AC-HPAT Chemistry Practice Test

The key idea is that for a strong acid, it fully dissociates in water, so the hydrogen ion concentration equals the acid concentration. With 0.020 M HCl, [H+] = 0.020 M. The pH is defined as pH = -log10([H+]). So pH = -log10(0.020) = -log(2.0×10^-2) = -(log 2.0 + log 10^-2) = -(0.3010 - 2) ≈ 1.699, which rounds to 1.70.

That matches the option around 1.70. The other values would correspond to different [H+] (for example, pH 2.00 corresponds to 0.01 M), which isn’t the case here since the acid concentration is 0.020 M and HCl is strong.