Calculate the pH of (1)0.150M KC2H3O2:
(2)0.200M pyridine chloride, C5H5NHCl: and(3) 0.500M NaCl
To calculate the pH of a solution, we need to determine the concentration of the hydronium ion (H3O+). We can do this by considering the dissociation of the solute in water and using the appropriate acid-base equilibrium expression.
(1) 0.150M KC2H3O2:
KC2H3O2 is the salt of a weak acid, acetic acid (CH3COOH). When it dissolves in water, it forms CH3COO- ions and K+ ions. The CH3COO- ions can react with water to form the weak acid, CH3COOH, and OH- ions through the following equilibrium: CH3COO- + H2O ⇌ CH3COOH + OH-
To calculate the pH, we need to consider the concentration of the hydronium ion (H3O+). Since CH3COOH is a weak acid, we can assume it only partially dissociates. However, the concentration of H3O+ from the dissociation of water itself is greater than the concentration of H3O+ from the dissociation of CH3COOH. Therefore, we neglect the contribution from CH3COOH and use the concentration of H3O+ from water.
The dissociation of water can be expressed as: H2O ⇌ H3O+ + OH-
At 25°C, the concentration of H3O+ and OH- in pure water is very small (10^-7 M).
Thus, the concentration of H3O+ for this solution is 10^-7 M, regardless of the concentration of KC2H3O2.
(2) 0.200M pyridine chloride, C5H5NHCl:
Pyridine chloride, C5H5NHCl, is a basic salt. When it dissolves in water, it forms C5H5NH+ ions and Cl- ions. The C5H5NH+ ions can react with water to form the weak acid, C5H5NH2 (pyridine), and H3O+ ions through the following equilibrium: C5H5NH+ + H2O ⇌ C5H5NH2 + H3O+
To calculate the pH, we need to consider the concentration of the hydronium ion (H3O+). Since C5H5NH2 is a weak base, we can assume it only partially reacts with water. However, the concentration of H3O+ from the dissociation of water itself is lesser than the concentration of H3O+ from the reaction with C5H5NH2. Therefore, we consider the contribution from the equilibrium reaction.
For each mole of C5H5NH+ that reacts with water, one mole of H3O+ is produced. Thus, the concentration of H3O+ can be considered equal to the concentration of C5H5NH+.
Therefore, the concentration of H3O+ for this solution is 0.200M.
(3) 0.500M NaCl:
NaCl is a salt that fully dissociates in water into Na+ and Cl- ions. It does not directly contribute H3O+ or OH- ions to the solution.
Therefore, the concentration of H3O+ for this solution is negligible because it depends on the dissociation of water, which remains unchanged.
In summary,
1) The pH for 0.150M KC2H3O2 solution is approximately 7 (neutral) due to the negligible contribution of CH3COOH.
2) The pH for 0.200M pyridine chloride, C5H5NHCl solution is approximately 0.30 (acidic) due to the contribution of C5H5NH+ ions reacting with water.
3) The pH for 0.500M NaCl solution is approximately 7 (neutral) because it does not directly contribute H3O+ or OH- ions to the solution.