Electrolytes are chemicals that break into ions (ionize) when they dissolve in water, producing a solution that conducts electricity. The positively-charged ions are called cations, while the negatively charged ions are called anions. Substances are categorized as strong electrolytes, weak electrolytes, or nonelectrolytes. The terms strong and weak describe how completely a substance ionizes, not how well the solution conducts electricity, which also depends on concentration and solubility.
Key Takeaways: Electrolytes
- Electrolytes are substances that form ions when dissolved in water so that the solution conducts electricity.
- Strong electrolytes completely ionize in water, even if the compound itself has low solubility.
- Weak electrolytes partially ionize and exist in equilibrium between ionized and non-ionized forms.
- Nonelectrolytes dissolve without forming ions and do not conduct electricity.
- Electrical conductivity depends on both the number of ions produced and their concentration in solution.
- Strong acids, strong bases, and soluble salts are strong electrolytes.
- Weak acids, weak bases, and many nitrogen-containing compounds are weak electrolytes.
- Most organic compounds such as sugars, fats, and alcohols are nonelectrolytes.
- Identifying whether a substance is a strong, weak, or non-electrolyte helps predict aqueous reactions and write ionic equations correctly.
What Makes a Good Electrolyte?
A good electrolyte is a substance that dissolves in water and produces a large number of ions, resulting in a solution that conducts electricity efficiently. The effectiveness of an electrolyte depends on two main factors:
- Degree of ionization: Strong electrolytes ionize completely in water, producing more free ions to carry electric current. Weak electrolytes only partially ionize, limiting conductivity.
- Solubility: Even if a compound ionizes completely, it must dissolve well in water to provide a high concentration of ions. For example, silver chloride (AgCl) is a strong electrolyte but has very low solubility, so it does not conduct electricity well.
In summary, a good electrolyte is both highly soluble and fully ionized in solution.
Strong Electrolytes
Strong electrolytes completely ionize in water. This means 100% of the dissolved chemical breaks into cations and anions. However, it does not mean the chemical completely dissolves in water! For example, some species are only slightly soluble in water, yet are strong electrolytes. This means that not very much dissolves, but all that dissolves dissociates completely into ions in solution. An example is the strong base strontium hydroxide, Sr(OH)2. It has a low solubility in water, but dissociates completely into Sr2+ and OH– ions. A flask of sodium hydroxide (NaOH) in water contains Na+ and OH– ions in water, but no actual NaOH, while a flask of aqueous strontium hydroxide contains Sr2+ and OH– ions, undissolved Sr(OH)2, and water.
Examples: Strong acids, strong bases, and salts are strong electrolytes.
Weak Electrolytes
Weak electrolytes partially ionize in water. Pretty much any dissociation into ions between 0% and 100% makes a chemical a weak electrolyte, but in practice, around 1% to 10% of a weak electrolyte breaks into ions.
Examples: Weak acids and weak bases are weak electrolytes. Most nitrogen-containing molecules are weak electrolytes. Pure water undergoes very limited autoionization into H⁺ and OH⁻ ions (Kw = 1 × 10⁻¹⁴ at 25°C), so it is sometimes classified as a very weak electrolyte or as a nonelectrolyte, depending on context.
Nonelectrolytes
If a substance doesn’t ionize in water at all, it’s a nonelectrolyte.
Examples: Most carbon compounds are nonelectrolytes. Fats, sugars, and alcohols are largely nonelectrolytes.
Electrolyte vs Nonelectrolyte ≠ Polar vs Nonpolar
Not all polar substances are electrolytes. For example, sugar dissolves readily in water and is polar, but it does not form ions and therefore does not conduct electricity. Ion formation, not polarity alone, determines whether a substance is an electrolyte.
Why Should You Care?
The most important reason to know whether a chemical is an electrolyte or not and how strongly it dissociates in water is because you need this information to determine the chemical reactions that can take place in water. Also, if you have a container of a chemical in water, it’s a good plan to know whether that substance dissolves in water (its solubility) and whether it dissociates into ions.
A classic example of why this matters is a sodium cyanide (NaCN) solution. You probably know cyanide is reactive and extremely toxic, so would you open a bottle of sodium cyanide in water? If you recognize sodium cyanide is a salt, you’ll know you’re safe (providing you don’t drink the solution) because there is no sodium cyanide in the water, just Na+ and CN– ions in water. The cyanide ions in solution are not volatile, so the solution does not release toxic gas under normal conditions. Contrast this with a bottle of hydrogen cyanide (HCN) in water. Would you open that bottle? If you recognize hydrogen cyanide is a weak acid, you know the bottle contains hydrogen cyanide gas, hydrogen ions, cyanide ions, and water. Opening that bottle could cost you your life!
