Lab 6 Colorimetric Determination of Phosphate Ion

Lab 6 Colorimetric Determination of Phosphate Ion - '...

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Unformatted text preview: ' Section a) EXPERIMENT 6 COLORIMETRIC DETERMINATION OF PHOSPHATE ION PRE-LABORATORY QUESTIONS The following preparatory questions should be answered before coming to lab. They are intended to introduce you to several ideas that are important to aspects of the experiment. You must turn in your work to your instructor before you will be allowed to begin the experiment. OOOOOICOOOOOIO .000000000... 1. Define the following: (if the definition cannot be found in your textbook, use a dictionary, an encyclopedia or use the “web”.) a. sequestering agent m «waémox {fowl {pgfiueem «a 15 ' a? E4 b. tripolyphosphate ion 5? {9,2} D I iv? :11» -i c. eutrophication d. superphosphate % ii 19“” Plifl'i‘fl if 7' 3f “‘7'; 1,"? ‘" r' 53’? f7 p 7' N”? “'7” I/ ’11.) € g {A L a“ fjiflfif _, g” 5 Ag” f, I I, f 2. Draw the structure of the orthophosphate ion, PO43' ' ‘5 Q 3 " ® ’ O I’- . u I l 7 * r U I f» a * ' a i i g 1 1 1 l a n. ( 2 9 U? 6 c Chem1515—Academic Year 2010/2011 6—1 3. Complete and balance the following reaction: (Use a reference.) P4010(s) + éHzOfl) —> *1 H? 60% 4. Calculate the volume of 1.00 x 10'3 M phosphate stock solution you must dilute to make 25.0 mL of 2.5 x 10’4 M phosphate. Show your work below. 2. a; » < ' w 3 ngwmwsawrfirxwlmm h», , X 9 a 2,: if : I“; 5. The tripolyphosophate ion, P30105‘, hydrolyzes to produce orthophosphate ions. This pH dependent reaction is catalyzed by H+ and Na+z _ _ O— 0 0‘ 0 (I) (I) I H+,Na+ I I I _ 'o—P—o—P—O—fi—O— + H20 M"0_H“O*fi’_0— I—0 ('l 3') 0 0 0 0‘ o o" —> 'O—-ll|’—O—Ill’—O—H + Ho—fi—O 0 o o + H20 another POP linkage cleaves Chernl 5 15—Academic Year 2010/201 1 6‘2 RESULTS PART ONE: CALIBRATION CURVE PREPARATION Standard solution Absorbance Blank O - Zoé 0.20x10'4 0,25%; g2“! 6, 4, Q‘ a } [5.00X10_4 {hit-fig“ : /,3zz)c/0 ' Equation of the best straight line : a: 0: 351200??? "‘ 0030‘3 7) a/ x ( 5 Chem1515—~Academic YeaI 2010/2011 6__9 Wat?“ PART TWO: PHOSPHATE CONCENTRATION OF TWO UNKNOWNS I ~\ Unknown # of phosphate solution: 3 ‘ C84 3 3 §’ % x153 ?)%,+,zos Absorbance .. ’f o v» 6"! .1 I Xi fl |_Unknown phosphate solution Q: Q? ' 7f 1: 4/, 2! Wed?“ Concentration of phosphate in unknown from calibration curve, M ‘1. 3’ 5 X/ 0%“, M Concentration of Hyponex in water (from bottle): , 463 [L \ ~\ | Absorbance I Hyponex Plant Food solution 1 , '7 77 o 1 Concentration of phosphate in Hyponex from calibration curve, M 9 $30 : J {35 ‘~ Calculation of PO43' in Hyponex plant food: 7.1-: r rnv'xmw1w My.» Miguww,“ , « Imam»wwwlm" “""m if 21/ '4’ rd: W11; i915: 5/, ’7 3; Q 233’ p 9 9 : ’D : in; it": i 3.... «a. waver: SIGN-OUT: All equipment is put away, and the student bench is clean and dry. TA Date ChemlSlS—Acadcmic Year 2010/2011 0 Section 0 0 5— POST LABORATORY QUESTIONS 1. For your information, the maximum allowable phosphate concentration (expressed as P205) in drinking water is 5 mg/L or 5 ppm. ( 1 mg/L = 1 ppm) a. For géiutiqggjniiifioia calculate the phosphate concentration as P205 in ppm, . M. A , Mi 5%n’3‘wh.yfls¢r—I‘M«>NWV f” (4 Kg; i P . gflxzc‘ti’Mny MK wigs»? 4 Kim! :10? fl- WW”- ., m M W5 f0 3/ 2.. b. What is the concentration of P043" in ppm in the plant food sample you analyzed? 2. Fertilizers are generally marked With 3 numbers to indicate nitrogenpphosphorus and potassium (N, P, and K) content. The Hyponex you analyzed is a 75\6;;l9 plant food. Phosphorus content in fertilizer is generally reported in % P205. Convert your % P043” to % P205 and compare your result with the % P205 indicated on the label. ChemlSlSfiAcademic Year 2010/2011 6 1 1 -\.,\7/ 3. B. D. Decker, by mistake, started the experiment with a solution fertilizer ( 0.55 g/L) another type of — ‘NPK fertilizer specially for potato ’ that has an NPK value of 16—5—21 At the end of the experiment (followed steps 4 to 8 of Part Two), she found the absorbance reading for the fertilizer to be 0.82. Calculate the % P205 in the plant food. How does her value compare to the value shown on the label? [Hint Consult the calibration curve in order to find the concentration of PO43' first] 1/3210 7f + .Zbé fits/z ChemlSlS—Academic Year 2010/2011 6_12 “K ...
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Lab 6 Colorimetric Determination of Phosphate Ion - '...

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