In chemistry, the pH value of a solution is a measure of its acidity. The pH value is defined by pH = −log(H⁺), where H⁺ is the hydrogen-ion concentration. If the pH of a sample of rainwater is 4.764, find the hydrogen-ion concentration. (If pH < 7, the solution is acid. If pH > 7, the solution is basic.) Acid rain has a pH between 4 and 5, and normal rain is slightly acidic with a pH of about 5.6.