A question about impedance
Yes, Ohm's Law works with impedances but you must be careful to use a complex impedance. For example, in your circuit the total impedance is $$Z = R - \frac{j}{\omega C}$$ The resulting current will not be in phase with the applied voltage. More importantly, the voltage across the resistor and the voltage across the capacitor will be 90 degrees out of phase, so the magnitudes of these voltages will not sum to be equal to the magnitude of the source voltage.

To answer your specific question, if your ac source is ideal then the voltage from A to B will never change and is not a function of frequency. The voltage across an ideal source is not affected by whatever you connect to it, and the voltage from A to B is just the voltage across the source.

However, the impedance will vary with frequency so the current will vary with frequency. Therefore, the voltages across the resistor and capacitor will vary with frequency. It sounds like you want to create a Bode plot of these voltages.