NaCl (s) –> Na + (aq) + Cl – (aq)
Positively charged elements, such as Na + , are the cations, and are called “sodium cations”, and negatively charged elements, such as Cl – are the anions, and are called “chloride anions”. The parentheses (aq) indicate that they are found in an aqueous medium. That is to say, the NaCl is initially in a solid state, and later it passes to an aqueous medium where its ions arise. Thus, the solute is said to be fully ionized.
In contrast, weak electrolytes are those that are not completely ionized, that is, instead of a completely shifted reaction towards products, an equilibrium takes place. Normally weak electrolytes are mostly organic acids, such as acetic acid (CH 3 COOH), and also some weak bases. The ionization equation, taking acetic acid as an example, would be given as follows:
CH 3 COOH (aq) <–> CH 3 COO – (aq) + H + (aq)
The fraction of a substance that undergoes ionization, that is, that splits into ions or becomes ionized, is often expressed as a percentage, and depends on the concentration of the solution. In addition, since an equilibrium takes place, a constant can be established for the previous reaction, which is defined as:
?= ([H + ][CH 3 COO − ])/[CH 3 COOH]
Water autoionization constant
Water also undergoes a process of ionization or self-ionization, which can be represented by the following equation:
H 2 O (l) <–> H 3 O + (aq) + OH – (aq)
And the equilibrium constant is: ?=([H 3 O + ][OH – ])/[H 2 O]
In many reactions that take place in water, or in very dilute aqueous solutions, the concentration of water can be omitted, and in this way results in the expression of the equilibrium constant that can be called the ionization constant, or also the dissociation constant . , autoionization constant or ionic product of water , and which is symbolized by Kw:
??=[H 3 O + ][OH – ]
Under standard conditions of pressure and temperature, which correspond to 1 atmosphere and 25 ºC (298 K), Kw has a value of 10 -14 . Furthermore, if there is no solute in water, it is known that the concentration of [H 3 O + ] is equal to that of [OH – ].
[H 3 O + ]=[OH – ]=10 −7
Importance of electrolytes in the human body
The human body, among many other things, is made up of electrolyte solutions. The electrolytes that our body mainly requires are cations, such as calcium, potassium, sodium and magnesium. You also need anions, such as chloride, carbonate, aminoacetate, phosphate, and iodide. In nutrition, these substances are called macrominerals , since the body needs them in large quantities.
Electrolyte balance is crucial for many bodily functions. Some examples of what can happen when there is no electrolyte balance can be:
- Elevated levels of potassium cations, which can lead to cardiac arrhythmias.
- Low extracellular levels of potassium cations, leading to paralysis.
- Excessively high levels of sodium cations, which cause fluid retention.
- Low plasma levels of calcium and magnesium cations, which can cause muscle spasms in the extremities.
References
Greenwood, Norman N.; Earnshaw, Alan. (1997) Chemistry of the Elements (second edition). Butterworth–Heineman
Brown, Theodore L.; Jr, H. Eugene LeMay; Bursten, Bruce E.; Burdge, Julia R. (2004). Chemistry. Pearson Education.
