The concentration of H^3O ions in a solution of 3.8 x 10^-9 M?

Question

a) is the solution acidic, basic, or neutral?
b) what is the concentration of OH- ions in the solution?

please explain!

Answer 1

It is basic : pH = - log 3.8 x 10^-9 = 8.4

If pH > 7 the solution is basic

[OH-][H3O+] = 1 x 10^-14
[OH-]= 1 x 10^-14 / 3.8 x 10^-9 = 2.5 x 10^-6 M

There is another way to get [OH-] :
pH + pOH = 14
pOH = 14 - pH = 14 - 8.4 = 5.6
[OH-] = 10^-5.6 = 2.5 x 10^-6 M

Answer 2

Dr. A has good math, his numbers are right, but explanation is lacking.
A) acidity, basicity, and neutrality are just referenced to water's pH. anything above 7 is basic, anything below 7 is acidic, and very little is exactly 7 or neutral. Your solution is over 7 so basic.
The "p" in pH is just a mathmatical operator meaning "negative log of" and H is the hydrogen ion concentration.
b) in a basic solution, the concentration oh OH- ions will exceed the concentration of H+ ions. And if you look at the formulas the good doctor lists, you can calulate it out and find out thats true.

Answer 3

Your question is confusing: The solution is 3.8x10^-9 M in WHAT?

The answers differ with the solute: if you're asking about a solution of hydrochloric acid, then the answer is 3.8x10^-9M.

If you are asking about a solution of sodium hydroxide, then the [H3O+] = (10^-14)/(3.8x10^-9) = 2.63x10^-6M

If you are asking about a solution of sodium chloride, then [H3O+] = 10^-7.

Or are you saying that [H3O+] = 3.8x10^-9?
In that case, the answers are:
a) basic
b) [OH-] = 2.63x10^-6

Always remember that in aqueous solution, [H3O+]*[OH-] = 10^-14