Achieve #5: Week 2 [ENDORSED]

[005801694]

Hi! When calculating the % protonated, why do you calculate the formal concentration of B (the base) by adding the concentration of B and BH+ together? I'm referring to the reaction: B+H20->(BH+)+OH-. Thanks!

[Joanna Zhao 1J]

When calculating the % protonated, we need to find the amount dissociated and divide it by the INITIAL concentration of B before it began dissociating. Since [B]equilibrium = [B]initial - x, and [BH+]equilibrium = x, I guess you can say to find the initial [B] you need to add the two together because [B]initial is [B]equilibrium plus whatever got dissociated. It's like putting the puzzle pieces back together.

[Chem_Mod]

The initial concentration of base can be calculated by adding the equilibrium concentrations of B and BH⁺ together.

The initial concentration of base is then used to calculate % protonated:

% protonated = [BH⁺]/[B]initial x 100