How to identify electrolytes is one of the basic principles of chemistry. As the name implies, the identification of electrolytes has to do with electricity and electrical charge. When trying to determine if a substance is an electrolyte vs. nonelectrolyte, the question that must be answered is: does it conduct electricity when melted or dissolved? If a material is electrically conductive in its molten or dissolved state, then it is an electrolyte. If it does not conduct electricity as a liquid, it is a nonelectrolyte.
A simple way to test if a material is an electrolyte or nonelectrolyte is to make an electrical circuit in which two metal bars are hooked up to the positive and negative poles of a battery to create a voltage difference between them. These positively and negatively charged metal electrodes are then immersed in a solution or melt of the substance we are interested in testing. A lightbulb and a device that measures electrical current flow (i.e., an ampere meter or ammeter) are included in the circuit to determine how much electricity flows through the solution between the immersed electrodes. If the solution contains an electrolyte, the lightbulb will glow, and the ammeter will measure a relatively high current flow. If the solution is a nonelectrolyte, the lightbulb will not light up, and very low current flow will be measured.
This simple experimental setup essentially measures the electrical conductance or conductivity of the liquid we are testing. Conductivity is a measure of the materials ability to conduct electricity. Different dissolved substances have different levels of conductivity. Strongly conductive materials are called strong electrolytes. These substances would cause the lightbulb in our experimental setup to glow brightly and register high current flows. There are other substances whose solutions only weakly conduct electricity. These weak electrolyte solutions would only dimly light up the bulb in our circuit and would register relatively low current flows on the ammeter. Some substances do not conduct electricity at all when dissolved or melted. For these nonelectrolytes no current would flow through our experimental conductivity circuit. Some everyday examples of strong and weak electrolytes are table salt (sodium chloride) and vinegar (dilute acetic acid), respectively. In comparison, sugar (sucrose) is an example of a nonelectrolyte.
In the following sections, we will discuss in more detail why electrolytes conduct electricity and why nonelectrolytes do not. We will also list and describe more examples of electrolytes and nonelectrolytes and discuss the essential roles that they play in natural, biological, and industrial processes.
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As discussed above, an electrolyte is a substance that conducts electricity when it is in a molten or dissolved state. This section will focus on dissolved electrolytes, specifically electrolytes dissolved in water, since these are the most common and important types of electrolyte solutions. We will also summarize the chemical principles that underly why and how electrolyte solutions conduct electricity.
Both electrolytes and nonelectrolytes can be dissolved to form solutions. The substance that dissolves in a solution is called the solute, and the bulk material into which it is dissolved is called the solvent. In this lesson, we are primarily interested in solutions in which water is the solvent, and the electrolyte and nonelectrolyte substances are the solutes. These water-based mixtures are called aqueous solutions (based on the Latin word for water: aqua). So, an aqueous solution is a homogeneous mixture in which one or more substances are dissolved in water. A homogeneous mixture is a solution in which the solutes and solvents are mixed uniformly at the atomic or molecular scale.
Many common minerals, salts, and some organic materials are composed of charged particles that break apart to form ions when they dissolve in water to form aqueous solutions. Ions are electrically charged particles created when atoms lose or gain electrons. Atoms are composed of a nucleus of positively charged particles (protons) and neutrally charged particles (neutrons) surrounded by negatively charged particles (electrons). Inter-atomic interactions that take place during chemical reactions cause some atoms to donate electrons to other atoms. The sharing of electrons between atoms results in the chemical bonds that hold substances together.
The sharing of electrons between atoms forms strong inter-atomic links called covalent bonds. When an atom completely loses electrons to another atom, it creates an ionic bond. In ionic bonding, the atom donating electrons becomes positively charged, and the atom receiving the electrons becomes negatively charged. In this type of bonding, the electrical attraction between the positively and negatively charged atoms holds the material together. A substance held together primarily through ionic bonding is called an ionic compound or ionic solid. A typical example of an electrolyte compound is table salt (sodium chloride) which is composed of a positively charged sodium ion ({eq}Na^+ {/eq}) and a negatively charged chlorine ion ({eq}Cl^- {/eq}). Ionic compounds such as salt are electrolytes.
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As discussed above, the key characteristic of electrolyte compounds (ionic compounds) is that they form electrically conductive liquids when melted or dissolved in water. When an ionic compound such as sodium chloride dissolves in water, its ions separate and disperse uniformly into the solution. The presence of these charged particles makes the solution electrically conductive. The positively charged ions in solution are called cations, and the negatively charged ions are called anions.
