Electrical currents are transported by ions in a given solution. As the concentration of ions increases, the conductivity increases. This is because conductivity increases as water dissolves more ionic compounds due to the ions transporting an electrical current in the solution.
Saltwater is an extremely resourceful aqueous solution as it provides almost half of our planet’s oxygen. When you look at a glass of saltwater, you probably wouldn’t even think about its potential to conduct electricity, but it can.
However, there is often confusion that all water bodies can conduct electricity, which is not the case. Pure water is a very poor conductor, therefore it does not conduct electricity.
However, if the water was to contain charged ions or impurities (imagine pouring bath salts into your bath as an example), it would become an ionic solution and therefore would be conductive.
This is why ionic solutions like saltwater can conduct electricity because of the charged particles that move freely in the solution.
Saltwater is the “box-standard” example when it comes to ionic solutions that can conduct electricity, however, understanding how ions can conduct electricity is not something that can be carried out in a home experiment. This is because to understand the relationship between ions and conductivity, we need to know the difference between ionic and covalent bonds, plus what happens when dissociated ions are exposed to electrical currents.
Ionic and covalent bonds are something you probably learned back in high school. However, let’s have a little refresh, as that subject is probably a little dusty before we look at how ions increase conductivity in solutions!
Ionic & Covalent Bonds
Covalent bonds are formed when atoms share electrons to complete their valence shells – the valence shell is the outer one! Hydrogen is a good example of forming covalent bonds. As hydrogen has one space for an electron, it can covalently bond with other hydrogen atoms, so both valence shells are filled.
Ionic bonds are slightly different. These bonds involve an attraction between oppositely charged ions or two atoms that have different electronegativities, which causes them to transfer electrons. For example, if one atom requires one more electron to complete its valence shell, an atom that has one or very few electrons can donate it to the other atom.
This process however causes an imbalance between nucleus charges. So, when an atom becomes charged, they are called ions and can attract negatively charged ions to form an ionic bond. Ionic compounds can conduct electricity as they are attracted to oppositely charged electrolyte solutions or electrodes.
How Do Ions Increase Conductivity?
First, let’s start with some basics, what is an ion? An ion is an atom or group of atoms that has a positive or negative charge. Positively charged ions are called cations, and negatively charged ions are called anions.
Conductivity is the measurement of electrical flow, usually measured in Siemens (S) per distance with a conductivity meter. Conductivity is determined by the number of charged ions, how fast they move, and the charge the ions carry. The more dissolved salts in an aqueous solution, the more ions, and therefore, the higher the conductivity measurement will be.
When a solution can conduct an electrical current, it is often referred to as an electrolytic solution or an ionic solution. When a substance is added to water and becomes conductive, it is known as an electrolyte (simplified to “ions in a solution”). An easy example of an electrolyte is sodium chloride (NaCl). When NaCl is added to water, it becomes readily conductive, this solution is better known as saltwater.
Ions can conduct electricity in solutions because they are able to move. In water, conductivity comes from the passing of electricity between ions, therefore when sodium (Na+) and chlorine (Cl-) form sodium chloride in saltwater, more electricity is carried, and therefore the conductivity increases. In simpler terms, as salinity increases, conductivity increases.
There are some exceptions to how conductive a solution can be. Once the conductive threshold has been reached for certain solutions, if you try to increase the ion concentration of the solution, it will alternatively lower the conductivity. This can be seen in sulfuric acid solutions.
Does Ion Size Affect Conductivity?
Generally, smaller ions are more conductive than larger ions because small ions can move through a solution with less hydrodynamic resistance. However, by increasing the ion size the likeness of ion-pair formation is reduced which results in a higher ionic strength and higher conductivity, therefore more studies on ion size and increasing conductivity in solutions are needed.
How Does The Dissociation Of Ionic Bonds Affect Conductivity?
In some cases, ionic bonds can be broken apart. When ions are dissolved in water, the molecules formed can dissociate into constituent ions (oppositely charged ions that are held together), which returns them to a charged state. This occurs at high temperatures, which affect the conductivity of the water. When molecules return to bonded, solid states, they cannot conduct electricity, however, when they are dissociated they can carry an electrical current, and therefore, conduct electricity.
This is all down to movement. Ions can move freely through the water, while electrons cannot.
What Affects The Conductivity Of Electrolyte Solutions?
The conductivity of an electrolyte (solution containing ions) solution can be affected by the following factors:
Ion concentration – as already mentioned, a higher ion concentration leads to higher conductivity.
The type of substance that is dissolved in the solution. For example, some substances may have a strong electrolyte concentration or weak electrolyte concentration. Ions are easily formed in strong electrolyte solutions, whereas weaker solutions do not form ions as easily, and non-electrolyte solutions (i.e. pure water) cannot form ions in a solution.
Temperature – the warmer the solution, the higher the conductivity due to the higher solubility of dissolved materials.
Ions can conduct electricity because they are able to move freely in a solution. An increase in a solution’s ion concentration increases the conductivity.
If you would like to learn more about conductivity, or what conductivity meter best suits your needs, do not hesitate to contact our world-class team at Atlas Scientific.
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