul><ul><li>Determine minimum concentration of one ion </li></ul><ul><ul><li>Write out ionic equation of problem </li></ul></ul><ul><ul><li>Substitute concentration of one ion, and K sp </li></ul></ul><ul><ul><li>Figure other concentration </li></ul></ul>
  14. 14. A Problem to solve <ul><li>Calcium ions in water are precipitated by adding sulfate ions </li></ul><ul><li>Given K sp = 3.0 x 10 -5 mol 2 dm -6 at 25˚C, calculate its molar solubility at 25˚ C </li></ul><ul><li>Determine if a precipitate will form when the concentrations are as follows [Ca (aq) 2+ ] = 1.0 x 10 -3 mol dm -3 and [ S0 4(aq) 2- ] = 1.0 x 10 -2 mol dm -3 </li></ul><ul><li>Calculate the minimum concentration of sulfate to precipitate the Ca (aq) 2+ ions, when [ S0 4(aq) 2- ] = 1.0 x 10 -3 mol dm -3 </li></ul>
  15. 15. Answer <ul><li>a) Ca (aq) 2+ + S0 4(aq) 2- = CaS0 4(aq) </li></ul><ul><li>b) [Ca (aq) 2+ ] [ S0 4(aq) 2- ] = 3.0 x 10 -5 </li></ul><ul><li>Molar solubility = √(3.0 x 10 -5 ) = 5.5 x 10 -3 mol dm -3 </li></ul><ul><li>c) 1.0 x 10 -3 x1.0 x 10 -2 =1.0 x 10 -5 mol dm -3 </li></ul><ul><li>1.0 x 10 -5 mol dm -3 < 3.0 x 10 -5 , therefore no precipitate </li></ul><ul><li>d) [Ca (aq) 2+ ] x 1.0 x 10 -3 = 3.0 x 10 -5 </li></ul><ul><li>[Ca (aq) 2+ ] = 3.0 x 10 -5 /1.0 x 10 -3 = 3 x 10 -2 mol dm -3 </li></ul>
  16. 16. Cation-exchange capacity <ul><li>Plants swap H + ions on the root hairs with negatively charged soil organic matter and clay particles </li></ul><ul><li>The more the soil can hold positive ions, the higher the CEC </li></ul><ul><li>The more acidic the soil, the higher the % of acidic cations, therefore pH of soil affects the CEC </li></ul><ul><ul><li>More acidic soil = lower CEC </li></ul></ul>