[cuongt]

THe iron content in a 0.200g sample of fencing wire was determined by dissolving the wire in dilute sulfuric acid and making up the resulting pale green solution Fe2+ ions to 25mL. THe solution was titrated with 0.0300molL KMnO4, which is purple in colour. A titre value of 20.22mL was obtained. THe solution of Mn2+ and Fe3+ ions produced by the reaction was almost colourless.

1. write an overall equation for the titration reaction.
MnO4^1- + Fe^2+ + 8H^1+ +4e-  ----> Mn^2+ + Fe^3+ +4H2O

2. Calculate, mol, the Fe^2+ ions in the 25.00 mL volume of soln.
n=cV
  =0.03*0.025
  =7.5*10^-4

3. Calculate the percentage by mass of iron in wire
m=nM
   =7.5*10^-4*55.85
   =0.0419g

%=0.0419/0.2   *100
   =20.94%

4. an indicator was not rquired in this titration. why not?
an indicator was not required because the KMnO4 was acting as the indicator purple to colourless.

can check these please i have a feeling they are wrong.

thanks  

[AWK]

THe iron content in a 0.200g sample of fencing wire was determined by dissolving the wire in dilute sulfuric acid and making up the resulting pale green solution Fe2+ ions to 25mL. THe solution was titrated with 0.0300molL KMnO4, which is purple in colour. A titre value of 20.22mL was obtained. THe solution of Mn2+ and Fe3+ ions produced by the reaction was almost colourless.

1. write an overall equation for the titration reaction.
MnO4^1- + Fe^2+ + 8H^1+ +4e-  ----> Mn^2+ + Fe^3+ +4H2O

2. Calculate, mol, the Fe^2+ ions in the 25.00 mL volume of soln.
n=cV
  =0.03*0.025
  =7.5*10^-4

3. Calculate the percentage by mass of iron in wire
m=nM
   =7.5*10^-4*55.85
   =0.0419g

%=0.0419/0.2   *100
   =20.94%

4. an indicator was not rquired in this titration. why not?
an indicator was not required because the KMnO4 was acting as the indicator purple to colourless.

can check these please i have a feeling they are wrong.

thanks  

MnO4^1- + 5Fe^2+ + 8H^1+  ----> Mn^2+ + 5Fe^3+ +4H2O

n=cV= 0.03 x 0.02022 x 5
an so on

[cuongt]

where did the 5 come from and dont u times it by 0.025 y 0.022?

[xiankai]

the 5 is obtained from the balancing of the rxn btw Fe2+ and MnO4-

the 0.02022 is because we're calculating the no. of moles, concentration and volume of KMnO4.

so do not add the values for Fe2+, because it just wouldnt make sense.

[cuongt]

MnO4^1- + 5Fe^2+ + 8H^1+  ----> Mn^2+ + 5Fe^3+ +4H2O

y is the 5 needed in awk equation the 5 is not needed right? the equation is already balanced.

[xiankai]

charge balancing, m'dear  

[cuongt]

i c. but cant u put electrons in the equations to balance out the charge.
wouldnt it be easier?

[xiankai]

but that would be an incomplete equation, because electrons do not really exist freely in nature, and hence are quickly attracted to something. what is the product which that electron makes negative?

also, bear in mind this is a redox reaction - electrons are being transferred; not liberated or consumed.  

[cuongt]

so smart...  

can u check my other questions( question 4)

[xiankai]

u have it right