11 Facts on H3PO4 + NaOH: With Several Elements Reaction

H3PO4 + NaOH reaction is one of the important reactions when it comes to studying acid-base chemistry. The complete detail of this reaction and the reactions associated with this combination are explained in this article.

H3PO4 + NaOH in an explanatory form is the reaction between a dilute phosphoric acid and a concentrated sodium hydroxide which produces sodium triphosphate as the main product and water as the by-product. The important thing to notify is that this reaction is warm which is evident after touching the reaction mixture beaker.

H3PO4 + NaOH reaction is an acid-base reaction or neutralization reaction. Here the acid is H3PO4 and the base is NaOH. Both of these reactants are strong acid and base where acid loses H+ and base loses OH- resulting in the formation of a by-product which is again responsible for the exothermic nature of the process.

Elaborating on each reactant involved in H3PO4 + NaOH reaction, then H3PO4 is named phosphoric acid. It is a colorless inorganic solid and is aqueous by 85%. It is a very common compound in the fertilizer and pesticide industry. In the presence of water, it dissociates resulting in the formation of triprotic acid. Phosphoric acid when compared to its other strong acid counterparts is weak but it can irritate the eyes and skin. Its long-term consumption in any form can lead to osteoporosis in women.

H3PO4 + NaOH
H3PO4 + NaOH reaction
Phosphoric acid in H3PO4 + NaOH reaction

Moving towards the base component of the H3PO4 + NaOH reaction then sodium hydroxide also denoted as caustic soda is an inorganic base made up of Na+ cation and OH- anion. It is a white solid crystal and has no peculiar smell. It is very much soluble in water and exists as hydrous sodium hydroxide. It is used in many chemical industries and academic laboratories. 

Sodium hydroxide in H3PO4 + NaOH reaction

There are many factors associated with H3PO4 + NaOH reactions some of which are discussed below:

  1. What happens when H3PO4 reacts with NaOH?
  2. What kind of reaction is H3PO4 + NaOH?
  3. H3PO4 + NaOH titration
  4. H3PO4 vs NaOH
  5. How To Balance H3PO4+NaOH=Na3PO4+H2O?
  6. How To Balance H3PO4+NaOH=na2hpo4+H2O?
  7. H3PO4+NaOH=Na3PO4+H2O net ionic equation
  8. H3PO4 NaOH buffer solution
  9. H3PO4+NaOH=NaH2PO4+H2O net ionic equation
  10. HCl + H3PO4 + NaOH
  11. H3PO4(aq)+NaOH(aq)

What happens when H3PO4 reacts with NaOH?

The reaction of H3PO4 + NaOH is a very common example of a neutralization reaction. In explanatory form, it means that a dilute solution of sodium hydroxide neutralizes concentrated phosphoric acid and results in the formation of a neutral compound that has pH 7 and shows green color on pH paper. 

The product of the H3PO4 + NaOH reaction is aqueous Na3PO4 and H2O. It is an exothermic reaction which is evident from the warm beaker containing the reaction mixture.

What kind of reaction are H3PO4 + NaOH?

There is a possibility of 2 types of reactions when H3PO4 and NaOH react. The first and most evident reaction is the acid-base neutralization reaction. The reason why it is considered a neutralization response is because H3PO4 is acid and NaOH is a base and their quantitative reaction results in salt. Along with this during the reaction mechanism of H3PO4 + NaOH, H+ and OH- ions are liberated which shapes up the by-product water molecule. 

Another type of reaction we encounter in H3PO4 + NaOH is the double displacement reaction. This is because there is the movement of anions and cations between the 2 reactants which leads to Trisodium phosphate and water.

H3PO4 + NaOH titration

The titration of H3PO4 with NaOH is very interesting. It is unlike any other acid-base titration which involves very strong acids like sulphuric acid and nitric acid.

Phosphoric acid is comparatively a weak acid with pka 1 = 2.15, pka2 = 7.20 and pka 3 = 12.35. All these pka values indicate that the titration curve of H3PO4 + NaOH has two inflection points and it can be titrated as monoprotic acid or diprotic acid. 

Indicators are used when dealing with titration reactions as they are evidence of the various pka values and formation of different acids with the release of H+ in H3PO4 + NaOH.  The mathematical titration of H3PO4 + NaOH is a tedious and complex area and is out of the scope of this article.

