25temperature in a solution of 0.1N of formic acid,2.25% of it's dissociates.Calculate it's dissociation constant?

1 Answer
May 14, 2018

#K_a# #"formic acid"# #-=# #5.18xx10^-5#

Explanation:

We interrogate the reaction...

#HC(=O)OH(aq) + H_2O(l)rightleftharpoonsHC(=O)O^(-) + H_3O^+#

Initially, #[HC(=O)OH(aq)]=0.1000*mol*L^-1.#

Finally, #[HC(=O)OH(aq)]=0.09775*mol*L^-1.#

And #[H_3O^+]=[HC(=O)O^(-)]=0.00225*mol*L^-1.#

And so we can calculate #K_a# directly...

#K_a=([HC(=O)O^(-)][H_3O^+])/([HC(=O)OH(aq)])=(0.00225)^2/(0.09775)=5.18xx10^-5#