Final answer:
In an ICE table, you can assume no significant change in the initial acid concentration if Kb/Ka is 10¹² times smaller than the initial concentration, making 'd' 10¹² the correct answer.
Step-by-step explanation:
In an ICE table (Initial, Change, Equilibrium), when solving for the change in concentration of an acid during its ionization, you can often assume no significant change in the initial concentration of the weak acid if the ratio Kb/Ka is much smaller than the initial concentration. This assumption simplifies calculations by allowing us to set the change in concentration, x, as negligible in comparison to the initial concentration. The general rule of thumb is that if Kb/Ka is 10¹² times smaller, the change can be considered negligible.
For weak acids with a Ka in the range of 10⁻³ to 10⁻¶, such as acetic acid with a Ka = 1.8 x 10⁻µ, the weak base it forms, acetate in this case, would have a Kb value calculated by the relationship Ka x Kb = 1.0 x 10⁻. Thus, if the initial concentration of the acid is substantially higher than the Kb value of the conjugate base, the assumption holds. Answer choice 'd' 10¹², is therefore the correct option.