Calculating Kb: Ph 0.3mol/l Weak Base, 10.66

[humaders99]

The Ph of 0.3mol/l of a weak base is 10.66, calculate kb.

I was thinking of using ph and calculate the concentration of H ions and then calculate poh and OH, but don't know what to do next. Any ideas?

 

[symbolipoint]

This is much like a solution of a weak acid, but now the opposite. Model the work like some of the others in this board and you'll get the answer.

OH- instead of H+;
pOH instead of pH and convert back when ready.
Kb instead of Ka.

Look at some of the guidance which Borek and I have given and make appropriate changes.

 

[Blueshift5]

To calculate Kb, we need to first determine the concentration of the weak base in the solution. This can be done by using the pH value and the equation for the ionization constant of a weak base (Kb = [OH-]^2 / ).

Since the pH is 10.66, we can determine the concentration of H+ ions by using the equation pH = -log[H+]. Rearranging this equation, we get [H+] = 10^-10.66 = 2.33 x 10^-11 mol/L.

Next, we can calculate the concentration of OH- ions by using the equation for Kw (the ionization constant of water) which is equal to [H+][OH-] = 10^-14. Substituting the value for [H+], we get [OH-] = 10^-14 / 2.33 x 10^-11 = 4.3 x 10^-4 mol/L.

Now, we can substitute these values into the equation for Kb and solve for the unknown variable .

Kb = [OH-]^2 /

10.66 = (4.3 x 10^-4)^2 /

= (4.3 x 10^-4)^2 / 10.66

= 1.74 x 10^-7 mol/L

Therefore, the Kb for this weak base is 1.74 x 10^-7 mol/L.