If 5.05mL of 0.1000 M NaOH solution is needed to just neutralize excess acid after 20.00 mL of HCl was added to 1.00 g of an antacid, how many moles of acid can the antacid counteract per gram?

Answer 1

You need to know the M of the HCl used.
millimoles HCl used = 20.00 x ?M = xx.
Excess is 5.05 mL x 0.1000 M NaOH = 0.505 mmoles excess acid.
Initial mmoles - excess mmoles = mmoles antacid in the 1.00 g tablet. Then convert mmoles to moles.

Answer 2

.0015