fertiliser prac

SULPHATE CONTENT OF A FERILISERDate 5th -6th May 2011 Aim To perform a first had investigation using gravimetric analysis to determine the sulphate content of a lawn fertiliser (a mixed fertiliser containing ammonium sulphate and potassium (or ammonium) nitrate). Background information There are a variety of techniques that are used by chemists to determine the concentration or amount of a particular element, ion or compound in a sample of solution or material. One of these techniques used by scientists is gravimetric analysis. Gravimetric analysis involves weighing materials and determining the percentage composition (by weight) of elements in compounds or components of mixture. The technique of gravimetric analysis usually involves the use of precipitation reactions1. Gravimetric analysis often involves some of the steps shown in the following diagram: In this investigation, the sulphate ion in the fertiliser is precipitated with barium ions from acid solution. The precipitate is then collected, dried and weighed2 Ba2+ (aq) + SO42- (aq) BaSO4 (s) 1 2 Quantitative analysis: Thickett, Geoffrey. Chemistry 2: HSC course (pg 266-267) Equations for precipitation reactions: http://dl.clackamas.edu/ch105-04/equation.htm To avoid contact with s in and eyes: . see medical assistance.Wear cloth d sho s .Wear s f t lo s .Wear clos d sho s.uk/hsci/chemicals/barium_chloride. call for medical help.ox. Permanent eye damage may result. Prolonged contact may result in burns. Rinse the affected area with water then wash thoroughly with soap and water.Ensure that the glassware is . . If irritation persists.It is harmful if inhaled and if it comes into contact with the s in (irritant).au/msdsfiles/hydrochloric%20acid. ulceration and corneal burns. and may be fatal if swallowed.net.in cont ct: Brief e posure may cause irritation.Wear lon sl d clothin to a person s eye. . .Glass are at is heate over the To avoid any ris s associated Bunsen flame hotplate becomes with glassware e tremely hot and contact with . Use water alone.Wear clos d sho s cont ct: immediately hold eyelids open and rinse the eye continuously with a gentle stream of clean running water for at least fifteen minutes.Cont ct with s in: Place the burnt area under running cold water.Heated apparatus may fall out of completely cooled before hands and towards the feet. in cont ct: Wash off with soap and water. if soap is unavailable. See medical attention if any soreness or inflammation of the s in persists Y Y ` ac ed T H ` Y ba` Y X X W U VUU T PS R Q P I F Barium Chloride (BaCl2 3 G .html i i i Y Y ed b ` ` `g ` f `g b a ` Y ` Y ba` Y i h Y ` ac ed Hydrochloric Acid (HCl) 4 .Wear s f t l ss s. If irritation persists.Wear s f t lo s. To avoid any contact with eyes and s in: . . If burning sensation persists. F D ED A B @ C ` ac 6 9 7 877 6 5 5 14 3 2 1 0 ' & )(' & % " " #  Y ` g ff $ " ! He e ss e e s s s .Is a co osi liquid .Heated solution may splash into . thus any contact must be avoided. See urgent medical attention . See medical attention. and swelling. instantly flushing for at least 10 minutes. cont ct: is irritating and may cause conjunctivitis.Wear s f t lo s.Wear s f t l ss s s in may produce redness pain.Wear s f t l ss s . .Barium chloride is poisonous. . .pdf ` f M t i l t t vx ss r rw v s r r ts r q fY `` d Yu Yp a ` Yd uY f` Y 3 f t t h t: B iu Chlo id http://cartwright.Wear lon sl d clothin to cover s in .in Cont ct: Remove contaminated clothing. handling conse uently burning the s in.Cont ct with s: Gently open damaged eye and pour cool water.Ris Ass ss  ¤§  ¥ £ § £© ¤£  © £¨ £§ ¦ ¥ ¤£ 4 M t i l f t t h t: d ochlo ic acid http://dkt.   ¡¢ ¡   nt . damaging the cover s in eye.ac. cont ct: Immediately remove any contact lenses and flush the eye with water. call for medical help.chem. .Wear p ot cti clothin . 5. All safety precautions were ensured. 