a) [H3O+] = 10^-14/2×10^-9 = 5×10^-6M
b) [H3O+] = [OH-] = 10^-7 M
c) [OH-] = 10^3×[H3O+]
[H3O+]×[OH-] = 10^-14 => [H3O+]+10^3×[H3O+> = 10^-14 => [H3O+]^2 = 10^-14/10^3 = 10^-17 => [H3O+] = 10^-8,5M
2) HNO3 - A.T => [HNO3] = C = [H3O+] = 0,15M
[OH-] = 10^-14/15×10^-2 = 6,66×10^-14M