Oxidation-Reduction Titration Page 2

In the corresponding oxidation h~Jf-reaction the Fel ion s oxidized to Fe)

Half-Reaction 3

Combining half-reactions 2 and 3 and balancing the number of electrons transferred gives me overshy

all reaction equation

8H(alt]) + Mn04-(aq) + 5Fe2(aq) -) Mnl(aq) + 5Fe3(aq) + 4H20(l) Reaction 4

The balanc~d equation shows that 5 moles of Fez are required to react with I mole of MnO~-

For tUs redox titration the e(jllivaence poinJ OCClliS when the exact number of moles of Fe2 + ions

has been added to react completely vitli all th-MnO~- ions in solution At this point

moles Fe2 = 5 x (moles MnO-) Equation 1

If the vohlme aTid molarity of the FeZ solution arc known thell

Equation 2

Rearranging Equation 2 yields the equation for the concentration of the potassium perrnanganate solution

(VFt2middot)(MFc2)

5 (YMnO-)

The indicator for this titration is the Mn04- ion itself The MnO- ion is purple in solution At the endpoint of the titration the solution changes from light pink to colorless

In Part 2 the concentration of an oxalic acid solution is detennined by titratlon with the pennanshyganate solution standardized in Part 1 ln this case the endpoint occurs when thepink color of the Mn04- ion persists The half-reaction for the oxidation of oxalic acid is

The oxidation state of carbon changes from (+3) in H2C]04 to (+4) in IhCO)

Experiment Overview

The purpose of this lab is to standardize a solution of potassium pennanganate by redox titralion with a standard solution of iron(lI) ions A solution of oxalic acid is then titrated with the permanshyganate solution lo detennine the exact concentration of oxalic acid

Pre-Lab Questions

1 Write the balanced )let iQJIic eqation for th reaction pclwe~ Mn04- iOll~and H2C20~in acid U solution ~ 1 (IJ ~ - t) lt 1 ~ ) - -=-_ lf~v- -gt l J 7_ I

2 How many moles of Fe~jons can be oxidize_d by O04~m~ r~lts Q[ MnO- io s r--~ Y 0 re 1 F ~ - S laquoI ) _ L l~ (Y ~ - ( j ~

3 1630 g of iron ore is dissolved in an acidicsolution This s t1rfatetl to apm endpoint _ 00 )~)l with2715mLofaO020MKMnOqsollltion QL-t7- - _ -J

(VI eJ middot - a ) 0 (f bull r I i Q How mallY moles ofMnO-jons were consumed 11 1 (+ i1 Qj)J)S -middot) o u I ~

t lt L_~-----1-~~- middot b How many moles of Fe2~ were in the iron ore sample 0 ~~ 1) V )7 ~)

c What is the percent of iron in the iron ore sample M~Slt F( r_ l ~ 1 1_ ~ - shy

~ 2003 FlinDScKnUfl( Inc All pjtJltsRexrved RcproducLioD pcfllliJsion is gtill1tccl only I01IUoCbaS who have plDth~ (hi-ltblion-Redoclion Tltralions Calnog No APaSJS from fl ~ Sd~6c hx to put of lbi =~ri gtl Y blt podo=l a IraquongtmihCd any fonn 0lt by Yn dlaquorrOJUc o~ mlaquohgtniru includ ing bu 1gt01 ))1)laquo10 pboHlt0PYbullceOJdiDg Clt VJ inf(nD - -1 1L shy on~=eJY1ltmw1hooIpamhsionin ri1iDgfroogtf1innScieofxlnc ~ ~ - __ j ~L 09 r -gt0 - ~ - 1 J i--- _

Oxidation-Reduction Titration Pilge 5 ========================--=-~=-=-==~=-=-=-====~=--=-============

Data Tables

Part 1

Molarity of Fe1 ~9_~M

Jnitial volume of MnO- solution

Final volume ofMnO~- solution

Volume of MnO - added mL

Part 2 _

Molarity of MnO- solution ~ M

~o0 9 vt I (~

Volume ofH2C20 solution titrated t-) O1L ~S mL

Initial volume of MnO~- solution mL mL

Final volume ofMnO- solution (j mL mL

Volume of MnO - added mL ) mL

Molarity ofH2C20 solution _ ____ M

f Post-Lab Cflculations

v 1 From the Part 1 standardization data calculate the molarity of the MnO- solution for each trial Average the values and enter the average in the Part 2 Data Table

_ ) -Ub 2 From the Part 2 titration data caJculate the molarity of he H2C20 4 solution for each trial - V1lt) CI Average tJJe values and enter the average in the Part 2 Data Table

~~~hg~

3 How my mol of Fo d Mo _ wore od 0 h Port 1 17 ~ 0) 1 ~V rgt~ ~ l l ) )Q Cl~J - 1 - euro 01lt)0 tn-C) (lt)

4 How many moles of oxa ic ada H2t~4 wj~ated in ~ach Part 2 tr~ ~ t] ~C) - lJ) ~

- 0 Sv ~C H- L) ) 1 (h lt) (y C -

() 2003 Flinn Sc~nLiht lDc AU Rjgbu Rtserved Rep1OOuctioo permiuion is gJanltd ooly 10 science [exben who hve pWtha3m Oxwhtion-Reduction 1itntioos Cta1og No AP8aS fioOO Flinn Scientific lot N() pl1l )(lhis malUial may be rtpiloouccd ()f tJ3Dsmined in an) fron or by ny me am dnnoruc Of llIeCb2nicaJ ioctuding bul not limited 10 pbotocopy rt(ording or any inftflll3 tiOf) ~Ionampe ard nbkil l)5kro without pcnni~jOfl in ritlng rsom Flinn Sc~Dlificlnc