Some substances, when dissolved in water, undergo either a physical or a chemical change that results in constituent cations and anions in the solution. This process of dissociation of a substance into its ions is known as ionization and the substances that undergo ionization are called electrolytes. Substances that do not ionize when dissolved in water are called nonelectrolytes.
Depending upon the extent or degree of ionization, the electrolytes are divided into two types:
Strong electrolytes are the chemical substances that ionize completely when dissolved in water, whereas weak electrolytes only ionize partially. This means that the principal species in solution for strong electrolytes are ions, while the principal species in solution for weak electrolytes is the un-ionized compound itself.
Strong vs. Weak Electrolytes
Strong electrolytes ionize completely when dissolved in water
Weak electrolytes ionize partially in water
There is 100% ionization, so the principal species are the ions of the electrolytes in the solution
The ionization is less, roughly 1-10%. The principal species in solution for weak electrolytes is the unionized electrolyte itself
Solutions containing a strong electrolyte will have high electrical conductivity
Solutions containing a weak electrolyte will have low electrical conductivity
Ostwald’s dilution law is not applicable
Ostwald’s dilution law is applicable
Strong acids, strong bases, and salts (except some) are strong electrolytes
Weak acids and weak bases are weak electrolytes
HCl, NaCl, NaOH are some examples of strong electrolytes
HF and NH3 are some examples of weak electrolytes
Weak Electrolytes and their Examples
The substances which ionize up to a small extent into ions are called weak electrolytes. The molecules of a weak electrolyte are in equilibrium with its ions in a solution. Therefore, the equation which involves the ionization of weak electrolytes is represented with double-headed arrows, meaning, the reaction is reversible, such as,
NH3 + H2O ⇌ NH4+ + OH–
CH3COOH + H2O ⇌ H3O+ + CH3COO–
Examples of weak electrolytes include acetic acid (CH3COOH), carbonic acid (H2CO3), ammonia (NH3), hydrogen fluoride (HF), hydrogen cyanide (HCN), and pyridine (C2H5N), etc.
Strong Electrolytes and their Examples
The substances which ionize completely into ions are known as strong electrolytes. Here the unionized molecules (electrolytes) are present in such a small amount that they can be neglected. Also, they are not of any significance to study the ionization constant of strong electrolytes. Unlike the weak electrolytes, the equation for the ionization of strong electrolytes is not represented with double-headed arrows, such as,
HCl + H2O → H3O+ + Cl–
HNO3 + H2O → H3O+ + NO3–
Examples of strong electrolytes are HCl, NaOH, NaCl, H2SO4, KBr, etc. A list of further examples is provided in the lower section of this article.
How to Categorize the Electrolytes
Substances may be categorized as strong, weak, or nonelectrolytes by studying their electrical conductance in an aqueous solution. The solution will conduct electricity if it contains free and charged ions. The nonelectrolytes are out of the discussion here as their aqueous solution would not conduct current due to the lack of charged species.
It is important to note that the conductivity of an electrolyte solution is related to the strength of the electrolyte. This means that the greater the ionic concentration of the solution there is, the greater will be the conduction. So, upon applying a voltage to electrodes immersed in a solution, one shall find out the ionic concentration quantitatively; by measuring the electric current, or by observing the brightness of a light bulb included in the circuit (such light is used in spectroscopic techniques to quantify data).
The quantitative applications of electrolysis imply colorimeters connected by salt bridges. Such applications lead to galvanic cells, electrochemical cells, standard electrode systems, Nelson cell, Down cell, etc.
Give a list of strong electrolytes.
Strong acids are strong electrolytes:
- Hydrochloric acid, HCl
- Hydroiodic acid, HI
- Hydrobromic acid, HBr
- Nitric acid, HNO3
- Sulfuric acid, H2SO4
- Chloric acid, HClO3
- Perchloric acid, HClO4
- Lithium hydroxide, LiOH
Strong bases are strong electrolytes:
Examples of some salts as strong electrolytes:
- Sodium chloride, NaCl
- Magnesium sulfate, MgSO4
- Ammonium nitrate, NH4NO3
- Calcium chloride, CaCl2
- Potassium bromide (KBr)
- Ammonium nitrate (NH4NO3)
- Sodium carbonate (Na2CO3), etc
How to know if a chemical is an electrolyte?
Electrolytes dissociate into ions when added to water. If a chemical is an electrolyte it must dissociate whether weak or strong.
Is CH3COOH a weak or strong electrolyte?
Acetic acid, CH3COOH is a weak electrolyte because it is a weak acid.
How can you tell if an electrolyte is strong or weak?
Depending on the extent of ionization in water, the electrolyte can be regarded as strong or weak. The more ionization, the stronger the electrolyte.
Is NH3 a weak or strong electrolyte?
Ammonia, NH3 is a weak electrolyte because it is a weak base.
Is HCl a strong or weak electrolyte?
HCl is a strong electrolyte as it is a strong acid.
Why can’t pure water be used as an electrolyte?
Water cannot be used as an electrolyte because pure water is not an electrolyte. The common concept of water being an electrolyte is due to the impurities present, that make it ionize itself, leading to electrolysis and being an electrolyte.
Is NaOH a strong or weak electrolyte?
Sodium hydroxide, NaOH is a strong base, so, it is a strong electrolyte as well.
Strong vs weak electrolyte conductivity
The greater the strength of the electrolyte, the higher will be the conductivity. This is because strong electrolyte solutions have more free-charged species (ions).
What is the difference between electrolyte and nonelectrolyte?
Electrolytes are substances that ionize in solutions and form ions whereas nonelectrolytes do not ionize when added into water or other solvents.
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- Introduction to Environmental Geotechnology by Hsai-Yang Fang (Lehigh University, Pennsylvania)
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