{eq}\text{NaCl}(solid)\;{\rightleftarrows}\;\text{Na}^{+}(dissolved)\;+\;\text{Cl}^{-}(dissolved) {/eq}
As mentioned above, ionic compounds are also referred to as electrolyte compounds or simply as electrolytes. The term electrolyte combines the Greek word for electrical (electro) with a suffix meaning to divide (lyte). Electrolyte compounds (electrolytes) are substances in which the electrical charges are divided into cations and anions. An electrolyte solution is one created by dissolving an ionic compound (electrolyte). When an electrolyte produces a high proportion of ions, when it dissolves, it forms a strong electrolyte solution. However, some substances only partially dissociate into ions when they dissolve. These substances are thus referred to as weak electrolytes and result in weakly conductive solutions.
Electrolyte solutions are ubiquitous. Common examples such as residential tap water and saltwater are used by billions of people every day. There are also less familiar examples that play essential roles in biological, environmental, and industrial systems worldwide. Many of the key examples of these are identified and described in the table below.
| Example | Ions Formed | Occurrence and Uses |
|---|---|---|
| Sodium Chloride | Na+, Cl- | >Environmental: major component of sea water |
| >Biological: Na+ is essential for proper cell hydration, Cl- is essential for maintaining internal pH levels. | ||
| >Industrial: Sodium chloride brines are used to provide dye coverage and adhesion in the textile industry. | ||
| Potassium Chloride | Na+, Cl- | >Environmental: major component of seawater |
| >Biological: K+ is essential for nervous system and muscle function. | ||
| >Industrial: Potassium chloride is used for surface treatment and as a hardening agent in the metal processing industry. | ||
| Calcium Phosphate | Ca2+, PO42- | >Environmental: naturally occurring deposits serve as major source of phosphorus. |
| >Biological: Ca2+ and PO42- form teeth and bone. | ||
| >Industrial: used primarily as fertilizer in agricultural industries. | ||
| Magnesium Sulfate (epsom salt) | Mg2+, SO42- | >Environmental: Major constituent of evaporite deposits that form around saline lakes in arid regions. |
| >Biological: Mg2+ is essential for nervous system and muscle function. | ||
| >Industrial: used to prepare cement insulation panels used in the construction industry. | ||
| Hydrochloric Acid | H+, Cl- | >Environmental: rare natural occurrence, may be produced due to volcanic outgassing. |
| >Biological: major component of gastric acid used to digest food. | ||
| >Industrial: used in metallurgical industry to remove oxides from steel surfaces before subsequent processing | ||
| Sulfuric Acid | H+, SO42- | >Environmental: formed by the natural weathering of sulfide minerals such as pyrite (FeS2). |
| >Biological: no uses - destroys biological materials. | ||
| >Industrial: acid used in lead automobile batteries. | ||
| Acetic Acid (vinegar) | H+, CH3COO- | >Environmental: produced by bacteria in soils, also occurs in rotting fruit. |
| >Biological: plays a role in the metabolism of carbohydrates and fats. | ||
| >Industrial: used in chemical industry to produce reagents such as acetic anhydride and metal acetates. |
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A nonelectrolyte is a compound that does not form an electrically conductive liquid when it dissolves or melts. That is, a material that does not separate into ions when melted or dissolved. A common example of a nonelectrolyte is sugar (sucrose). When sugar dissolves (i.e., becomes a solute) in the solvent water, its molecules do not break apart, so ions are not formed. This can be represented by the simple dissolution reaction shown below:
{eq}C_{12}H_{22}O_{11}(solid) \rightleftharpoons C_{12}H_{22}O_{11}(dissolved) {/eq}
A nonelectrolyte list of examples is shown in the table below. As with the electrolyte examples, nonelectrolyte solutions also play important roles in biological, and industrial processes.
