A salicyclic acid (MW= 138.123 g/mol) solution has a pH of 2.43. When 100 ml of this solution was evaporated 0.22g of dry salicylic acid was recovered. What is the Ka of salicylic acid?
I answered this below at your other post.
To find the Ka of salicylic acid, we need to use the equation that relates the pH to the concentration of the acid and its conjugate base. The Ka is a measure of the acid's strength or ability to dissociate in water.
Step 1: Calculate the concentration of salicylic acid in the initial solution.
To do this, we need to know the volume of the solution and the mass of the salicylic acid recovered.
Given: Volume = 100 mL = 0.100 L
Mass of salicylic acid recovered = 0.22 g
First, we need to convert the mass of salicylic acid to moles by using its molar mass:
Moles of salicylic acid = Mass / Molar mass
= 0.22 g / 138.123 g/mol
Step 2: Calculate the concentration of salicylic acid in the initial solution.
Concentration = Moles / Volume
= (0.22 g / 138.123 g/mol) / 0.100 L
Step 3: Calculate the concentration of the conjugate base.
Since salicylic acid is a monoprotic acid, the concentration of the conjugate base (A-) is the same as the concentration of salicylic acid.
Step 4: Calculate the concentration of H+ ions.
The pH of a solution is defined as -log[H+]. Therefore, we can calculate the concentration of H+ ions.
[H+] = 10^(-pH)
= 10^(-2.43)
Step 5: Apply the equation for Ka:
Ka = [H+][A-] / [HA]
Given that the concentration of the acid and its conjugate base are the same ([A-] = [HA]), we can rewrite the equation as:
Ka = [H+]^2 / [HA]
Step 6: Substitute the known values into the equation to calculate Ka.
Note: Be sure to convert the concentration to moles per liter (M) for accurate results.
Now you have all the steps needed to calculate the Ka of salicylic acid using the given information.