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 VOLUME Vol.05 Issue02 2025 

PAGE NO. 29-33 

DOI 10.37547/ajbspi/Volume05Issue02-08 

 
 
 
 

Electrometric determination of cu (ii) cations, Zn (ii) and 

Cr (iii) in aqueous, water-non-aqueous and mixed 

solutions 
 

Narbek Sapaevich Palvanov 

Candidate of Chemical Sciences, Associate Professor, Department of Medicinal and Biological Chemistry, Urgench branch of Tashkent 

Medical Academy, Urgench, Uzbekistan 

 

Adolat Farkhadovna Tillayeva 

Assistant, Department of Medicinal and Biological Chemistry, Urgench branch of Tashkent Medical Academy, Urgench, Uzbekistan 

 

 

Received: 23 December 2024; Accepted: 25 January 2025; Published: 27 February 2025 

 

Abstract: This work presents the results of the potentiometric determination of aqueous, non-aqueous and mixed 
solvents of copper (II), zinc (II) and chromium (III) cations: (propanol-2, acetone, methyl ethyl ketone, toluene, 
carbon tetrachloride, dimethylformamide) and their mixtures with water in a ratio of 1:1 and 1:19 by volume, the 
ratios of acid-base titrations are given. The quantitative results of the titration on a per kilote basis for the 
indicated cations Cu2+, Zn2+ and Cr3+ are based on the acidity constants of these cations assessed in the solvent 
environment specified above. The influence of the physical and chemical properties of solvents on acid-base 
titrations was studied. Due to the increase in the proportion of non-aqueous solvent in the solution, the dielectric 
constant of the solution decreases, and this leads to an increase in the ability to quantify acid-base titrations. 

 

Keywords: Potentiometry, metal cations, copper, zinc, chromium, dielectric constant, acidity constant. 

 

Introduction: It is known that heavy metal cations in 
solutions have their own acidic properties. Therefore, 
they are also called aprotic acids or Lewis acids. The 
acidic properties of metal ions depend on their position 
in the periodic table, on the ionic charge and on the 
number of anions associated with the cation. The 
cations Cu2+, Zn2+ and Cr3+ are aprotic acids, which do 
not retain protons, and have wetting acidic properties 
of varying strength in solutions depending on their ionic 
charge. According to the literature, there are few works 
on their titrimetric acid-base determination. Given 
their acidic properties, ions can be titrated as acids in a 
mixed aqueous-non-aqueous solution. Because of this, 
we carried out their titrimetric analysis in non-aqueous 
solvents mixed with water. It was of interest to 
determine the content of aprotic acids, which play an 
important role in the life of living organisms. To develop 
methods for the analysis of these aprotic acids, model 
solutions of the substances under study were taken and 
titrated based on acid-base reactions. As shown above, 

aprotic acids exhibit acidic properties of varying 
strength. Of the above aprotic acids, copper and zinc 
are dibasic acids, and chromium is a tribasic acid. 
Taking into account the acidity of various solutions of 
aprotic acids, methods of their acid-base 
potentiometric titration can be recommended. In 
aqueous solution they are mainly titrated according to 
the second acidity constant. The addition of non-
aqueous water-miscible solvents to water improves the 
conditions for titration of aprotic acids. In this case, it 
can be ensured that they can be titrated against all 
acidity constants. 

METHODS 

The chosen objects were chlorides and sulfates of 
aprotic acids of copper (II), zinc (II) and chromium (III). 
Thus, ethanol, 2-propanol, acetone, methyl ethyl 
ketone, toluene, carbon tetrachloride, 
dimethylformamide and their mixtures with water 
were used as solvents. 

