Chapter IV: DEVELOPMENT OF HAND-MADE CONDUCTIVITY
IV. APPLICATION OF HAND-MADE APPARATUS IN MEASUREMENT
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IV. APPLICATION OF HAND-MADE APPARATUS IN MEASUREMENT
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Table 4-2: Conductivities by handmade apparatus and by commercial Shimadzu portable Kohlrausch bridge BF-62A
Electrolyte solutions
Conductivity /S cm-1 Handmade conductivity
apparatus
Shimadzu portable Kohlrausch bridge BF-62A
0.010 M NaCl(aq) 0.0014 0.00130
0.012 M NaCl(aq) 0.0016 0.00150
0.014 M NaCl(aq) 0.0019 0.00170
0.006 M CuCl2(aq) 0.0015 0.00148
0.008 M CuCl2(aq) 0.0021 0.00192
0.010 M CuCl2(aq) 0.0027 0.00242
0.006 M AlCl3(aq) 0.0021 0.00219
0.008 M AlCl3(aq) 0.0029 0.00283
0.010 M AlCl3(aq) 0.0033 0.00344
Fig. 4-5. Electrical conductivity of NaCl(aq), CuCl2(aq), and AlCl3(aq)
0
NaCl(aq)
0
CuCl
2(aq)
0
AlCl
3(aq)
0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 0.0040
0 5 10 15
Cond uct ivit y (Scm
-1)
Electrolyte concentration (mM)
Linear (Handmade Conductivity meter) Linear (Portable Conductivity meter)
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2. Measurement of Conductivity of vegetables, fruit juice solution and dinks
The conductivity of several common vegetables, fruit juices and sports drink (Japanese products) was measured. Carrot, radish, cabbage, apple, orange, Pocari Sweat (sports drink), tea, coffee (Suntory Boss brand), tap water and river water were used for measuring their electrical conductivities.
<Preparing the vegetables and fruit juice solutions>
For drinks and river water, measurements were conducted directly from the original container and source. In preparing solutions that were from vegetables and fruits, for example apple, the solution was prepared as follow:
1. An apple was sliced and then 20 g of sliced apple was ground by using a mortar and pestle.
2. 20 mL of water was added to the ground apple in the mortar.
3. The apple in the mortar was continuously ground and stirred for one minute.
4. After stirring, the ground apple solution was filtered and kept for measuring its resistance.
The same procedure was applied for other vegetables and fruits.
In this research, the measurements were conducted at different times with the different electrode cell, so from time to time before starting new measurements the cell constant was determined again. After some improvements of the handmade conductivity meter, a solution of KCl(aq) at 10 mM could be used for determining the cell constant with a new electrode cell.
<Determine the cell constant>
This time, the standard solution of 10 mM of KCl(aq) was used to determine the cell constant. In this case, Rlow and Rhigh were 65 Ω and 115 Ω respectively given by the
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handmade conductivity measurement apparatus. Thus, R1 as the midpoint between the two resistances was determined as 90 Ω. Hence, RX was calculated to 4.5x102 Ω. The conductivity of 10 mM KCl(aq) is known as 0.0014114 S cm−1 (a standard solution). Therefore, the new cell constant was found to be 0.64 cm−1 by using Equation (8).
Even though the value of cell constant was different from the previous one, the results of electrical conductivities were almost the same as previously. With this change of cell constant value, the measurements of electrical conductivities of NaCl(aq) with different concentration were once again conducted in order to check and verify before measuring vegetables and fruit juices. The results of this verification are shown in Table 4-3 and Table 4-4 below.
