9. $\text{pH }=8,$ base

11. $\text{pH }\approx 4.64,$ acid

13. $[{\text{H}}^{+}]={10}^{-6},[{\text{OH}}^{-}]={10}^{-8}$

15. $[{\text{H}}^{+}]=3.16\cdot {10}^{-10}[{\text{OH}}^{-}]=3.16\cdot {10}^{-5}$

17.

1. ${10}^5{I}_0$

2. $7.94\cdot {10}^{11}$

19.

1. $6.3\cdot {10}^7{I}_0$

2. $1.26\cdot {10}^{16}$

21.

1. 6;

2. ${10}^6{I}_0$

23.

1. 5.1

2. $1.26\cdot {10}^5{I}_0$

25. 40

27. 55.4

29. ${10}^{-4}$

31. $2.95\cdot {10}^{-6}$

33. A#466 Hz, C523 Hz

35. $\approx 18$ cents; noticeable

37. A is $\approx 2.5\times {10}^6$ times brighter than B.

39. B is $\approx 6.31$ times brighter than A.