Calibration standards of known concentrations were prepared1 drop of phenolphthalein and dropwise of sufficient Naoh were added to Monash drain and South Quay samples and 5 replicate blank samplesSulfuric acidand combined reagent were added to the samples and blanks.The acidified phosphomolybdenum deeloped into a blue solutions after 1! minutes.The absorbance of all samples" samples and blanks were measure at ##!nm using a spectrophotometerConcentration of phosphate was then determined by plotting a calibration graph. Title$ Spectrophotometric determination of reactie phosphate in watersAim: The aim of this e%periment is to analy&e reactie phosphorus in south 'uay lake and monash drain by spectrophotometer measurement. Outline of method: Summary of results:(lank dataTable 1. )bsorbance" mean absorbance and standard deiation of the blank. Blank no. Abs 1 Abs 2 Abs 3Abs 4 Mean Abs n11 !.!!! !.!!# !.!!* !.!!+, !.!1- !.!!. !.!!# !.!!+- !.!!1 !.!1! !.!!* /!.!!-+ /!.!!1 !.!1+ !.!1- /!.!1!5 !.!1! !.!!! !.!!1 !.!!. !.!!5! 0.0052Calibration dataTable ,. The absorbance" mean and standard deiation of the phosphate0hosphate 12g0345)bs 1 )bs , )bs - Mean Abs n1! !.!!5! !.!!5,5! !.!+5 !.!+! !.!-6 !.!+!6 !.!!+!1!! !.!6! !.!66 !.!*6 !.!61- !.!,,-15! !.11* !.1,1 !.1!* !.11+- !.!!6*,!! !.1-# !.1+- !.1+, !.1+1! !.!!,*Calibration graph0 50 100 150 200 25000.020.040.060.080.10.120.140.16f(x) = 0x + 0.01R = 0.99Phosphate concentration (gP/L)Absorbance at 880nm7igure 1. 8raph of )bsorbance at ##!nm s Concentration of phosphate 12g0345Sample dataTable -. The absorbance at ##!nm" concentration and mean concentration for the water samples.!e"li#ate numberAbs 1 Abs 2 Abs 3 $on# 1 $on# 2 $on# 3 Mean #on# %&'()*+Mean $on# %&'()*+dilution#orr.Sam"le A1!.!-! !.!-5 !.!-- -5.,#56 +,.+,#* -..561+-..!.5,6#.1.!+Sam"le A2!.!,. !.!,# !.!,+ --.#561 -,.+,#* ,*.61+--1.!!!!*,.!!!!Sam"le A3!.!1. !.!,, !.!,5 1..561+ ,-.#561 ,#.1+,.,-.#561+6.61+,Sample ) mean 12g0345*,.*-+.9n/1 15.,+#!Sam"le B1!.!1# !.!,1 !.!1# 1#.1+,. ,,.+,#* 1#.1+,. 1..5615 -..1+-!Sam"le B2!.!1+ !.!16 !.!1- 1,.+,#* 1*.61+- 11.!!!! 1-.-#1! ,*.6*,!Sam"le B3!.!16 !.!,! !.!1. 1*.61+- ,1.!!!! 1..561+ 1..!.5, -#.1.!5Sample ) mean 12g0345-+.*.#+9n/1 *.##.6,$ )bs 1 )bs , )bs - Conc 1 Conc , Conc - Mean Conc 12g0345Mean Conc 12g0345 dilution corr.!.!66 !.!#! !.!6- 1!,.+,#*1!*.61+-.*.61+- 1!1..5,+/n1 -..1/. 0 !S1 4.22.2 0 !elati3e 4rror 1.2-24Sample ) : South Quay 4ake 1upstream5Sample ( : Monash drain 1downstream5Sample calculations (re"aration of standards $;sing C1 !.!!55 3 !.!!!6: 2-./14 &')*Summary TableTable +. Summary of the results. Sensitiity !.!!!6 2g/14 ,.1*6. % 1!/# mol/14Minimum detectable absorbance !.!,-4imit of detection ,5.61+ 2g34BeproducibilitySouth lakeMonash drainQC9n/1 15.,+#! *.##.6 5.!16!C BSD ,+.-++- 1..#5*! +..,!.)ccuracy C BE$ 1..5,+1is#ussion and $on#lusion7rom the graph aboe" the B, alue is !..#** which indicates a strong correlation between the concentration of phosphate and the absorbance at ##!nm. )ccuracy is a measure of how close the result of the measurement comes to the FtrueF" FactualF" or FacceptedF alue 1Queauiller" ,!!#5.Gn this e%periment" the accuracy of 'uality control is 1!1..5,+ 2g34 while the actual alue is 1!! 2g34" so the relatie percentage error is 1..5,+C. The relatie error of the measurement shows how large the error is in relation to the correct aluewhich compares the si&e of the error to the si&e of the obHect being measured.Since" the percentage error is lower than 5C" the data is good because there is lesser error and the alue is almost close to the correct alue. Gf the percentage error is more than 5C" 0recision is the reproducibility of results obtained in identical manner. The relatie standard deiation is widely used in analytical chemistry to e%press the precision and repeatability of an assay 1Bobinson" Skelly 7rame and 7rame GG" ,!1,5. ) lower percentage of BSD indicates a lower ariability in the data set. E'ually" a higher percentage indicates the data set is more aried. Gn this e%periment monash drain has a lower percentage BSD which is 1..#5*! C compared to the South Quay lake which is ,+.-++-C. Ience" Monash drain has a lower ariability and is more precise compared to South Quay. The sensitiity of this e%periment is !.!!!6 2g/14. This spectrophotometer has a minimum detectable absorbance !.!,-which means that the deice can detect up to !.!,- for the blank. 4imit detection is used to detect the lowest concentration of the spectrophotometer which is ,5.61+ 2g34. The higher concentration may be due to the reading alue of the blank and the standard solution. Colour of phosphomolybdenum blue which will fade in a long period of time can also contribute to the error in the e%periment as there is a prolog waiting time to take the result for all the sample data. The C BSD for south 'uay" monash drain and 'uality control is ,+.