Table 4-3. Verification of the cell constant value with NaCl(aq) standards Electrolyte
solutions
Rlow
(Ω)
Rhigh
(Ω)
R1: midpoint between Rlow and
Rhigh,(Ω)
RX = 5 R1
(Ω)
Conductivity
/S cm-1
0.010 M NaCl(aq) 70 116 93 4.6x102 0.0014
0.012 M NaCl(aq) 65 95 80 4.0x102 0.0016
0.014 M NaCl(aq) 62 80 71 3.6x102 0.0018
Table 4-4. Conductivities by handmade apparatus and by commercial apparatus Shimadzu portable Kohlrausch bridge BF-62A
Electrolyte solutions
Conductivity /S cm-1 Handmade conductivity
meter
Shimadzu portable Kohlrausch bridge BF-62A
0.010 M NaCl(aq) 0.0014 0.00132
0.012 M NaCl(aq) 0.0016 0.00153
0.014 M NaCl(aq) 0.0018 0.00172
After the sample solutions of vegetables and fruits were prepared, their resistances were measured by the same procedure as the conductivity of electrolyte solutions. The measurements started from the apple sample solution. The results of measurements are shown in Table 4-5 and Table 4-6 below.
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Table 4-5. Results of electrical conductivities of vegetables and fruits Sample
Rlow (Ω)
Rhigh (Ω)
R1: midpoint between Rlow and
Rhigh,(Ω)
RX = 5 R1
(Ω)
Conductivity
/S cm-1
Carrot 20 48 34 1.7x102 0.0038
Radish 25 80 53 2.7x102 0.0024
Cabbage 30 80 55 2.8x102 0.0023
Orange 50 136 93 4.6x102 0.0014
Apple 86 170 128 6.4x102 0.0010
Pocari Sweat 50 76 63 3.1x102 0.0020
Coffee* 45 63 54 2.7x102 0.0046
Tea ** ** ** ** **
River water ** ** ** ** **
Tap water ** ** ** ** **
* Measured with the cell constant value of 1.24 cm-1
** Resistances of these samples were too large for the handmade apparatus to measure.
Table 4-6: Electrical conductivities of vegetables and fruits solution by handmade apparatus compared with commercial apparatus
Electrolyte solutions
Conductivity /S cm-1 Handmade conductivity
meter
Shimadzu portable Kohlrausch bridge BF-62A
Carrot 0.0038 0.00368
Radish 0.0024 0.00243
Cabbage 0.0023 0.00227
Orange 0.0014 0.00136
Apple 0.0010 0.000971
Pocari Sweat 0.0020 0.00196
Coffee 0.0046 0.00425
Tea* * 0.00059
River water ** **
Tap water ** **
98 Note:
* Shimadzu portable Kohlrausch bridge BF-62A could measure, but handmade apparatus could not measure,
** Resistances of the samples were too large for either the Shimadzu portable Kohlrausch bridge BF-62A or handmade apparatus to measure.
3. Confirmation by Titration of vegetables and fruits
To verify the amount of electrolyte in vegetables and fruits whose electrical conductivity was measured, a titration was also carried out. In each titration we used the same mass (20 g) of sample as used when measuring its electrical conductivity.
In preparing ash solution from vegetables and fruits, for instance apple, first 20 g of fresh apple was burnt until it became ash. 50 mL of water was added to the ash in a beaker and then stirred and filtered to get an ash solution. The results from the titrations were converted to the total contents of alkali in 1 g of the fresh vegetable and fruit (Table 4-7).
Then, they were plotted versus to their conductivities as shown in Fig. 4-5. The results show that the conductivity of each fruit solution was consistent with its total contents shown by the titration. This means the hand-made conductivity can be used to examine the conductivity of the fruit solutions and assume to their total dissolved contents.
Table 4-7. The results of the titration Ash solution Volume of 10 mM
HCl(aq) used to reach equivalent point (mL)
Concentration of total alkalis, Cb/mM
Total alkali content in 1 g of vegetable or fruit
/mol.g1
Carrot 22.4 11.2 2.80x105
Radish 10.5 5.25 1.31x105
Cabbage 8.0 4.0 1.00x105
Orange 6.2 3.1 0.78x105
Apple 5.7 2.9 0.73x105
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Fig. 4-6. Alkali contents in vegetable and fruit versus the conductivities
Based on the correlations shown in Fig. 4-6, it can be assumed that the total contents in the sport drink like Pocari Sweat is about less than 1.0x105 mol/g. This is even below Cabbage juice, Radish juice and Carrot juice, due to its conductivity is only 0.0020 S.cm1.