What is the weak ionization constant (#K_a#) for #HCN# equal to?

1 Answer
anor277
Sep 5, 2016

#K_a"(hydrogen cyanide)"=10^(-9.21)#

Explanation:

We assess the reaction:

#H-C-=N + H_2O rightleftharpoons""^(-)C-=N + H_3O^+#

And #K_a# #=# #10^(-9.21)# #=# #([H_3O^+][""^(-)C-=N])/([HC-=N])#

Note that the value of #K_a# derives from careful and meticulous measurment under a standard set of conditions. The equilibrium is the reason why salts of hydrogen cyanide, i.e. #KCN# or #NaCN#, give a slightly basic solution upon dissolution in water.

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