The relationship between an ionic solution like salt water and its conductivity is a function of its concentration and the ability of its charged particles to move freely in the solution. Solutions that contain dissolved salts conduct electricity because they release charged. The more concentrated a solution is, the higher the conductivity is. In most cases it is a proportional relationship. As the ion concentration. Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to . The conductivity of a solution of a strong electrolyte at low concentration follows Kohlrausch's Law . In this case there is no limit of dilution below which the relationship between conductivity and concentration becomes linear.
Sciencing Video Vault Concentration of a Substance In basic terms, concentration simply refers to the amount of substance dissolved in a given amount of water.
Scientists use various units for specifying concentration, such as molarity, normality, mass percent and parts per million. The exact unit of concentration runs secondary, however, to the general principle that higher concentration means a larger quantity of dissolved salt per unit volume.
Electrical Conductivity Many people are surprised to learn that pure water is actually a poor conductor of electricity. Good conductors allow for the easy, sustained flow of electric current. In general, a good conductor possesses charged particles that are relatively mobile free to move. In the case of salts dissolved in water, the ions represent charged particles with relatively high mobility.
Conductivity and Concentration The conductivity of a solution depends on the number of charge carriers the concentrations of the ionsthe mobility of the charge carriers and their charge.
Theoretically, conductivity should increase in direct proportion to concentration. This implies that if the concentration of sodium chloride, for example, in a solution doubled, the conductivity should also double. In practice, this does not hold true. The concentration and mobility of the ions are not independent properties.
As the concentration of an ion increases, its mobility decreases.
A set amount of mass of salt is first measured using an electronic balance and used to create a mL solution in a volumetric flask. This would act as the standard solution with the concentration calculated using the formula: A second solution of the same composition but different concentration can then be obtained using dilution.
A fixed amount of the standard solution is extracted using a pipette; for higher accuracy and added to a new and clean volumetric flask before filling up the flask with distilled water to form a new diluted solution of volume mL. The theory used in dilution is that the number of moles in the extracted volume of the standard solution is the same as new solution formed.
Therefore, as a fixed amount of volume is extracted from the standard solution, a fraction of the moles of the standard is being transferred into the new solution.
When the solution is made into a mL solution by adding distilled water, the number of moles in the flask is retained but a decrease in concentration is observed due to the increase in volume. Hence, since the number of moles remains the same in both solutions but the volume increases, concentration decreases. This relationship can be shown by the following equation: The relationship between concentration and conductivity can then be found by measuring the conductivity of these solutions.
A conductivity meter is used for the accurate measurement of conductivity.
The Effect of Solution Concentration on Conductivity | Sciencing
Approximately 5mL of the solution would be poured out into a smaller cup and its conductivity is measured. Since the 5mL solution is taken to represent the conductivity of the entire solution, extra care has to be taken to ensure that the solution was swirled thoroughly. Also, the metal rods on the conductivity meter that takes the measurements have to be cleaned and dried properly. Contamination of the rod will lead to errors in the reading of conductivity while excess distilled water left on the rods after drying may dilute the solution and would defeat the purpose of the experiment.
With the results obtained, a conductivity-concentration curve can be constructed and linear interpolation can be carried out to find the conductivity of the unknown solution. This acts as the standard solution for the salt. Repeat this two more times until there is 30mL of standard solution in the flask. This is the first dilution needed of the standard salt solution.
Now there should be three salt solutions of different concentrations. It is important to label each of the volumetric flasks. Determining Conductivity of Solutions 1 The metal rods on the conductivity meter were washed with distilled water 2 The rods were then wiped dry with Kimwipes.
Assuming the conductivity of the extracted solution to be that of the standard solution. Weighing the Solutions 1 Label, clean with RO water, dry and weigh a pycnometer 2 Fill pycnometer with water, dry with a Kimwipe the outside surface of pycnometer and weigh it. Make sure to dry every spot where there may be any fluid bottom, treads, etc. The presence of fluids anywhere other than inside the pycnometer will influence the weight and produce error. Furthermore, it is key that the droplet at the tip of the pycnometer remains somewhat constant throughout each measurement to ensure a constant volume.
Lastly, do not put the Kimwipe directly into the hole of the pycnometer because it will absorb fluid found inside the pycnometer. Reference source not found.
The table suggests that a greater concentration of salt leads to greater density of Table 4 — Densities of Compounds at solution. This falls within reason because as is 22OC shown in Table 4, the densities Sigma-Aldrich of Compound Density all the salts are well above the density of water.
Another trend observed from Error! Reference source not Na2SO4 2. Once again this can also be described by the density values given in Table 4.
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Since Na2SO4 has the greatest density out of the three salts, a specific concentration in solution will result in a greater overall density of solution than any of the other salts at the specific concentration. This also explains why KCl has the lowest density at a specific concentration for all three solutions, because it has the lowest density of the salts. The two trends observed, density being proportional to concentration and the different densities given the salts, are based on the fact that the greater the density of a salt is, the more of an effect one mole of that salt will have on changing the density of the solution.
This is particularly true because the solvent, water, has a much lower density than any of the salts used in this particular experiment. The table Graph 2: Apart from minor deviations from the regressions, the relationships are all linear, which can be compared to true values, which on small scalesgive a linear relationship as well.
This observation is explained by analyzing each of the salts used.
Conductivity (electrolytic) - Wikipedia
Our tests indicate that Na2SO4 also has the highest conductivity in solution, and therefore one can conclude that conductivity is proportional to the number of ions that dissociate in solution from one mole of salt.
But this does not describe the difference between the conductivities of the NaCl and KCl solutions. During the experiment, an unknown salt solution was given, with the purpose of finding out its approximate concentration and type of salt, from the three salts used Na2SO4, KCl, NaCl.
Using the same testing techniques used throughout this lab the conductivity and density were determined. The necessary concentrations would be: To determine which type of salt is present in the unknown solution, use linear interpolation of the different concentrations against the known conductivity 7.