4. Meanwhile. The beaker was removed from the hotplate and onto the heat proof mat where it was allowed to cool for approximately 5-10 minutes.7% (w/v) Electronic balance 250mL beaker Distilled water Burette Hotplate Glass rod Quantitative filter paper Funnel Retort stand and clamp M thod: 1. 10 drops of concentrated hydrochloric acid were added into the dissolve solution. 7. 3. 6. The mass of the fertiliser was recorded. 25mL of warm distilled water from a measuring cylinder was added into the beaker to dissolve the crystals. The solution was stirred with a stirring rod after each addition. €y  . The mixture was gently re. 2. The mass of the filter paper was recorded.boiled for a further 5 minutes to coagulate the precipitate. 60 grams of the powdered lawn fertiliser was accurately weighed into a 250mL beaker. 8. From a burette the 7% barium chloride solution was slowly added into the hot sulphate solution until no further white precipitate formed. a circle of quantitative filter paper was weighed on the electronic balance. A hotplate was used to heat the mixture until it just boiled.Mat ials: Solid (soluble) fertiliser Concentrated HCl solution Barium Chloride solution . The apparatus was left overnight to ensure that water had completely been removed from the residue laying on the filter paper. The warm supernatant was poured and then the suspension of barium sulphate through the filter paper.9. 11.jpg ‚ hen they are dry. It was ensured that the entire solid was transferred from the beaker into the filter using small amounts of warm washing water (distilled water). iagrams from:http://www.micromountain. weigh the filter paper with the barium sulphate collected.com/sci_diagrams/sci_app/sci_app_assets/filter_lab_eng. the apparatus was set up for filtration (as shown below) 10. ƒ . The filter paper was folded and placed into a glass funnel. 12. Calculate the mass of barium sulphate collected. Mass of fertiliser (g) Mass of quantitati e filter paper (g) 1. quantitative filter paper as well as the calculated mass of barium sulphate that precipitated. Calculate the weight of sulphate in the sample.45 . % sulphate by weight= massofsulphate g    x100 = 2.45 (g) 60 g 1.07mol = 2.Results: The table below shows the mass of the fertiliser used.2422g 3. Step 1: Determine the moles of barium sulphate n (BaSO ) = mass g   = 0 59 233 97 = 2..86 = 0. Calculate the percentage by weight of sulphate in the sample.06% 4. Calculate the number of moles of barium sulphate collected.(aq) From equation n (BaSO ): n (SO42.)= 2. Mass (g) = Molar mass (g/mol) x Moles (mol) = 2.2422g/0.) = 1:1
n (SO 42.59g x100=41. Š‡”‡•—Ž–•ƒ„‘˜‡‹†‹…ƒ–‡–Šƒ––Š‡’‡”…‡–ƒ‰‡…‘–‡–‘ˆ•—Ž’Šƒ–‡‹‘•‹ƒŽƒ™ ˆ‡”–‹Ž‹•‡”™ƒ•ƒ’’”‘š‹ƒ–‡Ž› ˆ–‡”–ƒ„—Žƒ–‹‰–Š‡…Žƒ••”‡•—Ž–•ƒ†ƒ˜‡”ƒ‰‹‰ –Š‡ ‹–™ƒ•‹ŽŽ—•–”ƒ–‡†–Šƒ––Š‡ƒ˜‡”ƒ‰‡•—Ž’Š—”…‘–‡–‘ˆ–Š‡ˆ‡”–‹Ž‹•‡”™ƒ•  Š‹•”‡•—Ž–‡š…Ž—†‡†–Š‡‘—–Ž‹‡”‘ˆ‰”‘—’ ”‡•—Ž–• Š‡”‡ˆ‘”‡ ‹ ‰‘ˆˆ‡”–‹Ž‹•‡” –Š‡”‡ ‹• ‰‘ˆ•—Ž’Šƒ–‡      „ … „ Calculated mass of barium sulphate(g) 2.1.5216 x 10 ³mol BaSO4 (s) 2. Briefly describe the outcome of your investigation.86 g Mass of quantitati e paper + bariu sulphate (g) 2.59 g .5216 x 10 ³mol Step 2: Write a balanced equation of the precipitation reaction to determine the moles of sulphate present in the fertiliser sample Ba2+ (aq) + SO 42.5216 x 10 ³ x 96. Thus determine the number of moles of sulphate present in the fertiliser sample. (aq) Step 3: Determine the weight of sulphate in the sample.07mol = 2.5216 x 10 ³ x 96.06 .87%* (outlier.—‡•–‹‘•  ”‹–‡ƒ„ƒŽƒ…‡†‹‘‹…‡“—ƒ–‹‘ˆ‘”–Š‡’”‡…‹’‹–ƒ–‹‘”‡ƒ…–‹‘  In this investigation. % sulphate by weight Class average of % sulphate by weight ‰
