HClO4 => H+ + ClO4- [H+] = [HClO4] = 0.020 M pH = -log[H+] = -log(0.020) = 1.7 (2 significant figures) Solution HClO4 => H+ + ClO4- [H+] = [HClO4] = 0.020 M pH = -log[H+] = -log(0.020) = 1.7 (2 significant figures).Read less