-++- C" 1..#5*!C" +..,!.C respectiely.Error in measurement may be represented by a tolerance interal 1margin of error5.The spectrophotometer used in manufacturing often set tolerance interals" or ranges in which product measurements will be tolerated or accepted before they are considered flawed.To aoid errors" make the measurement with an instrument that has the highest leel of precision.The smaller the unit" or fraction of a unit" on the spectrophotometer" the more precisely the deice can measure.The precision of a measuring instrument is determined by the smallest unit to which it can measure 1Jenkel" ,!!-5. (esides that" randomi&ing samples or e%periment could also increase the accuracy by increasing the signal to noise ratio. ?ther than that" repeat the samemeasure seeral times to get a good aerage alue.Ience it can be concluded that" the concentration of phosphate in South Quay 1Sample )5 is 52.5342 &'()* 9 1-.247. and the concentration of phosphate in Monash drain 1Sample (5 is 34.5274 &'()* 9 5.772/. This shows that monash drain is cleaner as there is lesser concentrationof phosphate present it water. ,uestions: 1. Is there evidence from the sample measurements that the dissolved reactive phosphorus concentrations are deemed to be above the Interim National Quality Standards (INWQS) guideline values issued by Department of nvironment (D!) for a "lass III #ater source$7rom the website" the concentration of phosphate in class GGG is !.1 mg34 which is 1!! 2g34 There is no eidence that the dissoled reactie phosphorus concentrations are deemed to be aboe the GNKQS because the mean concentrations for South Quay 1*,.*-+. 2g0345 and Monash drain 1-+.*.#+ 2g0345 are lower than the concentration of phosphate. ,. stimate the improvement in sensitivity if a %cm cell rather than a 1cm cell #as used. Would this change the detection limit$The sensitiity of the sample will increase if a +cm cell is used rather than 1 cm cell. )ccording to the (eer 4ambert 4aw" the signal will increase if the path length used is increased. This would change the detection limit. Iigher sensitiity gies rise to a lower detection limit as the intensity of the transmitted light decreases e%ponentially as the path length of the sample increases 1Joch" ,!1,5.&. 'o# could you determine the accuracy of your e(periment method$)ccuracy is a measure of how close the result of the measurement comes to the FtrueF" FactualF" or FacceptedF alue. The accuracy of the e%periment method can be determined by using 'uality control of a known concentration which is used to gie a theoretical alue to be used to compare with the sample result 1Queauiller" ,!!#5. The C relatie error is obtainedby diiding the data alue oer the 'uality control to compare the si&e of the error to the si&e of the obHect being measured. The lesser the percentage relatie error" the higher the accuracyof the data obtained. To aoid errors and ma%imi&e the accuracy of results" make the measurement with an instrument that has the highest leel of precision.The smaller the unit" or fraction of a unit" on the spectrophotometer" the more precisely the deice can measure 1Jenkel" ,!!-5.+. Silicate also undergoes reactions #ith acidic molybdate to form silicomolybdic acid #hich can also be reduced to molybdenum blue. )riefly describe an e(periment that #ould enable you to determine #hether silicate is a chemical interference in the measurement of phosphate. Silicate can be tested through acid treatment and reaction with ammonium molybdate to gie a yellow coloured comple% or silicomolybdate comple%. Sodium sulphate is added as well to reduce the comple%. Gf the reaction turns blue" there may be possibility that silicate may be present in the solution. To determine the absorption" absorption spectrum need to be tested using spectrophotometer. The absorbance readings are then compared. Iigh alue of absorbance reading indicates that silicate is a chemical interference in the measurement of phosphate which leads to changes in intensity of the analyte signal in spectroscopy 1Ienriksen" ,!!15.!eferen#esHenriksen, A. (2001). Interference from silica in phosphate analysis. Analyst, 91(1081), pp.290291.Kenkel, . (200!). Analytical chemistry for technicians. 1st e". #oca $aton% &e'is ()*lishers.Koch, +. (2012). ,en years of Analytical an" #ioanalytical -hemistry. Analytical and bioanalytical chemistry, .02(1), pp.18/ 0189.$o*inson, ., 1kelly 2rame, 3. an" 2rame II, 4. (2012). Undergraduate Instrumental Analysis, Sixth Edition. 1st e". Ho*oken% ,aylor an" 2rancis. 5)e6a)6iller, (. (2008). Quality Assurance in Environmental Monitoring. 1st e". +iley 7-H.