n (S 2- 4 )= 2. The percentage by weight of sulphate in the sample calculated by each group is shown in the table below: Group no.59g x100=41.2422g Step 4: Calculate the percentage by weight of sulphate in the sample.06% 1 2 44% † aq) aq) = 2.5216 x 10 ³mol 65. the sulphate ion in the fertiliser is precipitated with barium ions from acid solution (Barium Chloride solution).69% ‰ From equation n (BaS ): n (S 2- 4 ) = 1:1 x100 = 2. Mass (g) = Molar mass (g/mol) x Moles (mol) = 2.5216 x 10 ³mol BaSO4 (s) 3 49% ˆ† ‡ ‡ † Ba2+ + O 2- BaSO ) ‰ 4 (my group) 41.2422g/0. % sulphate by weight= massofsulphate g    The steps above were followed by all of the groups in the class. The balanced ionic equation for this precipitation reaction is shown below: ƒŽ…—Žƒ–‡–Š‡’‡”…‡–ƒ‰‡„›™‡‹‰Š–‘ˆ•—Ž’Šƒ–‡‹‘•‹–Š‡ˆ‡”–‹Ž‹•‡” ˜‡”ƒ‰‡–Š‡”‡•—Ž–•‘ˆƒŽŽ ‰”‘—’•ƒ†™”‹–‡–Š‡…Žƒ••ƒ˜‡”ƒ‰‡  Š‡•–‡’•–ƒ‡–‘…ƒŽ…—Žƒ–‡–Š‡’‡”…‡–ƒ‰‡„›™‡‹‰Š–‘ˆ•—Ž’Šƒ–‡‹‘•‹–Š‡ ˆ‡”–‹Ž‹•‡”ƒ”‡ƒ• ˆ‘ŽŽ‘™•  Step 1: Determine the moles of barium sulphate n (BaSO ) = mass g   = 0 59 233 97 Step 2: Write a balanced equation of the precipitation reaction to determine the moles of sulphate present in the fertiliser sample Ba2+ (aq) + SO 42. not included in class average) 44. 40g of barium sulphate. and relevant analysis experiments as they have finer pores. These very fine pores prevent the small barium sulphate particles from being lost (i. One student considered varying the mass of the fertiliser used in the experiment.: used for rough work where it is not important to completely retrieve all the solids. the carbonate ions will decompose to give carbon dioxide gas. 6. Quantitative filter paper is chiefly used for weight analysis test in quantitative chemical analysis. However. Explain why the precipitate is heated for some time prior to filtration. is mainly used for qualitative chemical analysis as they have larger pores and do not restrict very small particles (i. Carbonate ions that may be in the solution (as an impurity) will form a precipitate with barium ions to form barium carbonate which is insoluble.e.90G of barium sulphate rather than 0. standard error decreases because estimates become more precise. The accuracy would be improved by precipitating 0. thus not very accurate in dealing with very small barium sulphate particles)5 5 Quantitative and qualitative filter paper: http://answers.90G of barium sulphate rather than 0. The solution is acidified prior to the addition of barium ions. Explain why the solution is acidified. heating the precipitate formed prior to filtration causes the barium sulphate particles to coagulate (clot) to ensure that they will not pass through the pores of the filter paper. 2 PO43-(aq) + 3Ba ² (aq) Ba (PO ) (s) By eliminating the carbonate ions and phosphate ions in the solution.e.com/question/index?qid=20100828073836AAhveEH . thus giving us more accurate results. Barium sulphate ions are very small and have the possibility to pass through the pores of the filter. Ba ² (aq) +CO ²(aq) BaCO (s) However in the presence of a dilute acid (usually HCl or HNO ). Explain why a quantitative filter paper leads to greater accuracy than using a qualitative filter paper.3. it becomes assured that all the precipitate formed when the barium ions are added are only barium sulphate (with no interference by the carbonate ions and phosphate ions) 4.40g of barium sulphate as the percentage error would be reduced. Explain why the accuracy would be improved by precipitating 0. The purpose of acidifying the solution prior to the addition of barium ions is to eliminate the possibility of interfering ions including carbonate ions and phosphate ions that may precipitate when barium ions is added. 