12. Spectrometric determination of the volumetric part of ethanol (%) in wine

BACKGROUND

The objective of the experiment is to determine the volumetric part of ethanol in wine.


EQUIPMENT

  • Automatic pipettes 20-200ml,
  • Blisters,
  • SpektraTM Spectrometer ,
  • Conical-shoulder bottle 50ml,
  • Apparatus for distillation,
  • Volumetric flask 50ml, 100ml,
  • Measuring pipette 10ml, 20ml.

 

 

REAGENTS

  • 0,25M K2Cr2O7,
  • 2,25M H2SO4,
  • 96% ethanol.

The preparation of reagents:

  • 0,25M K2Cr2O7: 3.675 g of K2Cr2O7 is weighed and quantitatively transferred into a 50ml volumetric flask, dissolved with deionised water and filled with it to the mark .
  • 2,25M H2SO4: 6 ml H2SO4 (r=1,816 g/ml) is diluted with deionised water in a 50ml volumetric flask.
  • Ethanol: 20ml of 96% ethanol is diluted with deionised water in a 100ml volumetric flask.

HAZARDS








Potassium dichromate is very toxic and dangerous to the environment. It is harmful in contact with skin and may cause sensitization by skin contact. It is toxic if swallowed. Wear protective gloves and goggles and avoid releasing it into the environment.
R: 49-46-21-25-26-37/38-41-43-50/53 S: 53-45-60-61

Potassium dichromate can cause cancer, genetic damages, it harms fertility, strengthens fire, it is fatal at inhalation, toxic at consumption, it causes bad injuries of eyes and skin, it can cause problems with breathing at inhalation, and allergic responses of skin. It is very poisonous for water organisms, with long-term effects. It must be used with protective gloves and glasses.
H: 350, 340, 360FD, 272, 330, 301, 312, 372, 314, 334, 317, 410
P: 201, 280, 301+330+331, 305+351+338, 304+341, 308+313



Sulphuric acid is corrosive and it causes severe burns. Wear suitable protective clothing, gloves and eye protection.
R: 35 S: 26-30-36/37/39-45

Sulphuric acid causes severe burns of skin and eye injuries. Use gloves, protective clothing and protection for eyes/face.
H: 314, 290, P: 280,301+330+331, 309, 310, 305+351+338

Ethanol is highly flammable. Its inhalation may cause coughing, headache, fatigue and drowsiness. It causes dry skin and redness of the eyes. Wear protective gloves and goggles.
R: 11 S: (2-)7-16

Ethanol is easily flammable fluid. It must be kept away from the heat and open fire.
H: 225, P: 210


PROCEDURE

Sample preparation:
100ml of wine (white or red) is measured with a 100ml volumetric flask into an apparatus for distillation. The volumetric flask is rinsed with deionised water which is poured into a distillation flask; 2-3 boiling stones are added and the distillation can start. Approximately 5ml of deionised water is poured into the 100ml volumetric flask, which is placed under the outflow of apparatus for distillation. The distillation is finished when 4/5 of primary sample volume goes from the distillation flask to the volumetric flask. The volumetric flask is filled with deionised water to the mark and stirred well.

Measurement:
The solutions of potassium dichromate (0.25 mol/L), sulphuric acid (2.25 mol/L), ethanol (19,20%), as well as deionised water and the sample are needed for the experiment. The procedure for the blank and for the sample is summarised in the table below. The reagent and acid are pipetted into the hollow of a blister. This is followed by the addition of deionised water and ethanol or sample. Immediately after the preparation, the transmittance is measured against the blank using the green LED. 

Table 1: Procedure of preparation

 

VK2Cr2O7 mL

VH2SO4 mL

VH2O
mL

Vethanol mL

Vdistillate of wine
mL

vol%
ethanol

T %

T

A

Calibr.sol.1

180

110

100

0

0

0

 

 

 

Calibr.sol.2

180

110

80

20

0

3,84

 

 

 

Calibr.sol.3

180

110

60

40

0

7,68

 

 

 

Calibr.sol.4

180

110

40

60

0

11,52

 

 

 

Calibr.sol.5

180

110

20

80

0

15,36

 

 

 

Calibr.sol.6

180

110

0

100

0

19,20

 

 

 

Sample

180

110

0

0

100

 

 

 

 

 


RESULTS OF THE EXPERIMENT

The calibration line is a function of the absorbance versus the volumetric part of ethanol (%) in wine. The volumetric part of ethanol in the sample can then be deduced.

Table 2: The results

 

VK2Cr2O7 mL

VH2SO4 mL

VH2O
mL

Vethanol mL

Vdistillate of wine
mL

vol%
ethanol

T %

T

A

Calibr.sol.1

180

110

100

0

0

0

100

1

0

Calibr.sol.2

180

110

80

20

0

3,84

99,0

0,99

0,004365

Calibr.sol.3

180

110

60

40

0

7,68

96,9

0,969

0,013676

Calibr.sol.4

180

110

40

60

0

11,52

94,7

0,947

0,02365

Calibr.sol.5

180

110

20

80

0

15,36

90,3

0,903

0,044312

Calibr.sol.6

180

110

0

100

0

19,20

88,2

0,882

0,054531

Sample

180

110

0

0

100

 

94,1

0,941

0,02641

Chart 1: The absorbance versus the volumetric part of ethanol (%).


CALCULATION

Asample = 0,02641
Volumetric part of ethanol (%) = 11,06......... from the calibration line

y = 0,0034x-0,0112
x = (y+0,0112)/0,0034 = (0,02641+0,0112)/0,0034
x = 11,06%
In our wine sample was 11,06 volumetric part of ethanol (%).

 

Developed and prepared by: mag. Marjana Dvoršek, Tadeja Polajnar, Kristina Frlic, Biotechnical Centre Naklo