Week 1Part 1. Preparation of Phosphorus Sorption SamplesPart 2. Preparation of Amorphous Iron OxidesWeek 2Part 3. Phosphate Sorption onto Amorphous Iron OxidesPart 4. Preparation of Standard Curve and Analysis of SamplesFactors Affecting Phosphorus Retention in SedimentsPart 1. Preparation of Phosphorus Sorption SamplesPart 2. Synthetic Preparation of Amorphous Iron OxidesPart 3. Phosphate Sorption onto Amorphous Iron OxidesPart 4. Preparation of Standard Curve and Analysis of SamplesCalculationsChemistry 104 Spring 2007Factors Affecting Phosphorus Retention in SedimentsIntroductionPhosphorus (P) is an essential nutrient for all living organisms. It is found in teeth, bones, DNA,and the molecules that transport energy throughout the body. In terrestrial and aquatic environ-ments, phosphorus is often the limiting nutrient for the growth of plants. This means that es-sentially all of the phosphorus available to the plants is immediately utilized in plant growth, andthat the resulting lack of available phosphorus limits further plant growth. Because of this, it isapplied in fertilizers both in commercial agriculture and home lawn and garden maintenance.Because adding phosphorus removes one of the limitations to plant growth, excess phosphoruscan be a problem in the aquatic environment and can lead to excess growth of multicellularplants (macrophytes) and algae. This can result in unsightly growth of undesirable plants, aswell as the blocking of light that would normally reach the submerged aquatic vegetation (SAV)which is necessary for proper ecosystem functioning. In addition, as these plants die and decom-pose, they consume oxygen, which can result in degradation of water quality in affected systems.This process is referred to as eutrophication.Once the phosphorus reaches the water body, there is no practical way to remove it. Therefore,the primary way to prevent phosphorus from negatively impacting water bodies is to prevent itfrom reaching them. Wetlands are well known for being able to trap phosphorus and prevent itfrom moving further down the watershed. This can occur when plants and microbes in the wet-land take in phosphorus as a nutrient. The phosphorus is then trapped in living biomass andcan’t move downstream as easily. Another way that phosphorus is trapped in wetlands is bysticking to wetland soils. This process is known as sorption and is most important when phos-phorus is in the form of phosphate (PO43-). If sorption occurs, it means that there is some at-traction between the PO43- and the soil particles.One factor that affects the ability of a soil to retain PO43- is the amount of certain types of iron inthe soil. Iron in the form of amorphous iron oxides has a large capacity for the sorption of PO43-.Amorphous iron oxides often form in environments like wetlands where the soil oscillates be-tween aerobic and anaerobic conditions.In this experiment, you will determine the ability of a soil to bind phosphorus in the form ofphosphate (PO43-). Once you determine how well the soil can bind PO43-, you will make somedecisions about how effective that soil is preventing negative effects from phosphorus from oc-curring further down in the watershed. You will also examine the effect of amorphous iron ox-ides on phosphorus sorption by synthetically preparing a sample of amorphous iron oxide andexamining the sorption of phosphorus onto this material.ProcedureMaterials: Dried sediment, NaH2PO4 solutions (5, 10, 20., 40, and 80 mg P/L), FeCl2(s), 3%H2O2, saturated NaHCO3, 1 M H2SO4, 0.1 M HCl, ammonium molybdate, ascorbic acidSpecial Equipment: Centrifuge, suction-filtration apparatus, spectrophotometer, cuvettesBe sure that your safety glasses are in place during all parts of this experiment.Week 1Part 1. Preparation of Phosphorus Sorption SamplesThis type of experiment gives us information about how many sites are available to hold PO43- onthe soil. Phosphate from the solutions interacts with the surface of the particles in the sedimentand some of the PO43- ions are attracted to those surfaces. We will generate a sorption isotherm(a graph showing the relationship between the amounts of bound and aqueous PO43-) by placingPO43- solutions of different concentrations in contact with samples of dried sediment. After thesediment has had time to interact with the PO43- solution, a portion of the solution will becentrifuged to remove suspended particles. In Part 4 below, the PO43- concentration will be mea-sured in each solution. The difference between the initial and final PO43- concentrations in thesolution will be used to determine the amount of PO43- sorbed onto the sediment.1. Weigh 2.0 g of soil into each of five 50-mL beakers. Record the exact weight of soil used ineach. Using labeling tape, label the beakers with the following numbers: 5, 10, 20, 40, and 80.2. Add 20 mL of the appropriate PO43- solution to each beaker (5, 10, 20, 40, or 80 mg P/L) andstir well to “wet” the soil particles. Place the beakers on the shaker table for 1 hour at 150 rpm.While the samples are on the shaker table, proceed to Part 2 below.3. After the appropriate amount of time has elapsed, remove the beakers from the shaker tableand allow their contents to settle for a few minutes. Transfer a portion of the overlying solutionfrom each beaker to a clean small test tube (at least ¾ full), then centrifuge them for at least 2minutes to remove solid particles. Don’t forget to balance the tubes in the centrifuge and to let itslow fully to a stop after it shuts off. Label the tubes clearly, cover them with Parafilm, andsave them in your lab drawer for Week 2 of the experiment.Part 2. Preparation of Amorphous Iron OxidesCaution: Hydrogen peroxide (H2O2) is a strong oxidizing agent. If you spill any on your skin,immediately flush the exposed skin with a large quantity of water.1. Weigh 1.0 g of FeCl2 into a 250-mL or larger beaker.2. Add 25 mL of water and swirl or stir gently with a glass stirring rod. Most of the solid shoulddissolve after mixing for a minute or two.3. Add 10 mL of saturated NaHCO3 (sodium bicarbonate; baking soda) and stir well. Recordany changes in color or texture. (If you do not see a significant amount of solid forming in themixture at this point, add a few more mL of the NaHCO3 solution and mix again.)4. Immediately add 8 mL of 3% H2O2 (hydrogen peroxide) and stir or swirl to mix. Bubblingwill occur, so cover