How Do You Know What Chemicals Are Electrolytes?
Now that you’re motivated to know what an electrolyte is, you’re probably wondering how to tell what type of electrolyte a chemical is based on its name or structure. You do this by the process of elimination. Here are some steps to follow to identify strong, weak, and non electrolytes.
- Is it a strong acid? There are only 7 of them and you’ll encounter them a lot in chemistry, so it’s a good plan to memorize them. Strong acids are strong electrolyte.
- Is it a strong base? This is a slightly larger group than the strong acids, but you can identify the strong bases because they are metal hydroxides. Any element from the first two columns of the periodic table combined with a hydroxide is a strong base. Strong bases are strong electrolytes.
- Is it a salt? Salts are strong electrolytes.
- Does the chemical formula contain nitrogen or “N”? It may be a weak base, which would make it a weak electrolyte.
- Does the chemical formula start with hydrogen or “H”? It may be a weak acid, which would make it a weak electrolyte.
- Is it a carbon compound? Most organic compounds are nonelectrolytes.
- Is it none of the above? There’s a good chance it’s a nonelectrolyte, though it may be a weak electrolyte.
Table of Strong Electrolytes, Weak Electrolytes, and Nonelectrolytes
This table summarizes groups of strong, weak, and nonelectrolytes, with examples of each category.
| Strong Electrolytes | |
| strong acids | HCl (hydrochloric acid) |
| HBr (hydrobromic acid) | |
| HI (hydroiodic acid) | |
| HNO3 (nitric acid) | |
| HClO3 | |
| HClO4 | |
| H2SO4 (sulfuric acid) | |
| strong bases | NaOH (sodium hydroxide) |
| KOH (potassium hydroxide) | |
| LiOH | |
| Ba(OH)2 | |
| Ca(OH)2 | |
| salts | NaCl |
| KBr | |
| MgCl2 | |
| Weak Electrolytes | |
| weak acids | HF (hydrofluoric acid) |
| HC2H3O2 (acetic acid) | |
| H2CO3 (carbonic acid) | |
| H3PO4 (phosphoric acid) | |
| weak bases | NH3 (ammonia) |
| (“N” compounds) | C5H5N (pyridine) |
| Non Electrolytes | |
| sugars and carbohydrate | C6H12O6 (glucose) |
| fats and lipids | cholesterol |
| alcohols | C2H5OH (ethyl alcohol) |
| other carbon compounds | C5H12 (pentane) |
Real-Life Applications of Electrolytes
Electrolytes play essential roles in chemistry, biology, industry, and daily life. Here are some important examples:
- Biology and Medicine: Electrolytes such as sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻), and bicarbonate (HCO₃⁻) are critical for nerve impulses, muscle contractions, hydration, and pH balance in the human body. Electrolyte imbalance can cause serious health issues.
- Sports Drinks: Commercial electrolyte drinks contain salts and sugars to help rehydrate the body and restore electrolyte levels after sweating or exercise.
- Electrochemistry and Batteries: Strong electrolytes are used in batteries and electrolysis processes to allow the flow of electric current between electrodes.
- Water Treatment: Measuring water conductivity helps determine its purity. Pure water is a poor conductor, while the presence of electrolytes increases conductivity.
- Chemical Reactions: Many aqueous reactions, including precipitation, acid-base, and redox reactions, depend on electrolytes to proceed.
Electrolytes are essential for understanding both theoretical chemistry and real-world applications ranging from bodily functions to battery technology.
References
- Andreev, M.; de Pablo, J.J.; et al. (2018). “Influence of ion solvation on the properties of electrolyte solutions”. The Journal of Physical Chemistry B. 122 (14): 4029–4034. doi:10.1021/acs.jpcb.8b00518
- Enderby, J.E.; Neilson, G.W. (1981). “The structure of electrolyte solutions”. Reports on Progress in Physics. 44 (6): 593–653. doi:10.1088/0034-4885/44/6/001
- Gregory, K.P.; Elliott, G.R.; et al. (2022). “Understanding specific ion effects and the Hofmeister series”. Physical Chemistry Chemical Physics. 24 (21): 12682–12718. doi:10.1039/D2CP00847E
- Kaminsky, M. (1957). “Ion-solvent interaction and the viscosity of strong-electrolyte solutions”. Discussions of the Faraday Society. 24: 171. doi:10.1039/DF9572400171
- Wilkins, L.W. (2007). Fluids and Electrolytes. Lippincott Williams & Wilkins. ISBN 978-1-58255-923-0.