| Example | Occurrence and Uses |
|---|---|
| Sugar (lactose, glucose, sucrose, fructose) | >Environmental/Biological: lactose occurs in milk products, glucose in fruit, fructose in honey and sucrose is from sugar cane plants. |
| >Industrial: besides the food industry, sugar is used as a clean carbon source by the fermentation industry and used for the production of pharmaceuticals. | |
| Ethyl Alcohol | >Environmental/Biological: produced as a metabolic byproduct of yeast and is found in over-ripe fruit. |
| >Industrial: used in chemical industries as a precursor for other organic compounds (e.g., acetic acid, ethyl halides, ethyl esters, and ethyl amines. | |
| Acetone | >Environmental/Biological: found in plants, volcanic gases and as a product of fat breakdown in animals. |
| >Industrial: used in many industries as a solvent in epoxies, paints and varnishes. | |
| Urea | >Environmental/Biological: metabolic product of protein breakdown. |
| >Industrial: used as a fertilizer (source of nitrogen) for agricultural industries. |
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As discussed above, the primary factor distinguishing electrolyte vs. nonelectrolyte solutions is that the former conducts electricity and the latter does not. This difference is caused by the tendency of electrolytes to dissociate into ions when dissolved and the tendency of nonelectrolytes to dissolve as neutral (not electrically charged) molecules (e.g., as shown in the sugar dissolution reaction shown above). The primary differences between electrolyte vs. nonelectrolyte are shown in the following table.
| Property | Electrolyte | Nonelectrolyte |
|---|---|---|
| Chemical Behavior | Dissociated into ions when melted or dissolved. | Do not dissociate into ions when melted or dissolved. |
| Electrical Conductivity | Electrolytes that fully ionize when melted or dissolved are highly conductivity (strong electrolyte), Electrolytes the partially ionize are weakly conductive (weak electrolytes). | Are not electrically conductive when melted or dissolved. |
| Chemical Bonding | Most examples have ionic bonding. | Most examples have covalent bonding. |
| Example Compounds | Salts (sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate), Acids (hydrochloric, sulfuric, vinegar), bases (sodium hydroxide, potassium hydroxide). | Sugars (lactose, fructose, sucrose, glucose), Organic liquids (Acetone, Alcohols, Urea, Toluene, Benzene). |
The degree to which an electrolyte solution conducts electricity will be determined by two factors: (1) the proportion of ions to neutral molecules that form when it dissolves, and (2) its concentration in solution. The dissolution behavior of the compound determines the proportion of ions formed. For example, the dissolution of acetic acid in water to form vinegar is summarized by the following reaction (note: (aq) is indicates that the material is dissolved in an aqueous solution):
{eq}CH_3COOH(aq) \rightleftharpoons CH_3COO^-(aq) + H^+(aq) {/eq}
When dissolved, acetic acid is present as the neutral molecule ({eq}CH_3COOH {/eq}) and the ions ({eq}CH_3COO^- {/eq}) and {eq}H^+ {/eq}. The two-way arrows in the reaction indicate that not all of the neutral molecule dissociates to form the ions; rather, there is a constant conversion back and forth.
Soon after dissolving acetic acid in water, this reaction reaches an equilibrium state in which the conversion rate of neutral molecules into ions equals the rate of recombination of ions to form the neutral molecule. So, in the equilibrium state, the concentrations of neutral molecules and ions remain constant with time. The amount of a solute per volume of solution is its concentration
Concentration is commonly expressed in grams of solute per liter of solution. So, in our vinegar example, in its equilibrium state, there is a relatively low concentration of the ions in solution (i.e., most of the dissolved acetic acid is present as the neutral molecule). Since the presence of ions is what makes an electrolyte solution electrically conductive and vinegar has a low equilibrium concentration of ions, it is a weak electrolyte.
Strong electrolytes such as sodium chloride do not form neutral molecules in solution. For these substances, the electrical conductivity of their solution is simply determined by their concentration in solution. So, an aqueous solution with a low concentration of sodium and chlorine ions is weakly conductive, but a more concentrated solution will be strongly conductive. That is, we can increase the electrical conductivity of the solution by simply adding more salt to it.
There are three important concentration units:
As mentioned, concentration is commonly expressed as grams of solute per liter of solution. These mass-based units can be converted to a convenient mass percent concentration unit that represents the mass of solute per mass of solution time 100.
{eq}\text{Mass Percent}=\dfrac{\text{Mass of Solute}}{\text{Mass of Solution}} \times \text{100} \% {/eq}
To make this conversion, we multiply the grams per liter concentration by the inverse of the solution density. The density of the solution is the mass of the solution (in grams) per volume of solution (in liters). The conversion is summarized by the following equation (note that the liters of solution cancel out in this equation):
{eq}\text{Mass Percent}=\dfrac{\text{grams of Solute}}{\require{cancel} \xcancel {\text{Liter of Solution}}} \times \dfrac{\require{cancel} \xcancel {\text{Liters of Solution}}} {\text{grams of Solution}} \times 100\% {/eq}
When performing calculations, chemists more commonly use concentration units based on moles or molar units. A mole is the international standard unit for quantifying the amount of a substance. More specifically, a mole is used to measure amounts of small particles such as atoms and molecules. By definition, one mole equals {eq}6.02\text{x}10^{23} {/eq} particles. So, the number of atoms or molecules in a mole is always the same; however, the weights of atoms and molecules vary. For example, there are 26.98 grams of aluminum per mole of aluminum, and there are 196.97 grams of gold per mole of gold. The grams of an atom or molecule per mole is called its atomic mass or molecular mass respectively.
