What is the pH of a 0.00001 molar HCl solution?
A. 1
B. 4
C. 5
D. 9
By definition pH is the negative log (logarithm) of the hydronium ion concentration. A 0.00001 molar solution has a H+ concentration of 10-5 M (move the decimal point 5 places to the right). The value of the negative exponent (-5) gives a pH of 5.