HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

K5Jul. 14,
2020

Purity determination of oxalic acid

Organic acid
1. Abstract

Oxalic acid has two carboxy groups (-COOH) in the molecule, it is called dicarboxylic acid. There are
two crystallization water molecules in the molecule. Oxalic acid is ortho acid and forms the following structure.
It is readily oxidized by the acid stronger than formic acid.

Oxalic acid is used as raw material of organic compound. In addition, sodium salt of oxalic acid is used as
standard substance of quantitative analysis because it quantitatively reacts with oxidizing agent like potassium
permanganate and is stably conservable. The determination method for oxalic acid is prescribed in JIS K8519,
it is determined by potassium permanganate standard solution. This report introduces an example of the purity
determination for oxalic acid using redox titration as described below (formula 1) and neutralization titration
with sodium hydroxide titrant (formula 2).

5{ (COOH)2・2H2O} + 2KMnO4 + 3H2SO4→ 2MnSO4 + 18H2O + 10CO2 + K2SO4(COOH)2・2H2O + 2NaOH→(COONa)2 + 4H2O・・・(1)・・・(2)

2. Configuration of instruments and reagents(1) Redox titration with potassium permanganate(i) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrodes:

Platinum electrodePT-301

Reference electrodeRE-201Z*Instead of the above electrodes, the following electrode is usable.
・Platinum-reference combination electrode PR-701BZ(ii) Reagents
Titrant:

0.02 mol/L Potassium permanganate standard solution

Additive:

Diluted sulfuric acid (1:1, [v/v])

(2) Neutralization titration with sodium hydroxide(i) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrodes:

Glass electrodeGE-101B

Reference electrodeRE-201Z*Instead of the above electrodes, the following electrodes are usable.
・Glass reference combination electrode GR-501BZ…Fixed sleeve type・Glass reference combination electrode GR-511BZ…Moveable sleeve type(ii) Reagent
Titrant:

1 mol/L Sodium hydroxide standard solution

3. Measurement procedure(1) Redox titration with potassium permanganate(i)

Take 0.2 g of sample into a 300 mL beaker and weigh accurately with 0.1 mg digit.

(ii) Add stirring bar and 200 mL of DI water and 20 mL of diluted sulfuric acid.
(iii) Dispense 30 mL of 0.02 mol/L potassium permanganate with stirring solution.
(vi) Heat the beaker at about 60 °C.
(v) Immerse electrodes and start titration with 0.02 mol/L potassium permanganate standard solution.
Perform the blank test in the same procedure without sample and procedure (iii).
(2) Neutralization titration with sodium hydroxide(i)Take 1.0 g of sample into a 100 mL beaker and weigh accurately with 0.1 mg digit.

(ii) Add stirring bar and 50 mL of DI water. Dissolve the sample by stirring.
(iii) Immerse electrodes and start titration with 1 mol/L sodium hydroxide standard solution.

4. Measurement conditions and results(1)Redox titration with potassium permanganate standard solution

Example of titration condition(i) Measurement of blank
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto
12mV
5000100
0.3
20sec
mLsec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKLUnitFormula10 g0 mL
0.02 mol/L
1.003
00mL
DDecimal Places
Auto In Pram.

3Non

Mode No.
Pre Int
Del KDel Sens
Int Time
Int Sens
Brt Speed
Pulse

1800055240Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

2200055240sec
mV
sec
mV(ii) Dispense 0.02 mol/L potassium permanganate standard solution.
Cndt No.
MethodBuret No.
S-Timer
Disp Vol.

2Disp
1530secmL(iii) Measurement of oxalic acid dihydrate
Cndt No.
MethodBuret No.
Amp No.
D. UnitS-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

3Auto12mV
10000.1
500
1.00
20sec
mL
sec
mL
mL
mL

ConstantNo.
3
Size
0.2 gBlank
0.074 mL
Molarity
0.02 mol/L
Factor
1.003
K126.07
L
2.5
Unit%
Formula (D+30-B)*K*F*M*L/(S*10)
Decimal Places
Auto In Pram.

sec
mV
sec
mV

3Non

* Enter the blank value to “B”, the molecular weight of oxalic acid dehydrate to “K”, and the reaction
ratio between oxalic acid dihydrate and potassium permanganate to “L”.

*Some measurement would not be possible depending on optional configuration of system.

Measurement results

Measurement results of blank

Measurement results of sample

Number ofSize

Titrant

Number ofSize

Titrant

PurityMeasurement(g)

Volume (mL)

Measurement(g)

Volume (mL)

(%)

1-

0.073

10.2007

1.779

99.8762-

0.074

20.20171.976

99.9990.074 mL

30.20121.876

99.933

Avg.
(Blank)Statistic
calculation

Measurement of blankAvg.

99.94 %

SD0.0616 %RSD

0.0616 %Measurement of sample

Examples of titration curves*Some measurement would not be possible depending on optional configuration of system.

(2) Neutralization titration with 1 mol/L sodium hydroxide standard solution

Example of titration condition(i) Measurement of oxalic acid dihydrate
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

4Auto
11pH
50001000
0.3
20sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKLUnit
Formula41.000 g0 mL
1.000 mol/L
1.005
126.07
2.0%(D-B)*K*F*M/(S*10*L)

Decimal Places
Auto In Pram.

3Non

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

80505
3240

secmVsecmV* Enter the molecular weight of oxalic acid dihydrate to “K”, and the valence of oxalic acid dihydrate to “L”.

Measurement results

Measurement
NumberSize(g)Titrant
Volume (mL)

Purity(%)

12
31.00671.00241.0001Avg.
SD
RSD

15.87415.82215.77599.94
0.0511
0.051199.89399.99399.925%%%

Statistic
calculation

Example of titration curve*Some measurement would not be possible depending on optional configuration of system.

5. Note(1) Measurement result
The purity of oxalic acid was determined by the following two method: redox titration with potassium
permanganate and neutralization titration with sodium hydroxide. There is no difference between the resultson these methods, the titration was possible without problem in each method. The neutralization titration isparticularly easy because of no pretreatment and the less waste solution.
(2) Collection of sample
The sample is collected directly to the beaker and weighed accurately. The accuracy of sample collection
influences the measurement accuracy. Please note that the sample should be carefully taken and accuratelyweighed.
(3) Control of titrant
The concentrated sodium hydroxide standard solution is used as titrant in this report. The carbon dioxide
gas absorber (soda lime) on reagent bottle has to be regularly exchanged because sodium hydroxide readily
absorbs carbon dioxide gas in the air (formula (3)). The standard solution of sodium hydroxide that hasabsorbed carbon dioxide contains sodium carbonate, and the inflection point on titration curve may beunclear due to buffer capacity of sodium hydrogen carbonate generated in the reaction with an acidic sample(formula (4)).
2NaOH+CO2→

Na2CO3Na2CO3+RCOOH→NaHCO3 ++H2 O・・・(3)

RCOONa・・・(4)Keywords: Oxalic acid, Potassium permanganate, Sodium hydroxide, Redox, Neutralization, JIS K 8519

*Some measurement would not be possible depending on optional configuration of system.