 

https://doi.org/10.37547/ajbspi/Volume05Issue02-08
https://doi.org/10.37547/ajbspi/Volume05Issue02-08
https://doi.org/10.37547/ajbspi/Volume05Issue02-08
https://doi.org/10.37547/ajbspi/Volume05Issue02-08


American Journal of Applied Science and Technology 30 https://theusajournals.com/index.php/ajast 

American Journal of Applied Science and Technology (ISSN: 2771-2745) 
 

 

During titration, solutions of potassium ethoxide and 
potassium propylites in ethanol and 1-propanol, as well 
as solutions of potassium acetate in suitable solvent 
media, were used as titrants. As a research method, we 
used potentiometric titration from electrochemical 
analysis methods. To estimate pKa values, the 
Henderson method was used, based on potentiometric 
titration with glass hydrogen-selective and silver-silver 
chloride electrodes. The essence of the method is that, 
under the same conditions, two acids are titrated with 
a strong alkali solution: one of them serves as a 
standard, and the second as the acid being studied. For 
a standard acid, the acidity constant in a given solvent 
must be known. Based on the results of potentiometric 
titration, titration curves are constructed and from 
these curves the values of half-titration potentials are 
determined and the values of acidity constants are 
calculated using the formula: 

  1/2 1/2

x o

x o

E E
pK pK



−
=   (1) 

Which is:  xpK  – indicator of the acidity constant of 

the acid under study;  opK  – indicator of the acidity 

constant of the acid standard; 
x

2/1E  – half-titration 

potential of the acid under study, мВ; 
o

2/1E – half-

titration potential of acid standard, мВ;  𝜃=58 

(above 200С) мВ or  𝜃=59 (above 250С) мВ. 
Benzoic acid was used as the standard acid. A 
hydrogen-selective electrode was used as an indicator 
electrode, which was adjusted according to the method 
attached to the pH meter using two buffer solutions (in 
an aqueous solution). The reference electrode was a 
silver chloride electrode filled with a saturated aqueous 
solution of doubly recrystallized potassium chloride. 

RESULTS 

Table 1 shows the results of the determination of 

chromium (III) 3CrCl  in the form and  342 )SO(Cr

not only in alcohols, but also in ketones, DMP, toluene 
and carbon tetrachloride. As can be seen from the data 
in Table 1, by decreasing the amount of acids in the test 
solution, the relative standard deviation increases 
slightly. For chromium (III), the relative standard 
deviation of the determination also depends on both 
the amount of the substance and the composition of 
the solvent and the dielectric constant of the medium. 
Thus, when titrating small amounts of chromium (III), it 
is higher. 

 

Table 1. Results of potentiometric determination of chromium (III) in solvents with different 

dielectric constants 

(n=5, xx  , P=0,95) 

Aprotic 

acid 
Solute  

Introduced, 

mg 
Found, mg s  rs  

3CrCl  

Water 78,3 8,64 8,66±0,05 0,04 0,005 

Ethanol-water (1:1) 51,3 6,94 6,71±0,02 0,02 0,003 

Ethanol 24,3 6,48 6,61±0,04 0,03 0,005 

Propanol-2 18,3 10,26 10,07±0,05 0,04 0,004 

Acetone-water (1:1) 49,6 5,41 5,40±0,05 0,04 0,007 

Acetone 20,9 6,48 6,76±0,10 0,08 0,012 

МEK- water (1:1) 48,3 5,67 5,74±0,07 0,06 0,010 

МEK 18,4 8,64 8,62±0,07 0,06 0,007 

DMPA- water (1:1) 57,5 5,67 5,72±0,11 0,09 0,015 

DMPA 36,7 6,21 6,50±0,10 0,08 0,012 

Acetone -toluene (1:1) 11,7 5,67 5,56±0,11 0,09 0,017 

Acetone -CCl4 (1:1) 11,6 5,67 5,68±0,12 0,10 0,018 



American Journal of Applied Science and Technology 31 https://theusajournals.com/index.php/ajast 

American Journal of Applied Science and Technology (ISSN: 2771-2745) 
 

 

