Lab 2 iron via redox titration PDF

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Mary%Athos%13275122% Lab%report%2%–%Proficiency%Testing% % Analysing%the%concentration%of%iron%in%an%iron%tablet%via%redox%titration% % ! Project!Objectives:! The%purpose%of%this%report%is%to%analyse%iron%tablets%supplements%by%the%company% “Super-Mega%Supplements”%and%to%calculate%the%total%weight%of%iron%present%via% redox%titration.%Values%obtained%from%this%experiment%will%be%compared%against%a% reference%value%to%determine%how%close%the%findings%were.%%It%is%hypothesised%that% the%value%obtained%from%the%experiment%will%be%in%close%range%to%the%reference%value.% % % Materials!and!Methods! Please%see%Practical%2%guidelines%pages%5-6%for%the%materials%and%methods%used,% these%are%under%the%subheadings%Preparation*of*standard*solution%and%Analysis*of* iron*tablets.*** Exact%mass%of%ammonium%iron(II)%sulfate%=%5.022g%±0.1mg% Amount%of%elemental%iron%per%tablet%=%119mg% % % Results!-!Preparation*of*standard*solution! * Net%ionic%equation:% 5Fe2++%MnO4-%+8H+%à5Fe3+%+%Mn2+%+%4H2O% % Table*1:*Molarity*of*standard*solutions* % Molarity%of%KMnO4% 0.0115%% solution%(mol/L)% Molarity%of%the% 0.0575% standard%iron(II)% solution%(mol/L)% Table%1%states%the%molarity%for%both%solutions%used,%see%appendices,%page%1,%for%the% calculations%of%these%results.% % Propagation%of%error:% !.!!"#!$! !.!"!

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) +( ( √ )! =%0.002%=%0.2%% !"# !"#.!"#! !.!"" % Absolute%uncertainty%=%relative%uncertainty%x%measured% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.002%x%0.0115% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.000023% % Therefore%the%molarity%of%KMnO4%=%0.0115%±%0.000023%moles/L%

% Table*2:**Titration*volumes*for*the*KMnO4+*solution,*standardised**with*the*Iron* standard.* % Attempt%1% Attempt%2% Attempt%3% Titration%volume%(mL)% 22.2% ±0.05mL% 22.2%% 22.1% Mean%titration%volume% 22.16% (mL)%±0.05mL% Standard%deviation% 0.0577% Standard%Error%of%the% mean% 0.0272% % This%table%shows%the%results%from%the%titration%of%the%KMnO4%solution%against%the% iron%standard.%The%three%attempts%were%averaged%to%obtain%a%mean%value.%All% volumes%have%an%uncertainty%of%±0.05mL%as%that%is%the%given%uncertainty%of%the% burette.% -Analysis*of*iron*tablets:* % 5Fe2++%MnO4-%+8H+%à5Fe3+%+%Mn2+%+%4H2O% % Table*3:**Titration*volumes*for*the*Iron*tablets*against*the*standardised*KMnO4* solution.* % % Flask%A% Flask%B% Titration%volume% 31.1%% 31.2% (mL) ±0.05mL% Mean%titration%volume% (mL)%±0.05mL% 31.25%% Standard%deviation% 0.0707% Standard%Error%of%the% 0.0353% mean% % This%table%represents%the%results%from%the%titration%of%the%iron%tablet%solution%against% the%KMnO4%standard.%Flask%A%and%B%were%averaged%to%obtain%a%mean%value%of%the% titration%endpoint.%All%volumes%have%an%uncertainty%of%±0.05mL%as%that%is%the%given% uncertainty%of%the%burette.% % Table*4:**The*average*mass*of*FeSO4*and*Fe*in*each*tablet*obtained*from*the*titration* volumes.* % Average%mass%per%tablet%(mg)% % % Fe% 100.4% % FeSO4% 273.1% % Table%4%shows%the%average%mass%of%each%element%and%compound%per%iron%tablet.% See%appendices,%page%2%for%the%calculations%of%the%masses%

% Propagation%of%error:% !.!!" !

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√( ) +( !"# )! =%0.00044%=%0.044%% !!.!"# % Absolute%uncertainty%=%relative%uncertainty%x%measured% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.00044%x%100.4mg% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.0044% % Therefore%the%mass%of%Fe%=%100.4%±%0.0044mg% % % % !.!!" !

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√( ) +( )! =%0.000041%=%0.041%% !"!.!"# !"# % % Absolute%uncertainty%=%relative%uncertainty%x%measured% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.000041%x%273.1mg% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%=%0.0011% Therefore%the%mass%of%FeSO4=%273.1%±%0.0011mg% % % % Table*5:*Comparison*of*the*mean*results*among*bench*2,*the*lab*the*experiment*was* conducted*with*and*all*labs*combined.* % QC%chemists% Mean%Results% Fe2+%(mg)% [KMno4]% FeSO4%(mg)% 0.02301% 74.68% 201.88% Bench%2% % 0.01399% 130.39% 173.49% % % Monday%9%am% % 0.01617% 109.98% 297.38% % % % % All%labs% 0.0047% 28.18% 138.92% % % % STDEV% % Table%5%shows%an%accumulation%of%results%from%a%range%of%chemists.%Including%a% smaller%focus%group,%a%class%and%results%form%the%cohort.%Results%that%were% completely%out%of%range%were%removed%as%they%skewed%the%data.% % ! ! !

