The indicator propyl red has a Ka of 3.3 X 10-6 . It is red at low pH and yellow at higher pH. What is the approximate pH range over which it changes color

4.48 - 6.48

Explanation:

A pH indicator works in a better way in a range of pH = pKa ± 1. That means we need to determine the pKa of the indicator propyl red to find the range over which it change its color. That is:

pKa = -log Ka

pKa = -log 3.3x10⁻⁶

pKa = 5.48

That means the range over propyl red will change from yellow to red or vice versa is:

4.48 - 6.48

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.

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.