342 )SO(Cr  

water 78,3 11,92 12,04±0,09 0,07 0,006 

Ethanol - water (1:1) 51,3 5,67 5,77±0,12 0,10 0,018 

Ethanol 24,3 9,22 9,18±0,11 0,09 0,010 

Propanol-2 18,3 6,94 6,96±0,12 0,10 0,015 

Acetone - water (1:1) 49,6 6,59 6,58±0,14 0,11 0,017 

Acetone 20,9 4,77 4,64±0,07 0,06 0,014 

МEK- water (1:1) 48,3 4,96 4,80±0,12 0,10 0,022 

МEK 18,4 6,59 6,68±0,11 0,09 0,014 

DMPA- water (1:1) 57,5 6,47 6,58±0,16 0,13 0,019 

DMPA 36,7 5,46 5,58±0,11 0,09 0,016 

Acetone -toluene (1:1) 11,7 4,46 4,34±0,20 0,16 0,037 

Acetone -CCl4 (1:1) 11,6 4,96 4,80±0,12 0,10 0,022 

As the data in Table 1 show, the relative standard 
deviation of the determination decreases with an 
increase in the proportion of non-aqueous solvent and 
a decrease in the dielectric constant of the medium. 
The exception is mixtures of acetone with toluene and 
carbon tetrachloride. In these solvents, although the 
dielectric constant is lower, the relative standard 
deviation is higher. It follows that the accuracy of the 
determination is influenced not only by the nature of 
the conjugate base (anion) of the acid being 
determined and the physical properties of the solvent, 

but also by its chemical nature. The accuracy of the 
determination of chromium (III) ions also depends on 
the conjugate base. Since chloride ions are a weaker 
base than sulfates, the accuracy of the determination 
of chromium chlorides is higher than the accuracy of 
the determination of sulfates. The same pattern 
persists when titrating zinc ions in mixed solvents. 
Table 2 shows the results of the determination of zinc 
chloride and sulfate in various solvents. 

 

Table 2. Results of potentiometric determination of various in 
+2Zn solvents with different 

dielectric constants 

(n=5, xx  , P=0,95) 

Aprotic 

acid 
Solute  

Introduced, 

mg 
Found, мг s  rs  

2ZnCl  

Water 78,3 15,26 15,24±0,10 0,08 0,005 

Ethanol-water (1:1) 51,3 12,58 12,60±0,16 0,13 0,010 

Ethanol 24,3 16,78 16,88±0,07 0,06 0,004 

Propanol -2 18,3 15,26 15,52±0,12 0,10 0,007 

Acetone-water (1:1) 49,6 10,18 10,47±0,11 0,09 0,008 

Acetone 20,9 13,24 13,09±0,04 0,03 0,002 

МEK-water (1:1) 48,3 13,24 13,66±0,07 0,06 0,005 

МEK 18,4 15,26 15,02±0,12 0,10 0,007 

DMPA-water (1:1) 57,5 12,22 11,85±0,12 0,10 0,009 

DMPA 36,7 13,24 13,53±0,12 0,10 0,007 

Acetone -CCl4 (1:1) 11,6 10,18 10,17±0,16 0,13 0,013 

Acetone - toluene (1:1) 11,7 13,24 13,52±0,16 0,13 0,009 



American Journal of Applied Science and Technology 32 https://theusajournals.com/index.php/ajast 

American Journal of Applied Science and Technology (ISSN: 2771-2745) 
 

 

4ZnSO  

Water 78,3 15,20 15,18±0,07 0,06 0,004 

Ethanol-water (1:1) 51,3 16,72 16,97±0,27 0,22 0,013 

Ethanol 24,3 16,72 16,91±0,17 0,14 0,008 

Propanol -2 18,3 10,14 10,86±0,22 0,18 0,017 

Acetone-water (1:1) 49,6 13,56 13,70±0,30 0,24 0,018 

Acetone 20,9 12,16 12,60±0,16 0,13 0,010 

МEK- water (1:1) 48,3 14,19 14,70±0,31 0,25 0,017 

МEK 18,4 15,20 15,30±0,39 0,31 0,020 

DMPA- water(1:1) 57,5 15,20 14,99±0,12 0,10 0,007 

DMPA 36,7 18,31 18,45±0,57 0,46 0,025 

Acetone -CCl4(1:1) 11,6 10,14 10,47±0,16 0,13 0,012 

Acetone -toluene (1:1) 11,7 12,16 11,95±0,16 0,13 0,011 

In order to more deeply study the role of the anion on 
the accuracy of the determination of aprotic acids, 
titration was also carried out with copper (II) not only 

chlorides and sulfates, but also acetates, which are 
stronger bases than sulfates and especially chlorides. 

