Purity determination of oxalic acid | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. K5 Jul. 14,2020
Organic acid Purity determination of oxalic 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).

2. Configuration of instruments and Reagents

(1) Redox titration with potassium permanganate

(i) Configuration of instruments
  Main unit : Hiranuma Automatic Titrator COM series
  Electrode : Platinum electrode PT-301
Reference electrode RE-201Z
*Instead of the above electrodes, the following electrodes are 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
  Electrode : Glass electrode GE-101B
Reference electrode RE-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) Reagents    
  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

Examples of titration conditions

(i) Measurement of blank

Cndt No 1
Method Auto
Buret No. 1
Amp No. 2
D. Unit mV
S-Timer 5 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 100
Over mL 0.3 mL
Max Vol. 20 mL
Constant No. 1
Size 0 g
Blank 0 mL
Molarity 0.02 mol/L
Factor 1.003
K 0
L 0
Unit mL
Formula D
Decimal Places 3
Auto input Param.
Non
Mode No. 18
Pre Int 0 sec
Del K 0
Del Sens 0 mV
Int Time 5 sec
Int Sens 5 mV
Brt Speed 2
Pulse 40

 

(ii) Dispense 0.02 mol/L potassium permanganate standard solution.

Cndt No 2  
Method Disp  
Buret No. 1  
S-Timer 5 sec
Disp Vol. 30 mL

 

(iii) Measurement of oxalic acid dihydrate
Cndt No 3
Method Auto
Buret No. 1
Amp No. 2
D. Unit mV
S-Timer 10 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0.1 mL
End Sens 500
Over mL 1 mL
Max Vol. 20 mL
Constant No. 3
Size 0.2 g
Blank 0.074 mL
Molarity 0.02 mol/L
Factor 1.003
K 126.07
L 2.5
Unit %
Formula
(D+30-B)*K*F*M*L/(S*10)
Decimal Places 3
Auto input Param.
Non
Mode No. 22
Pre Int 0 sec
Del K 0
Del Sens 0 mV
Int Time 5 sec
Int Sens 5 mV
Brt Speed 2
Pulse 40

* 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”.

Measurement results 

Number of
measurement
Size
(g)
Titrant
volume(mL)
1 0.073
2 0.074
Avg.(Blank) 0.074 mL

Examples of titration curves

Measurement results

Number of
measurement
Size
(g)
Titrant
volume(mL)
Purity (%)
1 0.2007 1.779 99.876
2 0.2017 1.976 99.999
3 0.2012 1.876 99.933
Statistic
calculation
Avg. 99.94 %
SD 0.0616 %
RSD 0.0616 %

Examples of titration curves

 

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

Examples of titration conditions

(i) Measurement of oxalic acid dihydrate

Cndt No 4
Method Auto
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 5 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 1000
Over mL 0.3 mL
Max Vol. 20 mL
Constant No. 4
Size 1 g
Blank 0 mL
Molarity 1 mol/L
Factor 1.005
K 126.07
L 2
Unit %
Formula
(D-B)*K*F*M/(S*10*L)
Decimal Places 3
Auto input Param.
Non
Mode No. 8
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 5 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

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

Measurement results

Number of
measurement
Size
(g)
Titrant
volume(mL)
Purity (%)
1 1.0067 15.874 99.893
2 1.0024 15.822 99.993
3 1.0001 15.775 99.925
Statistic
calculation
Avg. 99.94 %
SD 0.0511 %
RSD 0.0511 %

 

Examples of titration curves

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 results on these methods, the titration was possible without problem in each method. The neutralization titration is particularly 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 accurately weighed.

(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 has absorbed carbon dioxide contains sodium carbonate, and the inflection point on titration curve may be unclear due to buffer capacity of sodium hydrogen carbonate generated in the reaction with an acidic sample (formula (4)).

Keywords: Oxalic acid, Potassium permanganate, Sodium hydroxide, Redox, Neutralization, JIS K8519

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

Hiranuma aquacounter autotitrator com-a19Organic acid

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