What is the poh of a
2.6 x 10-6 m h+ solution?

Explanation:

pH and pOH

The pH is a way of expressing the hydrogen ion concentration.

pH = -log[H+] where [x] means "the concentration of x in moles per liter."

From pH you can compute pOH since at 25C pH + pOH = 14.00 (but only at 25C)

pH = -log(2.6x10^-6) = 5.585 which should be rounded to two significant digits: pH = 5.59

When taking the log of a number, only the digits to the right of the decimal reflect the precision in the original number. Since 2.6x10^-6 has two significant digits, a pH of 5.59 has two significant digits.

pOH + pH = 14.00

pOH = 14.00 - pH = 14.00 - 5.59 = 8.41 at 25C

We can also use the H+ ion concentration to get the hydroxide ion concentration and from that the pOH.

Kw = [H+][OH-] = 1.00x10^-14 at 25C like any Kc, the value changes with temperature

[OH-] = Kw / [H+] = 1.00x10^-14 / 2.6x10^-6 = 3.846x10^-9 to a couple of guard digits

pOH = -log[OH-] = -log(3.846x10^-9) = 8.415 round to two significant digits: pOH = 8.42 at 25C

Just for grins, you might want to know how Kw changes with temperature, and how [H+] and [OH-] are related at some other temperatures. The pH is the pH of a neutral solution at various temperatures. For instance at 10C a neutral solution has a pH of 7.27. That's not a basic pH. 7.27 is the pH of a neutral solution, but at a different temperature. In a neutral solution at 10C [H+] = [OH-] = 5.41x10^-8M.

pH and Kw for a neutral solution at different temperatures

T pH Kw

0 7.47 0.114 x 10-14

10 7.27 0.293 x 10-14

20 7.08 0.681 x 10-14

25 7.00 1.008 x 10-14

30 6.92 1.471 x 10-14

40 6.77 2.916 x 10-14

50 6.63 5.476 x 10-14

100 6.14 51.3 x 10-14

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.