 

 

Table 3. Results of potentiometric determination of chlorides, sulfates and acetates of copper (II) in 

solvents of various natures  

(n=4, xx  , P=0,95) 

Aprotic acid Solute  
Introduced, 

mg 
Found, mg s  

rs  

Water 78,3 

4CuSO  2,46 2,47±0,03 0,02 0,010 

2CuCl  2,54 2,51±0,03 0,02 0,007 

23 )COOCH(Cu  3,18 3,20±0,08 0,05 0,016 

Ethanol-water 

(19:1) 
27,0 

4CuSO  2,72 2,73±0,03 0,02 0,007 

2CuCl  2,60 2,55±0,02 0,01 0,005 

23 )COOCH(Cu  3,10 3,10±0,05 0,03 0,010 

Propanol -2-

water (19:1) 
21,3 

4CuSO  3,62 3,57±0,03 0,02 0,007 

2CuCl  2,65 2,60±0,02 0,01 0,005 

23 )COOCH(Cu  3,41 3,55±0,13 0,08 0,023 

Propanol -1-

water (19:1) 
23,0 

4CuSO  3,22 3,10±0,03 0,02 0,008 

2CuCl  2,65 2,70±0,03 0,02 0,007 

23 )COOCH(Cu  3,41 3,41±0,06 0,04 0,011 

DMPA- water 

(19:1) 
38,8 

4CuSO  3,22 3,24±0,03 0,02 0,008 

2CuCl  3,20 3,25±0,03 0,02 0,008 



American Journal of Applied Science and Technology 33 https://theusajournals.com/index.php/ajast 

American Journal of Applied Science and Technology (ISSN: 2771-2745) 
 

 

23 )COOCH(Cu  3,10 3,15±0,06 0,04 0,012 

DMPA- water 

(1:1) 
57,5 

2CuCl  2,65 2,68±0,05 0,03 0,012 

23 )COOCH(Cu  3,10 3,06±0,06 0,04 0,014 

The results of titration of chlorides, sulfates and 
acetates of copper (II) in various solvents are given in  

Table 3. Both anhydrous chlorides and acetate crystal 
hydrates were taken for analysis. 

As can be seen from the data in table. 3, the accuracy 
of the determination of copper aprotic acids depends 
on the strength of the conjugate base. At similar 
amounts of chlorides, sulfates, and acetates, the 
relative standard deviation increases with increasing 
basicity of the anion. 

The exception is mixtures of acetone with toluene and 
carbon tetrachloride. In these solvents, although the 
dielectric constant is lower, the relative standard 
deviation is higher. It follows that the accuracy of the 
determination is influenced not only by the nature of 
the conjugate base (anion) of the acid being 
determined and the physical properties of the solvent, 
but also by its chemical nature. Based on the developed 
analysis methods, the content of harmful heavy metal 
ions in various food products (meat, liver, spleen, milk, 
feta cheese, etc.) and other environmental objects was 
determined. 

CONCLUSIONS 

1. The possibility of potentiometric acid-base 
determination of the above metals in water, aqueous-
non-aqueous and mixed solutions was studied. 

2. The data obtained from potentiometric acid-base 
titration of aqueous aqueous-non-aqueous and mixed 
solutions of aprotic acids can be concluded that the 
studied acids are well titrated with solutions of 
hydroxide, ethylate, propylate, isopropylate and  

potassium acetate with a properly selected solvent. A 
decrease in the dielectric constant and autoprotolysis 
constant of the solvent improves the conditions for 
potentiometric titration, which is expressed in an 
increase in the potential jump on the titration curves. 

3. It has been established that the conditions for acid-
base potentiometric titration improve with an increase 
in the proportion of non-aqueous solvent, when the 
dielectric constant of the medium decreases. 

4. The developed methods of acid-base titrimetric 
analysis have been applied to the analysis of metal 
cations in various natural objects, such as meat, dairy 
products, water, soil and plants. 

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