! ! Discussion! % The%aim%of%this%report%was%to%analyse%iron%tablet%supplements%by%a%company%and%to% calculate%their%total%weight.%The%employer’s%goal%in%assigning%this%task%was%to%check%if% the%amount%of%iron%present%listed%was%as%advertised.%The%ingredients%stated%that% there%was%119mg%of%elemental%iron%present%in%per%tablet.%The%goal%has%been%fulfilled% as%a%value%were%able%to%be%obtained%by%a%redox%titration,%however%it%did%not%meet%the% hypothesis%as%the%value%was%100.4%grams,%which%was%lower%than%expected.% % % Table%1%includes%the%weight%of%ammonium%iron%sulphate.%The%method%stated%it% should%be%5.0g%and%the%value%used%for%the%experiment%was%5.022g,%which%is%still%a% sufficient%value%to%be%used%however%it%needs%to%be%recorded%and%used%for% calculations.%Table%1%also%includes%the%molarity%of%KMnO3%and%the%iron%standard% solution,%which%was%calculating%using%the%titrant%volume.%Table%2%and%3%of%the%results% represent%the%titration%volumes%in%both%parts%of%the%experiment.%The%initial%volume% in%burette%was%recorded%and%once%the%solution%had%reached%the%endpoint,%the%final% volume%was%recorded.%The%initial%volume%was%subtracted%from%the%final%volume%to% give%the%correct%amount.%The%measurements%had%to%be%within%0.1mL%of%each%other%in% order%to%improve%precision%and%overall%accuracy% % To%improve%accuracy%the%results%were%compared%against%other%chemists,%found%in% table%5.%This%table%represents%all%of%the%mean%values%and%it%can%be%seen%that%the% KMnO4%concentration%and%mass%of%FeSO4%are%higher%in%bench%2.%This%indicates%that% there%were%a%range%of%errors%and%personal%experimental%methods%when%the% procedure%was%being%carried%out.%When%analysing%the%iron%results,%there%are% differences%among%the%three%groups%in%the%amount%of%Fe2+%found%per%tablet%after%the% redox%titration.%However%it%is%notable%that%the%average%of%all%the%labs%combined%was% quite%strayed%from%the%reference%value%of%elemental%iron%of%119mg.%The%standard% deviation,%28.18%is%high%indicating%that%there%were%errors%throughout%the% experiment.%All%the%labs%combined%had%an%average%that%was%10mg%away%from%the% reference%given.%This%indicates%that%there%was%a%large%range%in%results%from%low%to% high%to%produce%this%value.% % Due%to%the%fact%that%the%iron%value%from%Table%5%:‘All%Labs”%was%obtained%using%the% most%amount%of%samples%indicates%that%proficiency%testing%by%comparing%between% labs%gives%a%more%accurate%value.%It%is%therefore%more%accurate%to%use%a%larger%scale% of%results%to%obtain%this%value.%However,%results%used%from%a%lesser%sample,%iron%mass% Bench%2,%is%much%lower%than%the%expected%value.%This%shows%it%is%important%to%look%at% the%labs%individually%and%see%what%chemists%are%not%following%procedures%correctly% therefore%not%producing%accurate%results.% % Possible%sources%of%error%in%the%results%are%personal%error,%random%error,%reading% instruments%and%miscalculations.%Personal%error%includes%an%individual%not%properly%

following%procedures.%This%can%be%seen%by%forgetting%steps,%misreading%instructions% or%using%instruments%incorrectly.%Random%error%could%also%be%a%factor%as%it%is%a% sudden%change%in%the%experimental%conditions%and%can%change%results%such%as% sudden%temperature%changes,%humidity,%or%voltage%fluctuations.%Another%source%of% error%could%be%misreading%instruments%or%not%taking%into%consideration%the% uncertainty.%Several%glassware%instruments%were%used%including%conical%flasks,% volumetric%flaks,%measuring%cylinders%and%a%burette,%all%of%which%had%a%listed% uncertainty%value,%which%is%seen%in%the%results%propagation%of%error.%The%greatest% contributing%source%of%error%for%the%results%was%most%likely%miscalculations,% including%using%the%wrong%value,%not%converting%units%properly%and%not%using%the% molar%ratio%correctly.%All%of%these%factors%could%have%contributed%to%the%results%and% are%henceforth%sources%of%error.% % ! Conclusion!! The%project%objectives%of%this%report%were%to%analyse%the%contents%of%iron%tablets%to% see%that%the%exact%mass%of%elemental%iron%was%consistent%with%what%the%mega% company%had%claimed.%After%performing%the%experiment%it%was%found%that%were%was% less%elemental%iron%than%what%was%hypothesised.%It%is%recommended%to%the%employer% to%do%reanalyse%the%iron%contents%as%among%all%the%chemists%within%the%laboratory% there%is%a%great%level%of%inconsistency%and%many%were%outside%the%reference%range.%...