Electrolytes

Were you ever told not to swim during a lightning storm because you would get electrocuted? Well, it turns out that water, in its pure form, is not electrically conductive. But, when electrolytes coming from your sweat or from the environment are dissolved in the water, they make it highly electrically conductive, making it dangerous to go swimming during a lightning storm!

Electrolytes: definition

Let's start by looking at the definition of electrolytes. These electrolyte solutions are able to carry an electric current.

• Conductivity is referred to as the ability of electric current to flow through a material.

For example, when sulfuric acid dissolves in water, it dissociates into hydrogen ions (H⁺) and sulfate anions (SO₄^2-).

$$ \text{H}_{2}\text{SO}_{4}\text{(aq)} \longrightarrow \text{2 H}^{+}\text{ (aq) + SO}_{4}^{2-}\text{(aq)} $$

Usually, electrical conductivity testers are used to test a solution's conductivity (figure 1). This test involves adding the aqueous solution to a beaker containing two electrical plates with opposite charges connected to a power source and a light bulb. Basically, when the charge runs to the plates, the positive ions are attracted to the negative plate, while the negative ions are attracted to the positive plate.

Types of Electrolytes

There are three types of electrolytes you should remember, and they are based on the degree to which they dissociate in water.

Strong Electrolytes

First up are strong electrolytes. In the category of strong electrolytes, we have soluble ionic compounds, strong acids, and strong bases.

Ionic compounds are usually composed of a metal and a non-metal or a metal and a polyatomic ion. A common example of a soluble ionic compound is sodium chloride (NaCl). However, not all ionic compounds are soluble in water (H₂O). Table 1 shows the Solubility rules for ionic compounds in water.

Let's look at an example.

Strong acids are acids that 100% dissociate in water to produce positive hydrogen ions (H⁺) and negative chlorine ions (Cl^-). The seven strong acids are HCl, HBr, HI, HClO₄, HClO₃, H₂SO₄, and HNO_3.

The figure below shows the dissociation of hydrochloric acid (HCl) in water.

Similar to strong acids, strong bases also completely dissociate in water. But, instead of forming H⁺ ions, they form hydroxide ions (OH^-) in the solution. For example, aqueous sodium hydroxide (NaOH) completely dissociates in water into aqueous sodium ions (Na⁺) and hydroxide (OH^-) ions.

$$ \text{NaOH (aq) } \longrightarrow \text{ Na}^{+}\text{(aq) + OH}^{-}\text{(aq)} $$

The strong bases include Group 1 metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) and Group 2 metal hydroxides (Ba(OH)₂, Sr(OH)₂, and Ca(OH)₂).

Weak Electrolytes

Next, we have weak electrolytes, and these are either weak acids or weak bases.

When dealing with weak electrolytes, we use half-arrows pointing in opposite directions, indicating that the reaction moves significantly in both directions.

$$ \text{CH}_{3}\text{COOH }\text{(aq)} \rightleftharpoons \text{CH}_{3}\text{COO}^{-}\text{ (aq) + H}^{+}\text{(aq)} $$

Table 2 shows a list of some common weak acids and weak bases.

Non-electrolytes

Non-electrolytes are actually molecular compounds. Molecular compounds are compounds made of non-metals that are not considered acids or bases.

Common examples of non-electrolytes include alcohol methanol (CH₃OH) and glucose sugar (C₆H₁₂O₆). Glucose is highly soluble in water, but even though it dissolves into water, it does not dissociate into ions. In other words, a non-electrolyte solution does not conduct electricity.

Electrolytes: properties

The properties of electrolytes depend on the type of electrolyte. Strong electrolytes completely dissociate in water, forming an aqueous solution with a high conductivity.

Weak electrolytes partially dissociate into its ions in water, so its aqueous solution has a low conductivity.

Non-electrolytes, on the other hand, are soluble in water, but they do not dissociate into ions. Therefore, an aqueous solution with a non-electrolyte does not conduct electric current.

Electrolytes: functions

Now that we know the different types of electrolytes that exist, let's dive into the functions of electrolytes. In chemistry, the most common use of electrolytes is probably in the process of Electrolysis.

The basic set-up for the electrolysis of sodium chloride (NaCl) can be seen in the figure below. Here, notice that we need a power source (for example, a battery), and two electrodes. These electrodes are then placed in the electrolyte (substance containing positive and negative ions, which is NaCl in this case).

When electricity is applied to the electrolyte, the positive ions from the electrolyte (Na⁺) are attracted to the negative electrode, whereas the negative ions (Cl^-) are attracted to the positive electrode.

Electrolytes are also very important in physiology. Salts containing sodium, potassium, and calcium ions are essential for the conduction of nerve impulses, muscle contraction, and osmotic regulation! When an electrolyte imbalance occurs, these very high or very low levels of electrolyte disrupt the cell function, leading to mild or life-threatening complications.

For example, low levels of sodium (Na⁺) ions might cause headaches, confusion, disrupted attention, and even cerebral edema (brain swelling), whereas high levels of sodium ions can cause agitation, and tachycardia (fast heart beat).

Chemical Equation of Electrolytes

Lastly, let's take a look at a chemical equation involving electrolytes. Let's start with calcium chloride (CaCl₂). The first thing we need to do is figure out whether CaCl₂ is soluble in H₂O. So, if you scroll up to the table containing the solubility rules for ionic compounds, you will notice that CaCl₂ is soluble in water, so it will dissolve in it.

Now, is it going to be a strong, weak or a non-electrolyte? Well, since CaCl₂ is an ionic compound, then it will be a strong electrolyte, and therefore, readily dissociate in H₂O into its ion equivalents.

$$ \text{CaCl}_{2}\text{(aq) } \text{ = Ca}^{2+}\text{(aq) } \text{ + Cl}^{-}\text{(aq) } $$

Now, I hope that you feel more confident in your understanding of electrolytes and how to determine whether a compound is a strong, weak or non-electrolyte!