Weak electrolytes are generally covalent compounds, whose molecules tend to remain neutral without acquiring ionic charges. Many of these electrolytes consist of organic molecules with ionizable functional groups, although there are also inorganic ones, including various oxacids.
Acetic acid, CH 3 COOH, is an example of a weak electrolyte. Its molecule has a functional group that characterizes its acidity in water. However, when it dissolves, not all its molecules produce H 3 O + ions, transforming into the acetate anion, CH 3 COO – , but they remain neutral, protonated.
Characteristics of weak electolites
They are covalent compounds
Generally speaking, weak electrolytes are covalent compounds, so their constituent units are molecules.
These molecules have the ability to acquire ionic charges. To do this, it participates in a hydrolysis equilibrium, in which a water molecule “breaks” into OH – , or accepts hydrogen to transform into H 3 O + .
The less likely or unstable the hydrolysis, the lower the quantity or concentrations of ions present in the dissolution of these electrolytes.
They have low conductivity
Weak electrolyte solutions are not as good a conductor of electricity compared to strong electrolytes. This is precisely due to its lower number of ions in solution, which makes it difficult for electrons to pass through water.
Examples of weak electrolytes
The carbonic acid molecule, H 2 CO 3 , when dissolved in water undergoes the following hydrolysis reaction:
H 2 CO 3 + H 2 O ⇌ HCO 3 – + H 3 O +
The problem is that not all of the H 2 CO 3 ionizes into HCO 3 – . In addition, H 2 CO 3 is disproportionate to carbon dioxide and water, which further reduces the conductivity of this solution.
For the remaining examples, we will repeat this fact: a molecule, which in principle is neutral, acquires ionic charge, and in the process mediated by hydrolysis, H 3 O + or OH – ions are produced .
The ammonia molecule, NH 3 , when dissolved in water undergoes the following hydrolysis reaction:
NH 3 + H 2 O ⇌ NH 4 + + OH –
These ammonia solutions give off a pungent odor.
This time we have OH – ions . Ammonia is a weak base, while carbonic acid is a weak acid. Therefore, weak acids and bases are classified as weak electrolytes, since they partially ionize without releasing high concentrations of H 3 O + or OH – ions , respectively.
Á acid phosph or rich
Phosphoric acid, H 3 PO 4 , is an example of a weak oxo acid, which in turn is an electrolyte:
H 3 PO 4 + H 2 O ⇌ H 2 PO 4 – + H 3 O +
Phosphoric acid is still capable of undergoing two other dissociations, one for each acid hydrogen (three in total). The concentration of H 3 O + produced is lower when compared to that of a strong oxo acid, such as nitric acid, HNO 3 , which is a strong electrolyte. The weaker the electrolyte, the less acidic or basic it will be.
Hyd fluoride or geno
Hydrogen fluoride, HF, is an example of a covalent inorganic compound that, without being an oxo acid, is a weak electrolyte because it is a weak acid. When dissolved in water, hydrofluoric acid is produced, which is partially ionized:
HF + H 2 O ⇌ F – + H 3 O +
Despite not being a strong electrolyte, hydrofluoric acid is capable of “eating” the glass of materials commonly used to store acidic solutions.
Pyridine, C 5 H 5 N, is an amine that hydrolyzes to form OH – ions :
C 5 H 5 N + H 2 O ⇌ C 5 H 5 NH + + OH –
Pyridine is more basic than ammonia, so its ionization will be higher and therefore it will produce higher concentrations of OH – ions .
Á acid cianh í Drico
Hydrocyanic acid, HCN, is also another example of a weak acid and electrolyte:
HCN + H 2 O ⇌ CN – + H 3 O +
This point is controversial. Until now weak electrolytes have been classified as weak acids or bases, characterized by their partial ionizations. However, water-insoluble salts, which are already ionized in their crystals, have also been considered weak electrolytes.
Because it is difficult to dissolve in water, the amount of ions released in solution is small when compared to soluble salts. In this sense, insoluble salts produce less conductive solutions, which somewhat overshadows them as strong electrolytes.
For this reason, it will be assumed here that these salts belong to the group of weak electrolytes, even though when dissolved they generate ions and not neutral molecules with degrees of ionization.
Silver chloride, AgCl, dissolves in water to produce Ag + and Cl – ions . However, it is a fairly insoluble salt. The amount of ions that are released is much less than it would be if it were totally soluble, as is the case with silver nitrate, AgNO 3 , a strong electrolyte.
Calcium carbonate, CaCO 3 , is an insoluble salt that, when partially dissolved, produces Ca 2+ and CO 3 2- ions . This salt, unlike AgCl, is basic, since CO 3 2- is hydrolyzed to generate OH – ions .
Zinc sulfate, ZnSO 4 , partially dissolves in water to produce Zn 2+ and SO 4 2- ions .
Calcium fluoride, CaF 2 , found naturally as the mineral fluorite, dissolves slightly in water to produce Ca 2+ and F – ions .
Magnesium oxide, MgO, is an ionic compound that is quite insoluble in water. The small portion that dissolves reacts to transform into the corresponding hydroxide, Mg (OH) 2 , which is actually responsible for the appearance of the Mg 2+ and OH – ions .
For this reason, MgO, despite being ionic, cannot be classified as a strong electrolyte, since in water it does not release ions from its own crystals (Mg 2+ and O 2- ).