Chapter 4, Exponential and Logarithmic Functions - Section 4.7 - Logarithmic Scales - 4.7 Exercises - Page 421: 5

$4.8\leq pH\leq 6.4$.

We know that pH is given by the formula: $pH=-\log[H^+]$. Hence, here the range of pH readings is: $-\log(4\cdot10^{-7})\approx6.4$ and $-\log(1.6\cdot10^{-5})\approx4.8$ Thus, the net pH range is $4.8\leq pH\leq 6.4$.