5.: they are trapped on top of the filter paper) in our experiment.yahoo. As sample size increases.Percentage error is the measure of how far off an estimate is from its true value. Qualitative filter paper however. Percentage of error is dependent on the size of the sample. Phosphate ions that may be in the solution (as an impurity) would also form a precipitate with barium ions to form barium phosphate which is insoluble. The precipitate that formed was entirely barium sulphate. this will adversely effect the validity of the results(i. The sinister glass can be heated to complete dryness as the glass will not absorb any water molecules. . Only be constant heating do we know that all the water molecules have been removed. a sintered glass filter can be used instead of filter paper.All the precipitate collected on the filter paper (i.: the mass of the water will be mistaken for barium sulphate) In order to improve accuracy. Explain why the precipitate on the filter paper should be heated to constant dryness? The precipitate on the filter paper should be heated to constant dryness to ensure that all the remaining water molecules are removed. pain. Explain why this procedure is more accurate. 10. the experiment must be repeated a minimum of five times whilst ensuring that all the variables are controlled. and not filter paper. The very fine pores of the sintered glass filter also ensure that all the barium sulphate will collect at the top of the glass disk.: no barium sulphate was lost) 9. and swelling. The accuracy of the experiment can be improved by filtering through a pre -weighed fine-pore sintered glass filter rather than a filter paper.e. It is harmful if it is inhaled and if it comes into contact with the skin (irritant).e.7.e. and may be fatal if swallowed.: any small error may impact dramatically on our results). The results of the repeated trials must also be averaged (making sure not to include the outrider result/s) 8. materials and solutions: If glassware that is heated over the Bunsen flame/hotplate may become extremely hot and if it gets into contact with skin. The investigation must also be repeated with extreme accuracy and precision as we are dealing with very fine particles (barium sulphate) and a very sensitive balance (i. as filter paper might burn in an oven. Chemist also use sintered glass filters. Filter paper is made out of cellulose. The main safety concerns of the experiment include: . On what assumption is the validity of the experiment dependant? The validity of the experiment is dependent on the following assumptions: . thus any contact must be avoided. The cellulose forms strong bonds with water molecules (due to the high polarity of water and cellulose). whenever the solid matter must be dried in an oven. 11. the skin may produce redness. Explain how reliability could be improved in this experiment.Barium Chloride (BaCl2): Barium chloride is poisonous. In order to improve the reliability of this investigation. If heated solution may splash into a person s eye it may damage the eye. All water molecules must be removed to ensure that the results are unaffected and valid. . Identify the main safety concerns of this experiment.Heated glassware.The hydrochloric acid eliminated all the carbonate and phosphate ions that were contaminating the solution (no foreign ions -other than sulphate ions-were in the solution) . . It becomes very difficult to break these strong bonds even if the filter paper is heated. . Wear closed shoes. It is irritating and may cause conjunctivitis.. The amount of sulphate in percentage by weight in the fertiliser was calculated to be 41. the following must be followed and implemented: y y y y y Wear safety glasses Wear safety gloves.69%.06% and on class average it was calculated to be 44. Prolonged contact may result in burns.Hydrochloric Acid (HCl): HCl is a corrosive liquid and exposure to skin may cause irritation. In order to prevent any of these safety concerns. ulceration and corneal burns if it comes into contact with the eyes. Wear long sleeved clothing to cover skin Ensure that the glassware is completely cooled before handling Conclusion: An investigation was conducted to determine the amount of sulphate present in the lawn fertiliser using gravimetric analysis.