Phosphoric acid is a triprotic acid, so H3PO4, H2PO4 -, and HPO4 2- are all acids. Which of the solutions below would have the lowest pH?
0.1 M NaH2PO4
0.1 M Na2HPO4
0.1 M Na3PO4
c is the highest
a is the lowest
thx
To determine which solution among 0.1 M NaH2PO4, 0.1 M Na2HPO4, and 0.1 M Na3PO4 would have the lowest pH, we need to consider the dissociation of the different acid species of phosphoric acid.
Phosphoric acid (H3PO4) is a triprotic acid. It can donate three protons (H+) successively to form H2PO4-, HPO4^2-, and PO4^3-.
The ionization reactions of phosphoric acid are as follows:
H3PO4 ⇌ H+ + H2PO4-
H2PO4- ⇌ H+ + HPO4^2-
HPO4^2- ⇌ H+ + PO4^3-
With this information, we can analyze the solutions:
1. 0.1 M NaH2PO4:
NaH2PO4 contains H2PO4- ions. When dissolved in water, these ions will dissociate to form H+ and HPO4^2-. Since there are more H+ ions present compared to the other solutions, the pH of this solution will be the lowest among the three.
2. 0.1 M Na2HPO4:
Na2HPO4 contains HPO4^2- ions. When dissolved in water, these ions will dissociate slightly to form H+ and PO4^3-. Since there are fewer H+ ions present compared to 0.1 M NaH2PO4, the pH of this solution will be higher.
3. 0.1 M Na3PO4:
Na3PO4 contains PO4^3- ions. When dissolved in water, these ions will dissociate slightly to form H+ ions. However, since there is only one H+ ion released per molecule of Na3PO4, the concentration of H+ ions will be the lowest compared to the other solutions. Hence, the pH of this solution will be the highest.
Therefore, the solution with the lowest pH is 0.1 M NaH2PO4.
To determine which of the solutions would have the lowest pH, we need to consider the dissociation of the salts. In this case, we have three salts: NaH2PO4, Na2HPO4, and Na3PO4.
When NaH2PO4 dissolves in water, it will dissociate into Na+ and H2PO4-. The H2PO4- ion can act as both a weak acid and a weak base. However, since H2PO4- is a stronger acid than its conjugate base (HPO4 2-), the solution will have an acidic pH.
When Na2HPO4 dissolves in water, it will dissociate into Na+ and HPO4 2-. The HPO4 2- ion can only act as a weak base, and it will not contribute to the acidity of the solution. Therefore, the solution will have a slightly basic pH.
When Na3PO4 dissolves in water, it will dissociate into 3Na+ and PO4 3-. The PO4 3- ion can only act as a strong base and will not contribute to the acidity of the solution. Therefore, the solution will have a basic pH.
Based on this information, we can conclude that the solution of 0.1 M NaH2PO4 will have the lowest pH among the three solutions.