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Atoms are the basic unit of a molecule, and molecules combine to form matter. Whenever acids react with water, they release hydrogen ions (H+). For example, when hydrochloric acid reacts with water, it releases Hydrogen ions and chlorine ions.
HCl(g) → H+ (aq) + Cl- (aq)
Hydrogen molecules contain one proton, one electron and zero protons.
The electrons revolve around the nucleus and hence, form the electron cloud, whereas the protons settle deep inside. Whenever hydrogen transforms into a hydronium ion, it loses an electron, and this is the reason it is sometimes referred to as a proton also.
The Hydronium ion Formation
While dealing with chemical reactions, the hydronium ion is the major molecule involved in an equery aqueous solution.
By knowing its value, we can easily measure the value of pH for a given compound or molecule. It is given by the chemical formula H3O+ and is formed as a result of a combination reaction between water and hydroxyl ions.
Properties of hydronium ions
The formation of hydronium ions is all dependent on the following given properties.
- It possesses a geometry of trigonal pyramid and
- Has a composition of one oxygen atom and three hydrogen atoms
- The lone pair of hydrogen is responsible for the formation of its shape.
- They possess a bond angle of 113 degrees.
Formation of hydronium ion example
- An example of the formation of hydronium ion is given by the reaction of hydrogen ion with hydroxyl ion:
H2O(l) ⇌OH-(aq) + H+ (aq)
- The above given is a reversible reaction that can occur in both directions. This is because once after the formation of water, it can rapidly dissociate again to hydroxyl and hydrogen ions.
The importance of Hydronium ion as a measure of pH
pH is the potential of hydrogen ions. It infers the number of H ions in a molecule/compound and solely is dependent on the number of hydronium ions. For pure water, the pH is 7 which can also be denoted as 1 × 10-7moles at standard room temperature conditions.
This can be figured out by the equation:
pH= − log (H3O+)
Since the pH of water is 7 so it is considered neutral. But it can vary accordingly with an increase or decrease with hydronium ion concentration.
They are inversely proportional to each other. This means that if the concentration of hydronium ions increases, then the pH of these samples decreases, and if the concentration decreases of hydronium ions, then the pH increases.
A decrease in pH value means the given solution is now acidic, and the case can only be obtained once we add acid into it. For instance, H+ ions break out from acid and bind with the molecule of water and hence the concentration of hydronium ions increases which will again increase the pH.
And for the case of increased pH, it means the solution is becoming basic and this can happen only if we add base in it. All bases have hydroxyl ions (OH-). These get dissociated from bases and get bound to H+ ions rather than water molecules as in the previously mentioned case.
Just like we can calculate the pH value from a given amount of hydronium ions, we can also calculate hydronium ions concentration from a given pH value.
This can be done by the following equation;
H3O+ = 10-pH
H3O+ = Antilog (-pH)
to understand put the value of 7 as pH we get 0.0000001 M and this is the value of Hydronium ions at pH 7.
The water molecule
Water is a polar molecule containing partial charges. It can easily attract hydrogen ions. The partial charge is a result of a negative charge for this case, and it is so because the oxygen molecule is supposed to be highly electronegative than the hydrogen molecule. So hence the bond between both of them pulls the oxygen harder on sharing the electrons.
This leads to the development of partial negative charge molecules, and so it is attracted to the positive charge of hydrogen ions to form the hydronium ion. Also, the water has a great dipole moment. Again, the water geometry is tetrahedral and bent, which is very unsymmetrical and forces the molecule to exhibit polarity and dipole moment, resulting in partial charge on the molecule.
Not only with the case of water, but hydronium icons can also be formed with acids. In this case, the acids break the Hydrogen ions, which further binds to the water molecule and form the hydronium ion. An example is a hydrochloric acid with water yielding hydronium ion and chlorine ion.
Conclusion
Hydronium ion is formed as a result of a combination of water and hydrogen ion i.e. H2O and H+. And the type of bond formed between them is the covalent bond. This whole reaction happens as the oxygen and Hydrogen in water (H2O) contains 6 and 2 electrons respectively. The two-electron pairs are shared with 2 hydrogen ions and the two electrons which are unshared and this completes their valence shell configuration of water to make it stable.