Titration of H3PO4 + NaOH reaction

H3PO4 Vs NaOH in H3PO4 + NaOH reaction

H3PO4 and NaOH in H3PO4 + NaOH reaction are opposite sides of the same coin which are poles apart in terms of their individual properties but are important when it comes to neutral compound formation. Discussing both of them then phosphoric acid as the name suggests is an inorganic weak acid and NaOH is a strong base. They titrate together with the eventual loss of hydrogen ions from the acid and OH or hydroxy ions from the base which shapes the water molecule. 

H3PO4 being an acid when undergoing an acid-base neutralization reaction first changes into monobasic acid with the loss of one H+ ion. Being a weak acid as compared to its other strong inorganic acid counterparts it will not be able to complete the reaction proceeds in a single lot but will take 2 to 3 turns and form 2 inflection points with 3 pka values. The last pka value is the highest one.

Discussing NaOH then it is a very strong base and instantly forms the neutral salt with loss of OH- ion. It is evident from the laboratory volumetric titration test by use of indicators like methyl orange and phenolphthalein.

How To Balance H3PO4+NaOH=Na3PO4+H2O?

Balancing the chemical reaction is very important to establish the equilibrium of the reaction and to make sure that the reactants can form the products.  For the balancing of H3PO4 and NaOH reactions, the stoichiometric requirements of reactants must be equal to products.

The concentration on the reactant side should balance the concentration on the product side. The balancing is shown in the diagram below.

H3PO4 + NaOH balanced equation

How To Balance H3PO4+NaOH=Na2HPO4+H2O?

This is another reaction of H3PO4 + NaOH which results in the formation of Na2HPO4 called sodium hydrogen phosphate. It is a white crystalline hygroscopic salt and exists in powdery form. Sometimes it is transparent as well.

H3PO4 + NaOH balanced equation with different product

H3PO4+NaOH=Na3PO4+H2O net ionic equation

The net ionic equation means when the molecules are dissociated into individual ions associated and then a net equation is found after removing all the spectator ions. In the case of H3PO4 + NaOH, it is very much clear from the above discussion that phosphoric acid is a weak acid so it cannot be shown to be completely dissociated in one instance.

It is partially dissociated so over here after dissociation phosphate ion is not considered a spectator ion and the water forms as a net ionic reaction. Due to the extra availability of OH- and Na+ being a spectator ion this reaction is an exception to the net ionic equation concept and it cannot be written with clarity.

H3PO4 + NaOH buffer solution

The H3PO4 + NaOH buffer solution is responsible for maintaining the pH of the solution. During the acid-base neutralization, process acid loses its proton in every volumetric titration. As far as H3PO4 + NaOH is concerned then it takes 2 titrations for complete dissociation which means it has 2 inflection points. 

Now it is clear that there are 2 types of buffers: Acidic buffers and basic buffers. In H3PO4 + NaOH reaction there are 3 removable hydrogens or protons hence the reaction is having acidic buffer solution which is usually a weak acid.

H3PO4+NaOH=NaH2PO4+H2O net ionic equation

H3PO4 dissociates into 3 hydrogen ions and 1 phosphate ion due to its weak acidic properties. On the other hand, NaOH dissociates into Na+ and OH- in a single response. This reaction results in a net ionic reaction where there is single hydrogen and hydroxyl ion.

The addition of more NaOH will be a problem as it will lead to further dissociation and lead to Na3PO4 instead of NaH2PO4.

HCl + H3PO4 + NaOH

The reaction between HCl + H3PO4 + NaOH involves two inorganic acids and one base. Here it is called an acid mixture because of the acid dominance. Here HCl and NaOH are strong inorganic acids and bases respectively.

H3PO4 through inorganic acid is weak as compared to hydrochloric acid. So the reaction between 3 leads to dissociation of one H+ from H3PO4 leading to the formation of dibasic acid H2PO4, neutral salt sodium chloride NaCl, and hydronium ion H3O. This is an already balanced equation.

H3PO4 + NaOH reaction with HCl

H3PO4 (aq)+NaOH(aq)

The presence of an aqueous solution of H3PO4 + NaOH reaction does not make any difference to the reaction procedure. It still leads to the formation of aqueous Na3PO4 and H2O like any other neutralization reaction.


The article can be summarized that the reaction H3PO4 + NaOH is an acid-base neutralization reaction with a little anomaly where H3PO4 is a weak inorganic acid as compared to its counterparts which clearly can be observed from volumetric titration. The H3PO4 + NaOH reaction can lead to many other products depending on the dissociation properties.

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