Final answer:
To calculate the pH of a 1.5 M HCN solution, the Ka value of HCN is used in an equilibrium expression to solve for the hydrogen ion concentration ([H+]), which is then used in the pH formula to find the pH value.
Step-by-step explanation:
Calculating pH of a 1.5 M HCN Solution
To calculate the pH of a 1.5 M HCN solution, you need to use the acid dissociation constant (Ka) and follow these steps:
Set up the equilibrium expression using the Ka value of HCN:
Ka = [H+][CN-] / [HCN].
Assume that the concentration of H+ ions produced is equal to x, and that the concentration of CN- will also be x because HCN dissociates into H+ and CN- in a 1:1 ratio.
The initial concentration of HCN is 1.5 M, and the change in concentration due to dissociation is negligible, allowing us to approximate [HCN] as still being 1.5 M since x is very small compared to 1.5.
Insert the values into the equilibrium expression:
Ka = x^2 / 1.5, and solve for x, which equals the concentration of H+.
Finally, apply the pH formula:
pH = -log[H+], and calculate the pH using the value of x found in the previous step.
Without the need for exact calculations here, we can assume the procedure would lead us to a value for the pH which is a measure of the acidity of the solution.