Concentration units of grams per liter can be converted to moles per liter using the molecular mass of the dissolved substance. For example, suppose we dissolve 50 grams of the strong electrolyte potassium chloride (KCl) to form 1 liter of aqueous solution. In that case, we can determine the molar concentration (moles solute per liter of solution) by simply dividing the grams per liter by the molecular weight (grams per mole) of KCl, which is 74.55 grams per mole.
{eq}\begin{align} \frac {50 \ \text{g} \: {KCl}} {\text{Liter}} \times \frac{1 \: \text{mole} \: {KCl}}{74.55 \: \text{g} \: {KCl}} &= \frac {0.67 \: \text{mole}} {\text{Liter}} \end{align} {/eq}
Another important that mole-based unit used by chemists is molality. Molality is moles solute per kilograms of solvent. The advantage of this unit is that it directly quantifies the masses of solute and solvent and is unaffected by temperature variations of the solution. For example, if the temperature of our solution increases, thermal expansion will cause its volume to increase, thus changing the liters of solution (i.e., it will no longer be 1.0 liters). The mass of solvent (in kilograms) does not change when the solution temperature changes.
An electrolyte or electrolyte compound is a substance that breaks into ions and forms an electrically conductive liquid when melted or dissolved. Ions are charged particles that form when an electrolyte breaks apart (i.e., dissociates) during dissolution or melting (e.g., NaCl dissociates into the ions {eq}Na^+ {/eq} and {eq}Cl^- {/eq}). The most common electrolyte solutions are created by dissolving an electrolyte compound in water. In these water-based or aqueous solutions, the dissolved electrolyte substances are called solutes, and the water into which they are dissolved is referred to as the solvent. An aqueous solution is a homogeneous mixture in which the solutes and solvents are mixed uniformly at the atomic or molecular scale. Examples of electrolytes include salts such as sodium chloride, acids such as hydrochloric, and bases such as sodium hydroxide. Electrolytes that completely dissociate into ions when dissolved are strong electrolytes (e.g., potassium chloride) and electrolytes that only partially dissociate into ions when dissolved are weak electrolytes (e.g., vinegar). A nonelectrolyte is a substance that neither breaks into ions nor forms an electrically conductive liquid when melted or dissolved. Examples of nonelectrolytes include sugars such as fructose, alcohol, and organic solvents such as acetone.
The electrical conductivity of electrolyte solutions depends on the concentration of solutes (ions) in solution. Concentration quantifies the amount of solute per amount of solution or solvent. There are a variety of ways to quantify concentrations. For example:
Each concentration unit has advantages or disadvantages depending on the types of experiments or calculations being performed.
In summary, the primary factor distinguishing electrolytes vs. nonelectrolytes is that the former conducts electricity when in a liquid form and the latter does not. As discussed above, both electrolyte and nonelectrolyte solutions play essential roles in biological, environmental, and industrial processes; thus, understanding their chemistry is an integral part of science education.
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The primary distinction between electrolyte vs. nonelectrolyte substances is that the former conducts electricity when dissolved or melted and the latter does not. Therefore, to determine whether a substance is a nonelectrolyte, one could dissolve or melt the material and then use a conductivity meter (i.e., an instrument that measures electrical conductivity) to determine whether the liquid is electrically conductive. If the solution or melt is not electrically conductive, the substance is a nonelectrolyte.
A nonelectrolyte list of typical examples includes: sugars (lactose, glucose, sucrose, fructose), alcohols (e.g., ethanol, methanol), organic solvents (e.g., acetone, toluene, benzene), and urea.
Sodium chloride (NaCl) is not a nonelectrolyte. This is because NaCl breaks into charged particles or ions (i.e., a positively charged sodium ion and a negatively charged chlorine ion) when it dissolves or melts. The presence of ions in a liquid make it electrically conductive. The primary distinction between electrolyte vs. nonelectrolyte substances is that the former conducts electricity when dissolved or melted and the latter does not. Therefore, NaCl is an electrolyte rather than a nonelectrolyte.
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