Calculate [H3O+] for solution

Question

Calculate [H3O+] for solution of pH= 4.778

Answer 1

pH is defined as the negative log of the hydronium ion concentration: 

pH=−log₁₀([H₃O⁺])

pH was given (4.778), so we can apply the rules of logs to solve for H₃O⁺

[H₃O⁺]=10^−4.778

[H₃O⁺]=1.667 x 10^-5 mol/L