8/12/2019 Titration Lab Redox

1/2

Chemistry Lab

Determination of Iron Percentage by Redox Titration

Pre-Lab Discussion

Titration can be a useful method for analyzing redox reactions. An oxidation-reductionredox! reaction is one "here electrons are transferred from a reducing agent to an

oxidizing agent. The math for a redox titration "or#s $ust li#e an acid-base titration.

Assuming a one-to-one stoichiometry% the number of moles of oxidizing agent "ill e&ualthe number of moles of reducing agent. That allo"s us to use the same titration e&uation%

'()(* '+)+

If the stoichiometric ratio is not one-to-one% "e need to ad$ust the e&uation $ust li#e "e

did for ,oly,rotic acids.

The ,ermanganate 'n-!ion is often used in redox titrations because it is a strong

oxidizing agent and it has a bright ,ur,le color. If a solution containing ,ermanganate is

titrated into an analyte% the ,ur,le color "ill disa,,ear as the ,ermanganate oxidizes the

analyte and is reacted a"ay. /e #no" the reaction is com,lete "hen the ,ur,le color,ersists in the solution. Thus% the ,ermanganate ion is a self-indicator0 that is% it acts as

its o"n indicator.

In this lab% "e "ill use ,otassium ,ermanganate to oxidize the iron II! ion to iron III!.

The reaction must occur in acidic solution to ,re1ent the unstable 2e +3ion from oxidizing"ith the air. Thus% "e "ill add sulfuric acid to the solution before titrating. Also% the

addition of ,hos,horic acid "ill ,re1ent the a,,earance of the yello" color of 2e43ions

"hich "ould other"ise ma#e it difficult to see the ,ermanganate color. 5sing the result

of the titration% "e can determine the moles of 2e in the analyte% con1ert to grams% andfind the ,ercent 2e for the sam,le.

b$ecti1e

The ob$ecti1e of this lab is to find the ,ercent iron in an iron II! com,ound.

'ethodology

(. 'ass out roughly (.66 g of an iron II! com,ound and add it to an 7rlenmeyer flas#.

+. 5se a 1olumetric flas# to ma#e a 6.(66 ' solution of 8'n.

4. Clean a buret and fill it "ith your 8'nsolution.

. Dissol1e the iron com,ound in 96 mL of ( ' :+;.

9. Immediately titrate the 8'ninto the solution. /hen a light yello" color de1elo,s

in the solution% add 4.6 mL of :4Pand continue titrating.

(

8/12/2019 Titration Lab Redox

2/2

Chemistry Lab

Determination of Iron Percentage by Redox Titration

(0 that is% 9 mol of 2e+3react for e1ery ( mol of

'n-. To get the moles of iron% "e need to multi,ly the abo1e result by fi1e. If "e then

multi,ly the moles by the atomic mass of iron% "e can find the mass of iron in that "as in

the sam,le>

m * n'

The ,ercent iron is then found by di1iding the mass of iron by the mass of the original

sam,le and multi,lying by (66. If you ran more than one trial% a1erage the ,ercentageresults. If you #no" the identity of the iron com,ound% com,ute the theoretical 1alue for

the ,ercent of iron and find your relati1e error.

+