Question

Typically the concentration of hydronium, H3O+, or hydroxide, OH−, ions in an aqueous solution is less than 1 M. It is not uncommon to have hydronium ion concentrations that are much smaller, such as 2.60×10−5. pH, therefore, is a convenient way to restate the hydronium concentration. pH is equal to the negative log of a hydronium ion concentration in solution:

pH=−log[H3O+]

Access the pH calculation simulation, which will open in a new window. Edit the concentration by typing a value between 1.0×10−7 and 1.8×101 into the space provided. Select a compound from the dropdown menu and click Dip. The pH value will display in the History field.

Part C

Use the data in the simulation to find the Ka value of HF, hydrofluoric acid.

Express your answer to two significant figures.

Answer 1

c)

find Ka fo rHF

Ka = [H+][F-]/[HF]

once you get pH, and initial concentration of acid, M...

[H+] = 10^-pH

[F-] = [H+] due to stoichiometry

[HF]in equilbirium = M - 10^-pH

then

Ka = (10^-pH)(10^-pH) / ( M - 10^-pH)

Ka = (10^-2pH) / ( M - 10^-pH)

the actual vlaue of Ka is

Ka = 7.2*10^-4

therefore, you msut get a value near that