Chemistry lab experiment 2 - titration of Potassium permanganate with Oxalic acid

1. Chemistry Lab Experiment 2
Reaction of Potassium Manganate
with Oxalic acid
Mashiat and
Kausar

2. Purpose of experiment
• To carry out oxidation of hydrated Oxalic acid
(Ethanedioic acid) (H2C2O4.xH2O) by Potassium
manganate (VII) (KMnO4) in the presence of
acid by titration.
• To determine the value of x in H2C2O4.xH2O
2MnO4- (aq) + 5H2C2O4 (aq) + 6H+ (aq) 2Mn2+ (aq)
+ 10CO2(g) + 8H2O(l)

3. PROCEDURE

4. Reagents
FA1: 5.00 dm-3 of H2C2O4.xH2O
FA2: 2.37 dm-3 of KMnO4
1.00 moldm-3 H2SO4
40 cm-3 distilled water

5. Apparatus used
Burette
Beaker
Pipette
Bunsen burner
Thermometer
Conical flask
Measuring cylinder

6. Method
1. Burette is filled with purple KMnO4
solution.
2. 25.0 cm3 of H2C2O4.xH2O pipetted
into conical flask.
3. 25 cm3 of 1.00 moldm-3 of H2S04
poured using measuring cylinder.
4. 40 cm3 distilled water added using
measuring cylinder.
5. The flask is heated using Bunsen
burner and temperature observed on
thermometer till a little over 65◦C.
6. Flask placed under burette and
titration carried out.
7. Flask is swirled continuously until
end-point reached.

7. Results & Observation

8. 1) A strong pungent smell was released when the acidified
solution was heated using Bunsen burner.
2) On reaching end-point, the color of the solution turned from
colorless to a permanent pale pink completing the oxidation of
Oxalic acid. Hence, no indicator is required as KMnO4 acts as
an indicator itself.

9. Conclusion
• Volume of FA2 used with 25.0 cm3 of FA1:
27.00 cm3
• Moles of KMnO4 used: 0.0004 mol
• Moles of Oxalic acid reacted: 0.001 mol
• Value of x in C2H2O4.xH2O: 1.95 mol

10. What I learnt
• Potassium permanganate is a strong oxidizing agent.
• Excess dilute H2SO4 is needed, otherwise it forms
brown ppt. of hydrated manganese dioxide,
interfering with obtaining the correct end-point.
• The oxidation reaction is slow in room temperature,
so heating the acidified solution is required to speed
up the rate. Heating also releases carbon dioxide that
helps the reaction to be completed.

11. Safety Precautions

12. • The upper meniscus should be used for burette
readings of colored solutions (KMnO4) as the lower
meniscus isn’t clearly visible.
• Handle flask carefully while heating. Hold the neck
of flask using folded paper towel if it’s too hot to
hold safely.
• Wear gloves while heating and prevent skin contact
with Oxalic acid as it’s corrosive.
• Potassium permanganate decomposes in bright light,
and so cannot be exposed in these conditions for
long.

13. Real-life Applications of Oxalate

14. • Reducing agent for development of photographic
films.
• Bleaching agent for wood and stone. Wood turns
grey when exposed to weather elements. When
Oxalic acid is added to it, the natural color of wood
is retained.
• Removing stains and rust. Oxalic acid is a gentle
stain remover that effectively gets rid of stains
without wearing the base away.
• Wastewater treatment as Oxalic acid can effectively
remove Calcium from wastewater.

15. Critical-thinking question
Why is dilute H2SO4 added in KMnO4 titrations
instead of HCl or HBr and HNO3?

16. Ans: Potassium manganate(VII) can't be used
in titrations in the presence of ions like
chloride or bromide as they consume some
KMnO4 and liberate Cl2 and Br2 , while HNO3
is a stronger oxidizing agent than KMnO4 .