3/3 Results: Table 1: Standardization of KMno4 Trial 1 Trial 2 Trial 3 Vol Nazc2

Question

3/3 Results: Table 1: Standardization of KMno4 Trial 1 Trial 2 Trial 3 Vol Nazc204 (mL) O Initial Buret (mL) 31. Final Buret (mL) us.5 Moles C2042 (mol) *remember the concentration Moles KMno4 (mol) Molarity KMno4 (M) Average Molarity (M) Standard Deviation (M) RSD Table 2: Determination of Iron (II) Percentage Trial 3 Trial 2 Trial e 40 L 2 1.3s 12 Mass of Fe salt (g) Initial Buret (mL) IO. (o t 33. Final Buret (ml) 44, Vol KMno4 ml) 33 01. 33.4 Moles KMno4 Moles Fe(II) Mass of Fe in sample Fe in Sample Average Standard Deviation RSD

Explanation / Answer

Potassium permanganate is a strong oxidising agent in acidic, alkaline and neutral medium.

in acidic medium: MnO4- + 8H+ + 5e- === Mn2+ + 4H2O

in alkaline/neutral medium: MnO4- + 2H2O + 3e- === MnO2 + 4OH-

KMnO4 is standardise using suitable primary standard such as sodium oxalate or oxalic acid or Mohr's salt, which asre solids and can be weighed accurately. KMnO4 is standardise in acidic medium using dil. H2SO4 and by titrating against standard solution of sodium oxalate. the process involves:

Oxdn half: [ MnO4- + 8H+ + 5e- === Mn2+ + 4H2O ] X 2

Redn half: [ C2O4-2 - 2e- === 2CO2 ] X 5

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2MnO4- + 16H+ + 5C2O4-2 === 2Mn2+ + 8H2O + 10CO2

pink colourless

Standardization of KMnO4 : Trial 1

volume of dilute sodium oxalate taken = V1 cc = 10 cc

strength of sodium oxalate solution = S1 = 0.05 M

volume of KMnO4 solution consumed = V2 cc (from burette reading) = 17.25 cc

strength of KMnO4 = S2 = ?

we know V1 X S1 = V2 X S2

or S2 = (V1 X S1)/V2 = (10 X 0.05)/17.25 = 0.03 M

strength of sodium oxalate solution = 0.05 M

So moles of C2O4-2 in 10 cc = 0.0005

strength of KMnO4 solution = 0.03 M

so 1000 ml contains 0.03 moles

17.25 ml contains = (0.03 X 17.25)/1000 = 0.0005

Determination Ferrous ion

reaction involved

oxdn half: [ Fe+2 - e- ==== Fe+3] X 5

red half:   [ MnO4- + 8H+ + 5e- === Mn2+ + 4H2O ]

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MnO4- + 8H+ + 5Fe+2 === Mn2+ + 5Fe+3 + 4H2O

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