How does H2O effect NaH2PO4 during an acid titration?
IT dilutes it, so more volume is used for the same amount of phosphate.
I mean how it effects the acid-dissociation constant(Ka). How does water effect the Ka value of a weak acid?
To understand how H2O affects NaH2PO4 during an acid titration, we need to consider the chemical properties of both compounds and the reaction that takes place during the titration.
NaH2PO4 is a salt composed of sodium ions (Na+) and dihydrogen phosphate ions (H2PO4-). It is a weak acid salt because the H2PO4- ion can donate a proton (H+) to water to form H3PO4 (phosphoric acid) and the hydroxide ion (OH-).
During an acid titration, a strong acid is added to a solution containing the weak acid salt, NaH2PO4. The strong acid reacts with the weak acid salt, causing the weak acid salt to undergo hydrolysis.
Let's consider the role of H2O in this process:
1. At the beginning of the titration, NaH2PO4 is dissolved in water. The water molecules hydrate the sodium ions (Na+) and the dihydrogen phosphate ions (H2PO4-). This hydration process stabilizes the ions in solution.
2. As the strong acid is added drop by drop, it reacts with the dihydrogen phosphate ions (H2PO4-) to form phosphoric acid (H3PO4). The reaction involves the transfer of a proton (H+) from the strong acid to the weak acid salt.
The overall reaction can be represented as follows:
H2PO4- + H+ (from the strong acid) → H3PO4
3. This reaction reduces the concentration of dihydrogen phosphate ions (H2PO4-) in the solution. As a result, the equilibrium of the weak acid salt is shifted to the left, favoring the formation of more dihydrogen phosphate ions from the water molecules.
The equilibrium reaction can be represented as follows:
H2PO4- + H2O ↔ HPO4^2- + H3O+
4. The excess H3O+ ions formed from the strong acid will react with the remaining dihydrogen phosphate ions (H2PO4-) to form more phosphoric acid (H3PO4). This process continues until most of the NaH2PO4 is consumed.
In summary, H2O plays an essential role in the acid-base reaction between the strong acid and NaH2PO4 during a titration. It initially provides stability by hydrating the ions, and then it acts as a reactant and product in the equilibrium reactions involved in the hydrolysis process.